<?php
/**
 * Settings configuration manager.
 *
 * @package AISupportAssistant\Admin
 */

namespace AISupportAssistant\Admin;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Class Settings
 */
class Settings {

	/**
	 * Single instance of the class.
	 *
	 * @var Settings|null
	 */
	private static ?Settings $instance = null;

	/**
	 * Option key in wp_options.
	 *
	 * @var string
	 */
	private const OPTION_KEY = 'ai_support_assistant_settings';

	/**
	 * Cached settings.
	 *
	 * @var array|null
	 */
	private ?array $settings = null;

	/**
	 * Get the active instance of the class.
	 *
	 * @return Settings
	 */
	public static function get_instance(): Settings {
		if ( null === self::$instance ) {
			self::$instance = new self();
		}
		return self::$instance;
	}

	/**
	 * Settings constructor.
	 */
	private function __construct() {
		$this->load();
	}

	/**
	 * Get default settings values.
	 *
	 * @return array
	 */
	public function get_defaults(): array {
		$default_provider = \AISupportAssistant\Providers\WordPressAIProvider::is_available() ? 'wp_native_ai' : 'gemini';
		return array(
			'ai_provider'            => $default_provider,
			'openai_api_key'         => '',
			'openai_chat_model'      => '',
			'openai_embedding_model' => '',
			'gemini_api_key'         => '',
			'gemini_chat_model'      => '',
			'gemini_embedding_model' => '',
			'vector_store'           => 'mysql',
			'temperature'            => 0.2,
			'max_tokens'             => 1000,
			'top_k'                  => 5,
			'similarity_threshold'   => 0.5,
			'chunk_size'             => 700,
			'chunk_overlap'          => 100,
			'enable_streaming'       => 1,
			'enable_chat_history'    => 1,
			'enable_citations'       => 1,
			'chat_rate_limit'        => 20,
			'show_powered_by'        => 0,
			'chat_widget_title'      => 'AI Support Assistant',
			'chat_widget_greeting'   => 'Hello! I am your documentation assistant. Ask me anything, and I will search our guide files to help you.',
			'ai_system_instruction'  => 'You are a customer support assistant. Answer ONLY using the supplied documentation. Do not invent information. Provide concise and accurate answers.',
			'chat_fallback_message'  => 'I couldn\'t find that information in the uploaded documentation.',
		);
	}

	/**
	 * Load settings from database.
	 *
	 * @return void
	 */
	private function load(): void {
		$db_options = get_option( self::OPTION_KEY, array() );
		if ( ! is_array( $db_options ) ) {
			$db_options = array();
		}
		$this->settings = wp_parse_args( $db_options, $this->get_defaults() );
	}

	/**
	 * Get all settings array.
	 *
	 * @return array
	 */
	public function get_all(): array {
		if ( null === $this->settings ) {
			$this->load();
		}
		return $this->settings;
	}

	/**
	 * Get a specific settings value by key.
	 *
	 * @param string $key Settings key.
	 * @param mixed  $default Optional default fallback.
	 * @return mixed
	 */
	public function get( string $key, $default = null ) {
		$all = $this->get_all();
		if ( array_key_exists( $key, $all ) ) {
			return $all[ $key ];
		}
		return $default;
	}

	/**
	 * Read a provider credential without requiring it to be stored in wp_options.
	 * Hosts may define these constants in wp-config.php.
	 */
	public function get_secret( string $key ): string {
		$constants = array(
			'openai_api_key' => 'AI_SUPPORT_ASSISTANT_OPENAI_API_KEY',
			'gemini_api_key' => 'AI_SUPPORT_ASSISTANT_GEMINI_API_KEY',
		);
		if ( isset( $constants[ $key ] ) && defined( $constants[ $key ] ) ) {
			return trim( (string) constant( $constants[ $key ] ) );
		}
		return trim( (string) $this->get( $key, '' ) );
	}

