<?php
/**
 * Academic Certificate Verification - Admin Class
 *
 * This file handles all admin-side functionality including menu creation,
 * certificate management, settings, and bulk operations.
 *
 * @package     AcademicCertificateVerification
 * @subpackage  Admin
 * @author      Syed Tarikul Islam
 * @copyright   2024 QueueCommerce
 * @license     GPL-2.0-or-later
 *
 * @since       1.0.0
 */

defined( 'ABSPATH' ) || exit;

/**
 * Class ACCEVE_Certificate_Verification_Admin
 *
 * Main admin class for the Academic Certificate Verification plugin.
 * Handles admin menu, settings, certificate management, and AJAX operations.
 *
 * @since 1.0.0
 */
class ACCEVE_Certificate_Verification_Admin {

    /**
     * Instance of this class.
     *
     * @since 1.0.0
     *
     * @var ACCEVE_Certificate_Verification_Admin|null
     */
    private static $instance = null;

    /**
     * Get singleton instance of the class.
     *
     * @since 1.0.0
     *
     * @return ACCEVE_Certificate_Verification_Admin The instance.
     */
    public static function get_instance() {
        if (null === self::$instance) {
            self::$instance = new self();
        }

        return self::$instance;
    }

    /**
     * Constructor.
     *
     * Initializes hooks and actions for admin functionality.
     *
     * @since 1.0.0
     *
     * @return void
     */
    private function __construct() {

        add_action('admin_menu', array($this, 'add_admin_menu'));
        add_action('admin_init', array($this, 'register_settings'));
        add_action('admin_init', array($this, 'create_verification_page'));
        add_action('admin_init', array($this, 'handle_certificate_actions'));
        add_action('admin_post_certificate_verification_add_certificate', array($this, 'process_add_certificate'));
        add_action('wp_ajax_acceve_export_certificates_csv', array($this, 'handle_csv_export'));
        add_action('wp_ajax_acceve_bulk_delete_certificates', array($this, 'handle_bulk_delete'));
        add_action('admin_enqueue_scripts', array($this, 'load_admin_assets'));
    }

    /**
     * Create verification page.
     *
     * Creates or updates the verification page with the shortcode.
     * The page is used for frontend certificate verification.
     *
     * @since 1.0.0
     *
     * @global wpdb $wpdb WordPress database abstraction object.
     *
     * @return void
     */
    public function create_verification_page() {
        $page_slug = 'verify-certificate';
        $page      = get_page_by_path($page_slug);

        if (!$page) {
            // Create post object
            $page_data = array(
                'post_title'     => __('Verify Certificate', 'academic-certificate-verification'),
                'post_name'      => $page_slug,
                'post_content'   => '<!-- wp:shortcode -->[acceve_certificate_display]<!-- /wp:shortcode -->',
                'post_status'    => 'publish',
                'post_type'      => 'page',
                'post_author'    => get_current_user_id(),
                'comment_status' => 'closed',
                'ping_status'    => 'closed',
                'meta_input'     => array(
                    '_wp_page_template' => 'default'
                )
            );

            // Insert the page
            $page_id = wp_insert_post($page_data);

            // Store page ID in options for future reference
            if (!is_wp_error($page_id)) {
                update_option('acceve_certificate_verification_page_id', $page_id);
            }
        } else {
            // Update existing page with shortcode if needed
            if (false === strpos($page->post_content, '[acceve_certificate_display]')) {
                $page_data = array(
                    'ID'           => $page->ID,
                    'post_content' => $page->post_content . "\n[acceve_certificate_display]"
                );
                wp_update_post($page_data);
            }
            // Store page ID in options
            update_option('acceve_certificate_verification_page_id', $page->ID);
        }
    }

    /**
     * Add admin menu pages.
     *
     * Creates the main menu and submenu items in WordPress admin.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function add_admin_menu() {

        add_menu_page(
            __('Certificate Verification', 'academic-certificate-verification'),
            __('Certificates', 'academic-certificate-verification'),
            'manage_options',
            'certificate_verification',
            array($this, 'admin_dashboard'),
            'dashicons-awards',
            30
        );

        add_submenu_page(
            'certificate_verification',
            __('All Certificates', 'academic-certificate-verification'),
            __('All Certificates', 'academic-certificate-verification'),
            'manage_options',
            'certificate_verification',
            array($this, 'admin_dashboard')
        );

        add_submenu_page(
            'certificate_verification',
            __('Add New Certificate', 'academic-certificate-verification'),
            __('Add New', 'academic-certificate-verification'),
            'manage_options',
            'certificate_verification_add',
            array($this, 'add_certificate_page')
        );

        add_submenu_page(
            'certificate_verification',
            __('Import Certificates', 'academic-certificate-verification'),
            __('Import', 'academic-certificate-verification'),
            'manage_options',
            'certificate_verification_import',
            array($this, 'import_certificates_page')
        );

        add_submenu_page(
            'certificate_verification',
            __('Settings', 'academic-certificate-verification'),
            __('Settings', 'academic-certificate-verification'),
            'manage_options',
            'certificate_verification_settings',
            array($this, 'settings_page')
        );

        add_submenu_page(
            'certificate_verification',
            __('Custom Fields', 'academic-certificate-verification'),
            __('Custom Fields', 'academic-certificate-verification'),
            'manage_options',
            'manage_custom_fields',
            array($this, 'manage_custom_fields_page')
        );

        add_submenu_page(
            'certificate_verification',
            __('Add Courses', 'academic-certificate-verification'),
            __('Add Courses', 'academic-certificate-verification'),
            'manage_options',
            'manage_add_courses',
            array($this, 'manage_add_courses_page')
        );

        add_submenu_page(
            'certificate_verification',
            __('Add Batches', 'academic-certificate-verification'),
            __('Add Batches', 'academic-certificate-verification'),
            'manage_options',
            'manage_add_batches',
            array($this, 'manage_add_batches_page')
        );

        add_submenu_page(
            'certificate_verification',
            __('Certificate Maker', 'academic-certificate-verification'),
            __('Certificate Maker', 'academic-certificate-verification'),
            'manage_options',
            'certificate_maker',
            array($this, 'certificate_maker_page')
        );

        add_submenu_page(
            'certificate_verification',
            __('Upgrade Pro', 'academic-certificate-verification'),
            __('Upgrade Pro', 'academic-certificate-verification'),
            'manage_options',
            'certificate_verification_pro',
            array($this, 'upgrade_pro_page')
        );

