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    <h3>Editing: wc-stock-functions.php</h3>
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/**
 * WooCommerce Stock Functions
 *
 * Functions used to manage product stock levels.
 *
 * @package WooCommerce\Functions
 * @version 3.4.0
 */

defined( 'ABSPATH' ) || exit;

use Automattic\WooCommerce\Checkout\Helpers\ReserveStock;

/**
 * Update a product's stock amount.
 *
 * Uses queries rather than update_post_meta so we can do this in one query (to avoid stock issues).
 *
 * @since  3.0.0 this supports set, increase and decrease.
 *
 * @param  int|WC_Product $product        Product ID or product instance.
 * @param  int|null       $stock_quantity Stock quantity.
 * @param  string         $operation      Type of operation, allows 'set', 'increase' and 'decrease'.
 * @param  bool           $updating       If true, the product object won't be saved here as it will be updated later.
 * @return bool|int|null
 */
function wc_update_product_stock( $product, $stock_quantity = null, $operation = 'set', $updating = false ) {
	if ( ! is_a( $product, 'WC_Product' ) ) {
		$product = wc_get_product( $product );
	}

	if ( ! $product ) {
		return false;
	}

	if ( ! is_null( $stock_quantity ) &amp;&amp; $product-&gt;managing_stock() ) {
		// Some products (variations) can have their stock managed by their parent. Get the correct object to be updated here.
		$product_id_with_stock = $product-&gt;get_stock_managed_by_id();
		$product_with_stock    = $product_id_with_stock !== $product-&gt;get_id() ? wc_get_product( $product_id_with_stock ) : $product;
		$data_store            = WC_Data_Store::load( 'product' );

		// Fire actions to let 3rd parties know the stock is about to be changed.
		if ( $product_with_stock-&gt;is_type( 'variation' ) ) {
			// phpcs:disable WooCommerce.Commenting.CommentHooks.MissingSinceComment
			/** This action is documented in includes/data-stores/class-wc-product-data-store-cpt.php */
			do_action( 'woocommerce_variation_before_set_stock', $product_with_stock );
		} else {
			// phpcs:disable WooCommerce.Commenting.CommentHooks.MissingSinceComment
			/** This action is documented in includes/data-stores/class-wc-product-data-store-cpt.php */
			do_action( 'woocommerce_product_before_set_stock', $product_with_stock );
		}

		// Update the database.
		$new_stock = $data_store-&gt;update_product_stock( $product_id_with_stock, $stock_quantity, $operation );

		// Update the product object.
		$data_store-&gt;read_stock_quantity( $product_with_stock, $new_stock );

		// If this is not being called during an update routine, save the product so stock status etc is in sync, and caches are cleared.
		if ( ! $updating ) {
			$product_with_stock-&gt;save();
		}

		// Fire actions to let 3rd parties know the stock changed.
		if ( $product_with_stock-&gt;is_type( 'variation' ) ) {
			// phpcs:disable WooCommerce.Commenting.CommentHooks.MissingSinceComment
			/** This action is documented in includes/data-stores/class-wc-product-data-store-cpt.php */
			do_action( 'woocommerce_variation_set_stock', $product_with_stock );
		} else {
			// phpcs:disable WooCommerce.Commenting.CommentHooks.MissingSinceComment
			/** This action is documented in includes/data-stores/class-wc-product-data-store-cpt.php */
			do_action( 'woocommerce_product_set_stock', $product_with_stock );
		}

		return $product_with_stock-&gt;get_stock_quantity();
	}
	return $product-&gt;get_stock_quantity();
}

/**
 * Update a product's stock status.
 *
 * @param int    $product_id Product ID.
 * @param string $status     Status.
 */
function wc_update_product_stock_status( $product_id, $status ) {
	$product = wc_get_product( $product_id );

	if ( $product ) {
		$product-&gt;set_stock_status( $status );
		$product-&gt;save();
	}
}

