<?php

declare(strict_types=1);

namespace LIT\MCP\Integrations\Media;

use RuntimeException;
use WP_Error;
use WP_Post;

/**
 * Writes the editable metadata of an attachment (alt text, title, caption, description) and
 * restores it from a snapshot taken before (lit/media-update rolls a batch back with it).
 * Every failure is a RuntimeException with an internal message for the PHP error log.
 *
 * Both apply() and restore() save through wp_update_post(), which runs the kses filters again
 * for users without unfiltered_html: a caption or description with markup the current user may
 * not save comes back filtered on restore (like any save of that user in the media library).
 */
final class MediaMetaWriter
{
    public const ALT_KEY = '_wp_attachment_image_alt';

    /** Input key => posts column. */
    public const COLUMNS = ['title' => 'post_title', 'caption' => 'post_excerpt', 'description' => 'post_content'];

    /**
     * The current values of everything $changes will write.
     *
     * @param array<string, string> $changes Sanitized values by input key (alt, title, caption, description).
     * @return array{id: int, columns: array<string, string>, alt_changed: bool, alt: ?string}
     *         alt null = there was no alt text (it is removed again on restore).
     */
    public function snapshot(WP_Post $attachment, array $changes): array
    {
        $id = (int) $attachment->ID;
        $columns = [];
        foreach (self::columns($changes) as $column => $value) {
            $columns[$column] = (string) $attachment->{$column};
        }

        $altChanged = array_key_exists('alt', $changes);
        $alt = $altChanged && metadata_exists('post', $id, self::ALT_KEY)
            ? (string) get_post_meta($id, self::ALT_KEY, true)
            : null;

        return ['id' => $id, 'columns' => $columns, 'alt_changed' => $altChanged, 'alt' => $alt];
    }

    /**
     * @param array<string, string> $changes Sanitized values by input key.
     * @param bool                  $touched Set to true as soon as something may have been written.
     * @throws RuntimeException
     */
    public function apply(int $id, array $changes, bool &$touched): void
    {
        $columns = self::columns($changes);
        if ($columns !== []) {
            // Set before the call: a throwing save_post hook runs after the row was written.
            $touched = true;
            $result = wp_update_post(wp_slash(array_merge($columns, ['ID' => $id])), true);
            if ($result instanceof WP_Error || ! $result) {
                // wp_update_post() reports errors before it writes anything.
                $touched = false;
                throw new RuntimeException(sprintf(
                    'Attachment %d not updated: %s',
                    $id,
                    $result instanceof WP_Error ? $result->get_error_message() : 'unknown error'
                ));
            }
        }

        if (array_key_exists('alt', $changes)) {
            $touched = true;
            $this->saveAlt($id, $changes['alt']);
        }
    }

    /**
     * @param array{id: int, columns: array<string, string>, alt_changed: bool, alt: ?string} $snapshot
     * @throws RuntimeException
     */
    public function restore(array $snapshot): void
    {
        $id = $snapshot['id'];
        if ($snapshot['columns'] !== []) {
            $result = wp_update_post(wp_slash(array_merge($snapshot['columns'], ['ID' => $id])), true);
            if ($result instanceof WP_Error || ! $result) {
                throw new RuntimeException(sprintf(
                    'Attachment %d not restored: %s',
                    $id,
                    $result instanceof WP_Error ? $result->get_error_message() : 'unknown error'
                ));
            }
        }

        if (! $snapshot['alt_changed']) {
            return;
        }

        if ($snapshot['alt'] !== null) {
            $this->saveAlt($id, $snapshot['alt']);
        } elseif (! delete_post_meta($id, self::ALT_KEY) && metadata_exists('post', $id, self::ALT_KEY)) {
            throw new RuntimeException(sprintf('Alt text of attachment %d not removed again.', $id));
        }
    }

    /**
     * @param array<string, string> $changes
     * @return array<string, string> Column => value.
     */
    private static function columns(array $changes): array
    {
        $columns = [];
        foreach (self::COLUMNS as $key => $column) {
            if (array_key_exists($key, $changes)) {
                $columns[$column] = $changes[$key];
            }
        }

        return $columns;
    }

    /** @throws RuntimeException */
    private function saveAlt(int $id, string $alt): void
    {
        // update_post_meta() is also false when the value is already stored.
        $stored = update_post_meta($id, self::ALT_KEY, wp_slash($alt)) !== false
            || (string) get_post_meta($id, self::ALT_KEY, true) === $alt;
        if (! $stored) {
            throw new RuntimeException(sprintf('Alt text of attachment %d not saved.', $id));
        }
    }
}