feat: add timestamp during product prep to track sync latency

includes/fbproduct.php

@@ -2204,6 +2204,9 @@ public function prepare_product( $retailer_id = null, $type_to_prepare_for = sel
 			$product_data['external_update_time'] = $date_modified->getTimestamp();
 		}
 
+		// Add product preparation timestamp
+		$product_data['product_prepare_time'] = time();
+
 		// Only use checkout URLs if they exist.
 		$checkout_url = $this->build_checkout_url( $product_url );
 		if ( $checkout_url ) {

includes/fbproductfeed.php

@@ -421,7 +421,7 @@ public function get_product_feed_header_row() {
 		'additional_image_link,sale_price_effective_date,sale_price,condition,' .
 		'visibility,gender,color,size,pattern,google_product_category,default_product,' .
 		'variant,gtin,quantity_to_sell_on_facebook,rich_text_description,internal_label,external_update_time,' .
-		'external_variant_id, is_woo_all_products_sync' . PHP_EOL;
+		'product_prepare_time,external_variant_id, is_woo_all_products_sync' . PHP_EOL;
 	}
 
 
@@ -581,6 +581,7 @@ private function prepare_product_for_feed( $woo_product, &$attribute_variants )
 		static::format_string_for_feed( static::get_value_from_product_data( $product_data, 'rich_text_description' ) ) . ',' .
 		static::format_internal_labels_for_feed( static::get_value_from_product_data( $product_data, 'internal_label' ) ) . ',' .
 		static::get_value_from_product_data( $product_data, 'external_update_time' ) . ',' .
+		static::get_value_from_product_data( $product_data, 'product_prepare_time' ) . ',' .
 		static::get_value_from_product_data( $product_data, 'external_variant_id' ) . ',' .
 		static::format_string_for_feed( $is_woo_all_products_sync ) . PHP_EOL;
 	}

tests/Unit/fbproductTest.php

@@ -1085,6 +1085,26 @@ public function test_external_update_time_unset() {
 		$this->assertEquals(isset($data['external_update_time']), false);
 	}
 
+	/**
+	 * Test product_prepare_time is populated
+	 * @return void
+	 */
+	public function test_product_prepare_time_set() {
+		$woo_product = WC_Helper_Product::create_simple_product();
+
+		$before_time = time();
+		$fb_product = new \WC_Facebook_Product( $woo_product );
+		$data = $fb_product->prepare_product();
+		$after_time = time();
+
+		$this->assertArrayHasKey('product_prepare_time', $data);
+		$this->assertIsNumeric($data['product_prepare_time']);
+
+		// Verify the timestamp is within the expected range (between before and after the product_prepare call)
+		$this->assertGreaterThanOrEqual($before_time, $data['product_prepare_time']);
+		$this->assertLessThanOrEqual($after_time, $data['product_prepare_time']);
+	}
+
 	/**
 	 * Test fallback to main description when it's less than 1000 characters.
 	 */