/**
 * When a payment is complete, we can reduce stock levels for items within an order.
 *
 * @since 3.0.0
 * @param int $order_id Order ID.
 */
function wc_maybe_reduce_stock_levels( $order_id ) {
	$order = wc_get_order( $order_id );

	if ( ! $order ) {
		return;
	}

	$stock_reduced  = $order-&gt;get_data_store()-&gt;get_stock_reduced( $order_id );
	$trigger_reduce = apply_filters( 'woocommerce_payment_complete_reduce_order_stock', ! $stock_reduced, $order_id );

	// Only continue if we're reducing stock.
	if ( ! $trigger_reduce ) {
		return;
	}

	wc_reduce_stock_levels( $order );

	// Ensure stock is marked as &quot;reduced&quot; in case payment complete or other stock actions are called.
	$order-&gt;get_data_store()-&gt;set_stock_reduced( $order_id, true );
}
add_action( 'woocommerce_payment_complete', 'wc_maybe_reduce_stock_levels' );
add_action( 'woocommerce_order_status_completed', 'wc_maybe_reduce_stock_levels' );
add_action( 'woocommerce_order_status_processing', 'wc_maybe_reduce_stock_levels' );
add_action( 'woocommerce_order_status_on-hold', 'wc_maybe_reduce_stock_levels' );

/**
 * When a payment is cancelled, restore stock.
 *
 * @since 3.0.0
 * @param int $order_id Order ID.
 */
function wc_maybe_increase_stock_levels( $order_id ) {
	$order = wc_get_order( $order_id );

	if ( ! $order ) {
		return;
	}

	$stock_reduced    = $order-&gt;get_data_store()-&gt;get_stock_reduced( $order_id );
	$trigger_increase = (bool) $stock_reduced;

	// Only continue if we're increasing stock.
	if ( ! $trigger_increase ) {
		return;
	}

	wc_increase_stock_levels( $order );

	// Ensure stock is not marked as &quot;reduced&quot; anymore.
	$order-&gt;get_data_store()-&gt;set_stock_reduced( $order_id, false );
}
add_action( 'woocommerce_order_status_cancelled', 'wc_maybe_increase_stock_levels' );
add_action( 'woocommerce_order_status_pending', 'wc_maybe_increase_stock_levels' );

/**
 * Reduce stock levels for items within an order, if stock has not already been reduced for the items.
 *
 * @since 3.0.0
 * @param int|WC_Order $order_id Order ID or order instance.
 */
function wc_reduce_stock_levels( $order_id ) {
	if ( is_a( $order_id, 'WC_Order' ) ) {
		$order    = $order_id;
		$order_id = $order-&gt;get_id();
	} else {
		$order = wc_get_order( $order_id );
	}
	// We need an order, and a store with stock management to continue.
	if ( ! $order || 'yes' !== get_option( 'woocommerce_manage_stock' ) || ! apply_filters( 'woocommerce_can_reduce_order_stock', true, $order ) ) {
		return;
	}

	$changes = array();

	// Loop over all items.
	foreach ( $order-&gt;get_items() as $item ) {
		if ( ! $item-&gt;is_type( 'line_item' ) ) {
			continue;
		}

		// Only reduce stock once for each item.
		$product            = $item-&gt;get_product();
		$item_stock_reduced = $item-&gt;get_meta( '_reduced_stock', true );

		if ( $item_stock_reduced || ! $product || ! $product-&gt;managing_stock() ) {
			continue;
		}

		/**
		 * Filter order item quantity.
		 *
		 * @param int|float             $quantity Quantity.
		 * @param WC_Order              $order    Order data.
		 * @param WC_Order_Item_Product $item Order item data.
		 */
		$qty       = apply_filters( 'woocommerce_order_item_quantity', $item-&gt;get_quantity(), $order, $item );
		$item_name = $product-&gt;get_formatted_name();
		$new_stock = wc_update_product_stock( $product, $qty, 'decrease' );

		if ( is_wp_error( $new_stock ) ) {
			/* translators: %s item name. */
			$order-&gt;add_order_note( sprintf( __( 'Unable to reduce stock for item %s.', 'woocommerce' ), $item_name ) );
			continue;
		}

