<?php
/**
 * AKSRT SEO Head — 单一 head 输出装配器
 *
 * Phase 7 收口：站点 SEO、单篇 SEO、OpenGraph/Twitter、JSON-LD、canonical、
 * favicon、robots 全部从这里一次性装配输出，替代此前散落在
 * inc/helpers/aksrt-template-tags.php 的多个 wp_head 闭包。
 *
 * 所有取值只经过 AKSRT_Settings + 模板 helper，不直接 raw get_option()。
 * 唯一 head 来源，便于追踪。详见 seo-output-matrix.md。
 *
 * @package AKSRT
 */

defined('ABSPATH') || exit;

class AKSRT_SEO_Head {

    private static $instance = null;

    public static function get_instance(): self {
        if (null === self::$instance) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    public function init(): void {
        // seo_enabled 主开关：关闭时不挂载任何 wp_head 输出
        if (class_exists('AKSRT_Settings')) {
            $seo = AKSRT_Settings::get_seo_settings();
            if (empty($seo['seo_enabled'])) return;
        }
        // 单一出口：所有 SEO/OG/JSON-LD 输出集中在 priority 2。
        add_action('wp_head', [$this, 'render'], 2);
        // robots：dl token 页面 noindex（独立、最早输出）。
        add_action('wp_head', [$this, 'render_robots'], 1);
    }

    /**
     * 站点级 SEO 配置（带 per-request memo）。
     *
     * @return array<string,mixed>
     */
    private function config(): array {
        static $cache = null;
        if ($cache !== null) {
            return $cache;
        }

        if (class_exists('AKSRT_Settings')) {
            $s = AKSRT_Settings::get_all();
        } else {
            $s = [];
        }

        $cache = [
            'connector'      => trim((string) ($s['seo_connector'] ?? '-')) ?: '-',
            'site_title'     => trim((string) ($s['seo_title'] ?? '')),
            'description'    => trim((string) ($s['seo_description'] ?? ($s['site_description'] ?? ''))),
            'keywords'       => trim((string) ($s['seo_keywords'] ?? '')),
            'canonical'      => !isset($s['canonical_tag']) || !empty($s['canonical_tag']),
            'og_enabled'     => empty($s['disable_og_meta']),
            'jsonld'         => !isset($s['seo_jsonld']) || !empty($s['seo_jsonld']),
            'jsonld_single'  => !isset($s['seo_jsonld_single']) || !empty($s['seo_jsonld_single']),
            'jsonld_page'    => !isset($s['seo_jsonld_page']) || !empty($s['seo_jsonld_page']),
            'default_image'  => trim((string) ($s['seo_image_default'] ?? '')),
            'always_default' => !empty($s['seo_image_always_default']),
        ];

        return $cache;
    }

    /**
     * 解析当前请求的规范 SEO 负载。
     *
     * @return array{title:string,description:string,keywords:string,canonical:string,image:string,og_type:string,object:?WP_Post}
     */
    private function resolve_payload(): array {
        $cfg = $this->config();
        $site_name = get_bloginfo('name');

        $payload = [
            'title'       => wp_get_document_title(),
            'description' => $cfg['description'],
            'keywords'    => $cfg['keywords'],
            'canonical'   => home_url(isset($_SERVER['REQUEST_URI']) ? wp_unslash($_SERVER['REQUEST_URI']) : '/'),
            'image'       => $cfg['default_image'],
            'og_type'     => 'website',
            'object'      => null,
        ];

        if (is_singular()) {
            $post = get_queried_object();
            if ($post instanceof WP_Post) {
                $payload['object'] = $post;
                $payload['canonical'] = (string) get_permalink($post);
                $payload['og_type'] = in_array($post->post_type, ['post', 'aksrt_resource'], true) ? 'article' : 'website';

                // 单篇 SEO 覆盖：per-post meta → 文章字段 → 站点默认。
                $meta = $this->post_seo_meta($post->ID);

                $payload['title'] = $meta['title'] !== '' ? $meta['title'] : wp_strip_all_tags(get_the_title($post));
                if ($meta['description'] !== '') {
                    $payload['description'] = $meta['description'];
                } else {
                    $excerpt = has_excerpt($post)
                        ? wp_strip_all_tags(get_the_excerpt($post))
                        : wp_trim_words(wp_strip_all_tags((string) $post->post_content), 40, '…');
                    $payload['description'] = trim((string) $excerpt);
                }
                if ($meta['keywords'] !== '') {
                    $payload['keywords'] = $meta['keywords'];
                } elseif ($payload['keywords'] === '') {
                    $payload['keywords'] = $this->terms_to_keywords($post);
                }

