<?php
namespace AccessNow\SimpleLMS;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

// This class reads and writes the plugin's own {prefix}slms_* tables, so direct
// queries are required; the data is per-user and changes on every action, so it is
// not cached. Table names are built from $wpdb->prefix and fixed strings, and every
// value goes through $wpdb->prepare() or $wpdb->insert/update/delete.
// phpcs:disable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching

class Content_Integrity {

	public static function init() {
		add_action( 'save_post_slms_lesson', array( __CLASS__, 'on_lesson_save' ), 20, 2 );
		add_action( 'save_post_slms_quiz', array( __CLASS__, 'on_quiz_save' ), 20, 2 );
	}

	/**
	 * Compute a content hash for a lesson (and its quiz if present).
	 */
	public static function compute_content_hash( $lesson_id ) {
		$lesson = get_post( $lesson_id );
		if ( ! $lesson ) {
			return '';
		}

		$content = $lesson->post_content;

		// Include quiz questions in the hash if the lesson has a quiz
		$quiz = get_posts(
			array(
				'post_type'      => 'slms_quiz',
				'posts_per_page' => 1,
				'meta_key'       => '_slms_parent_lesson', // phpcs:ignore WordPress.DB.SlowDBQuery.slow_db_query_meta_key -- course structure is stored as post meta.
				'meta_value'     => $lesson_id, // phpcs:ignore WordPress.DB.SlowDBQuery.slow_db_query_meta_value -- course structure is stored as post meta.
				'fields'         => 'ids',
			)
		);

		if ( ! empty( $quiz ) ) {
			$content .= '||quiz||' . self::quiz_hash_data( $quiz[0] );
		}

		return md5( $content );
	}

	/**
	 * Compute hash of lesson content only (without quiz).
	 */
	public static function compute_lesson_only_hash( $lesson_id ) {
		$lesson = get_post( $lesson_id );
		return $lesson ? md5( $lesson->post_content ) : '';
	}

	/**
	 * Compute hash of quiz questions only.
	 */
	public static function compute_quiz_hash( $quiz_id ) {
		return md5( self::quiz_hash_data( $quiz_id ) );
	}

	/**
	 * What a quiz's change detection hashes: its stored questions (exactly as before 1.1.0, so
	 * existing hashes still match), plus anything accessnow_slms_content_hash_data adds.
	 *
	 * @param int $quiz_id Quiz ID.
	 * @return string
	 */
	private static function quiz_hash_data( $quiz_id ) {
		$data = maybe_serialize( get_post_meta( $quiz_id, '_slms_questions', true ) );

		/**
		 * The text a quiz's change detection hashes. Add what else counts as the quiz's content,
		 * e.g. the questions of a question bank it draws from; a change then asks students to redo it.
		 *
		 * @since 1.1.0
		 *
		 * @param string $data    Serialised stored questions.
		 * @param int    $quiz_id Quiz ID.
		 */
		return (string) apply_filters( 'accessnow_slms_content_hash_data', $data, (int) $quiz_id );
	}

	/**
	 * When a lesson is saved, check if its content changed and invalidate progress if needed.
	 */
	public static function on_lesson_save( $post_id, $post ) {
		if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
			return;
		}
		if ( 'publish' !== $post->post_status ) {
			return;
		}

		$unit_id   = get_post_meta( $post_id, '_slms_parent_unit', true );
		$course_id = $unit_id ? get_post_meta( $unit_id, '_slms_parent_course', true ) : 0;
		if ( ! $course_id ) {
			return;
		}

		$mode = get_post_meta( $course_id, '_slms_content_change_mode', true );
		if ( ! $mode || 'off' === $mode ) {
			return;
		}

		// Only invalidate for lesson content changes if mode includes lessons
		if ( 'lesson' !== $mode && 'both' !== $mode ) {
			return;
		}

		self::invalidate_if_changed( $post_id, $course_id );
	}

	/**
	 * When a quiz is saved, check if its questions changed and invalidate the parent lesson's progress.
	 */
	public static function on_quiz_save( $post_id, $post ) {
		if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
			return;
		}
		if ( 'publish' !== $post->post_status ) {
			return;
		}

		$lesson_id = get_post_meta( $post_id, '_slms_parent_lesson', true );
		if ( ! $lesson_id ) {
			return;
		}

		$unit_id   = get_post_meta( $lesson_id, '_slms_parent_unit', true );
		$course_id = $unit_id ? get_post_meta( $unit_id, '_slms_parent_course', true ) : 0;
		if ( ! $course_id ) {
			return;
		}

		$mode = get_post_meta( $course_id, '_slms_content_change_mode', true );
		if ( ! $mode || 'off' === $mode ) {
			return;
		}

		// Only invalidate for quiz changes if mode includes quizzes
		if ( 'quiz' !== $mode && 'both' !== $mode ) {
			return;
		}

		self::invalidate_if_changed( $lesson_id, $course_id );
	}

	/**
	 * Compare current content hash with stored hashes in progress records.
	 * If different, set progress status to 'invalidated'.
	 */
	private static function invalidate_if_changed( $lesson_id, $course_id ) {
		global $wpdb;

		$current_hash = self::compute_content_hash( $lesson_id );
		if ( ! $current_hash ) {
			return;
		}

		$table = $wpdb->prefix . 'slms_progress';

		// Find all completed progress records for this lesson where the hash differs
		$affected = $wpdb->get_results(
			$wpdb->prepare(
				"SELECT id, content_hash FROM {$wpdb->prefix}slms_progress WHERE lesson_id = %d AND status = 'complete'",
				$lesson_id
			)
		);

		$invalidated = 0;
		foreach ( $affected as $row ) {
			if ( $row->content_hash && $row->content_hash !== $current_hash ) {
				$invalidated += (int) $wpdb->update(
					$table,
					array( 'status' => 'invalidated' ),
					array( 'id' => $row->id ),
					array( '%s' ),
					array( '%d' )
				);
			}
		}

		// Students who had finished the course have work to redo again.
		if ( $invalidated ) {
			Enrollment::reopen_course( $course_id );
		}
	}
}