feat: add PR_Core_Internal_Posts_Provider implementation

includes/core/class-pr-core-internal-posts-provider.php

@@ -0,0 +1,102 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Fetches posts related to a peptide via taxonomy and fallback text search.
+ *
+ * What: Implements PR_Core_Related_Posts_Provider by querying posts tagged
+ *       with the peptide's slug as a peptide_topic term. Falls back to
+ *       full-text search if no taxonomy matches found.
+ * Who calls it: PR_Core_Related_Posts_Section instantiates and calls this.
+ * Dependencies: PR_Core_Related_Posts_Provider interface, WP_Query,
+ *               peptide_topic taxonomy.
+ *
+ * @see includes/interfaces/interface-related-posts-provider.php
+ * @see includes/core/class-related-posts-section.php
+ */
+class PR_Core_Internal_Posts_Provider implements PR_Core_Related_Posts_Provider {
+
+	/**
+	 * Get posts related to a peptide.
+	 *
+	 * 1. Queries posts tagged with the peptide slug as a peptide_topic term.
+	 * 2. If 0 posts found, falls back to full-text search on post_title.
+	 * 3. Caches result as a transient (1 hour TTL).
+	 * 4. Never exceeds $limit posts.
+	 *
+	 * Side effects: Sets/updates transient cache for this peptide.
+	 *
+	 * @param int $peptide_id The peptide post ID.
+	 * @param int $limit      Maximum number of posts to return.
+	 * @return array<int, \WP_Post> Array of WP_Post objects (may be empty).
+	 */
+	public function get_posts( int $peptide_id, int $limit ): array {
+		$peptide = get_post( $peptide_id );
+		if ( ! $peptide || 'peptide' !== $peptide->post_type ) {
+			return [];
+		}
+
+		$cache_key = 'pr_core_related_' . $peptide_id;
+		$cached    = get_transient( $cache_key );
+		if ( is_array( $cached ) ) {
+			return array_slice( $cached, 0, $limit );
+		}
+
+		// Primary: query posts tagged with peptide's slug as peptide_topic.
+		$posts = $this->query_by_taxonomy( $peptide->post_name, $limit );
+
+		// Fallback: if empty, search by peptide title.
+		if ( empty( $posts ) ) {
+			$posts = $this->query_by_search( $peptide->post_title, $limit );
+		}
+
+		// Cache for 1 hour.
+		set_transient( $cache_key, $posts, HOUR_IN_SECONDS );
+
+		return $posts;
+	}
+
+	/**
+	 * Query posts tagged with a specific peptide_topic term.
+	 *
+	 * @param string $peptide_slug The peptide's post_name (slug).
+	 * @param int    $limit        Maximum posts to return.
+	 * @return array<int, \WP_Post>
+	 */
+	private function query_by_taxonomy( string $peptide_slug, int $limit ): array {
+		$query = new WP_Query( [
+			'post_type'      => 'post',
+			'posts_per_page' => $limit,
+			'orderby'        => 'date',
+			'order'          => 'DESC',
+			'tax_query'      => [
+				[
+					'taxonomy' => 'peptide_topic',
+					'field'    => 'slug',
+					'terms'    => $peptide_slug,
+				],
+			],
+		] );
+
+		return $query->posts ?: [];
+	}
+
+	/**
+	 * Fallback: query posts by full-text search on post_title.
+	 *
+	 * @param string $search_term The peptide's display title.
+	 * @param int    $limit       Maximum posts to return.
+	 * @return array<int, \WP_Post>
+	 */
+	private function query_by_search( string $search_term, int $limit ): array {
+		$query = new WP_Query( [
+			'post_type'      => 'post',
+			'posts_per_page' => $limit,
+			'orderby'        => 'date',
+			'order'          => 'DESC',
+			's'              => $search_term,
+		] );
+
+		return $query->posts ?: [];
+	}
+}