    }

    /**
     * Register plugin settings.
     *
     * Registers settings, sections, and fields for the plugin.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function register_settings() {

        register_setting(
            'certificate_verification_settings',
            'acceve_certificate_verification_options',
            array(
                'type'              => 'array',
                'sanitize_callback' => array($this, 'acceve_sanitize_settings'),
                'default'           => array(
                    'default_institution' => '',
                    'certificate_prefix' => 'CERT-',
                    'certificate_template' => 'template_one'
                )
            )
        );
        add_settings_section(
            'general_settings',
            __('General Settings', 'academic-certificate-verification'),
            array($this, 'general_settings_section_callback'),
            'certificate_verification_settings'
        );

        add_settings_field(
            'default_institution',
            __('Default Institution', 'academic-certificate-verification'),
            array($this, 'default_institution_callback'),
            'certificate_verification_settings',
            'general_settings'
        );

        add_settings_field(
            'certificate_prefix',
            __('Certificate ID Prefix', 'academic-certificate-verification'),
            array($this, 'certificate_prefix_callback'),
            'certificate_verification_settings',
            'general_settings'
        );

        add_settings_field(
            'certificate_template',
            __('Certificate Template', 'academic-certificate-verification'),
            array($this, 'certificate_template_callback'),
            'certificate_verification_settings',
            'general_settings'
        );

        add_settings_field(
            'enable_date_of_birth',
            __('Enable Date of Birth for Certificate Verification', 'academic-certificate-verification'),
            array($this, 'enable_date_of_birth_callback'),
            'certificate_verification_settings',
            'general_settings'
        );

        add_settings_field(
            'enable_download_button',
            __('Enable Download Button', 'academic-certificate-verification'),
            array($this, 'enable_download_button_callback'),
            'certificate_verification_settings',
            'general_settings'
        );

        add_settings_field(
            'download_button_bg',
            __('Verification form Button Background Color', 'academic-certificate-verification'),
            array($this, 'download_button_bg_callback'),
            'certificate_verification_settings',
            'general_settings'
        );

        add_settings_field(
            'download_button_text',
            __('Verification form Button Text Color', 'academic-certificate-verification'),
            array($this, 'download_button_text_callback'),
            'certificate_verification_settings',
            'general_settings'
        );

        add_settings_field(
            'verification_message',
            __('Verification Message', 'academic-certificate-verification'),
            array($this, 'verification_message_callback'),
            'certificate_verification_settings',
            'general_settings'
        );


        $this->register_filter_settings();
    }

    /**
     * General settings section callback.
     *
     * Displays description for the general settings section.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function general_settings_section_callback() {
        echo '<p>' . esc_html__('Configure general settings for the certificate verification system.', 'academic-certificate-verification') . '</p>';
    }

    /**
     * Default institution field callback.
     *
     * Renders the default institution input field.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function default_institution_callback() {
        $options = get_option('acceve_certificate_verification_options');
        echo '<input type="text" id="default_institution" name="acceve_certificate_verification_options[default_institution]" value="' . esc_attr($options['default_institution'] ?? '') . '" class="regular-text">';
    }

    /**
     * Certificate prefix field callback.
     *
     * Renders the certificate ID prefix input field.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function certificate_prefix_callback() {
        $options = get_option('acceve_certificate_verification_options');
        echo '<input type="text" id="certificate_prefix" name="acceve_certificate_verification_options[certificate_prefix]" value="' . esc_attr($options['certificate_prefix'] ?? 'CERT-') . '" class="regular-text">';
        echo '<p class="description">' . esc_html__('This will be prepended to all certificate IDs.', 'academic-certificate-verification') . '</p>';
    }

    /**
     * Certificate template field callback.
     *
     * Renders the certificate template selection dropdown.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function certificate_template_callback() {
        $options  = get_option('acceve_certificate_verification_options');
        $template = isset($options['certificate_template']) ? $options['certificate_template'] : 'template_one';
        $is_pro   = class_exists('ACCEVE_Academic_Certificate_Verification_Pro');
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();

        // Get certificate templates from database if pro version is active
        $certificate_templates = array();
        if ($is_pro) {
            global $wpdb;
            $table_name = $wpdb->prefix . 'acceve_certificate_templates';
            if ($wpdb->get_var("SHOW TABLES LIKE '$table_name'") == $table_name) {
                $certificate_templates = $wpdb->get_results("SELECT id, template_name FROM $table_name ORDER BY template_name ASC", ARRAY_A);
            }
        }
        ?>

        <select name="acceve_certificate_verification_options[certificate_template]" id="certificate_template_select">
            <option value="template_one" <?php selected($template, 'template_one'); ?>>
                <?php esc_html_e('Template One', 'academic-certificate-verification'); ?>
            </option>

            <option <?php if(!$is_pro || !$is_active){ ?> disabled <?php }?> value="template_two" <?php selected($template, 'template_two'); ?>>
                <?php esc_html_e('Template Two', 'academic-certificate-verification'); ?>
            </option>

            <option <?php if(!$is_pro || !$is_active){ ?> disabled <?php }?> value="custom_template" <?php selected($template, 'custom_template'); ?>>
                <?php esc_html_e('Custom Template', 'academic-certificate-verification'); ?>
            </option>
        </select>

        <!-- Certificate Template Selector (shown only when custom_template is selected) -->
        <div id="custom_template_selector" style="margin-top: 10px; <?php echo ($template === 'custom_template' && $is_pro) ? '' : 'display: none;'; ?>">
            <label for="certificate_custom_template"><?php esc_html_e('Select Custom Template', 'academic-certificate-verification'); ?></label>
            <select name="acceve_certificate_verification_options[certificate_custom_template]" id="certificate_custom_template">
                <option value=""><?php esc_html_e('-- Select a template --', 'academic-certificate-verification'); ?></option>
                <?php if (!empty($certificate_templates)): ?>
                    <?php foreach ($certificate_templates as $ct): ?>
                        <option value="<?php echo esc_attr($ct['id']); ?>" <?php selected(isset($options['certificate_custom_template']) ? $options['certificate_custom_template'] : '', $ct['id']); ?>>
                            <?php echo esc_html($ct['template_name']); ?>
                        </option>
                    <?php endforeach; ?>
                <?php else: ?>
                    <option value="" disabled><?php esc_html_e('No custom templates found. Create templates in Certificate Maker.', 'academic-certificate-verification'); ?></option>
                <?php endif; ?>
            </select>
            <p class="description">
                <?php esc_html_e('Select a custom template created in Certificate Maker.', 'academic-certificate-verification'); ?>
                <?php if (!$is_pro): ?>
                    <br>
                    <span style="color: #dc3232;">
                    <?php esc_html_e('This feature requires the Pro version.', 'academic-certificate-verification'); ?>
                </span>
                <?php endif; ?>
            </p>
        </div>

        <p class="description">
            <?php esc_html_e('This will show different certificate templates on the frontend.', 'academic-certificate-verification'); ?>
        </p>

