Tag products by their price ranges, with Mechanic.

shopify/products/create
shopify/products/update
mechanic/user/trigger
mechanic/shopify/bulk_operation

{% assign tag_prefix = options.tag_prefix__required %}
{% assign range_max = options.range_maximum__required_number | round %}
{% assign range_min = options.range_minimum__required_number | round %}
{% assign range_increment = options.range_increment__required_number | round %}
{% assign use_only_the_single_smallest_range = options.use_only_the_single_smallest_range_that_applies_to_each_variant__boolean %}
{% assign use_every_range = options.use_every_range_that_applies_to_each_variant__boolean %}

{% assign range_steps = range_max | minus: range_min | divided_by: range_increment %}

{% if range_max <= range_min %}
  {% error "'Range maximum' is smaller than or equal to 'Range minimum'. Try again!" %}
{% endif %}

{% assign range_max_mod = range_max | minus: range_min | modulo: range_increment %}

{% if range_max_mod != 0 %}
  {% error %}
    "Ensure both 'Range maximum' is an even multiple of {{ range_increment }} away from 'Range minimum'."
  {% enderror %}
{% endif %}

{% if use_only_the_single_smallest_range and use_every_range %}
  {% error "Use only one of the 'Use only...' options. :)" %}

{% elsif use_only_the_single_smallest_range == false and use_every_range == false %}
  {% error "Use exactly one of the 'Use only...' options. :)" %}
{% endif %}

{% if event.topic == "shopify/products/create" or event.topic == "shopify/products/update" %}
  {% 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
          variants(
            first: 250
            after: {{ cursor | json }}
          ) {
            pageInfo {
              hasNextPage
              endCursor
            }
            nodes {
              price
            }
          }
        }
      }
    {% endcapture %}

    {% assign result = query | shopify %}

    {% if event.preview %}
      {% capture result_json %}
        {
          "data": {
            "product": {
              "id": "gid://shopify/Product/1234567890",
              "tags": {{ tag_prefix | append: "1-99999999999999999" | json }},
              "variants": {
                "nodes": [
                  {
                    "price": {{ range_min | plus: 0.01 | json }}
                  },
                  {
                    "price": {{ range_max | minus: 0.01 | json }}
                  }
                ]
              }
            }
          }
        }
      {% 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" %}
  {% comment %}
    -- get all active and draft products in the shop, and all of their variant prices
  {% endcomment %}

  {% capture bulk_operation_query %}
    query {
      products(
        query: "-status:archived"
      ) {
        edges {
          node {
            __typename
            id
            tags
            variants {
              edges {
                node {
                  __typename
                  id
                  price
                }
              }
            }
          }
        }
      }
    }
  {% 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":[{{ tag_prefix | append: "1-99999999999999999" | json }}]}
      {"__typename":"ProductVariant","id":"gid://shopify/ProductVariant/1234567890","price":{{ range_min | plus: 0.01 | json }},"__parentId":"gid://shopify/Product/1234567890"}
      {"__typename":"ProductVariant","id":"gid://shopify/ProductVariant/2345678901","price":{{ range_max | minus: 0.01 | json }},"__parentId":"gid://shopify/Product/1234567890"}
    {% endcapture %}

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

  {% 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 %}

  {% assign existing_price_range_tags = array %}
  {% assign applicable_price_range_tags = array %}

  {% for tag in product.tags %}
    {% assign possible_prefix = tag | slice: 0, tag_prefix.size %}

    {% if possible_prefix == tag_prefix %}
      {% assign existing_price_range_tags = existing_price_range_tags | push: tag %}
    {% endif %}
  {% endfor %}

  {% if use_only_the_single_smallest_range %}
    {% for variant in variants %}
      {% assign variant_price = variant.price | times: 1 %}
      {% assign variant_price_left = variant_price | divided_by: range_increment | floor | times: range_increment %}
      {% assign variant_price_right = variant_price_left | plus: range_increment %}

      {% capture tag %}{{ tag_prefix }}{{ variant_price_left }}-{{ variant_price_right }}{% endcapture %}

      {% unless applicable_price_range_tags contains tag %}
        {% assign applicable_price_range_tags = applicable_price_range_tags | push: tag %}
      {% endunless %}
    {% endfor %}

  {% elsif use_every_range %}
    {% for i in (0..range_steps) %}
      {% for j in (i..range_steps) %}
        {% if j <= i %}
          {% continue %}
        {% endif %}

        {% assign step_min = i | times: range_increment | plus: range_min %}
        {% assign step_max = j | times: range_increment | plus: range_min %}

        {% for variant in variants %}
          {% assign variant_price = variant.price | times: 1 %}

          {% if variant_price >= step_min and variant_price <= step_max %}
            {% capture tag %}{{ tag_prefix }}{{ step_min }}-{{ step_max }}{% endcapture %}

            {% unless applicable_price_range_tags contains tag %}
              {% assign applicable_price_range_tags = applicable_price_range_tags | push: tag %}
            {% endunless %}
          {% endif %}
        {% endfor %}
      {% endfor %}
    {% endfor %}
  {% endif %}

  {% assign tags_to_add = array %}
  {% assign tags_to_remove = array %}

  {% for tag in applicable_price_range_tags %}
    {% unless existing_price_range_tags contains tag %}
      {% assign tags_to_add = tags_to_add | push: tag %}
    {% endunless %}
  {% endfor %}

  {% for tag in existing_price_range_tags %}
    {% unless applicable_price_range_tags contains tag %}
      {% assign tags_to_remove = tags_to_remove | push: tag %}
    {% endunless %}
  {% endfor %}

  {% if tags_to_add != blank or tags_to_remove != blank %}
    {% action "shopify" %}
      mutation {
        {% if tags_to_add != blank %}
          tagsAdd(
            id: {{ product.id | json }}
            tags: {{ tags_to_add | json }}
          ) {
            userErrors {
              field
              message
            }
          }
        {% endif %}
        {% if tags_to_remove != blank %}
          tagsRemove(
            id: {{ product.id | json }}
            tags: {{ tags_to_remove | json }}
          ) {
            userErrors {
              field
              message
            }
          }
        {% endif %}
      }
    {% endaction %}
  {% endif %}
{% endfor %}