require 'forwardable'
require 'active_support/core_ext/class/attribute'
require 'middleman-core/configuration'
require 'middleman-core/contracts'

module Middleman
  # Middleman's Extension API provides the ability to add functionality to Middleman
  # and to customize existing features. Internally, most features in Middleman are
  # implemented as extensions. A good way to figure out how to write your own extension
  # is to look at the source of the built-in extensions or popular extension gems like
  # `middleman-blog` or `middleman-syntax`.
  #
  # The most basic extension looks like:
  #
  #     class MyFeature < Middleman::Extension
  #       def initialize(app, options_hash={}, &block)
  #         super
  #       end
  #     end
  #     ::Middleman::Extensions.register(:my_feature, MyFeature)
  #
  # A more complicated example might look like:
  #
  #     class MyFeature < Middleman::Extension
  #       option :my_option, 'cool', 'A very cool option'
  #
  #       def initialize(app, options_hash={}, &block)
  #         super
  #         puts "My option is #{options.my_option}"
  #       end
  #
  #       def after_configuration
  #         puts "The project has been configured"
  #       end
  #
  #       def manipulate_resource_list(resources)
  #         resources.each do |resource|
  #           # Make all .jpg's get built or served with a .jpeg extension.
  #           if resource.ext == '.jpg'
  #             resource.destination_path = resource.destination_path.sub('.jpg', '.jpeg')
  #           end
  #         end
  #       end
  #     end
  #
  #     ::Middleman::Extensions.register :my_feature do
  #       MyFeature
  #     end
  #
  # Extensions can add helpers (via {Extension.helpers}), add to the sitemap or change it (via {#manipulate_resource_list}), or run
  # arbitrary code at different parts of the Middleman application's lifecycle. They can have options (defined via {Extension.option} and accessed via {#options}).
  #
  # Common lifecycle events can be handled by extensions simply by implementing an appropriately-named method:
  #
  # * {#after_configuration}
  # * {#after_build}
  # * {#before_build}
  #
  # There are also some less common hooks that can be listened to from within an extension's `initialize` method:
  #
  # * `app.before_render {|body, path, locs, template_class| ... }` - Manipulate template sources before they are rendered.
  # * `app.after_render {|content, path, locs, template_class| ... }` - Manipulate output text after a template has been rendered. It is also common to install a Rack middleware to do this instead.
  # * `app.ready { ... }` - Run code once Middleman is ready to serve or build files (after `after_configuration`).

  #
  # @see http://middlemanapp.com/advanced/custom/ Middleman Custom Extensions Documentation
  class Extension
    extend Forwardable
    include Contracts

    def_delegator :@app, :logger

    # @!attribute supports_multiple_instances
    #   @!scope class
    #   @return [Boolean] whether or not an extension can be activated multiple times, generating multiple instances of the extension.
    #   By default extensions can only be activated once in a project. This is an advanced option.
    class_attribute :supports_multiple_instances, instance_reader: false, instance_writer: false

    # @!attribute defined_helpers
    #   @!scope class
    #   @api private
    #   @return [Array<Module>] a list of all the helper modules this extension provides. Set these using {#helpers}.
    class_attribute :defined_helpers, instance_reader: false, instance_writer: false

    # @!attribute exposed_to_application
    #   @!scope class
    #   @api private
    #   @return [Hash<Symbol, Symbol>] a list of all the methods modules this extension exposes to app. Set these using {#expose_to_application}.
    class_attribute :exposed_to_application, instance_reader: false, instance_writer: false

    # @!attribute exposed_to_config
    #   @!scope class
    #   @api private
    #   @return [Hash<Symbol, Symbol>] a list of all the methods modules this extension exposes to config. Set these using {#expose_to_config}.
    class_attribute :exposed_to_config, instance_reader: false, instance_writer: false

    # @!attribute exposed_to_template
    #   @!scope class
    #   @api private
    #   @return [Hash<Symbol, Symbol>] a list of all the methods modules this extension exposes to templates. Set these using {#expose_to_template}.
    class_attribute :exposed_to_template, instance_reader: false, instance_writer: false

    # @!attribute exposed_to_template
    #   @!scope class
    #   @api private
    #   @return [Array<Any>] a list of method generators.
    class_attribute :resources_generators, instance_reader: false, instance_writer: false

    # @!attribute ext_name
    #   @!scope class
    #   @return [Symbol] the name this extension is registered under. This is the symbol used to activate the extension.
    class_attribute :ext_name, instance_reader: false, instance_writer: false

