Clear the month dropdown cache when a post is saved and the posts mon…

…th is not included

src/alley/wp/alleyvate/features/class-cache-slow-queries.php

@@ -18,39 +18,92 @@
  * Cache slow queries that do not perform well for large sites.
  */
 final class Cache_Slow_Queries implements Feature {
+	/**
+	 * Whether to cache the months dropdown.
+	 *
+	 * @var bool
+	 */
+	public bool $cache_months_dropdown = false;
+
 	/**
 	 * Boot the feature.
 	 */
 	public function boot(): void {
+		/**
+		 * Filter if the months dropdown query should be cached.
+		 *
+		 * @param bool $cache_months_dropdown Whether to cache the months dropdown. Default true.
+		 */
 		if ( apply_filters( 'alleyvate_cache_months_dropdown', true ) ) {
 			add_filter( 'pre_months_dropdown_query', [ $this, 'filter__pre_months_dropdown_query' ], 10, 2 );
 			add_filter( 'months_dropdown_results', [ $this, 'filter__months_dropdown_results' ], 10, 2 );
+			add_action( 'save_post', [ $this, 'action__save_post' ], 10, 2 );
 		}
 	}
 
 	/**
 	 * Filter the pre months dropdown query to return the cached result.
 	 *
-	 * @param object|false $months 'Months' drop-down results. Default false.
-	 * @param string       $post_type The post type.
-	 * @return object|false
+	 * @param object[]|false $months 'Months' drop-down results. Default false.
+	 * @param string         $post_type The post type.
+	 * @return object[]|false
 	 */
 	public function filter__pre_months_dropdown_query( $months, $post_type ) {
 		$cache = wp_cache_get( $post_type, 'alleyvate_months_dropdown' );
 
-		return false !== $cache && \is_object( $cache ) ? $cache : $months;
+		if ( is_array( $cache ) ) {
+			return $cache;
+		}
+
+		// Set the flag to cache the months dropdown.
+		$this->cache_months_dropdown = true;
+
+		return $months;
 	}
 
 	/**
 	 * Filter the months dropdown results.
 	 *
-	 * @param object $months    Array of the months drop-down query results.
-	 * @param string $post_type The post type.
-	 * @return object|false
+	 * @param object[] $months    Array of the months drop-down query results.
+	 * @param string   $post_type The post type.
+	 * @return object[]|false
 	 */
 	public function filter__months_dropdown_results( $months, $post_type ) {
-		wp_cache_set( $post_type, $months, 'alleyvate_months_dropdown', DAY_IN_SECONDS );
+		if ( $this->cache_months_dropdown ) {
+			wp_cache_set( $post_type, $months, 'alleyvate_months_dropdown', DAY_IN_SECONDS );
+
+			$this->cache_months_dropdown = false;
+		}
 
 		return $months;
 	}
+
+	/**
+	 * Action to delete the cache when a post is published.
+	 *
+	 * @param int      $post_id The post ID.
+	 * @param \WP_Post $post    The post object.
+	 */
+	public function action__save_post( $post_id, $post ): void {
+		if ( 'publish' !== $post->post_status ) {
+			return;
+		}
+
+		$cache = wp_cache_get( $post->post_type, 'alleyvate_months_dropdown' );
+
+		if ( ! is_array( $cache ) ) {
+			return;
+		}
+
+		// Check if the post's month is in the cache.
+		$cache = array_map(
+			fn ( $month ) => "{$month->year}-{$month->month}",
+			$cache,
+		);
+
+		// Clear the month dropdown cache if the post's month is not in the cache.
+		if ( ! in_array( get_the_date( 'Y-n', $post ), $cache, true ) ) {
+			wp_cache_delete( $post->post_type, 'alleyvate_months_dropdown' );
+		}
+	}
 }

tests/alley/wp/alleyvate/features/test-cache-slow-queries.php

@@ -90,4 +90,31 @@ public function test_optimize_months_dropdown(): void {
 
 		$this->assertNotEmpty( wp_cache_get( 'post', 'alleyvate_months_dropdown' ) );
 	}
+
+	/**
+	 * Test that the cache is cleared for the months dropdown query when the post is published.
+	 */
+	public function test_optimize_months_dropdown_cache_cleared_on_publish() {
+		self::factory()->post->create( [ 'post_date' => '2020-01-05 00:00:00' ] );
+
+		// Prime the cache with some old months.
+		wp_cache_set(
+			'post',
+			[
+				(object) [
+					'year'  => 2020,
+					'month' => 1,
+				],
+			],
+			'alleyvate_months_dropdown'
+		);
+
+		// Boot feature.
+		$this->feature->boot();
+
+		// Publish a post which should clear the cache.
+		self::factory()->post->create( [ 'post_date' => '2022-02-05 00:00:00' ] );
+
+		$this->assertEmpty( wp_cache_get( 'post', 'alleyvate_months_dropdown' ) );
+	}
 }