Apply a coupon programmatically in Woocommerce

Question

In Woocommerce I'm trying to find a way to apply a 10% discount to an entire customer's order if the weight in the cart is over 100 lbs. I'm partway to achieving this. For the next step, I'm looking for a way to programmatically apply a coupon code via action/hook through functions.php.

It appears that I can use the function woocommerce_ajax_apply_coupon to do this ( http://docs.woothemes.com/wc-apidocs/function-woocommerce_ajax_apply_coupon.html ) but I am unsure of how to use it.

So far I've modified cart.php to get the total weight of all the products in the cart, I've created a coupon that applies the discount (if entered manually) and I've added some code to functions.php to check the weight and display a message to the user.

EDIT: Partial code removed, completed code included in the solution below.

---

Thanks for the guidance Freney. Here's the working end result which successfully applies the discount coupon when the condition is met and also removes it when it's no longer met:

/* Mod: 10% Discount for weight greater than 100 lbs 
Works with code added to child theme: woocommerce/cart/cart.php lines 13 - 14: which gets $total_weight of cart:
        global $total_weight;
        $total_weight = $woocommerce->cart->cart_contents_weight;
*/
add_action('woocommerce_before_cart_table', 'discount_when_weight_greater_than_100');
function discount_when_weight_greater_than_100( ) {
    global $woocommerce;
    global $total_weight;
    if( $total_weight > 100 ) {
        $coupon_code = '999';
        if (!$woocommerce->cart->add_discount( sanitize_text_field( $coupon_code ))) {
            $woocommerce->show_messages();
        }
        echo '<div class="woocommerce_message"><strong>Your order is over 100 lbs so a 10% Discount has been Applied!</strong> Your total order weight is <strong>' . $total_weight . '</strong> lbs.</div>';
    }
}

/* Mod: Remove 10% Discount for weight less than or equal to 100 lbs */
add_action('woocommerce_before_cart_table', 'remove_coupon_if_weight_100_or_less');
function remove_coupon_if_weight_100_or_less( ) {
    global $woocommerce;
    global $total_weight;
    if( $total_weight <= 100 ) {
        $coupon_code = '999';
        $woocommerce->cart->get_applied_coupons();
        if (!$woocommerce->cart->remove_coupons( sanitize_text_field( $coupon_code ))) {
            $woocommerce->show_messages();
        }
        $woocommerce->cart->calculate_totals();
    }
}

Answer 1

First, create a discount coupon (via http://docs.woothemes.com/document/create-a-coupon-programatically/):

$coupon_code = 'UNIQUECODE'; // Code - perhaps generate this from the user ID + the order ID
$amount = '10'; // Amount
$discount_type = 'percent'; // Type: fixed_cart, percent, fixed_product, percent_product

$coupon = array(
    'post_title' => $coupon_code,
    'post_content' => '',
    'post_status' => 'publish',
    'post_author' => 1,
    'post_type'     => 'shop_coupon'
);    

$new_coupon_id = wp_insert_post( $coupon );

// Add meta
update_post_meta( $new_coupon_id, 'discount_type', $discount_type );
update_post_meta( $new_coupon_id, 'coupon_amount', $amount );
update_post_meta( $new_coupon_id, 'individual_use', 'no' );
update_post_meta( $new_coupon_id, 'product_ids', '' );
update_post_meta( $new_coupon_id, 'exclude_product_ids', '' );
update_post_meta( $new_coupon_id, 'usage_limit', '1' );
update_post_meta( $new_coupon_id, 'expiry_date', '' );
update_post_meta( $new_coupon_id, 'apply_before_tax', 'yes' );
update_post_meta( $new_coupon_id, 'free_shipping', 'no' );

Then apply that coupon to your order:

if (!$woocommerce->cart->add_discount( sanitize_text_field( $coupon_code )))
    $woocommerce->show_messages();

That last function returns a BOOL value: TRUE if the discount was successful, FALSE if it fails for any one of a variety of reasons.