Generate a product discount when a voucher product is purchased, with Mechanic.

shopify/orders/paid
mechanic/actions/perform

{% 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_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 %}
      {
        "email": "customer@example.com",
        "customer": {
          "id": 1234567890,
          "first_name": "TEST"
        },
        "line_items": [
          {
            "id": 1234567890,
            "product_id": {{ ve_product_ids_keyval.first.first }},
            "quantity": 1
          }
        ]
      }
    {% endcapture %}

    {% assign order = order_json | parse_json %}
  {% endif %}

  {% if order.customer == blank %}
    {% log "This order has no related customer. Skipping" %}
    {% break %}
  {% endif %}

  {% if order.email == blank %}
    {% log "This order has no email address. Skipping" %}
    {% break %}
  {% endif %}

  {% assign customer_id = order.customer.id | prepend: "gid://shopify/Customer/" %}

  {% for line_item in order.line_items %}
    {% assign voucher_product_title = line_item.title %}
    {% assign voucher_product_id = line_item.product_id %}
    {% assign voucher_product_id_string = voucher_product_id | append: "" %}
    {% assign entitled_product_id = ve_product_ids_keyval[voucher_product_id_string] %}

    {% if entitled_product_id == blank %}
      {% continue %}
    {% endif %}

    {% comment %}
      -- make sure the entitled product exists in the shop and get its title
    {% endcomment %}

    {% capture query %}
      query {
        product(id: {{ entitled_product_id | prepend: "gid://shopify/Product/" | json }}) {
          id
          title
        }
      }
    {% endcapture %}

    {% assign result = query | shopify %}

    {% if event.preview %}
      {% capture result_json %}
        {
          "data": {
            "product": {
              "id": "gid://shopify/Product/1234567890",
              "title": "Widget"
            }
          }
        }
      {% endcapture %}

      {% assign result = result_json | parse_json %}
    {% endif %}

    {% assign entitled_product = result.data.product %}

    {% if entitled_product == blank %}
      {% action "echo"
        __error: "Entitled product not found in the shop. Discount code will not be created.",
        entitled_product_id: entitled_product_id,
        voucher_product_id: voucher_product_id
      %}
      {% continue %}
    {% endif %}

    {% 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 %}
        mutation {
          discountCodeBasicCreate(
            basicCodeDiscount: {
              code: {{ discount_code | json }}
              customerSelection: {
                customers: {
                  add: {{ array | push: customer_id | json }}
                }
              }
              title: {{ discount_code | json }}
              startsAt: {{ "now" | date: "%FT%T%:z" | json }}
              customerGets: {
                items: {
                  products: {
                    productsToAdd: {{ array | push: entitled_product.id | json }}
                  }
                }
                value: {
                  {% 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
            }
          ) {
            codeDiscountNode {
              id
              codeDiscount {
                ... on DiscountCodeBasic {
                  codes(first: 1) {
                    nodes {
                      id
                      code
                    }
                  }
                  summary
                }
              }
            }
            userErrors {
              code
              extraInfo
              field
              message
            }
          }
        }
      {% endcapture %}

      {% action %}
        {
          "type": "shopify",
          "options": {
            "query": {{ mutation | json }}
          },
          "meta": {
            "customer_first_name": {{ order.customer.first_name | default: "there" | json }},
            "order_email": {{ order.email | json }},
            "order_name": {{ order.name | json }},
            "discount_code": {{ discount_code | json }},
            "entitled_product_title": {{ entitled_product.title | json }},
            "voucher_product_title": {{ voucher_product_title | json }}
          }
        }
      {% endaction %}
    {% endfor %}
  {% endfor %}

{% elsif event.topic == "mechanic/actions/perform" %}
  {% comment %}
    -- only process a successful discountCodeBasicCreate shopify action; the Error reporter task should be used to respond to failures
  {% endcomment %}

  {% unless action.type == "shopify" and action.run.ok == true %}
    {% break %}
  {% endunless %}

  {% assign customer_first_name = action.meta.customer_first_name %}
  {% assign order_email = action.meta.order_email %}
  {% assign order_name = action.meta.order_name %}
  {% assign discount_code = action.meta.discount_code %}
  {% assign entitled_product_title = action.meta.entitled_product_title %}
  {% assign voucher_product_title = action.meta.voucher_product_title %}

  {% comment %}
    -- send a customer email for the created discount code
  {% endcomment %}

  {% assign email_subject = email_subject
    | replace: 'CUSTOMER_FIRST_NAME', customer_first_name
    | replace: 'DISCOUNT_CODE', discount_code
    | replace: 'ENTITLED_PRODUCT_TITLE', entitled_product_title
    | replace: 'ORDER_NAME', order_name
    | replace: 'VOUCHER_PRODUCT_TITLE', voucher_product_title
  %}
  {% assign email_body = email_body
    | replace: 'CUSTOMER_FIRST_NAME', customer_first_name
    | replace: 'DISCOUNT_CODE', discount_code
    | replace: 'ENTITLED_PRODUCT_TITLE', entitled_product_title
    | replace: 'ORDER_NAME', order_name
    | replace: 'VOUCHER_PRODUCT_TITLE', voucher_product_title
  %}

  {% action "email" %}
    {
      "to": {{ order_email | json }},
      "subject": {{ email_subject | strip | json }},
      "body": {{ email_body | strip | newline_to_br | json }},
      "reply_to": {{ shop.customer_email | json }},
      "from_display_name": {{ shop.name | json }}
    }
  {% endaction %}
{% endif %}