module Appfuel
  module Repository
    # The mapping registry holds all entity to db mappings. Mappings are
    # contained within a DbEntityMapEntry object and are arranged by
    # entity name. Each entity will hold a hash where the keys are the
    # attribute names and the value is the entry
    class Mapper
      attr_reader :container_root_name

      def initialize(app_name, map = nil)
        @container_root_name = app_name
        if !map.nil? && !map.is_a?(Hash)
          fail "repository mappings must be a hash"
        end
        @map = map
      end

      # The map represents domain mappings to one or more storage systems.
      # Currently one map represents all storage. So if you have a file, and
      # database storage for a given domain the storage attributes are the same
      # for each interface. This will load the repository mappings from the
      # application container if no map as been manually set.
      #
      # @example a map has the following structure
      #   {
      #     domain_name: {
      #       domain_attr1: <MappingEntry>,
      #       domain_attr1: <MappingEntry>
      #     }
      #     ...
      #   }
      # @return [Hash]
      def map
        @map ||= mappings_from_container
      end

      # Determine if an entity has been added
      #
      # @param entity [String]
      # @return [Boolean]
      def entity?(entity_name)
        map.key?(entity_name)
      end

      # Determine if an attribute is mapped for a given entity
      #
      # @param entity [String] name of the entity
      # @param attr [String] name of the attribute
      # @return [Boolean]
      def entity_attr?(entity_name, entity_attr)
        return false unless entity?(entity_name)

        map[entity_name].key?(entity_attr)
      end

      # Returns a mapping entry for a given entity
      #
      # @raise [RuntimeError] when entity not found
      # @raise [RuntimeError] when attr not found
      #
      # @param entity_name [String] qualified entity name "<feature>.<entity>"
      # @param entity_attr [String] name of the attribute
      # @return [Boolean]
      def find(entity_name, entity_attr)
        validate_domain(entity_name)

        unless map[entity_name].key?(entity_attr)
          fail "Entity (#{entity_name}) attr (#{entity_attr}) is not registered"
        end
        map[entity_name][entity_attr]
      end

      # Iterates over all entries for a given entity
      #
      # @yield [attr, entry] expose the entity attr name and entry
      #
      # @param entity_name [String] qualified entity name "<feature>.<entity>"
      # @return [void]
      def each_entity_attr(entity_name)
        validate_domain(entity_name)
        map[entity_name].each do |_attr, entry|
          yield entry
        end
      end

      # Determine if an column is mapped for a given entity
      #
      # @param entity_name [String] qualified entity name "<feature>.<entity>"
      # @param storage_attr [String] name the persistence attr
      # @return [Boolean]
      def storage_attr_mapped?(entity_name, storage_attr)
        each_entity_attr(entity_name) do |entry|
          return true if storage_attr == entry.storage_attr
        end

        false
      end

      # Returns a column name for an entity's attribute
      #
      # @raise [RuntimeError] when entity not found
      # @raise [RuntimeError] when attr not found
      #
      # @param entity_name [String] qualified entity name "<feature>.<entity>"
      # @param entity_attr [String] name of the attribute
      # @return [String]
      def storage_attr(entity_name, entity_attr)
        find(entity_name, entity_attr).storage_attr
      end

      # Returns the storage class based on type
      # mapping foo.bar, db: auth.foo_bar,
      #
      # @raise [RuntimeError] when entity not found
      # @raise [RuntimeError] when attr not found
      # @raise [Dry::Contriner::Error] when db_class is not registered
      #
      # @param entity [String] name of the entity
      # @param attr [String] name of the attribute
      # @return [Object]
      def storage_class(domain_name, domain_attr, type)
        entry = find(domain_name, attr)

        unless entry.storage?(type)
          fail "No (#{type}) storage has been mapped"
        end

        container_name = entry.container_name
        unless container_root_name == container_name
          fail "You can not access a mapping outside of this container " +
            "(#{container_root_name}, #{container_name})"
        end
        app_container = Appfuel.app_container(entry.container)
        key = entry.storage(type)
        app_container[key]
      end

      def to_entity_hash(domain_name,  data, opts = {})
        entity_attrs = {}
        each_entity_attr(domain_name) do |entry|
          attr_name   = entry.storage_attr
          domain_attr = entry.domain_attr
          next unless data.key?(attr_name)

          update_entity_hash(domain_attr, data[attr_name], entity_attrs)
        end

        entity_attrs
      end

      def update_entity_hash(domain_attr, value, hash)
        if domain_attr.include?('.')
          hash.deep_merge!(create_entity_hash(domain_attr, value))
        else
          hash[domain_attr] = value
        end
      end

      def entity_value(domain, map_entry)
        value = resolve_entity_value(domain, map_entry.domain_attr)
        if map_entry.computed_attr?
          value = map_entry.compute_attr(domain, value)
        end

        value = nil if undefined?(value)

        value
      end

      def create_entity_hash(domain_attr, value)
        domain_attr.split('.').reverse.inject(value) do |result, nested_attr|
          {nested_attr => result}
        end
      end

      def undefined?(value)
        value == Types::Undefined
      end

      def resolve_entity_value(domain, entity_attr)
        chain  = entity_attr.split('.')
        target = domain
        chain.each do |attr_method|
          return nil unless target.respond_to?(attr_method)
          target = target.public_send(attr_method)
        end
        target
      end

      private
      def validate_domain(entity_name)
        unless entity?(entity_name)
          fail "Entity (#{entity_name}) is not registered"
        end
      end

      def mappings_from_container
        container = Appfuel.app_container(container_root_name)
        container[:repository_mappings]
      end
    end
  end
end