Send follow-up emails after sending a draft order invoice, with Mechanic.

user/draft_orders/followup+24.hours
shopify/draft_orders/update

{% comment %}
  This is here to make sure that this option sits at the top of the task form. :)
{% endcomment %}
{% assign _ = options.send_daily_emails__boolean %}

{% if event.topic == "shopify/draft_orders/update" %}
  {% assign five_minutes_ago_seconds = "now" | date: "%s" | divided_by: 1 | minus: 300 %}
  {% assign draft_order_invoice_sent_at_seconds = draft_order.invoice_sent_at | date: "%s" | divided_by: 1 %}
  {% capture draft_order_followup_cache_key %}draft-order-followup-{{ draft_order.id }}{% endcapture %}

  {% comment %}
    This being the draft update event, we only want to trigger the followup
    loop if *all* of the following are true:

    1. The draft has an email on file (because shopify doesn't report to us what
       email was actually used to send the draft previously, making the draft's
       on-file email our only option)
    2. The draft's status is "invoice_sent" (because that's the only status that
       we care about)
    3. If the invoice was actually sent in the last five minutes (to avoid
       triggering the loop for super old drafts that receive an update)
    4. If we haven't cached a flag marking the draft as having gotten follow-up
  {% endcomment %}
  {% assign draft_order_qualifies = false %}
  {% if draft_order.email == blank %}
    {% capture log_message %}No email on file; not sending followup{% endcapture %}
  {% elsif draft_order.status != "invoice_sent" %}
    {% capture log_message %}Draft status is {{ draft_order.status }}, not "invoice_sent"; not sending followup{% endcapture %}
  {% elsif draft_order_invoice_sent_at_seconds <= five_minutes_ago_seconds %}
    {% capture log_message %}Draft was sent more than 5min ago, making that event appear stale; not sending followup{% endcapture %}
  {% elsif cache[draft_order_followup_cache_key] != blank %}
    {% capture log_message %}Mechanic has already set up followup for this draft; not sending followup{% endcapture %}
  {% else %}
    {% assign draft_order_qualifies = true %}
  {% endif %}

  {% if log_message != blank %}
    {"log": {{ log_message | json }}}
  {% endif %}

  {% comment %}
    The only thing we do here is kick off the followup loop, and flag the
    draft in our cache.
  {% endcomment %}
  {% if event.preview or draft_order_qualifies %}
    {
      "action": {
        "type": "event",
        "options": {
          "topic": "user/draft_orders/followup",
          "data": {
            "draft_order_id": {{ draft_order.id | json }}
          }
        }
      }
    }

    {
      "action": {
        "type": "cache",
        "options": {
          "set": {
            "key": {{ draft_order_followup_cache_key | json }},
            "value": true
          }
        }
      }
    }
  {% endif %}
{% elsif event.topic == "user/draft_orders/followup" %}
  {% assign draft_order = shop.draft_orders[event.data.draft_order_id] %}

  {% assign draft_order_qualifies = false %}
  {% if draft_order and draft_order.order_id == blank %}
    {% assign draft_order_qualifies = true %}
  {% endif %}

  {% comment %}
    This is the loop! We send the email, and - if looping is enabled, since
    that's actually optional - we schedule the loop's next run.
  {% endcomment %}
  {% if event.preview or draft_order_qualifies %}
    {
      "action": {
        "type": "email",
        "options": {
          "to": {{ draft_order.email | json }},
          "subject": {{ options.email_subject__required | json }},
          "body": {{ options.email_body__multiline_required | strip | newline_to_br | json }},
          "reply_to": {{ shop.customer_email | json }},
          "from_display_name": {{ shop.name | json }}
        }
      }
    }

    {% if options.send_daily_emails__boolean %}
      {
        "action": {
          "type": "event",
          "options": {
            "topic": "user/draft_orders/followup",
            "data": {
              "draft_order_id": {{ draft_order.id | json }}
            }
          }
        }
      }
    {% endif %}
  {% endif %}
{% endif %}