        <?php
    }

    /**
     * Enable date of birth callback.
     *
     * @since 1.0.2
     *
     * @return void
     */
    public function enable_date_of_birth_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $enabled = ! empty($options['enable_date_of_birth']);
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();
        ?>

        <label>
            <input type="checkbox"
                   name="acceve_certificate_verification_options[enable_date_of_birth]"
                   value="1" <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?>
                <?php checked($enabled, true); ?>>
            <?php esc_html_e('Show date of birth input field on certificate verification page', 'academic-certificate-verification'); ?>
        </label>

        <?php
    }

    /**
     * Enable download button callback.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function enable_download_button_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $enabled = ! empty($options['enable_download_button']);
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();
        ?>

        <label>
            <input type="checkbox"
                   name="acceve_certificate_verification_options[enable_download_button]"
                   value="1" <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?>
                <?php checked($enabled, true); ?>>
            <?php esc_html_e('Show download button on certificate page', 'academic-certificate-verification'); ?>
        </label>

        <?php
    }

    public function download_button_bg_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $color   = $options['download_button_bg_color'] ?? '#2271b1';
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();
        ?>

        <input type="color"
               class="acceve-color-picker" <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?>
               name="acceve_certificate_verification_options[download_button_bg_color]"
               value="<?php echo esc_attr($color); ?>"
               data-default-color="#2271b1">

        <p class="description">
            <?php esc_html_e('Select background color for the button.', 'academic-certificate-verification'); ?>
        </p>

        <?php
    }


    public function download_button_text_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $color   = $options['download_button_text_color'] ?? '#ffffff';
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();
        ?>

        <input type="color"
               class="acceve-color-picker" <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?>
               name="acceve_certificate_verification_options[download_button_text_color]"
               value="<?php echo esc_attr($color); ?>"
               data-default-color="#ffffff">

        <p class="description">
            <?php esc_html_e('Select text color for the button.', 'academic-certificate-verification'); ?>
        </p>

        <?php
    }

    /**
     * Verification message callback.
     *
     * @since 1.0.0
     */
    public function verification_message_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $default_message = __('This certificate is genuine and was issued by {institution} on {issue_date}.', 'academic-certificate-verification');
        $message = $options['verification_message'] ?? $default_message;
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();

        ?>
        <textarea <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?>
                name="acceve_certificate_verification_options[verification_message]"
                rows="3"
                class="large-text"><?php echo esc_textarea($message); ?></textarea>

        <p class="description">
            <?php esc_html_e('Available placeholders:', 'academic-certificate-verification'); ?>
            <code>{institution}</code>,
            <code>{issue_date}</code>,
            <code>{certificate_id}</code>,
            <code>{student_name}</code>
        </p>
        <?php
    }



    /**
     * Register filter settings
     * Add this to your register_settings() method
     */
    public function register_filter_settings() {
        // Add filter settings section
        add_settings_section(
            'filter_settings',
            __('Certificate Filter Settings', 'academic-certificate-verification'),
            array($this, 'filter_settings_section_callback'),
            'certificate_verification_settings'
        );

        add_settings_field(
            'filter_enabled',
            __('Enable Certificate Filter', 'academic-certificate-verification'),
            array($this, 'filter_enabled_callback'),
            'certificate_verification_settings',
            'filter_settings'
        );

        add_settings_field(
            'filter_fields',
            __('Filter By Fields', 'academic-certificate-verification'),
            array($this, 'filter_fields_callback'),
            'certificate_verification_settings',
            'filter_settings'
        );

        add_settings_field(
            'filter_layout',
            __('Filter Result Layout', 'academic-certificate-verification'),
            array($this, 'filter_layout_callback'),
            'certificate_verification_settings',
            'filter_settings'
        );
    }

    /**
     * Filter settings section callback
     */
    public function filter_settings_section_callback() {
        echo '<p>' . esc_html__('Configure certificate filtering options for the frontend.', 'academic-certificate-verification') . '</p>';
        echo '<p><strong>' . esc_html__('Shortcode:', 'academic-certificate-verification') . '</strong> <code>[acceve_certificate_filter]</code></p>';
    }

    /**
     * Filter enabled field callback
     */
    public function filter_enabled_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $enabled = isset($options['filter_enabled']) ? $options['filter_enabled'] : 0;
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();
        ?>
        <label>
            <input type="checkbox"
                   name="acceve_certificate_verification_options[filter_enabled]"
                   value="1" <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?>
                <?php checked($enabled, 1); ?>>
            <?php esc_html_e('Enable certificate filtering on frontend', 'academic-certificate-verification'); ?>
        </label>
        <?php
    }

    /**
     * Filter fields callback
     */
    public function filter_fields_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $selected_fields = isset($options['filter_fields']) ? $options['filter_fields'] : array();
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();

        $available_fields = array(
            'course_name' => __('Course Name', 'academic-certificate-verification'),
            'course_type' => __('Course Type', 'academic-certificate-verification'),
            'batch_name' => __('Batch Name', 'academic-certificate-verification'),
            'institution' => __('Institution', 'academic-certificate-verification'),
            'issue_date' => __('Issue Date', 'academic-certificate-verification'),
        );

        echo '<fieldset>';
        foreach ($available_fields as $field_key => $field_label) {
            $checked = is_array($selected_fields) && in_array($field_key, $selected_fields) ? 'checked' : '';
            ?>
            <label style="display: block; margin-bottom: 8px;">
                <input type="checkbox" <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?>
                       name="acceve_certificate_verification_options[filter_fields][]"
                       value="<?php echo esc_attr($field_key); ?>"
                    <?php echo $checked; ?>>
                <?php echo esc_html($field_label); ?>
            </label>
            <?php
        }
        echo '</fieldset>';
        echo '<p class="description">' . esc_html__('Select which fields to use for filtering certificates.', 'academic-certificate-verification') . '</p>';
    }

    /**
     * Filter layout callback
     */
    public function filter_layout_callback() {
        $options = get_option('acceve_certificate_verification_options');
        $layout = isset($options['filter_layout']) ? $options['filter_layout'] : 'grid';
        $license_handler = ACCEVE_License_Handler::get_instance();
        $is_active       = $license_handler->is_license_active();
        ?>
        <select <?php echo (!class_exists( 'ACCEVE_Academic_Certificate_Verification_Pro' ) || !$is_active) ? 'disabled' : ''; ?> name="acceve_certificate_verification_options[filter_layout]">
            <option value="grid" <?php selected($layout, 'grid'); ?>>
                <?php esc_html_e('Grid Layout', 'academic-certificate-verification'); ?>
            </option>
            <option value="list" <?php selected($layout, 'list'); ?>>
                <?php esc_html_e('List Layout', 'academic-certificate-verification'); ?>
            </option>
        </select>
        <p class="description"><?php esc_html_e('Choose how to display filtered results.', 'academic-certificate-verification'); ?></p>
        <?php
    }

