Auto-update inventory policy based on a "preorder" tag, with Mechanic.

{% if options.run_on_product_create_and_update_instead_of_daily__boolean %}
  shopify/products/create
  shopify/products/update
{% else %}
  mechanic/scheduler/daily
{% endif %}
mechanic/shopify/bulk_operation
mechanic/user/trigger

{% if event.topic == "shopify/products/create" or event.topic == "shopify/products/update" %}
  {% comment %}
    -- only check published products
  {% endcomment %}

  {% if product.published_at == blank %}
    {% unless event.preview %}
      {% log "Product is not published; skipping scan" %}
      {% break %}
    {% endunless %}
  {% endif %}

  {% comment %}
    -- query product and variant data, up to 2K variants
  {% endcomment %}

  {% assign products = array %}
  {% assign variants = array %}
  {% assign cursor = nil %}

  {% for n in (1..8) %}
    {% capture query %}
      query {
        product(id: {{ product.admin_graphql_api_id | json }}) {
          id
          tags
          variants(
            first: 250
            after: {{ cursor | json }}
          ) {
            pageInfo {
              hasNextPage
              endCursor
            }
            nodes {
              id
              inventoryPolicy
            }
          }
        }
      }
    {% endcapture %}

    {% assign result = query | shopify %}

    {% if event.preview %}
      {% capture result_json %}
        {
          "data": {
            "product": {
              "id": "gid://shopify/Product/1234567890",
              "tags": "preorder",
              "variants": {
                "nodes": [
                  {
                    "id": "gid://shopify/ProductVariant/1234567890",
                    "inventoryPolicy": "DENY"
                  }
                ]
              }
            }
          }
        }
      {% endcapture %}

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

    {% comment %}
      -- only save the product ID and tags from the product object; a separate array is used to support 2K variants
    {% endcomment %}

    {% assign products[0] = result.data.product | except: "variants" %}
    {% assign variants = variants | concat: result.data.product.variants.nodes %}

    {% if result.data.product.variants.pageInfo.hasNextPage %}
      {% assign cursor = result.data.product.variants.pageInfo.endCursor %}
    {% else %}
      {% break %}
    {% endif %}
  {% endfor %}

{% elsif event.topic == "mechanic/user/trigger" or event.topic contains "mechanic/scheduler/" %}
  {% comment %}
    -- get all published products in the shop, and all of their variants
  {% endcomment %}

  {% capture bulk_operation_query %}
    query {
      products(
        query: "gift_card:false published_status:published"
      ) {
        edges {
          node {
            __typename
            id
            tags
            variants {
              edges {
                node {
                  __typename
                  id
                  inventoryPolicy
                }
              }
            }
          }
        }
      }
    }
  {% endcapture %}

  {% action "shopify" %}
    mutation {
      bulkOperationRunQuery(
        query: {{ bulk_operation_query | json }}
      ) {
        bulkOperation {
          id
          status
        }
        userErrors {
          field
          message
        }
      }
    }
  {% endaction %}

  {% break %}

{% elsif event.topic == "mechanic/shopify/bulk_operation" %}
  {% if event.preview %}
    {% capture jsonl_string %}
      {"__typename":"Product","id":"gid://shopify/Product/1234567890","tags":["preorder"]}
      {"__typename":"ProductVariant","id":"gid://shopify/ProductVariant/1234567890","inventoryPolicy":"DENY","__parentId":"gid://shopify/Product/1234567890"}
    {% endcapture %}

    {% assign bulkOperation = hash %}
    {% assign bulkOperation["objects"] = jsonl_string | parse_jsonl %}
  {% endif %}

  {% comment %}
    -- products and variants will be separate lines in the JSONL, so filter them into their own arrays
    -- match variants to their parents in the products processing loop (this prevents creating another potentially large array in memory)
  {% endcomment %}

  {% assign products = bulkOperation.objects | where: "__typename", "Product" %}
  {% assign bulk_variants = bulkOperation.objects | where: "__typename", "ProductVariant" %}
{% endif %}

{% comment %}
  -- using products array, either process the product which triggered the event, or all products from bulk op query
{% endcomment %}

{% for product in products %}
  {% if event.topic == "mechanic/shopify/bulk_operation" %}
    {% assign variants = bulk_variants | where: "__parentId", product.id %}
  {% endif %}

  {% comment %}
    -- overselling should be disabled unless this product has a preorder tag
  {% endcomment %}

  {% assign expected_inventory_policy = "DENY" %}

  {% for tag in product.tags %}
    {% assign tag_parts = tag | split: "_" %}

    {% if tag_parts[0] == "preorder" %}
      {% assign expected_inventory_policy = "CONTINUE" %}
      {% break %}
    {% endif %}
  {% endfor %}

  {% comment %}
    -- save GraphQL mutation inputs for variants that need to have their inventory policy updated to match what is expected based on product tags
  {% endcomment %}

  {% assign variant_inputs = array %}

  {% for variant in variants %}
    {% if variant.inventoryPolicy != expected_inventory_policy %}
      {% assign variant_input = hash %}
      {% assign variant_input["id"] = variant.id %}
      {% assign variant_input["inventoryPolicy"] = expected_inventory_policy %}
      {% assign variant_inputs = variant_inputs | push: variant_input %}
    {% endif %}
  {% endfor %}

  {% if variant_inputs != blank %}
    {% comment %}
      -- pass variant inputs as GraphQL variables to handle products with a very large number of variants to update
    {% endcomment %}

    {% assign variables = hash %}
    {% assign variables["variants"] = variant_inputs %}

    {% capture query %}
      mutation productVariantsBulkUpdate($variants: [ProductVariantsBulkInput!]!) {
        productVariantsBulkUpdate(
          productId: {{ product.id | json }}
          variants: $variants
        ) {
          product {
            id
            title
            tags
          }
          userErrors {
            field
            message
          }
        }
      }
    {% endcapture %}

    {% action "shopify" query: query, variables: variables %}
  {% endif %}
{% endfor %}