                $payload['image'] = $this->resolve_image($post, $cfg);
            }
        } elseif (is_home() || is_front_page()) {
            if ($cfg['site_title'] !== '') {
                $payload['title'] = $cfg['site_title'];
            }
            $payload['canonical'] = home_url('/');
        } elseif (is_category() || is_tag() || is_tax()) {
            $term = get_queried_object();
            if ($term instanceof WP_Term) {
                $payload['canonical'] = (string) get_term_link($term);
                $term_desc = trim(wp_strip_all_tags((string) term_description($term)));
                if ($term_desc !== '') {
                    $payload['description'] = $term_desc;
                }
            }
        }

        if ($cfg['always_default'] && $cfg['default_image'] !== '') {
            $payload['image'] = $cfg['default_image'];
        }

        /**
         * 允许扩展（如 AI SEO）在最终输出前调整 head 负载。
         *
         * @param array $payload 规范 SEO 负载。
         */
        return apply_filters('aksrt_seo_head_payload', $payload);
    }

    /**
     * 读取单篇 SEO 覆盖（per-post meta）。
     *
     * @param int $post_id Post ID.
     * @return array{title:string,description:string,keywords:string}
     */
    private function post_seo_meta(int $post_id): array {
        $get = static function (string $key) use ($post_id): string {
            return trim((string) get_post_meta($post_id, $key, true));
        };

        return [
            'title'       => $get('_aksrt_seo_title'),
            'description' => $get('_aksrt_seo_description'),
            'keywords'    => $get('_aksrt_seo_keywords'),
        ];
    }

    /**
     * 由分类/标签生成关键词回退。
     */
    private function terms_to_keywords(WP_Post $post): string {
        $names = [];
        foreach ((array) get_the_category($post->ID) as $cat) {
            if ($cat instanceof WP_Term) {
                $names[] = $cat->name;
            }
        }
        $tags = get_the_terms($post, 'post_tag');
        if (is_array($tags)) {
            foreach ($tags as $tag) {
                $names[] = $tag->name;
            }
        }

        return implode(',', array_slice(array_values(array_unique(array_filter($names))), 0, 10));
    }

    /**
     * 解析单篇缩略图：特色图 → 内容首图 → 站点默认 → logo。
     */
    private function resolve_image(WP_Post $post, array $cfg): string {
        if (has_post_thumbnail($post)) {
            $image = (string) get_the_post_thumbnail_url($post, 'large');
            if ($image !== '') {
                return $image;
            }
        }
        if (function_exists('aksrt_get_first_content_image_url')) {
            $image = (string) aksrt_get_first_content_image_url($post->ID);
            if ($image !== '') {
                return $image;
            }
        }
        if ($cfg['default_image'] !== '') {
            return $cfg['default_image'];
        }
        if (class_exists('AKSRT_Settings')) {
            return (string) AKSRT_Settings::logo_url();
        }
        return '';
    }

    /**
     * dl token 页面 noindex。
     */
    public function render_robots(): void {
        if (function_exists('get_query_var') && get_query_var('aksrt_dl_token')) {
            echo '<meta name="robots" content="noindex,nofollow">' . "\n";
        }
    }

    /**
     * 输出 head（favicon + canonical + description/keywords + OG/Twitter + JSON-LD）。
     */
    public function render(): void {
        $cfg = $this->config();
        $payload = $this->resolve_payload();

        echo "\n<!-- AKSRT SEO -->\n";

        // Favicon（无站点图标时回退）。
        if (function_exists('aksrt_get_favicon_url')) {
            $favicon = (string) aksrt_get_favicon_url();
            if ($favicon !== '' && !has_site_icon()) {
                printf('<link rel="icon" href="%s">' . "\n", esc_url($favicon));
            }
        }

        // Canonical。
        if ($cfg['canonical'] && !is_404() && $payload['canonical'] !== '') {
            printf('<link rel="canonical" href="%s">' . "\n", esc_url($payload['canonical']));
        }

        // Description / Keywords。
        if ($payload['description'] !== '') {
            printf('<meta name="description" content="%s">' . "\n", esc_attr($payload['description']));
        }
        if ($payload['keywords'] !== '') {
            printf('<meta name="keywords" content="%s">' . "\n", esc_attr($payload['keywords']));
        }

        // OpenGraph + Twitter。
        if ($cfg['og_enabled']) {
            $this->render_open_graph($payload);
        }

