module Middleman
  module Configuration
    # Access to a global configuration manager for the whole Middleman project, 
    # plus backwards compatibility mechanisms for older Middleman projects.
    module Global
      def self.included(app)
        app.send :extend, ClassMethods
      end

      module ClassMethods
        # Global configuration for the whole Middleman project.
        # @return [ConfigurationManager]
        def config
          @_config ||= ConfigurationManager.new
        end

        # Set attributes (global variables)
        #
        # @deprecated Prefer accessing settings through "config".
        #
        # @param [Symbol] key Name of the attribue
        # @param value Attribute value
        # @return [void]
        def set(key, default=nil, &block)
          config.define_setting(key, default)
          @inst.set(key, default, &block) if @inst
        end

        # Access global settings as methods, to preserve compatibility with
        # old Middleman.
        #
        # @deprecated Prefer accessing settings through "config".
        def method_missing(method, *args)
          if config.defines_setting? method
            config[method]
          else
            super
          end
        end

        # Needed so that method_missing makes sense
        def respond_to?(method, include_private = false)
          super || config.defines_setting?(method)
        end
      end

      def config
        self.class.config
      end

      # Backwards compatibilty with old Sinatra template interface
      #
      # @deprecated Prefer accessing settings through "config".
      #
      # @return [ConfigurationManager]
      alias :settings :config

      # Set attributes (global variables)
      #
      # @deprecated Prefer accessing settings through "config".
      #
      # @param [Symbol] key Name of the attribue
      # @param value Attribute value
      # @return [void]
      def set(key, value=nil, &block)
        value = block if block_given?
        config[key] = value
      end

      # Access global settings as methods, to preserve compatibility with
      # old Middleman.
      #
      # @deprecated Prefer accessing settings through "config".
      def method_missing(method, *args)
        if config.defines_setting? method
          config[method]
        else
          super
        end
      end

      # Needed so that method_missing makes sense
      def respond_to?(method, include_private = false)
        super || config.defines_setting?(method)
      end
    end

    # A class that manages a collection of documented settings.
    # Can be used by extensions as well as the main Middleman
    # application. Extensions should probably finalize their instance
    # after defining all the settings they want to expose.
    class ConfigurationManager
      def initialize
        # A hash from setting key to ConfigSetting instance.
        @settings = {}
        @finalized = false
      end

      # Get all settings, sorted by key, as ConfigSetting objects.
      # @return [Array<ConfigSetting>]
      def all_settings
        @settings.values.sort_by(&:key)
      end

      # Get a full ConfigSetting object for the setting with the give key.
      # @return [ConfigSetting]
      def setting(key)
        @settings[key]
      end

      # Get the value of a setting by key. Returns nil if there is no such setting.
      # @return [Object]
      def [](key)
        setting = @settings[key]
        setting ? setting.value : nil
      end

      # Set the value of a setting by key. Creates the setting if it doesn't exist.
      # @param [Symbol] key
      # @param [Object] val
      def []=(key, val)
        setting = @settings[key] || define_setting(key)
        setting.value = val
      end

      # Allow configuration settings to be read and written via methods
      def method_missing(method, *args)
        if defines_setting?(method) && args.size == 0
          self[method]
        elsif method =~ /^(\w+)=$/ && args.size == 1
          self[$1.to_sym] = args[0]
        else
          super
        end
      end

      # Needed so that method_missing makes sense
      def respond_to?(method, include_private = false)
        super || defines_setting?(method) || (method =~ /^(\w+)=$/ && defines_setting?($1))
      end

      # Does this configuration manager know about the setting identified by key?
      # @param [Symbol] key
      # @return [Boolean]
      def defines_setting?(key)
        @settings.has_key?(key)
      end

      # Define a new setting, with optional default and user-friendly description.
      # Once the configuration manager is finalized, no new settings may be defined.
      #
      # @param [Symbol] key
      # @param [Object] default
      # @param [String] description
      # @return [ConfigSetting]
      def define_setting(key, default=nil, description=nil)
        raise "Setting #{key} doesn't exist" if @finalized
        raise "Setting #{key} already defined" if @settings.has_key?(key)
        raise "Setting key must be a Symbol" unless key.is_a? Symbol

        @settings[key] = ConfigSetting.new(key, default, description)
      end

      # Switch the configuration manager is finalized, it switches to read-only
      # mode and no new settings may be defined.
      def finalize!
        @finalized = true
      end

      # Deep duplicate of the configuration manager
      def dup
        copy = ConfigurationManager.new
        @settings.each do |key, setting|
          copy_setting = copy.define_setting setting.key, setting.default, setting.description
          copy_setting.value = setting.value if setting.value_set?
        end
        copy
      end

      def to_h
        hash = {}
        @settings.each do |key, setting|
          hash[key] = setting.value
        end
        hash
      end

      def to_s
        to_h.inspect
      end
    end

    # An individual configuration setting, with an optional default and description.
    # Also models whether or not a value has been set.
    class ConfigSetting
      # The name of this setting
      attr_accessor :key

      # The default value for this setting
      attr_accessor :default

      # A human-friendly description of the setting
      attr_accessor :description

      def initialize(key, default, description)
        @value_set = false
        self.key = key
        self.default = default
        self.description = description
      end

      # The user-supplied value for this setting, overriding the default
      def value=(value)
        @value = value
        @value_set = true
      end

      # The effective value of the setting, which may be the default
      # if the user has not set a value themselves. Note that even if the
      # user sets the value to nil it will override the default.
      def value
        value_set? ? @value : default
      end

      # Whether or not there has been a value set beyond the default
      def value_set?
        @value_set
      end
    end
  end
end