Shopify script to show shipping rates if products have certain tags

Shipping_rate_by_product_tag.rb

# ================================ Customizable Settings ================================
# ================================================================
# Show Rate(s) for Product Tag
#
# If we have a product with matching tag, the entered rate(s) will be
# shown, and all others will be hidden. Otherwise, the entered
# rate(s) will be hidden.
#
#   - 'product_tag_match_type' determines whether we look for the
#     product to be tagged with any of the entered tags or not.
#     Can be:
#       - ':include' to check if the product is tagged
#       - ':exclude' to make sure the product isn't tagged
#   - 'product_tags' is a list of product tags to trigger the
#     campaign
#   - 'rate_match_type' determines whether the below strings
#     should be an exact or partial match. Can be:
#       - ':exact' for an exact match
#       - ':partial' for a partial match
#   - 'rate_names' is a list of strings to identify rates
# ================================================================
SHOW_RATES_FOR_PRODUCT_TAG = [
  {
    product_tag_match_type: :include,
    product_tags: ["free_shipping"],
    rate_match_type: :exact,
    rate_names: ["Free Shipping"],
  },
]

# ================================ Script Code (do not edit) ================================
# ================================================================
# ProductTagSelector
#
# Finds whether the supplied product has any of the entered tags.
# ================================================================
class ProductTagSelector
  def initialize(match_type, tags)
    @comparator = match_type == :include ? 'any?' : 'none?'
    @tags = tags.map { |tag| tag.downcase.strip }
  end

  def match?(product_tags)
    product_tags_cleaned = product_tags.map { |tag| tag.downcase.strip }
    (@tags & product_tags_cleaned).send(@comparator)
  end
end

# ================================================================
# RateNameSelector
#
# Finds whether the supplied rate name matches any of the entered
# names.
# ================================================================
class RateNameSelector
  def initialize(match_type, rate_names)
    @comparator = match_type == :exact ? '==' : 'include?'
    @rate_names = rate_names.map { |rate_name| rate_name.downcase.strip }
  end

  def match?(shipping_rate)
    @rate_names.any? { |name| shipping_rate.name.downcase.send(@comparator, name) }
  end
end

# ================================================================
# ShowRateForProductTagCampaign
#
# If we have a product with matching tags, the entered rate(s) will be
# shown, and all others will be hidden. Otherwise, the entered
# rate(s) will be hidden.
# ================================================================
class ShowRateForProductsTagCampaign
  def initialize(campaigns)
    @campaigns = campaigns
  end

  def run(cart, shipping_rates)
    @campaigns.each do |campaign|
      product_tag_selector = ProductTagSelector.new(
        campaign[:product_tag_match_type],
        campaign[:product_tags]
      )
      
      # Get all the product tags from the line items
      product_tags = []
      cart.line_items.map{|item| product_tags.concat(item.variant.product.tags) }
      product_tags.uniq!

      product_match = product_tag_selector.match?(product_tags)

      rate_name_selector = RateNameSelector.new(
        campaign[:rate_match_type],
        campaign[:rate_names]
      )

      shipping_rates.delete_if do |shipping_rate|
        rate_name_selector.match?(shipping_rate) != product_match
      end
    end
  end
end

CAMPAIGNS = [
  ShowRateForProductsTagCampaign.new(SHOW_RATES_FOR_PRODUCT_TAG),
]

CAMPAIGNS.each do |campaign|
  campaign.run(Input.cart, Input.shipping_rates)
end

Output.shipping_rates = Input.shipping_rates