require 'addressable/uri'

module ROM

  # Abstract adapter class
  #
  # @api public
  class Adapter
    include Equalizer.new(:connection)

    @adapters = []

    # Return connection URI associated with the adapter
    #
    # @return [String]
    #
    # @api public
    attr_reader :uri

    # Return connection object
    #
    # @return [Object] type varies depending on the adapter
    #
    # @api public
    attr_reader :connection

    # Setup an adapter instance with the given connection URI
    #
    # @example
    #
    #   Adapter = Class.new(ROM::Adapter)
    #
    #   adapter = Adapter.new('mysql://localhost/test')
    #
    #   adapter.uri.scheme # => 'mysql'
    #   adapter.uri.host # => 'localhost'
    #   adapter.uri.path # => '/test'
    #
    # @param [String] uri_string
    #
    # @return [Adapter]
    #
    # @api public
    def self.setup(uri_string)
      uri = Addressable::URI.parse(uri_string)

      unless adapter = self[uri.scheme]
        raise ArgumentError, "#{uri_string.inspect} uri is not supported"
      end

      adapter.new(uri)
    end

    # Register adapter class
    #
    # @example
    #
    #   Adapter = Class.new(ROM::Adapter) {
    #     def self.schemes
    #       [:super_db]
    #     end
    #   }
    #
    #   ROM::Adapter.register(Adapter)
    #   ROM::Adapter[:super_db] # => Adapter
    #
    # @return [Array] registered adapters
    #
    # @api public
    def self.register(adapter)
      @adapters.unshift adapter
    end

    # Return adapter class for the given scheme
    #
    # @see Adapter.register
    #
    # @return [Class] adapter class
    #
    # @api public
    def self.[](scheme)
      @adapters.detect { |adapter| adapter.schemes.include?(scheme.to_sym) }
    end

    # @api private
    def initialize(uri)
      @uri = uri
    end

    # Extension hook for adding adapter-specific behavior to a relation class
    #
    # @param [Class] klass Relation class generated by ROM
    #
    # @return [Class] extended relation class
    #
    # @api public
    def extend_relation_class(klass)
      klass
    end

    # Extension hook for adding adapter-specific behavior to a relation instance
    #
    # @param [Relation] relation
    #
    # @return [Relation] extended relation instance
    #
    # @api public
    def extend_relation_instance(relation)
      relation
    end

    # Builds a command
    #
    # @param [Symbol] name of the command
    # @param [Relation] relation used by the command
    # @param [CommandDSL::Definition] command definition object
    #
    # @return [Object] created command instance
    #
    # @api public
    def command(name, relation, definition)
      type = definition.type || name

      klass =
        case type
        when :create then command_namespace.const_get(:Create)
        when :update then command_namespace.const_get(:Update)
        when :delete then command_namespace.const_get(:Delete)
        else
          raise ArgumentError, "#{type.inspect} is not a supported command type"
        end

      klass.new(relation, definition.to_h)
    end

    # Schema inference hook
    #
    # Every adapter that supports schema inference should implement this method
    #
    # @return [Array] array with datasets and their names
    #
    # @api private
    def schema
      []
    end

    # Return namespace with adapter-specific command classes
    #
    # @return [Module]
    #
    # @api private
    def command_namespace
      self.class.const_get(:Commands)
    end

  end

end