		$item-&gt;add_meta_data( '_reduced_stock', $qty, true );
		$item-&gt;save();

		$change    = array(
			'product' =&gt; $product,
			'from'    =&gt; $new_stock + $qty,
			'to'      =&gt; $new_stock,
		);
		$changes[] = $change;

		/**
		 * Fires when stock reduced to a specific line item
		 *
		 * @param WC_Order_Item_Product $item Order item data.
		 * @param array $change  Change Details.
		 * @param WC_Order $order  Order data.
		 * @since 7.6.0
		 */
		do_action( 'woocommerce_reduce_order_item_stock', $item, $change, $order );
	}

	wc_trigger_stock_change_notifications( $order, $changes );

	do_action( 'woocommerce_reduce_order_stock', $order );
}

/**
 * After stock change events, triggers emails and adds order notes.
 *
 * @since 3.5.0
 * @param WC_Order $order order object.
 * @param array    $changes Array of changes.
 */
function wc_trigger_stock_change_notifications( $order, $changes ) {
	if ( empty( $changes ) ) {
		return;
	}

	$order_notes     = array();
	$no_stock_amount = absint( get_option( 'woocommerce_notify_no_stock_amount', 0 ) );

	foreach ( $changes as $change ) {
		$order_notes[]    = $change['product']-&gt;get_formatted_name() . ' ' . $change['from'] . '&amp;rarr;' . $change['to'];
		$low_stock_amount = absint( wc_get_low_stock_amount( wc_get_product( $change['product']-&gt;get_id() ) ) );
		if ( $change['to'] &lt;= $no_stock_amount ) {
			/**
			 * Action to signal that the value of 'stock_quantity' for a variation is about to change.
			 *
			 * @since 4.9
			 *
			 * @param int $product The variation whose stock is about to change.
			 */
			do_action( 'woocommerce_no_stock', wc_get_product( $change['product']-&gt;get_id() ) );
		} elseif ( $change['to'] &lt;= $low_stock_amount ) {
			/**
			 * Action to signal that the value of 'stock_quantity' for a product is about to change.
			 *
			 * @since 4.9
			 *
			 * @param int $product The product whose stock is about to change.
			 */
			do_action( 'woocommerce_low_stock', wc_get_product( $change['product']-&gt;get_id() ) );
		}

		if ( $change['to'] &lt; 0 ) {
			/**
			 * Action fires when an item in an order is backordered.
			 *
			 * @since 3.0
			 *
			 * @param array $args {
			 *     @type WC_Product $product  The product that is on backorder.
			 *     @type int        $order_id The ID of the order.
			 *     @type int|float  $quantity The amount of product on backorder.
			 * }
			 */
			do_action(
				'woocommerce_product_on_backorder',
				array(
					'product'  =&gt; wc_get_product( $change['product']-&gt;get_id() ),
					'order_id' =&gt; $order-&gt;get_id(),
					'quantity' =&gt; abs( $change['from'] - $change['to'] ),
				)
			);
		}
	}

	$order-&gt;add_order_note( __( 'Stock levels reduced:', 'woocommerce' ) . ' ' . implode( ', ', $order_notes ) );
}

/**
 * Check if a product's stock quantity has reached certain thresholds and trigger appropriate actions.
 *
 * This functionality was moved out of `wc_trigger_stock_change_notifications` in order to decouple it from orders,
 * since stock quantity can also be updated in other ways.
 *
 * @param WC_Product $product        The product whose stock level has changed.
 *
 * @return void
 */
function wc_trigger_stock_change_actions( $product ) {
	if ( true !== $product-&gt;get_manage_stock() ) {
		return;
	}