    /**
     * Sanitize settings callback.
     *
     * Sanitizes and validates plugin settings before saving.
     *
     * @since 1.0.0
     *
     * @param array $input The input values from the form.
     *
     * @return array Sanitized values.
     */
    public function acceve_sanitize_settings($input) {
        $sanitized = array();

        if (isset($input['default_institution'])) {
            $sanitized['default_institution'] = sanitize_text_field($input['default_institution']);
        }

        if (isset($input['certificate_prefix'])) {
            $sanitized['certificate_prefix'] = preg_replace('/[^A-Za-z0-9\-]/', '', $input['certificate_prefix']);
            if (empty($sanitized['certificate_prefix'])) {
                $sanitized['certificate_prefix'] = 'CERT-';
            }
        }

        if (isset($input['certificate_template'])) {
            $allowed_templates = array('template_one', 'template_two', 'custom_template');
            $sanitized['certificate_template'] = in_array($input['certificate_template'], $allowed_templates)
                ? $input['certificate_template']
                : 'template_one';

            // Only save custom template ID if custom_template is selected
            if ($input['certificate_template'] === 'custom_template' && isset($input['certificate_custom_template'])) {
                $sanitized['certificate_custom_template'] = intval($input['certificate_custom_template']);
            }
        }

        // NEW: Download button settings
        $sanitized['enable_date_of_birth']   = isset($input['enable_date_of_birth']) ? 1 : 0;
        $sanitized['enable_download_button'] = isset($input['enable_download_button']) ? 1 : 0;

        if (isset($input['download_button_bg_color'])) {
            $sanitized['download_button_bg_color'] = sanitize_hex_color($input['download_button_bg_color']);
        }

        if (isset($input['download_button_text_color'])) {
            $sanitized['download_button_text_color'] = sanitize_hex_color($input['download_button_text_color']);
        }

        if (isset($input['verification_message'])) {
            $sanitized['verification_message'] = sanitize_textarea_field($input['verification_message']);
        }

        // NEW: Filter settings sanitization
        $sanitized['filter_enabled'] = isset($input['filter_enabled']) ? 1 : 0;

        if (isset($input['filter_fields']) && is_array($input['filter_fields'])) {
            $sanitized['filter_fields'] = array_map('sanitize_text_field', $input['filter_fields']);
        } else {
            $sanitized['filter_fields'] = array();
        }

        if (isset($input['filter_layout'])) {
            $sanitized['filter_layout'] = in_array($input['filter_layout'], array('grid', 'list'))
                ? $input['filter_layout']
                : 'grid';
        }

        return $sanitized;
    }

    /**
     * Admin dashboard page.
     *
     * Displays the main certificates listing with statistics.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function admin_dashboard() {

        if (!class_exists('WP_List_Table')) {
            require_once ABSPATH . 'wp-admin/includes/class-wp-list-table.php';
        }

        require_once ACCEVE_PATH . 'includes/class-certificates-list-table.php';

        // Create an instance of our custom list table
        $certificates_table = new ACCEVE_Certificates_List_Table();
        $certificates_table->prepare_items();

        $total_certificates   = $this->get_certificate_count();
        $active_certificates  = $this->get_certificate_count('active');
        $expired_certificates = $this->get_certificate_count('expired');

        include ACCEVE_PATH . 'templates/admin/dashboard.php';
    }

    /**
     * Get certificate count by status.
     *
     * Retrieves the count of certificates based on status.
     *
     * @since 1.0.0
     *
     * @global wpdb $wpdb WordPress database abstraction object.
     *
     * @param string $status The status to filter by: 'all', 'active', or 'expired'.
     *
     * @return int Number of certificates.
     */
    private function get_certificate_count($status = 'all') {
        global $wpdb;
        $table_name = $wpdb->prefix . 'acceve_certificate_verification';
        $query      = "SELECT COUNT(*) FROM $table_name";

        switch ($status) {
            case 'active':
                $query .= " WHERE is_active = 1 AND (expiry_date IS NULL OR expiry_date >= CURDATE())";
                break;
            case 'expired':
                $query .= " WHERE (expiry_date IS NOT NULL AND expiry_date < CURDATE()) OR is_active = 0";
                break;
        }

        // phpcs:ignore
        return $wpdb->get_var($query);
    }

    /**
     * Add/Edit certificate page.
     *
     * Displays the form for adding or editing a certificate.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function add_certificate_page() {
        $certificate = null;

        // Check if this is an edit request
        if (isset($_GET['action']) && $_GET['action'] === 'edit' && isset($_GET['certificate_id'])) {
            $db = ACCEVE_Certificate_Verification_Database::get_instance();
            // phpcs:ignore
            $certificate = $db->get_certificate(sanitize_text_field(wp_unslash($_GET['certificate_id'])));

            if (!$certificate) {
                wp_die(esc_html__('Certificate not found.', 'academic-certificate-verification'));
            }
        }

        // phpcs:ignore
        if ($_SERVER['REQUEST_METHOD'] === 'POST' && check_admin_referer('add_certificate')) {
            $this->process_add_certificate();
        }

        include ACCEVE_PATH . 'templates/admin/add-certificate.php';
    }

    /**
     * Process add/edit certificate form submission.
     *
     * Handles the submission of the certificate form for both
     * adding new certificates and editing existing ones.
     * Save custom fields data when certificate is saved
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function process_add_certificate() {
        // Verify nonce
        if (!isset($_POST['_wpnonce']) || !wp_verify_nonce(sanitize_text_field(wp_unslash($_POST['_wpnonce'])), 'add_certificate')) {
            wp_die(esc_html__('Security check failed.', 'academic-certificate-verification'));
        }

        // Check user capabilities
        if (!current_user_can('manage_options')) {
            wp_die(esc_html__('You do not have sufficient permissions to access this page.', 'academic-certificate-verification'));
        }

