Tag products by their price ranges, with Mechanic.

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

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

{% assign products = array %}

{% if event.preview %}
  {% assign products[0] = hash %}
  {% assign products[0]["admin_graphql_api_id"] = "gid://shopify/Product/1234567890" %}

  {% assign tags = array %}
  {% assign tags[tags.size] = "red" %}
  {% assign tags[tags.size] = "blue" %}
  {% assign tags[tags.size] = tag_prefix | append: "1-99999999999999999" %}

  {% assign products[0]["tags"] = tags | join: ", " %}
  {% assign products[0]["variants"] = array %}
  {% assign products[0]["variants"][0] = hash %}
  {% assign products[0]["variants"][0]["price"] = options.range_minimum__required_number | plus: 0.01 %}
  {% assign products[0]["variants"][1] = hash %}
  {% assign products[0]["variants"][1]["price"] = options.range_maximum__required_number | minus: 0.01 %}
{% elsif event.topic == "mechanic/user/trigger" %}
  {% assign products = shop.products %}
{% elsif event.topic == "shopify/products/create" or event.topic == "shopify/products/update" %}
  {% assign products[0] = product %}
{% endif %}

{% for product in products %}
  {% assign product_tags = product.tags | split: ", " %}
  {% 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.size] = tag %}
    {% endif %}
  {% endfor %}

  {% if options.use_only_the_single_smallest_range_that_applies_to_each_variant__boolean %}
    {% for variant in product.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.size] = tag %}
      {% endunless %}
    {% endfor %}
  {% elsif options.use_every_range_that_applies_to_each_variant__boolean %}
    {% 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 product.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.size] = 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.size] = tag %}
    {% endunless %}
  {% endfor %}

  {% for tag in existing_price_range_tags %}
    {% unless applicable_price_range_tags contains tag %}
      {% assign tags_to_remove[tags_to_remove.size] = tag %}
    {% endunless %}
  {% endfor %}

  {% if tags_to_add != empty or tags_to_remove != empty %}
    {% action "shopify" %}
      mutation {

        {% if tags_to_add != empty %}
          tagsAdd(
            id: {{ product.admin_graphql_api_id | json }}
            tags: {{ tags_to_add | json }}
          ) {
            userErrors {
              field
              message
            }
          }
        {% endif %}

        {% if tags_to_remove != empty %}
          tagsRemove(
            id: {{ product.admin_graphql_api_id | json }}
            tags: {{ tags_to_remove | json }}
          ) {
            userErrors {
              field
              message
            }
          }
        {% endif %}

      }
    {% endaction %}
  {% endif %}
{% endfor %}