	$no_stock_amount  = absint( get_option( 'woocommerce_notify_no_stock_amount', 0 ) );
	$low_stock_amount = absint( wc_get_low_stock_amount( $product ) );
	$stock_quantity   = $product-&gt;get_stock_quantity();

	if ( $stock_quantity &lt;= $no_stock_amount ) {
		/**
		 * Action fires when a product's stock quantity reaches the &quot;no stock&quot; threshold.
		 *
		 * @since 3.0
		 *
		 * @param WC_Product $product The product whose stock quantity has changed.
		 */
		do_action( 'woocommerce_no_stock', $product );
	} elseif ( $stock_quantity &lt;= $low_stock_amount ) {
		/**
		 * Action fires when a product's stock quantity reaches the &quot;low stock&quot; threshold.
		 *
		 * @since 3.0
		 *
		 * @param WC_Product $product The product whose stock quantity has changed.
		 */
		do_action( 'woocommerce_low_stock', $product );
	}
}

/**
 * Increase stock levels for items within an order.
 *
 * @since 3.0.0
 * @param int|WC_Order $order_id Order ID or order instance.
 */
function wc_increase_stock_levels( $order_id ) {
	if ( is_a( $order_id, 'WC_Order' ) ) {
		$order    = $order_id;
		$order_id = $order-&gt;get_id();
	} else {
		$order = wc_get_order( $order_id );
	}

	// We need an order, and a store with stock management to continue.
	if ( ! $order || 'yes' !== get_option( 'woocommerce_manage_stock' ) || ! apply_filters( 'woocommerce_can_restore_order_stock', true, $order ) ) {
		return;
	}

	$changes = array();

	// Loop over all items.
	foreach ( $order-&gt;get_items() as $item ) {
		if ( ! $item-&gt;is_type( 'line_item' ) ) {
			continue;
		}

		// Only increase stock once for each item.
		$product            = $item-&gt;get_product();
		$item_stock_reduced = $item-&gt;get_meta( '_reduced_stock', true );

		if ( ! $item_stock_reduced || ! $product || ! $product-&gt;managing_stock() ) {
			continue;
		}

		$item_name = $product-&gt;get_formatted_name();
		$new_stock = wc_update_product_stock( $product, $item_stock_reduced, 'increase' );
		$old_stock = $new_stock - $item_stock_reduced;

		if ( is_wp_error( $new_stock ) ) {
			/* translators: %s item name. */
			$order-&gt;add_order_note( sprintf( __( 'Unable to restore stock for item %s.', 'woocommerce' ), $item_name ) );
			continue;
		}

		$item-&gt;delete_meta_data( '_reduced_stock' );
		$item-&gt;save();

		$changes[] = $item_name . ' ' . $old_stock . '&amp;rarr;' . $new_stock;

		/**
		 * Fires when stock restored to a specific line item
		 *
		 * @since 9.1.0
		 * @param WC_Order_Item_Product $item Order item data.
		 * @param int $new_stock  New stock.
		 * @param int $old_stock Old stock.
		 * @param WC_Order $order  Order data.
		 */
		do_action( 'woocommerce_restore_order_item_stock', $item, $new_stock, $old_stock, $order );
	}

	if ( $changes ) {
		$order-&gt;add_order_note( __( 'Stock levels increased:', 'woocommerce' ) . ' ' . implode( ', ', $changes ) );
	}

	do_action( 'woocommerce_restore_order_stock', $order );
}

/**
 * See how much stock is being held in pending orders.
 *
 * @since 3.5.0
 * @param WC_Product $product Product to check.
 * @param integer    $exclude_order_id Order ID to exclude.
 * @return int
 */
function wc_get_held_stock_quantity( WC_Product $product, $exclude_order_id = 0 ) {
	/**
	 * Filter: woocommerce_hold_stock_for_checkout
	 * Allows enable/disable hold stock functionality on checkout.
	 *
	 * @since 4.3.0
	 * @param bool $enabled Default to true if managing stock globally.
	 */
	if ( ! apply_filters( 'woocommerce_hold_stock_for_checkout', wc_string_to_bool( get_option( 'woocommerce_manage_stock', 'yes' ) ) ) ) {
		return 0;
	}

