<?php
/**
 * AI Response Cache
 *
 * Caches AI responses using WordPress Transients API to reduce
 * redundant API calls and improve performance.
 *
 * @package    Schema_AI
 * @subpackage Schema_AI/includes/ai
 * @since      1.0.0
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

class Schema_AI_Cache {

    /**
     * Cache key prefix.
     *
     * @var string
     */
    const CACHE_PREFIX = 'schema_ai_cache_';

    /**
     * Default time-to-live in seconds (1 week).
     *
     * @var int
     */
    const DEFAULT_TTL = WEEK_IN_SECONDS;

    /**
     * Get a cached value by key.
     *
     * @param string $key The cache key.
     * @return mixed|false Cached data or false if not found or expired.
     */
    public function get( $key ) {
        $full_key = $this->build_key( $key );
        $data     = get_transient( $full_key );

        if ( false === $data ) {
            return false;
        }

        return $data;
    }

    /**
     * Set a value in the cache.
     *
     * @param string $key  The cache key.
     * @param mixed  $data The data to cache.
     * @param int    $ttl  Time-to-live in seconds. Defaults to 1 week.
     * @return bool True on success, false on failure.
     */
    public function set( $key, $data, $ttl = 0 ) {
        if ( 0 === $ttl ) {
            $ttl = self::DEFAULT_TTL;
        }

        $full_key = $this->build_key( $key );

        return set_transient( $full_key, $data, $ttl );
    }

    /**
     * Delete a cached value by key.
     *
     * @param string $key The cache key.
     * @return bool True on success, false on failure.
     */
    public function delete( $key ) {
        $full_key = $this->build_key( $key );

        return delete_transient( $full_key );
    }

    /**
     * Flush all Schema AI cache entries.
     *
     * Removes every transient whose option name begins with the plugin prefix.
     *
     * @return int Number of cache entries deleted.
     */
    public function flush() {
        global $wpdb;

        $prefix  = '_transient_' . self::CACHE_PREFIX;
        // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Required for custom table; no WP API alternative exists.
        $results = $wpdb->get_col(
            $wpdb->prepare(
                'SELECT option_name FROM ' . $wpdb->options . ' WHERE option_name LIKE %s',
                $wpdb->esc_like( $prefix ) . '%'
            )
        );

        $count = 0;
        foreach ( $results as $option_name ) {
            // Strip the '_transient_' prefix to get the transient name.
            $transient_name = str_replace( '_transient_', '', $option_name );
            if ( delete_transient( $transient_name ) ) {
                $count++;
            }
        }

        return $count;
    }

    /**
     * Generate a cache key for a specific post based on its content.
     *
     * The key is built from the post ID and a hash of the post's title and
     * content so that the cache automatically invalidates when the post is
     * edited.
     *
     * @param int $post_id WordPress post ID.
     * @return string Cache key in the format {post_id}_{content_hash}.
     */
    public function generate_post_key( $post_id ) {
        $content_hash = $this->generate_content_hash( $post_id );

        return $post_id . '_' . $content_hash;
    }

    /**
     * Generate a content hash from the post title and content.
     *
     * @param int $post_id WordPress post ID.
     * @return string MD5 hash of the post title concatenated with its content.
     */
    public function generate_content_hash( $post_id ) {
        $post = get_post( $post_id );

        if ( ! $post ) {
            return md5( (string) $post_id );
        }

        $raw = $post->post_title . $post->post_content;

        return md5( $raw );
    }

    /**
     * Build the full transient key by prepending the cache prefix.
     *
     * WordPress limits transient names to 172 characters. If the resulting key
     * exceeds that length it is hashed to guarantee it fits.
     *
     * @param string $key Short cache key.
     * @return string Full transient key.
     */
    private function build_key( $key ) {
        $full = self::CACHE_PREFIX . $key;

        // WordPress transient name limit is 172 chars.
        if ( strlen( $full ) > 172 ) {
            $full = self::CACHE_PREFIX . md5( $key );
        }

        return $full;
    }
}