	/**
	 * Update settings.
	 *
	 * @param array $new_settings Settings to update.
	 * @return bool True if value changed and update succeeded.
	 */
	public function save( array $new_settings ): bool {
		$current   = $this->get_all();
		$sanitized = array();

		foreach ( $this->get_defaults() as $key => $default_val ) {
			if ( isset( $new_settings[ $key ] ) ) {
				// Secret inputs are intentionally blank in the UI. Blank means preserve the existing value.
				if ( in_array( $key, array( 'openai_api_key', 'gemini_api_key' ), true ) && '' === trim( (string) $new_settings[ $key ] ) ) {
					$sanitized[ $key ] = $current[ $key ] ?? $default_val;
					continue;
				}
				if ( is_int( $default_val ) ) {
					$sanitized[ $key ] = (int) $new_settings[ $key ];
				} elseif ( is_float( $default_val ) ) {
					$sanitized[ $key ] = (float) $new_settings[ $key ];
				} else {
					$sanitized[ $key ] = sanitize_text_field( $new_settings[ $key ] );
				}
			} else {
				$sanitized[ $key ] = $current[ $key ] ?? $default_val;
			}
		}

		$sanitized['chat_rate_limit'] = max( 1, min( 1000, (int) $sanitized['chat_rate_limit'] ) );
		$sanitized['similarity_threshold'] = max( -1.0, min( 1.0, (float) $sanitized['similarity_threshold'] ) );
		$sanitized['chunk_size'] = max( 2, min( 8000, (int) $sanitized['chunk_size'] ) );
		$sanitized['chunk_overlap'] = max( 0, min( $sanitized['chunk_size'] - 1, (int) $sanitized['chunk_overlap'] ) );
		$sanitized['top_k'] = max( 1, min( 50, (int) $sanitized['top_k'] ) );

		if ( ! \AISupportAssistant\Providers\WordPressAIProvider::is_available() && 'wp_native_ai' === $sanitized['ai_provider'] ) {
			$sanitized['ai_provider'] = 'gemini';
		}

		foreach ( array( 'openai_chat_model', 'openai_embedding_model' ) as $model_key ) {
			if ( '' !== $sanitized[ $model_key ] && ! preg_match( '/^[A-Za-z0-9._:-]+$/', (string) $sanitized[ $model_key ] ) ) {
				throw new \Exception( esc_html__( 'The configured OpenAI model ID is invalid.', 'ai-support-assistant' ) );
			}
		}
		foreach ( array( 'gemini_chat_model', 'gemini_embedding_model' ) as $model_key ) {
			if ( '' !== $sanitized[ $model_key ] && ! preg_match( '/^gemini-[A-Za-z0-9._-]+$/', (string) $sanitized[ $model_key ] ) ) {
				throw new \Exception( esc_html__( 'The configured Gemini model ID is invalid.', 'ai-support-assistant' ) );
			}
		}

		$this->validate_api_keys_and_models( $sanitized );

		$this->settings = $sanitized;
		return update_option( self::OPTION_KEY, $sanitized );
	}

	/**
	 * Validate models and API key endpoints live before saving settings.
	 *
	 * @param array $sanitized Settings payload to validate.
	 * @throws \Exception If API key validation or model test fails.
	 */
	private function validate_api_keys_and_models( array $sanitized ): void {
		$old_settings   = $this->settings;
		$this->settings = $sanitized;

		$provider_name = $sanitized['ai_provider'] ?? 'wp_native_ai';

		if ( 'wp_native_ai' === $provider_name ) {
			return;
		}

		if ( 'openai' === $provider_name ) {
			$direct_key = trim( (string) ( $sanitized['openai_api_key'] ?? '' ) );
			if ( ! empty( $direct_key ) ) {
				$provider = new \AISupportAssistant\Providers\OpenAIProvider( $direct_key );
				try {
					$provider->get_embedding( 'test' );
				} catch ( \Exception $e ) {
					$this->settings = $old_settings;
					/* translators: %s: OpenAI embedding model validation error message. */
					throw new \Exception( esc_html( sprintf( __( 'OpenAI Embedding Model validation failed: %s', 'ai-support-assistant' ), $e->getMessage() ) ) );
				}
			}
		} elseif ( 'gemini' === $provider_name ) {
			$direct_key = trim( (string) ( $sanitized['gemini_api_key'] ?? '' ) );
			if ( ! empty( $direct_key ) ) {
				$provider = new \AISupportAssistant\Providers\GeminiProvider( $direct_key );
				try {
					$provider->get_embedding( 'test' );
				} catch ( \Exception $e ) {
					$this->settings = $old_settings;
					/* translators: %s: Gemini embedding model validation error message. */
					throw new \Exception( esc_html( sprintf( __( 'Gemini Embedding Model validation failed: %s', 'ai-support-assistant' ), $e->getMessage() ) ) );
				}
			}
		}
	}
}