	$reserve_stock = new ReserveStock();
	return $reserve_stock-&gt;get_reserved_stock( $product, $exclude_order_id );
}

/**
 * Hold stock for an order.
 *
 * @throws ReserveStockException If reserve stock fails.
 *
 * @since 4.1.0
 * @param \WC_Order|int $order Order ID or instance.
 */
function wc_reserve_stock_for_order( $order ) {
	/**
	 * Filter: woocommerce_hold_stock_for_checkout
	 * Allows enable/disable hold stock functionality on checkout.
	 *
	 * @since @since 4.1.0
	 * @param bool $enabled Default to true if managing stock globally.
	 */
	if ( ! apply_filters( 'woocommerce_hold_stock_for_checkout', wc_string_to_bool( get_option( 'woocommerce_manage_stock', 'yes' ) ) ) ) {
		return;
	}

	$order = $order instanceof WC_Order ? $order : wc_get_order( $order );

	if ( $order ) {
		$reserve_stock = new ReserveStock();
		$reserve_stock-&gt;reserve_stock_for_order( $order );
	}
}
add_action( 'woocommerce_checkout_order_created', 'wc_reserve_stock_for_order' );

/**
 * Release held stock for an order.
 *
 * @since 4.3.0
 * @param \WC_Order|int $order Order ID or instance.
 */
function wc_release_stock_for_order( $order ) {
	/**
	 * Filter: woocommerce_hold_stock_for_checkout
	 * Allows enable/disable hold stock functionality on checkout.
	 *
	 * @since 4.3.0
	 * @param bool $enabled Default to true if managing stock globally.
	 */
	if ( ! apply_filters( 'woocommerce_hold_stock_for_checkout', wc_string_to_bool( get_option( 'woocommerce_manage_stock', 'yes' ) ) ) ) {
		return;
	}

	$order = $order instanceof WC_Order ? $order : wc_get_order( $order );

	if ( $order ) {
		$reserve_stock = new ReserveStock();
		$reserve_stock-&gt;release_stock_for_order( $order );
	}
}
add_action( 'woocommerce_checkout_order_exception', 'wc_release_stock_for_order' );
add_action( 'woocommerce_payment_complete', 'wc_release_stock_for_order', 11 );
add_action( 'woocommerce_order_status_cancelled', 'wc_release_stock_for_order', 11 );
add_action( 'woocommerce_order_status_completed', 'wc_release_stock_for_order', 11 );
add_action( 'woocommerce_order_status_processing', 'wc_release_stock_for_order', 11 );
add_action( 'woocommerce_order_status_on-hold', 'wc_release_stock_for_order', 11 );

/**
 * Return low stock amount to determine if notification needs to be sent
 *
 * Since 5.2.0, this function no longer redirects from variation to its parent product.
 * Low stock amount can now be attached to the variation itself and if it isn't, only
 * then we check the parent product, and if it's not there, then we take the default
 * from the store-wide setting.
 *
 * @param  WC_Product $product Product to get data from.
 * @since  3.5.0
 * @return int
 */
function wc_get_low_stock_amount( WC_Product $product ) {
	$low_stock_amount = $product-&gt;get_low_stock_amount();

	if ( '' === $low_stock_amount &amp;&amp; $product-&gt;is_type( 'variation' ) ) {
		$product          = wc_get_product( $product-&gt;get_parent_id() );
		$low_stock_amount = $product-&gt;get_low_stock_amount();
	}

	if ( '' === $low_stock_amount ) {
		$low_stock_amount = get_option( 'woocommerce_notify_low_stock_amount', 2 );
	}

	return (int) $low_stock_amount;
}
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