        // Prepare certificate data - START WITH BASIC FIELDS
        $data = array(
            'certificate_id' => isset($_POST['certificate_id']) ? sanitize_text_field(wp_unslash($_POST['certificate_id'])) : '',
            'student_name'   => isset($_POST['student_name']) ? sanitize_text_field(wp_unslash($_POST['student_name'])) : '',
            'birth_date'     => isset($_POST['birth_date']) ? sanitize_text_field(wp_unslash($_POST['birth_date'])) : '0000-00-00',
            'course_type'    => isset($_POST['course_type']) ? sanitize_text_field(wp_unslash($_POST['course_type'])) : '',
            'course_name'    => isset($_POST['course_name']) ? sanitize_text_field(wp_unslash($_POST['course_name'])) : '',
            'batch_name'     => isset($_POST['batch_name']) ? sanitize_text_field(wp_unslash($_POST['batch_name'])) : '',
            'institution'    => isset($_POST['institution']) ? sanitize_text_field(wp_unslash($_POST['institution'])) : '',
            'issue_date'     => isset($_POST['issue_date']) ? sanitize_text_field(wp_unslash($_POST['issue_date'])) : '',
            'is_active'      => 1
        );

        // Handle custom fields - MOVE THIS TO BE PART OF THE MAIN DATA ARRAY
        if (isset($_POST['custom_fields']) && is_array($_POST['custom_fields'])) {
            $custom_fields_data = array();
            foreach ($_POST['custom_fields'] as $field_name => $field_value) {
                // Sanitize based on type
                if (is_array($field_value)) {
                    // For checkboxes - store as comma-separated string
                    $sanitized_values = array_map('sanitize_text_field', $field_value);
                    $custom_fields_data[sanitize_key($field_name)] = implode(',', $sanitized_values);
                } else {
                    $custom_fields_data[sanitize_key($field_name)] = sanitize_text_field($field_value);
                }
            }
            $data['custom_fields'] = wp_json_encode($custom_fields_data);
        } else {
            // If no custom fields are submitted, set to empty JSON
            $data['custom_fields'] = wp_json_encode(array());
        }

        // Handle optional fields
        if (!empty($_POST['expiry_date'])) {
            $data['expiry_date'] = sanitize_text_field(wp_unslash($_POST['expiry_date']));
        } else {
            $data['expiry_date'] = null;
        }

        if (!empty($_POST['additional_data'])) {
            $data['additional_data'] = sanitize_textarea_field(wp_unslash($_POST['additional_data']));
        }

        $db = ACCEVE_Certificate_Verification_Database::get_instance();

        // Check if this is an update
        if (!empty($_POST['original_certificate_id'])) {
            $original_id = sanitize_text_field(wp_unslash($_POST['original_certificate_id']));
            $result = $db->update_certificate($original_id, $data);
        } else {
            // New certificate
            $options = get_option('acceve_certificate_verification_options');
            $data['verification_code'] = wp_generate_password(8, false);
            $result = $db->add_certificate($data);
        }

        // Handle result
        if ($result) {
            wp_safe_redirect(admin_url('admin.php?page=certificate_verification&updated=1'));
            exit;
        } else {
            $error = __('Error saving certificate.', 'academic-certificate-verification');
            if (!empty($_POST['original_certificate_id'])) {
                // phpcs:ignore
                wp_safe_redirect(admin_url('admin.php?page=certificate_verification_add&action=edit&certificate_id=' . urlencode($_POST['original_certificate_id']) . '&error=' . urlencode($error)));
            } else {
                wp_safe_redirect(admin_url('admin.php?page=certificate_verification_add&error=' . urlencode($error)));
            }
            exit;
        }
    }

    /**
     * Import certificates page.
     *
     * Displays the import certificates interface.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function import_certificates_page() {
        include ACCEVE_PATH . 'templates/admin/import-certificates.php';
    }

    /**
     * Handle certificate actions.
     *
     * Processes certificate actions like delete from URL parameters.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function handle_certificate_actions() {
        // phpcs:ignore
        if (isset($_GET['action']) && $_GET['action'] === 'delete' && isset($_GET['certificate_id'])) {
            $this->delete_certificate();
        }
    }

    /**
     * Delete a single certificate.
     *
     * Handles deletion of individual certificates with security checks.
     *
     * @since 1.0.0
     *
     * @return void
     */
    private function delete_certificate() {
        if (!isset($_GET['certificate_id']) || !isset($_GET['_wpnonce'])) {
            wp_die(esc_html__('Invalid request.', 'academic-certificate-verification'));
        }

        $certificate_id = sanitize_text_field(wp_unslash($_GET['certificate_id']));

        $nonce = sanitize_text_field(wp_unslash($_GET['_wpnonce']));

        // Verify nonce
        if (!wp_verify_nonce($nonce, 'delete_certificate_' . $certificate_id)) {
            wp_die(esc_html__('Security check failed.', 'academic-certificate-verification'));
        }

        $db = ACCEVE_Certificate_Verification_Database::get_instance();
        $result = $db->delete_certificate($certificate_id);

        if ($result) {
            wp_safe_redirect(admin_url('admin.php?page=certificate_verification&deleted=1'));
            exit;
        } else {
            wp_safe_redirect(admin_url('admin.php?page=certificate_verification&deleted=0'));
            exit;
        }
    }

    /**
     * Settings page.
     *
     * Displays the plugin settings page.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function settings_page() {
        include ACCEVE_PATH . 'templates/admin/settings.php';
    }

    /**
     * Upgrade Pro page.
     *
     * Displays the Pro version upgrade page with features and contact information.
     *
     * @since 1.0.0
     *
     * @return void
     */

    public function upgrade_pro_page() {
        // Security check
        if (!current_user_can('manage_options')) {
            wp_die(esc_html__('You do not have sufficient permissions.', 'academic-certificate-verification'));
        }

        // Get license handler
        $license_handler = ACCEVE_License_Handler::get_instance();
        $license_info = $license_handler->get_license_info();
        $is_active = $license_handler->is_license_active();

        ?>
        <div class="wrap">
            <h1><?php esc_html_e('Upgrade to Pro', 'academic-certificate-verification'); ?></h1>

            <?php if ($is_active): ?>
                <!-- License Active -->
                <div class="notice notice-success">
                    <p>
                        <strong><?php esc_html_e('✓ Pro License Active', 'academic-certificate-verification'); ?></strong>
                    </p>
                </div>
            <?php else: ?>
                <!-- License Inactive -->
                <div class="notice notice-info">
                    <p><?php esc_html_e('Activate your Pro license to unlock all features.', 'academic-certificate-verification'); ?></p>
                </div>
            <?php endif; ?>

            <div style="display: flex; gap: 20px; margin-top: 20px;">
                <!-- License Activation Card -->
                <div class="card" style="flex: 1; max-width: 500px;">
                    <h2 class="title"><?php esc_html_e('License Activation', 'academic-certificate-verification'); ?></h2>
                    <div class="inside">
                        <?php if (!$is_active): ?>
                            <!-- Activation Form -->
                            <form id="license-activation-form">
                                <?php wp_nonce_field('acceve_license_nonce', 'acceve_license_nonce'); ?>

