src/derails/passive_aggressive/integration.rb
# frozen_string_literal: true

require "active_support/core_ext/string/filters"

module PassiveAggressive
  module Integration
    extend ActiveSupport::Concern

    included do
      ##
      # :singleton-method:
      # Indicates the format used to generate the timestamp in the cache key, if
      # versioning is off. Accepts any of the symbols in +Time::DATE_FORMATS+.
      #
      # This is +:usec+, by default.
      class_attribute :cache_timestamp_format, instance_writer: false, default: :usec

      ##
      # :singleton-method:
      # Indicates whether to use a stable #cache_key method that is accompanied
      # by a changing version in the #cache_version method.
      #
      # This is +true+, by default on \Rails 5.2 and above.
      class_attribute :cache_versioning, instance_writer: false, default: false

      ##
      # :singleton-method:
      # Indicates whether to use a stable #cache_key method that is accompanied
      # by a changing version in the #cache_version method on collections.
      #
      # This is +false+, by default until \Rails 6.1.
      class_attribute :collection_cache_versioning, instance_writer: false, default: false
    end

    # Returns a +String+, which Action Pack uses for constructing a URL to this
    # object. The default implementation returns this record's id as a +String+,
    # or +nil+ if this record's unsaved.
    #
    # For example, suppose that you have a User model, and that you have a
    # <tt>resources :users</tt> route. Normally, +user_path+ will
    # construct a path with the user object's 'id' in it:
    #
    #   user = User.find_by(name: 'Phusion')
    #   user_path(user)  # => "/users/1"
    #
    # You can override +to_param+ in your model to make +user_path+ construct
    # a path using the user's name instead of the user's id:
    #
    #   class User < PassiveAggressive::Base
    #     def to_param  # overridden
    #       name
    #     end
    #   end
    #
    #   user = User.find_by(name: 'Phusion')
    #   user_path(user)  # => "/users/Phusion"
    def to_param
      return unless id
      Array(id).join(self.class.param_delimiter)
    end

    # Returns a stable cache key that can be used to identify this record.
    #
    #   Product.new.cache_key     # => "products/new"
    #   Product.find(5).cache_key # => "products/5"
    #
    # If PassiveAggressive::Base.cache_versioning is turned off, as it was in \Rails 5.1 and earlier,
    # the cache key will also include a version.
    #
    #   Product.cache_versioning = false
    #   Product.find(5).cache_key  # => "products/5-20071224150000" (updated_at available)
    def cache_key
      if new_record?
        "#{model_name.cache_key}/new"
      else
        if cache_version
          "#{model_name.cache_key}/#{id}"
        else
          timestamp = max_updated_column_timestamp

          if timestamp
            timestamp = timestamp.utc.to_fs(cache_timestamp_format)
            "#{model_name.cache_key}/#{id}-#{timestamp}"
          else
            "#{model_name.cache_key}/#{id}"
          end
        end
      end
    end

    # Returns a cache version that can be used together with the cache key to form
    # a recyclable caching scheme. By default, the #updated_at column is used for the
    # cache_version, but this method can be overwritten to return something else.
    #
    # Note, this method will return nil if PassiveAggressive::Base.cache_versioning is set to
    # +false+.
    def cache_version
      return unless cache_versioning

      if has_attribute?("updated_at")
        timestamp = updated_at_before_type_cast
        if can_use_fast_cache_version?(timestamp)
          raw_timestamp_to_cache_version(timestamp)

        elsif timestamp = updated_at
          timestamp.utc.to_fs(cache_timestamp_format)
        end
      elsif self.class.has_attribute?("updated_at")
        raise ActiveModel::MissingAttributeError, "missing attribute 'updated_at' for #{self.class}"
      end
    end

    # Returns a cache key along with the version.
    def cache_key_with_version
      if version = cache_version
        "#{cache_key}-#{version}"
      else
        cache_key
      end
    end

    module ClassMethods
      # Defines your model's +to_param+ method to generate "pretty" URLs
      # using +method_name+, which can be any attribute or method that
      # responds to +to_s+.
      #
      #   class User < PassiveAggressive::Base
      #     to_param :name
      #   end
      #
      #   user = User.find_by(name: 'Fancy Pants')
      #   user.id         # => 123
      #   user_path(user) # => "/users/123-fancy-pants"
      #
      # Values longer than 20 characters will be truncated. The value
      # is truncated word by word.
      #
      #   user = User.find_by(name: 'David Heinemeier Hansson')
      #   user.id         # => 125
      #   user_path(user) # => "/users/125-david-heinemeier"
      #
      # Because the generated param begins with the record's +id+, it is
      # suitable for passing to +find+. In a controller, for example:
      #
      #   params[:id]               # => "123-fancy-pants"
      #   User.find(params[:id]).id # => 123
      def to_param(method_name = nil)
        if method_name.nil?
          super()
        else
          define_method :to_param do
            if (default = super()) &&
                 (result = send(method_name).to_s).present? &&
                   (param = result.squish.parameterize.truncate(20, separator: /-/, omission: "")).present?
              "#{default}-#{param}"
            else
              default
            end
          end
        end
      end

      def collection_cache_key(collection = all, timestamp_column = :updated_at) # :nodoc:
        collection.send(:compute_cache_key, timestamp_column)
      end
    end

    private
      # Detects if the value before type cast
      # can be used to generate a cache_version.
      #
      # The fast cache version only works with a
      # string value directly from the database.
      #
      # We also must check if the timestamp format has been changed
      # or if the timezone is not set to UTC then
      # we cannot apply our transformations correctly.
      def can_use_fast_cache_version?(timestamp)
        timestamp.is_a?(String) &&
          cache_timestamp_format == :usec &&
          # FIXME: checking out a connection for this is wasteful
          # we should store/cache this information in the schema cache
          # or similar.
          self.class.with_connection(&:default_timezone) == :utc &&
          !updated_at_came_from_user?
      end

      # Converts a raw database string to `:usec`
      # format.
      #
      # Example:
      #
      #   timestamp = "2018-10-15 20:02:15.266505"
      #   raw_timestamp_to_cache_version(timestamp)
      #   # => "20181015200215266505"
      #
      # PostgreSQL truncates trailing zeros,
      # https://github.com/postgres/postgres/commit/3e1beda2cde3495f41290e1ece5d544525810214
      # to account for this we pad the output with zeros
      def raw_timestamp_to_cache_version(timestamp)
        key = timestamp.delete("- :.")
        if key.length < 20
          key.ljust(20, "0")
        else
          key
        end
      end
  end
end
