module Clamp
  class Option

    module Parsing

      # For :flag options with environment variables attached, this is a list
      # of possible values that are accepted as 'true'
      #
      # Example:
      #  
      #   option "--foo", :flag, "Use foo", :env => "FOO"
      #
      # All of these will set 'foo' to true:
      #
      #   FOO=1 ./myprogram
      #   FOO=true ./myprogram
      #   FOO=yes ./myprogram
      #   FOO=on ./myprogram
      #   FOO=enable ./myprogram
      #
      # See {Clamp::Command.option} for more information.
      TRUTHY_ENVIRONMENT_VALUES = %w(1 yes enable on true)

      protected

      def parse_options
        while remaining_arguments.first =~ /^-/

          switch = remaining_arguments.shift
          break if switch == "--"

          case switch
          when /^(-\w)(.+)$/ # combined short options
            switch = $1
            remaining_arguments.unshift("-#{$2}")
          when /^(--[^=]+)=(.*)/
            switch = $1
            remaining_arguments.unshift($2)
          end
            
          option = find_option(switch)
          value = option.extract_value(switch, remaining_arguments)

          begin
            send("#{option.attribute_name}=", value)
          rescue ArgumentError => e
            signal_usage_error "option '#{switch}': #{e.message}"
          end

        end

        # Verify that all required options are present
        self.class.recognised_options.each do |option|
          # If this option is required and the value is nil, there's an error.
          if option.required? and send(option.attribute_name).nil?
            message = "option '#{option.switches.first}'"
            if option.environment_variable
              message += " (or env #{option.environment_variable})"
            end
            message += " is required"
            signal_usage_error message
          end
        end
      end

      def parse_environment_options
        self.class.recognised_options.each do |option|
          next if option.environment_variable.nil?
          next unless ENV.has_key?(option.environment_variable)
          value = ENV[option.environment_variable]
          if option.flag?
            # Set true if the environment value is truthy.
            send("#{option.attribute_name}=", TRUTHY_ENVIRONMENT_VALUES.include?(value))
          else
            send("#{option.attribute_name}=", value)
          end
        end
      end

      private

      def find_option(switch)
        self.class.find_option(switch) || 
        signal_usage_error("Unrecognised option '#{switch}'")
      end

    end

  end
end