                                <table class="form-table">
                                    <tr>
                                        <th><label for="license_key"><?php esc_html_e('License Key', 'academic-certificate-verification'); ?></label></th>
                                        <td>
                                            <input type="text"
                                                   name="license_key"
                                                   id="license_key"
                                                   class="regular-text"
                                                   placeholder="XXXXXXXX-XXXXXXXX-XXXXXXXX-XXXXXXXX"
                                                   value="<?php echo esc_attr($license_info['license_key'] ?? ''); ?>"
                                                   required>
                                            <p class="description">
                                                <?php esc_html_e('Enter your license key received after purchase', 'academic-certificate-verification'); ?>
                                            </p>
                                        </td>
                                    </tr>
                                </table>

                                <p class="submit">
                                    <button type="submit" class="button button-primary" id="activate-license-btn">
                                        <?php esc_html_e('Activate License', 'academic-certificate-verification'); ?>
                                    </button>
                                    <span class="spinner" style="float: none; margin: 0 10px;"></span>
                                </p>

                                <div id="license-message" style="margin-top: 10px;"></div>
                            </form>
                        <?php else: ?>
                            <!-- License Info -->
                            <table class="form-table">
                                <tr>
                                    <th><?php esc_html_e('License Key', 'academic-certificate-verification'); ?></th>
                                    <td>
                                        <code><?php echo esc_html($license_info['license_key']); ?></code>
                                    </td>
                                </tr>
                                <tr>
                                    <th><?php esc_html_e('Status', 'academic-certificate-verification'); ?></th>
                                    <td>
                                    <span style="color: #46b450; font-weight: bold;">
                                        ✓ <?php esc_html_e('Active', 'academic-certificate-verification'); ?>
                                    </span>
                                    </td>
                                </tr>
                                <?php if (!empty($license_info['expiry'])): ?>
                                    <tr>
                                        <th><?php esc_html_e('Expiry Date', 'academic-certificate-verification'); ?></th>
                                        <td>
                                            <?php
                                            $expiry_date = strtotime($license_info['expiry']);
                                            echo date('F j, Y', $expiry_date);

                                            $days_left = ceil(($expiry_date - time()) / 86400);
                                            if ($days_left > 0) {
                                                echo ' <small>(' . sprintf(_n('%d day left', '%d days left', $days_left, 'academic-certificate-verification'), $days_left) . ')</small>';
                                            }
                                            ?>
                                        </td>
                                    </tr>
                                <?php else: ?>
                                    <tr>
                                        <th><?php esc_html_e('License Type', 'academic-certificate-verification'); ?></th>
                                        <td><?php esc_html_e('Lifetime', 'academic-certificate-verification'); ?></td>
                                    </tr>
                                <?php endif; ?>
                                <?php if (!empty($license_info['data'])): ?>
                                    <tr>
                                        <th><?php esc_html_e('Activations', 'academic-certificate-verification'); ?></th>
                                        <td>
                                            <?php echo esc_html($license_info['data']['active_sites']); ?> /
                                            <?php echo esc_html($license_info['data']['total_sites']); ?>
                                        </td>
                                    </tr>
                                <?php endif; ?>
                                <?php if (!empty($license_info['last_check'])): ?>
                                    <tr>
                                        <th><?php esc_html_e('Last Verified', 'academic-certificate-verification'); ?></th>
                                        <td>
                                            <?php echo human_time_diff($license_info['last_check'], time()) . ' ' . __('ago', 'academic-certificate-verification'); ?>
                                        </td>
                                    </tr>
                                <?php endif; ?>
                            </table>
                        <?php endif; ?>

                        <hr style="margin: 20px 0;">

                        <p style="text-align: center;">
                            <strong><?php esc_html_e('Don\'t have a license yet?', 'academic-certificate-verification'); ?></strong><br>
                            <a href="https://wa.me/8801703008720"
                               target="_blank"
                               class="button button-secondary"
                               style="margin-top: 10px;">
                                <span class="dashicons dashicons-whatsapp" style="vertical-align: middle;"></span>
                                <?php esc_html_e('Contact on WhatsApp', 'academic-certificate-verification'); ?>
                            </a>
                        </p>
                    </div>
                </div>

                <!-- Pro Features Card -->
                <div class="card" style="flex: 1;">
                    <h2 class="title"><?php esc_html_e('Pro Version Features', 'academic-certificate-verification'); ?></h2>
                    <div class="inside">
                        <ul style="list-style-type: none; padding: 0;">
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Custom Certificate Templates', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Certificate Maker (Drag & Drop Editor)', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Custom Fields Support', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Course Management', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Batch Management', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Bulk Import/Export (CSV & Excel)', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Advanced Certificate Filtering', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('PDF Download with Customization', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Date of Birth Verification', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Custom Verification Messages', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0; border-bottom: 1px solid #eee;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Advanced Reporting', 'academic-certificate-verification'); ?>
                            </li>
                            <li style="padding: 10px 0;">
                                <span class="dashicons dashicons-yes" style="color: #46b450;"></span>
                                <?php esc_html_e('Priority Support & Updates', 'academic-certificate-verification'); ?>
                            </li>
                        </ul>
                    </div>
                </div>
            </div>
        </div>

        <script>
            jQuery(document).ready(function($) {
                // Activate License
                $('#license-activation-form').on('submit', function(e) {
                    e.preventDefault();

                    var $form = $(this);
                    var $btn = $('#activate-license-btn');
                    var $spinner = $form.find('.spinner');
                    var $message = $('#license-message');
                    var license_key = $('#license_key').val().trim();

                    if (!license_key) {
                        $message.html('<div class="notice notice-error inline"><p><?php esc_html_e('Please enter a license key', 'academic-certificate-verification'); ?></p></div>');
                        return;
                    }

                    $btn.prop('disabled', true);
                    $spinner.addClass('is-active');
                    $message.html('');

                    $.ajax({
                        url: ajaxurl,
                        type: 'POST',
                        data: {
                            action: 'acceve_activate_license',
                            nonce: $('#acceve_license_nonce').val(),
                            license_key: license_key
                        },
                        success: function(response) {
                            if (response.success) {
                                $message.html('<div class="notice notice-success inline"><p>' + response.data.message + '</p></div>');
                                setTimeout(function() {
                                    location.reload();
                                }, 1500);
                            } else {
                                $message.html('<div class="notice notice-error inline"><p>' + response.data + '</p></div>');
                            }
                        },
                        error: function() {
                            $message.html('<div class="notice notice-error inline"><p><?php esc_html_e('An error occurred. Please try again.', 'academic-certificate-verification'); ?></p></div>');
                        },
                        complete: function() {
                            $btn.prop('disabled', false);
                            $spinner.removeClass('is-active');
                        }
                    });
                });
            });
        </script>