    # @!attribute resource_list_manipulator_priority
    #   @!scope class
    #   @return [Numeric] the priority for this extension's `manipulate_resource_list` method, if it has one.
    #   @see Middleman::Sitemap::Store#register_resource_list_manipulator
    class_attribute :resource_list_manipulator_priority, instance_reader: false, instance_writer: false

    class << self
      # @api private
      # @return [Middleman::Configuration::ConfigurationManager] The defined options for this extension.
      def config
        @_config ||= ::Middleman::Configuration::ConfigurationManager.new
      end

      # Add an option to this extension.
      # @see Middleman::Configuration::ConfigurationManager#define_setting
      # @example
      #   option :compress, false, 'Whether to compress the output'
      # @param [Symbol] key The name of the option
      # @param [Object] default The default value for the option
      # @param [String] description A human-readable description of what the option does
      def option(key, default=nil, description=nil, options={})
        config.define_setting(key, default, description, options)
      end

      # @api private
      # @return [Middleman::Configuration::ConfigurationManager] The defined global options for this extension.
      def global_config
        @_global_config ||= ::Middleman::Configuration::ConfigurationManager.new
      end

      # Add an global option to this extension.
      # @see Middleman::Configuration::ConfigurationManager#define_setting
      # @example
      #   option :compress, false, 'Whether to compress the output'
      # @param [Symbol] key The name of the option
      # @param [Object] default The default value for the option
      # @param [String] description A human-readable description of what the option does
      def define_setting(key, default=nil, description=nil, options={})
        global_config.define_setting(key, default, description, options)
      end

      # Short-hand for simple Sitemap manipulation
      # @example A generator which returns an array of resources
      #   resources :make_resources
      # @example A generator which maps a path to a method
      #   resources make_resource: :make_it
      # @example A generator which maps a path to a string
      #   resources make_resource: 'Hello'
      # @param [Array] generators The generator definitions
      def resources(*generators)
        self.resources_generators ||= []
        self.resources_generators += generators
      end

      # Declare helpers to be added the global Middleman application.
      # This accepts either a list of modules to add on behalf
      # of this extension, or a block whose contents will all
      # be used as helpers in a new module.
      # @example With a block:
      #   helpers do
      #     def my_helper
      #       "I helped!"
      #     end
      #   end
      # @example With modules:
      #   helpers FancyHelpers, PlainHelpers
      # @param [Array<Module>] modules An optional list of modules to add as helpers
      # @param [Proc] block A block which will be evaluated to create a new helper module
      # @return [void]
      def helpers(*modules, &block)
        self.defined_helpers ||= []

        if block_given?
          mod = Module.new
          mod.module_eval(&block)
          modules = [mod]
        end

        self.defined_helpers += modules
      end

      # Takes a method within this extension and exposes it globally
      # on the main `app` instance. Used for very low-level extensions
      # which many other extensions depend upon. Such as Data and
      # File watching.
      # @example with Hash:
      #   expose_to_application global_name: :local_name
      # @example with Array:
      #   expose_to_application :method1, :method2
      # @param [Array<Sumbol>, Hash<Symbol, Symbol>] symbols An optional list of symbols representing instance methods to exposed.
      # @return [void]
      def expose_to_application(*symbols)
        self.exposed_to_application ||= {}

        if symbols.first && symbols.first.is_a?(Hash)
          self.exposed_to_application.merge!(symbols.first)
        elsif symbols.is_a? Array
          symbols.each do |sym|
            self.exposed_to_application[sym] = sym
          end
        end
      end

      # Takes a method within this extension and exposes it inside the scope
      # of the config.rb sandbox.
      # @example with Hash:
      #   expose_to_config global_name: :local_name
      # @example with Array:
      #   expose_to_config :method1, :method2
      # @param [Array<Sumbol>, Hash<Symbol, Symbol>] symbols An optional list of symbols representing instance methods to exposed.
      # @return [void]
      def expose_to_config(*symbols)
        self.exposed_to_config ||= {}

        if symbols.first && symbols.first.is_a?(Hash)
          self.exposed_to_config.merge!(symbols.first)
        elsif symbols.is_a? Array
          symbols.each do |sym|
            self.exposed_to_config[sym] = sym
          end
        end
      end

