Generate a discount code when a certain product is purchased, with Mechanic.

shopify/orders/paid

{% comment %}
  Options order:

  {{ options.required_product_id__number_required }}
  {{ options.discount_collection_id__number }}
  {{ options.discount_code_prefix }}
  {{ options.discount_fixed_amount__number }}
  {{ options.discount_percentage__number }}
  {{ options.discount_applies_to_each_line_item_individually__boolean }}
  {{ options.discount_lifetime_in_days__number }}
  {{ options.discount_can_be_used_by_anyone__boolean }}
  {{ options.email_subject__required }}
  {{ options.email_body__multiline_required }}
{% endcomment %}

{% if options.discount_percentage__number == blank and options.discount_fixed_amount__number == blank %}
  {% error "Please fill either the discount percentage or discount fixed amount." %}
{% elsif options.discount_percentage__number != blank and options.discount_fixed_amount__number != blank %}
  {% error "Please choose between the discount percentage and discount fixed amount - only one is permitted." %}
{% endif %}

{% if event.preview %}
  {% capture order_json %}
    {
      "email": "customer@example.com",
      "customer": {
        "admin_graphql_api_id": "gid://shopify/Customer/1234567890"
      },
      "line_items": [
        {
          "id": 1234567890,
          "product_id": {{ options.required_product_id__number_required | json }},
          "quantity": 1
        }
      ]
    }
  {% endcapture %}

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

{% for line_item in order.line_items %}
  {% if line_item.product_id != options.required_product_id__number_required %}
    {% continue %}
  {% endif %}

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

  {% if order.email == blank %}
    {% log "This order has no email address. Skipping" %}
    {% 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: options.discount_code_prefix %}

    {% assign email_subject = options.email_subject__required | replace: 'DISCOUNT_CODE', discount_code %}
    {% assign email_body = options.email_body__multiline_required | replace: 'DISCOUNT_CODE', discount_code %}

    {% 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 %}

    {% action "shopify" %}
      mutation {
        priceRuleCreate(
          priceRule: {
            allocationMethod: {% if options.discount_applies_to_each_line_item_individually__boolean %}EACH{% else %}ACROSS{% endif %}
            customerSelection: {
              {% if options.discount_can_be_used_by_anyone__boolean %}
                forAllCustomers: true
              {% else %}
                customerIdsToAdd: [
                  {{ order.customer.admin_graphql_api_id | json }}
                ]
              {% endif %}
            }
            itemEntitlements: {
              {% if options.discount_collection_id__number != blank %}
                collectionIds: [
                  {{ shop.collections[options.discount_collection_id__number].admin_graphql_api_id | json }}
                ]
              {% else %}
                targetAllLineItems: true
              {% endif %}
            }
            target: LINE_ITEM
            title: {{ discount_code | json }}
            validityPeriod: {
              start: {{ "now" | date: "%FT%T%:z" | json }}

              {% if options.discount_lifetime_in_days__number != blank %}
                {% assign validity_days_s = 60 | times: 60 | times: 24 | times: options.discount_lifetime_in_days__number %}
                end: {{ "now" | date: "%s" | plus: validity_days_s | date: "%FT%T%:z" | json }}
              {% endif %}
            }
            value: {
              {% if options.discount_percentage__number != blank %}
                percentageValue: {{ options.discount_percentage__number | abs | times: -1 | json }}
              {% endif %}

              {% if options.discount_fixed_amount__number != blank %}
                fixedAmountValue: {{ options.discount_fixed_amount__number | abs | times: -1 | append: "" | json }}
              {% endif %}
            }
          }
          priceRuleDiscountCode: {
            code: {{ discount_code | json }}
          }
        ) {
          priceRule {
            id
            allocationMethod
            endsAt
            target
            summary
          }
          priceRuleUserErrors {
            code
            field
            message
          }
          priceRuleDiscountCode {
            code
            id
          }
        }
      }
    {% endaction %}
  {% endfor %}
{% endfor %}