        <style>
            .notice.inline {
                margin: 0;
                padding: 8px 12px;
            }
            .notice.inline p {
                margin: 0.5em 0;
            }
        </style>
        <?php
    }

    /**
     * Custom fields page.
     *
     * This is pro version.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function manage_custom_fields_page(){
        // Security check
        if (!current_user_can('manage_options')) {
            wp_die(esc_html__('You do not have sufficient permissions.', 'academic-certificate-verification'));
        }

        global $wpdb;
        $table_name = $wpdb->prefix . 'acceve_custom_fields';

        // Get custom fields
        $custom_fields = $this->get_all_custom_fields();

        // Get field for editing if action is edit
        $edit_field = null;
        if (isset($_GET['action']) && $_GET['action'] === 'edit' && isset($_GET['field_id'])) {
            $field_id = intval($_GET['field_id']);
            $edit_field = $wpdb->get_row($wpdb->prepare("SELECT * FROM {$table_name} WHERE id = %d", $field_id));
        }

        // Include template
        include ACCEVE_PATH . 'templates/admin/custom-fields.php';
    }

    /**
     * Get all custom fields.
     *
     * @return array
     * @since 1.0.2
     */
    private function get_all_custom_fields() {
        global $wpdb;
        $table_name = $wpdb->prefix . 'acceve_custom_fields';

        return $wpdb->get_results("SELECT * FROM {$table_name} ORDER BY field_order ASC, id ASC", ARRAY_A);
    }

    /**
     * All Courses page.
     *
     * This is pro version.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function manage_add_courses_page(){
        // Security check
        if (!current_user_can('manage_options')) {
            wp_die(esc_html__('You do not have sufficient permissions.', 'academic-certificate-verification'));
        }

        // Include template
        include ACCEVE_PATH . 'templates/admin/add-courses.php';
    }

    /**
     * All Batches page.
     *
     * This is pro version.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function manage_add_batches_page(){
        // Security check
        if (!current_user_can('manage_options')) {
            wp_die(esc_html__('You do not have sufficient permissions.', 'academic-certificate-verification'));
        }

        // Include template
        include ACCEVE_PATH . 'templates/admin/add-batches.php';
    }

    /**
     * Certificate maker page.
     *
     * This is pro version.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function certificate_maker_page(){
        // Security check
        if (!current_user_can('manage_options')) {
            wp_die(esc_html__('You do not have sufficient permissions.', 'academic-certificate-verification'));
        }

        // Get saved templates
        $templates = $this->get_certificate_templates();
        $current_template_id = isset($_GET['template_id']) ? intval($_GET['template_id']) : 0;
        $current_template = null;

        if ($current_template_id > 0) {
            foreach ($templates as $template) {
                if ($template['id'] == $current_template_id) {
                    $current_template = $template;
                    break;
                }
            }
        }

        include ACCEVE_PATH . 'templates/admin/certificate-maker.php';
    }

    /**
     * Get all certificate templates from database.
     *
     * @return array
     * @since 1.0.0
     */
    private function get_certificate_templates() {
        global $wpdb;
        $table_name = $wpdb->prefix . 'acceve_certificate_templates';

        $results = $wpdb->get_results("SELECT * FROM {$table_name} ORDER BY created_at DESC", ARRAY_A);

        return $results ? $results : array();
    }

    /**
     * Handle CSV export.
     *
     * Processes AJAX request for exporting certificates to CSV format.
     *
     * @since 1.0.0
     *
     * @global wpdb $wpdb WordPress database abstraction object.
     *
     * @return void Sends CSV file as download.
     */
    public function handle_csv_export() {
        // Verify nonce
        check_ajax_referer('certificate_verification_nonce_admin', 'security');

        // Check permissions
        if (!current_user_can('manage_options')) {
            wp_die('Unauthorized');
        }

        global $wpdb;
        $table_name = $wpdb->prefix . 'acceve_certificate_verification';

        // phpcs:ignore
        $certificate_ids = isset($_POST['certificate_ids']) ? array_map('sanitize_text_field', $_POST['certificate_ids']) : array();

        // Build query
        if (!empty($certificate_ids)) {
            $placeholders = array_fill(0, count($certificate_ids), '%s');
            $format = implode(', ', $placeholders);
            // phpcs:ignore
            $query = $wpdb->prepare("SELECT * FROM {$table_name} WHERE certificate_id IN ($format)",$certificate_ids);
        } else {
            // Export all if none selected
            $query = "SELECT * FROM {$table_name}";
        }

        // phpcs:ignore
        $results = $wpdb->get_results($query, ARRAY_A);

        if (empty($results)) {
            wp_die('No certificates found');
        }

        // Set headers for CSV download
        header('Content-Type: text/csv; charset=utf-8');
        header('Content-Disposition: attachment; filename=certificates_' . gmdate('Y-m-d_H-i-s') . '.csv');

        // Create output stream
        $output = fopen('php://output', 'w');

        // phpcs:ignore
        fputs($output, $bom = (chr(0xEF) . chr(0xBB) . chr(0xBF)));

        // Add headers
        $headers = array(
            'Certificate ID',
            'Student Name',
            'Date of Birth',
            'Course Type',
            'Course Name',
            'Batch Name',
            'Institution',
            'Issue Date',
            'Expiry Date',
            'Verification Code',
            'Status',
            'Created At'
        );
        fputcsv($output, $headers);

        // Add data rows
        foreach ($results as $row) {
            $status = 'Active';
            if (!$row['is_active']) {
                $status = 'Inactive';
            } elseif ($row['expiry_date'] && strtotime($row['expiry_date']) < time()) {
                $status = 'Expired';
            }

            $data = array(
                $row['certificate_id'],
                $row['student_name'],
                $row['birth_date'],
                $row['course_type'],
                $row['course_name'],
                $row['batch_name'] ?? '',
                $row['institution'],
                $row['issue_date'],
                $row['expiry_date'],
                $row['verification_code'],
                $status,
                $row['created_at']
            );
            fputcsv($output, $data);
        }

        // phpcs:ignore
        fclose($output);
        exit;
    }

    /**
     * Handle bulk delete.
     *
     * Processes AJAX request for bulk deletion of certificates.
     *
     * @since 1.0.0
     *
     * @global wpdb $wpdb WordPress database abstraction object.
     *
     * @return void Sends JSON response with success or error.
     */
    public function handle_bulk_delete() {
        // Verify nonce
        check_ajax_referer('certificate_verification_nonce_admin', 'security');

        // Check permissions
        if (!current_user_can('manage_options')) {
            wp_send_json_error('Unauthorized');
        }

