<?php
namespace Zadex\Frontend;

defined('ABSPATH') || exit;

/**
 * Makes a post WordPress's current post (the global `$post` and the template-tag globals `setup_postdata()` fills),
 * through WordPress's own API and without touching the main query: a `WP_Query` whose current post is that post,
 * then `WP_Query::reset_postdata()`, which is what core does after a secondary loop. No SQL query runs (the post
 * is already loaded). Used where third-party code reads the current post while Zadex renders another one: loop
 * items, the post-content dynamic tag (nested `the_content`), editor previews and the maintenance page.
 */
final class PostData
{
    /** The current post (the global post), or null. */
    public static function current(): ?\WP_Post
    {
        $post = $GLOBALS['post'] ?? null;
        return $post instanceof \WP_Post ? $post : null;
    }

    /** Makes $post the current post (no-op for anything that is not a post). */
    public static function set($post): void
    {
        if (!$post instanceof \WP_Post || !class_exists('WP_Query')) {
            return;
        }
        $query = new \WP_Query();
        $query->post = $post;
        $query->reset_postdata();
    }

    /** Puts back the post that was current before set(); when there was none, there is none again. */
    public static function restore(?\WP_Post $previous): void
    {
        if ($previous instanceof \WP_Post) {
            self::set($previous);
            return;
        }
        unset($GLOBALS['post']); // the request had no current post (REST, 404 …): do not leave ours behind
    }

    /**
     * Runs $callback with $post as the current post, then restores the previous one.
     *
     * @template T
     * @param callable(): T $callback
     * @return T
     */
    public static function with($post, callable $callback)
    {
        if (!$post instanceof \WP_Post) {
            return $callback();
        }
        $previous = self::current();
        self::set($post);
        try {
            return $callback();
        } finally {
            self::restore($previous);
        }
    }
}