      # Takes a method within this extension and exposes it inside the scope
      # of the templating engine. Like `helpers`, but scoped.
      # @example with Hash:
      #   expose_to_template global_name: :local_name
      # @example with Array:
      #   expose_to_template :method1, :method2
      # @param [Array<Sumbol>, Hash<Symbol, Symbol>] symbols An optional list of symbols representing instance methods to exposed.
      # @return [void]
      def expose_to_template(*symbols)
        self.exposed_to_template ||= {}

        if symbols.first && symbols.first.is_a?(Hash)
          self.exposed_to_template.merge!(symbols.first)
        elsif symbols.is_a? Array
          symbols.each do |sym|
            self.exposed_to_template[sym] = sym
          end
        end
      end

      # Reset all {Extension.after_extension_activated} callbacks.
      # @api private
      # @return [void]
      def clear_after_extension_callbacks
        @_extension_activation_callbacks = {}
      end

      # Register to run a block after a named extension is activated.
      # @param [Symbol] name The name the extension was registered under
      # @param [Proc] block A callback to run when the named extension is activated
      # @return [void]
      def after_extension_activated(name, &block)
        @_extension_activation_callbacks ||= {}
        @_extension_activation_callbacks[name] ||= []
        @_extension_activation_callbacks[name] << block if block_given?
      end

      # Notify that a particular extension has been activated and run all
      # registered {Extension.after_extension_activated} callbacks.
      # @api private
      # @param [Middleman::Extension] instance Activated extension instance
      # @return [void]
      def activated_extension(instance)
        name = instance.class.ext_name
        return unless @_extension_activation_callbacks && @_extension_activation_callbacks.key?(name)
        @_extension_activation_callbacks[name].each do |block|
          block.arity == 1 ? block.call(instance) : block.call
        end
      end
    end

    # @return [Middleman::Configuration::ConfigurationManager] options for this extension instance.
    attr_reader :options

    # @return [Middleman::Application] the Middleman application instance.
    attr_reader :app

    # @!method after_extension_activated(name, &block)
    #   Register to run a block after a named extension is activated.
    #   @param [Symbol] name The name the extension was registered under
    #   @param [Proc] block A callback to run when the named extension is activated
    #   @return [void]
    def_delegator :"::Middleman::Extension", :after_extension_activated

    # Extensions are instantiated when they are activated.
    # @param [Middleman::Application] app The Middleman::Application instance
    # @param [Hash] options_hash The raw options hash. Subclasses should not manipulate this directly - it will be turned into {#options}.
    # @yield An optional block that can be used to customize options before the extension is activated.
    # @yieldparam [Middleman::Configuration::ConfigurationManager] options Extension options
    def initialize(app, options_hash={}, &block)
      @_helpers = []
      @app = app

      expose_methods
      setup_options(options_hash, &block)

      # Bind app hooks to local methods
      bind_before_configuration
      bind_after_configuration
      bind_before_build
      bind_after_build
      bind_ready
    end

    # @!method before_configuration
    #   Respond to the `before_configuration` event.
    #   If a `before_configuration` method is implemented, that method will be run before `config.rb` is run.
    #   @note Because most extensions are activated from within `config.rb`, they *will not run* any `before_configuration` hook.

    # @!method after_configuration
    #   Respond to the `after_configuration` event.
    #   If an `after_configuration` method is implemented, that method will be run before `config.rb` is run.

    # @!method before_build
    #   Respond to the `before_build` event.
    #   If an `before_build` method is implemented, that method will be run before the builder runs.

    # @!method after_build
    #   Respond to the `after_build` event.
    #   If an `after_build` method is implemented, that method will be run after the builder runs.

    # @!method ready
    #   Respond to the `ready` event.
    #   If an `ready` method is implemented, that method will be run after the app has finished booting up.

    # @!method manipulate_resource_list(resources)
    #   Manipulate the resource list by transforming or adding {Sitemap::Resource}s.
    #   Sitemap manipulation is a powerful way of interacting with a project, since it can modify each {Sitemap::Resource} or generate new {Sitemap::Resources}. This method is used in a pipeline where each sitemap manipulator is run in turn, with each one being fed the output of the previous manipulator. See the source of built-in Middleman extensions like {Middleman::Extensions::DirectoryIndexes} and {Middleman::Extensions::AssetHash} for examples of how to use this.
    #   @note This method *must* return the full set of resources, because its return value will be used as the new sitemap.
    #   @see http://middlemanapp.com/advanced/sitemap/ Sitemap Documentation
    #   @see Sitemap::Store
    #   @see Sitemap::Resource
    #   @param [Array<Sitemap::Resource>] resources A list of all the resources known to the sitemap.
    #   @return [Array<Sitemap::Resource>] The transformed list of resources.

