require 'relax/query'

module Relax
  # Request is intended to be a parent class for requests passed to
  # Service#call.
  class Request
    def initialize(options = {})
      self.class.class_variables.each do |variable|
        instance_variable_set(variable.slice(1..-1), self.class.send(:class_variable_get, variable))
      end

      options.each do |key, value|
        instance_variable_set "@#{key}", value
      end
    end

    # Converts this request into a Query object.
    def to_query
      keys.inject(Query.new) do |parameters, key|
        parameters[convert_key(key)] = send(key)
        parameters
      end
    end

    # Converts this request into a query string for use in a URL.
    def to_s
      to_query.to_s
    end

    class << self
      # Specifies a parameter to create on the request class.
      #
      # Options:
      # - <tt>:value</tt>: The default value for this parameter.
      def parameter(name, options = {})
        attr_accessor name
        class_variable_set("@@#{name}", options.delete(:value)) if options[:value]
      end

      # Adds a template value to a request class. Equivalent to creating a
      # parameter with a default value.
      def []=(key, value)
        parameter(key, {:value => value})
      end
    end

    protected

    # Returns an array of the parameter names for this request.
    def keys
      instance_variables.collect { |v| v.sub('@', '') }
    end

    # Converts a key when the Request is converted to a query. By default, no
    # conversion actually takes place, but this method can be overridden by
    # child classes to perform standard manipulations, such as replacing
    # underscores.
    def convert_key(key)
      key
    end
  end
end