<?php

/**
 * Class WP_Memory_Leak_Tests
 *
 * This class tests two cases that cause memory leaks in WordPress that could
 * lead to crashes, particularly in CLI jobs that work on larger batches.  For
 * each of the cases ( one for the wpdb class and one for the global
 * $wp_object_cache ), we perform some seemingly innocuous task many times -
 * enough times to require that PHP allocate more memory because of a specific
 * action.
 *
 * Neither of the tests here show a particularly large memory increase, but I've
 * personally had both occur for me on large jobs hitting WP API functions.  The
 * one with $wpdb->queries particularly has a tendency to blow up.
 */
class WP_Memory_Leak_Tests extends \WP_UnitTestCase {

	/**
	 * This tests a condition which exposes a memory leak in the WPDB class.
	 * If 'SAVEQUERIES' is defined as truthy, then the $wpdb->queries property
	 * can grow indefinitely.
	 */
	public function test_WPDB_Memory_Leak() {

		// Once a constant is defined, it can't be undefined
		define( 'SAVEQUERIES', true );

		// I'll just start my cron job to read the import file I've got.  It's
		// got a decent number of records.
		$number_of_records = 1000;

		global $wpdb;
		$memory = memory_get_usage( true );
		$peak   = memory_get_peak_usage( true );
		foreach ( [ 'first', 'second' ] as $pass ) {
			// first pass through, we'll apply a fix for this memory leak.
			// second pass through, we'll bypass the fix and the tests will fail.
			for ( $i = 1; $i <= $number_of_records; $i ++ ) {
				if ( 'first' === $pass ) {
					$wpdb->queries = [];
				}

				// for this test, we'll do direct calls to $wpdb
				$wpdb->query( $wpdb->prepare( "SELECT * FROM $wpdb->posts WHERE ID = %d", $i ) );
			}
			$this->assertEquals( $memory, memory_get_usage( true ), "$pass pass" );
			$this->assertEquals( $peak, memory_get_peak_usage( true ), "$pass pass" );
		}

	}

	/**
	 * This tests a condition which exposes a memory leak in wp cache API.  If
	 * a large batch job attempts to do a lot of something that ends up caching
	 * things ( like, for example, get_post or wp_insert_post ), then unless
	 * the cache is flushed regularly, the memory usage grows indefinitely.
	 */
	public function test_WP_Cache_Memory_Leak() {

		// I'll just start my cron job to read the import file I've got.  It's
		// got a decent number of records.
		$number_of_records = 1000;

		global $wpdb;
		$memory = memory_get_usage( true );
		$peak   = memory_get_peak_usage( true );
		foreach ( [ 'first', 'second' ] as $pass ) {
			// first pass through, we'll apply a fix for this memory leak.
			// second pass through, we'll bypass the fix and the tests will fail.
			for ( $i = 1; $i <= $number_of_records; $i ++ ) {
				if ( 'first' === $pass ) {
					wp_cache_flush();
				}

				// Because our last test defined 'SAVEQUERIES', we need to
				// always apply this fix, otherwise that memory leak manifests.
				// With us doing a core API function `wp_insert_post`, the number
				// of queries is quite large and memory __really__ grows.
				$wpdb->queries = [];

				// let's say we're inserting posts, maybe from an excel file.
				// this caches some things, so $wp_object_cache grows.
				wp_insert_post([
					'post_type' => 'post',
					'post_title' => "post $i",
					'post_content' => "pass $pass"
				]);
			}
			$this->assertEquals( $memory, memory_get_usage( true ), "$pass pass" );
			$this->assertEquals( $peak, memory_get_peak_usage( true ), "$pass pass" );
		}

	}

}