        // phpcs:ignore
        $certificate_ids = isset($_POST['certificate_ids']) ? array_map('sanitize_text_field', $_POST['certificate_ids']) : array();

        if (empty($certificate_ids)) {
            wp_send_json_error('No certificates selected');
        }

        global $wpdb;
        $table_name = $wpdb->prefix . 'acceve_certificate_verification';
        $deleted    = 0;

        foreach ($certificate_ids as $certificate_id) {
            // phpcs:ignore
            $result = $wpdb->delete(
                $table_name,
                array('certificate_id' => $certificate_id),
                array('%s')
            );

            if ($result !== false) {
                $deleted++;
            }
        }

        if ($deleted > 0) {
            wp_send_json_success(array(
                /* translators: %d: Number of certificates deleted */
                'message' => sprintf(__('%d certificate(s) deleted successfully', 'academic-certificate-verification'), $deleted)
            ));
        } else {
            wp_send_json_error('Failed to delete certificates');
        }
    }


    /**
     * Get all active custom fields
     *
     * @return array
     * @since 1.0.2
     */
    public function get_custom_fields_for_certificate() {
        global $wpdb;
        $table_name = $wpdb->prefix . 'acceve_custom_fields';

        return $wpdb->get_results("SELECT * FROM {$table_name} ORDER BY field_order ASC, id ASC");
    }

    /**
     * Render custom fields in certificate form
     *
     * @param object|null $certificate Certificate object if editing
     * @return void
     * @since 1.0.2
     */
    public function render_custom_fields_in_form($certificate = null) {
        $custom_fields = $this->get_custom_fields_for_certificate();

        if (empty($custom_fields)) {
            return;
        }

        // Get existing custom field values
        $custom_values = array();
        if ($certificate && !empty($certificate->custom_fields)) {
            $custom_values = json_decode($certificate->custom_fields, true);
            if (!is_array($custom_values)) {
                $custom_values = array();
            }
        }

        echo '<h3>' . esc_html__('Custom Fields', 'academic-certificate-verification') . '</h3>';

        foreach ($custom_fields as $field) {
            $field_value = isset($custom_values[$field->field_name]) ? $custom_values[$field->field_name] : '';
            $required = $field->is_required ? 'required' : '';
            $required_mark = $field->is_required ? ' <span class="required">*</span>' : '';

            echo '<div class="form-group">';
            echo '<label for="custom_' . esc_attr($field->field_name) . '">';
            echo esc_html($field->field_label) . $required_mark;
            echo '</label>';

            switch ($field->field_type) {
                case 'textarea':
                    echo '<textarea name="custom_fields[' . esc_attr($field->field_name) . ']" ';
                    echo 'id="custom_' . esc_attr($field->field_name) . '" ';
                    echo 'rows="4" ' . esc_attr($required) . '>';
                    echo esc_textarea($field_value);
                    echo '</textarea>';
                    break;

                case 'select':
                    $options = explode("\n", $field->field_options);
                    echo '<select name="custom_fields[' . esc_attr($field->field_name) . ']" ';
                    echo 'id="custom_' . esc_attr($field->field_name) . '" ' . esc_attr($required) . '>';
                    echo '<option value="">-- ' . esc_html__('Select', 'academic-certificate-verification') . ' --</option>';
                    foreach ($options as $option) {
                        $option = trim($option);
                        if (!empty($option)) {
                            $selected = ($field_value === $option) ? 'selected' : '';
                            echo '<option value="' . esc_attr($option) . '" ' . esc_attr($selected) . '>';
                            echo esc_html($option);
                            echo '</option>';
                        }
                    }
                    echo '</select>';
                    break;

                case 'checkbox':
                    $options = explode("\n", $field->field_options);
                    // Handle stored comma-separated values
                    if (is_string($field_value)) {
                        $selected_values = explode(',', $field_value);
                    } else {
                        $selected_values = is_array($field_value) ? $field_value : array();
                    }
                    $selected_values = array_map('trim', $selected_values);

                    echo '<div class="checkbox-group">';
                    foreach ($options as $option) {
                        $option = trim($option);
                        if (!empty($option)) {
                            $checked = in_array($option, $selected_values) ? 'checked' : '';
                            echo '<label style="display: block; margin-bottom: 5px;">';
                            echo '<input type="checkbox" ';
                            echo 'name="custom_fields[' . esc_attr($field->field_name) . '][]" ';
                            echo 'value="' . esc_attr($option) . '" ' . esc_attr($checked) . '> ';
                            echo esc_html($option);
                            echo '</label>';
                        }
                    }
                    echo '</div>';
                    break;

                case 'number':
                case 'email':
                case 'url':
                case 'date':
                    echo '<input type="' . esc_attr($field->field_type) . '" ';
                    echo 'name="custom_fields[' . esc_attr($field->field_name) . ']" ';
                    echo 'id="custom_' . esc_attr($field->field_name) . '" ';
                    echo 'value="' . esc_attr($field_value) . '" ' . esc_attr($required) . '>';
                    break;

                default: // text
                    echo '<input type="text" ';
                    echo 'name="custom_fields[' . esc_attr($field->field_name) . ']" ';
                    echo 'id="custom_' . esc_attr($field->field_name) . '" ';
                    echo 'value="' . esc_attr($field_value) . '" ' . esc_attr($required) . '>';
                    break;
            }

            echo '</div>';
        }
    }

    /**
     * Load admin assets.
     *
     * Enqueues CSS and JavaScript files for admin pages.
     *
     * @since 1.0.0
     *
     * @param string $hook The current admin page hook.
     *
     * @return void
     */
    public function load_admin_assets($hook){
        wp_enqueue_style(
            'cert-maker-admin',
            ACCEVE_URL . 'assets/css/certificate-maker.css',
            array(),
            ACCEVE_VERSION
        );

        if (strpos($hook, 'certificate_verification') === false) {
            return;
        }

        $options = get_option('acceve_certificate_verification_options');

        wp_enqueue_style('wp-color-picker');
        wp_enqueue_style(
            'cert-verification-admin',
            ACCEVE_URL . 'assets/css/admin.css',
            array(),
            ACCEVE_VERSION
        );

        wp_enqueue_script(
            'cert-verification-admin',
            ACCEVE_URL . 'assets/js/admin.js',
            array('jquery', 'wp-color-picker'),
            ACCEVE_VERSION,
            true
        );

        wp_localize_script( 'cert-verification-admin',
            'acceve_certificate_verification_admin',
            array(
                'nonce'               => wp_create_nonce( 'certificate_verification_nonce_admin' ),
                'ajax_url'            => admin_url( 'admin-ajax.php' ),
                'certificate_prefix'  => $options['certificate_prefix'] ?? 'CERT-',
            )
        );
    }
}