correct loop variable; add percentage discount option (#419)

docs/generate-a-product-discount-when-a-voucher-product-is-purchased/README.md

@@ -2,7 +2,7 @@
 
 Tags: Discounts, Products, Watch
 
-Use this task to generate discounts for future purchases. When a customer buys a "voucher" product, they will be emailed a single-use discount code for a fixed amount of money off a purchase on a corresponding "entitled" product".
+Use this task to generate discounts for future purchases. When a customer buys a "voucher" product, they will be emailed a single-use discount code for either a fixed amount of money or percentage off a purchase on a corresponding "entitled" product".
 
 * View in the task library: [tasks.mechanic.dev/generate-a-product-discount-when-a-voucher-product-is-purchased](https://tasks.mechanic.dev/generate-a-product-discount-when-a-voucher-product-is-purchased)
 * Task JSON, for direct import: [task.json](../../tasks/generate-a-product-discount-when-a-voucher-product-is-purchased.json)
@@ -33,15 +33,16 @@ mechanic/actions/perform
 
 ## Documentation
 
-Use this task to generate discounts for future purchases. When a customer buys a "voucher" product, they will be emailed a single-use discount code for a fixed amount of money off a purchase on a corresponding "entitled" product".
+Use this task to generate discounts for future purchases. When a customer buys a "voucher" product, they will be emailed a single-use discount code for either a fixed amount of money or percentage off a purchase on a corresponding "entitled" product".
 
 If a customer purchases more than one voucher product, they will receive more than one email, each containing a unique discount code.
 
 ### Options
 
 - **Voucher product IDs and entitled product IDs:** Enter the IDs of the voucher products you're selling on the left, and the IDs of products you want to be discounted on the right. ([Learn how to find the product IDs.](https://learn.mechanic.dev/techniques/finding-a-resource-id))
 - **Discount code prefix:** A small piece of text to add to the beginning of the generated discount code.
-- **Discount value:** The money value to be subtracted.
+- **Discount fixed amount:** The money value to be subtracted. If you choose this option, you cannot choose a discount percentage.
+- **Discount percentage:** The percentage to be subtracted (e.g. 15). If you choose this option, you cannot choose a fixed discount amount.
 - **Email subject, body:** The content to email to the customer. May use the following variables:
   - CUSTOMER_FIRST_NAME
   - DISCOUNT_CODE

docs/generate-a-product-discount-when-a-voucher-product-is-purchased/script.liquid

@@ -1,9 +1,17 @@
 {% assign ve_product_ids_keyval = options.voucher_product_ids_and_entitled_product_ids__keyval_number_required %}
 {% assign discount_code_prefix = options.discount_code_prefix__required %}
-{% assign discount_value = options.discount_value__number_required %}
+{% assign discount_fixed_amount = options.discount_fixed_amount__number %}
+{% assign discount_percentage = options.discount_percentage__number %}
 {% assign email_subject = options.email_subject__required %}
 {% assign email_body = options.email_body__multiline_required %}
 
+{% if discount_percentage == blank and discount_fixed_amount == blank %}
+  {% error "Please fill either the discount percentage or discount fixed amount." %}
+
+{% elsif discount_percentage != blank and discount_fixed_amount != blank %}
+  {% error "Please choose between the discount percentage and discount fixed amount - only one is permitted." %}
+{% endif %}
+
 {% if event.topic == "shopify/orders/paid" %}
   {% if event.preview %}
     {% capture order_json %}
@@ -89,7 +97,7 @@
       {% continue %}
     {% endif %}
 
-    {% for line_item_n in (1..line_item.quantity) %}
+    {% for n in (1..line_item.quantity) %}
       {% assign discount_code = line_item.id | append: n | split: "" | reverse | join: "" | slice: 0, 4 | append: order.order_number | base64 | replace: "=", "" | upcase | prepend: discount_code_prefix %}
 
       {% capture mutation %}
@@ -111,10 +119,14 @@
                   }
                 }
                 value: {
-                  discountAmount: {
-                    amount: {{ discount_fixed_amount | abs | times: 1.0 | json }}
-                    appliesOnEachItem: false
-                  }
+                  {% if discount_percentage != blank %}
+                    percentage: {{ discount_percentage | abs | divided_by: 100.0 | json }}
+                  {% else %}
+                    discountAmount: {
+                      amount: {{ discount_fixed_amount | abs | times: 1.0 | json }}
+                      appliesOnEachItem: false
+                    }
+                  {% endif %}
                 }
               }
               usageLimit: 1