<?php
/**
 * Plugin Name: Generic Structured Data for Blog Posts
 * Plugin URI: https://neo.astrowave.jp/
 * Description: シンプルな BlogPosting の構造化データ(JSON-LD)を、投稿ページに自動追加する超汎用プラグインです。
 * Version: 1.0.0
 * Author: サイガモ
 * Author URI: https://neo.astrowave.jp/
 * License: GPL v2 or later
 * License URI: https://www.gnu.org/licenses/gpl-2.0.html
 * Text Domain: generic-structured-data
 */

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

/**
 * BlogPosting の JSON-LD を出力
 */
function gsd_output_blogposting_schema() {
    // 個別投稿ページ（post など）以外では出さない
    if ( ! is_single() ) {
        return;
    }

    global $post;
    if ( ! $post instanceof WP_Post ) {
        return;
    }

    $post_id = $post->ID;

    // 基本情報
    $headline  = get_the_title( $post_id );
    $permalink = get_permalink( $post_id );

    // 抜粋（なければ本文から自動生成）
    if ( has_excerpt( $post_id ) ) {
        $description = get_the_excerpt( $post_id );
    } else {
        $content     = wp_strip_all_tags( $post->post_content );
        $description = wp_trim_words( $content, 40, '…' ); // 約40語
    }

    // アイキャッチ画像
    $image_url = get_the_post_thumbnail_url( $post_id, 'full' );

    // カテゴリー（先頭1件を articleSection に）
    $article_section = '';
    $categories      = get_the_category( $post_id );
    if ( ! empty( $categories ) && ! is_wp_error( $categories ) ) {
        $article_section = $categories[0]->name;
    }

    // タグ → keywords
    $keywords = '';
    $tags     = get_the_tags( $post_id );
    if ( $tags && ! is_wp_error( $tags ) ) {
        $tag_names = wp_list_pluck( $tags, 'name' );
        $keywords  = implode( ', ', $tag_names );
    }

    // 著者情報
    $author_id   = $post->post_author;
    $author_name = get_the_author_meta( 'display_name', $author_id );
    $author_url  = get_author_posts_url( $author_id );

    // サイト情報（publisher）
    $site_name = get_bloginfo( 'name' );
    $site_icon = get_site_icon_url(); // 設定されていない場合は空文字

    $schema = array(
        '@context'        => 'https://schema.org',
        '@type'           => 'BlogPosting',
        'mainEntityOfPage'=> array(
            '@type' => 'WebPage',
            '@id'   => $permalink,
        ),
        'headline'        => $headline,
        'description'     => $description,
        'inLanguage'      => 'ja',
        'datePublished'   => get_the_date( DATE_W3C, $post_id ),
        'dateModified'    => get_the_modified_date( DATE_W3C, $post_id ),

        'author'          => array(
            '@type' => 'Person',
            'name'  => $author_name,
            'url'   => $author_url,
        ),

        'publisher'       => array(
            '@type' => 'Organization',
            'name'  => $site_name,
        ),
    );

    // サイトアイコンがあればロゴとして追加
    if ( $site_icon ) {
        $schema['publisher']['logo'] = array(
            '@type' => 'ImageObject',
            'url'   => $site_icon,
        );
    }

    // カテゴリ
    if ( $article_section ) {
        $schema['articleSection'] = $article_section;
    }

    // アイキャッチ
    if ( $image_url ) {
        $schema['image'] = array(
            '@type' => 'ImageObject',
            'url'   => $image_url,
        );
    }

    // キーワード
    if ( $keywords ) {
        $schema['keywords'] = $keywords;
    }

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

<script type="application/ld+json">
{
    "@context": "https://schema.org",
    "@type": "BlogPosting",
    "mainEntityOfPage": {
        "@type": "WebPage",
        "@id": "https://neo.astrowave.jp/blog/19361/"
    },
    "headline": "【WordPress】AI最適化 LLMs.txtプラグインを作る",
    "description": "AI検索をフレンドリーにするllms.txtの育成プラグインの記事を書いていまし…",
    "inLanguage": "ja",
    "datePublished": "2025-05-07T18:48:18+09:00",
    "dateModified": "2025-12-04T14:02:56+09:00",
    "author": {
        "@type": "Person",
        "name": "サイガモ",
        "url": "https://neo.astrowave.jp/author/akira/"
    },
    "publisher": {
        "@type": "Organization",
        "name": "astrowave",
        "logo": {
            "@type": "ImageObject",
            "url": "https://neo.astrowave.jp/wp-content/uploads/2022/04/cropped-siteicon.png"
        }
    },
    "articleSection": "BLOG",
    "image": {
        "@type": "ImageObject",
        "url": "https://neo.astrowave.jp/wp-content/uploads/2025/05/llms_plugin_main.jpg"
    },
    "keywords": "PHP, SEO, WEBログ, WordPress, プラグイン"
}
</script>