    def add_exposed_to_context(context)
      (self.class.exposed_to_template || {}).each do |k, v|
        context.define_singleton_method(k, &method(v))
      end
    end

    private

    def expose_methods
      (self.class.exposed_to_application || {}).each do |k, v|
        app.define_singleton_method(k, &method(v))
      end

      (self.class.exposed_to_config || {}).each do |k, v|
        app.config_context.define_singleton_method(k, &method(v))
      end

      (self.class.defined_helpers || []).each do |m|
        app.template_context_class.send(:include, m)
      end
    end

    # @yield An optional block that can be used to customize options before the extension is activated.
    # @yieldparam Middleman::Configuration::ConfigurationManager] options Extension options
    def setup_options(options_hash)
      @options = self.class.config.dup
      @options.finalize!

      options_hash.each do |k, v|
        @options[k] = v
      end

      yield @options, self if block_given?

      @options.all_settings.each do |o|
        next unless o.options[:required] && !o.value_set?

        logger.error "The `:#{o.key}` option of the `#{self.class.ext_name}` extension is required."
        exit(1)
      end
    end

    def bind_before_configuration
      @app.before_configuration(&method(:before_configuration)) if respond_to?(:before_configuration)
    end

    def bind_after_configuration
      ext = self

      @app.after_configuration do
        ext.after_configuration if ext.respond_to?(:after_configuration)

        if ext.respond_to?(:manipulate_resource_list)
          ext.app.sitemap.register_resource_list_manipulator(ext.class.ext_name, ext, ext.class.resource_list_manipulator_priority)
        end

        if ext.class.resources_generators && !ext.class.resources_generators.empty?
          ext.app.sitemap.register_resource_list_manipulator(
            :"#{ext.class.ext_name}_generator",
            ext,
            ext.class.resource_list_manipulator_priority,
            :generate_resources
          )
        end
      end
    end

    def generate_resources(resources)
      generator_defs = self.class.resources_generators.reduce({}) do |sum, g|
        resource_definitions = if g.is_a? Hash
          g
        elsif g.is_a? Symbol
          definition = method(g)

          if definition.arity == 0
            send(g)
          else
            send(g, resources)
          end
        else
          {}
        end

        sum.merge(resource_definitions)
      end

      resources + generator_defs.map do |path, g|
        if g.is_a? Symbol
          definition = method(g)

          g = if definition.arity == 0
            send(g)
          else
            send(g, resources)
          end
        end

        ::Middleman::Sitemap::StringResource.new(
          app.sitemap,
          path,
          g
        )
      end
    end

    def bind_before_build
      ext = self
      return unless ext.respond_to?(:before_build)

      @app.before_build do |builder|
        if ext.method(:before_build).arity == 1
          ext.before_build(builder)
        else
          ext.before_build
        end
      end
    end

    def bind_after_build
      ext = self
      return unless ext.respond_to?(:after_build)

      @app.after_build do |builder|
        if ext.method(:after_build).arity == 1
          ext.after_build(builder)
        elsif ext.method(:after_build).arity == 2
          ext.after_build(builder, builder.thor)
        else
          ext.after_build
        end
      end
    end

    def bind_ready
      @app.ready(&method(:ready)) if respond_to?(:ready)
    end
  end

  class ConfigExtension < Extension
    def initialize(app, config={}, &block)
      @descriptors = {}
      @wrapped = {}

      self.class.exposed_to_config.each do |k, v|
        @descriptors[k] = []

        define_singleton_method(:"__original_#{v}", &method(v))
        define_singleton_method(v) do |*args, &b|
          @descriptors[k] << method(:"__original_#{v}").call(*args, &b)
          @app.sitemap.rebuild_resource_list!(:"first_run_change_#{v}")
        end
      end

      super
    end

    def after_configuration
      self.class.exposed_to_config.each do |k, v|
        ::Middleman::CoreExtensions::Collections::StepContext.add_to_context(k, &method(:"__original_#{v}"))
      end
    end

    # Update the main sitemap resource list
    # @return Array<Middleman::Sitemap::Resource>
    Contract ResourceList => ResourceList
    def manipulate_resource_list(resources)
      @descriptors.values.flatten.reduce(resources) do |sum, c|
        c.execute_descriptor(app, sum)
      end
    end
  end
end