        // JSON-LD。
        if ($cfg['jsonld']) {
            $this->render_jsonld($payload, $cfg);
        }

        echo "<!-- /AKSRT SEO -->\n";
    }

    /**
     * 输出 OpenGraph + Twitter Card。
     */
    private function render_open_graph(array $payload): void {
        $site_name = get_bloginfo('name');
        $locale = str_replace('-', '_', get_locale());

        $og = [
            ['property' => 'og:type', 'content' => $payload['og_type']],
            ['property' => 'og:locale', 'content' => $locale],
            ['property' => 'og:site_name', 'content' => $site_name],
            ['property' => 'og:title', 'content' => $payload['title']],
            ['property' => 'og:url', 'content' => $payload['canonical']],
        ];
        if ($payload['description'] !== '') {
            $og[] = ['property' => 'og:description', 'content' => $payload['description']];
        }
        if ($payload['image'] !== '') {
            $og[] = ['property' => 'og:image', 'content' => $payload['image']];
        }

        if ($payload['og_type'] === 'article' && $payload['object'] instanceof WP_Post) {
            $post = $payload['object'];
            $published = get_the_date('c', $post);
            $modified = get_the_modified_date('c', $post);
            $author = get_the_author_meta('display_name', (int) $post->post_author);
            if ($published) $og[] = ['property' => 'article:published_time', 'content' => $published];
            if ($modified)  $og[] = ['property' => 'article:modified_time', 'content' => $modified];
            if ($author)    $og[] = ['property' => 'article:author', 'content' => $author];

            $cats = get_the_category($post->ID);
            if (!empty($cats)) {
                $og[] = ['property' => 'article:section', 'content' => $cats[0]->name];
            }
            $tags = get_the_terms($post, 'post_tag');
            if (is_array($tags)) {
                foreach ($tags as $tag) {
                    $og[] = ['property' => 'article:tag', 'content' => $tag->name];
                }
            }
        }

        foreach ($og as $tag) {
            printf('<meta property="%s" content="%s">' . "\n", esc_attr($tag['property']), esc_attr($tag['content']));
        }

        $twitter = [
            ['name' => 'twitter:card', 'content' => $payload['image'] !== '' ? 'summary_large_image' : 'summary'],
            ['name' => 'twitter:title', 'content' => $payload['title']],
        ];
        if ($payload['description'] !== '') {
            $twitter[] = ['name' => 'twitter:description', 'content' => $payload['description']];
        }
        if ($payload['image'] !== '') {
            $twitter[] = ['name' => 'twitter:image', 'content' => $payload['image']];
        }
        foreach ($twitter as $tag) {
            printf('<meta name="%s" content="%s">' . "\n", esc_attr($tag['name']), esc_attr($tag['content']));
        }
    }

    /**
     * 输出 JSON-LD 结构化数据。
     */
    private function render_jsonld(array $payload, array $cfg): void {
        $graph = [];

        // WebSite（全站）。
        $graph[] = [
            '@type'    => 'WebSite',
            '@id'      => home_url('/#website'),
            'url'      => home_url('/'),
            'name'     => get_bloginfo('name'),
            'inLanguage' => get_locale(),
        ];

        if (is_singular('post') && $cfg['jsonld_single'] && $payload['object'] instanceof WP_Post) {
            $post = $payload['object'];
            $node = [
                '@type'         => 'Article',
                'headline'      => $payload['title'],
                'url'           => $payload['canonical'],
                'datePublished' => get_the_date('c', $post),
                'dateModified'  => get_the_modified_date('c', $post),
                'author'        => [
                    '@type' => 'Person',
                    'name'  => get_the_author_meta('display_name', (int) $post->post_author),
                ],
                'publisher'     => [
                    '@type' => 'Organization',
                    'name'  => get_bloginfo('name'),
                ],
            ];
            if ($payload['description'] !== '') {
                $node['description'] = $payload['description'];
            }
            if ($payload['image'] !== '') {
                $node['image'] = $payload['image'];
            }
            $graph[] = $node;
        } elseif (is_page() && $cfg['jsonld_page'] && $payload['object'] instanceof WP_Post) {
            $graph[] = [
                '@type' => 'WebPage',
                'url'   => $payload['canonical'],
                'name'  => $payload['title'],
            ];
        }

        if (empty($graph)) {
            return;
        }

        $doc = [
            '@context' => 'https://schema.org',
            '@graph'   => $graph,
        ];

        echo '<script type="application/ld+json">'
            . wp_json_encode($doc, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES)
            . '</script>' . "\n";
    }
}