require 'set'
require 'thread'

module Seahorse
  module Client
    class PluginList

      include Enumerable

      # @param [Array, Set] plugins
      # @option options [Mutex] :mutex
      def initialize(plugins = [], options = {})
        @mutex = options[:mutex] || Mutex.new
        @plugins = Set.new
        if plugins.is_a?(PluginList)
          plugins.send(:each_plugin) { |plugin| _add(plugin) }
        else
          plugins.each { |plugin| _add(plugin) }
        end
      end

      # Adds and returns the `plugin`.
      # @param [Plugin] plugin
      # @return [void]
      def add(plugin)
        @mutex.synchronize do
          _add(plugin)
        end
        nil
      end

      # Removes and returns the `plugin`.
      # @param [Plugin] plugin
      # @return [void]
      def remove(plugin)
        @mutex.synchronize do
          @plugins.delete(PluginWrapper.new(plugin))
        end
        nil
      end

      # Replaces the existing list of plugins.
      # @param [Array<Plugin>] plugins
      # @return [void]
      def set(plugins)
        @mutex.synchronize do
          @plugins.clear
          plugins.each do |plugin|
            _add(plugin)
          end
        end
        nil
      end

      # Enumerates the plugins.
      # @return [Enumerator]
      def each(&block)
        each_plugin do |plugin_wrapper|
          yield(plugin_wrapper.plugin)
        end
      end

      private

      # Not safe to call outside the mutex.
      def _add(plugin)
        @plugins << PluginWrapper.new(plugin)
      end

      # Yield each PluginDetail behind the mutex
      def each_plugin(&block)
        @mutex.synchronize do
          @plugins.each(&block)
        end
      end

      # A utility class that computes the canonical name for a plugin
      # and defers requiring the plugin until the plugin class is
      # required.
      # @api private
      class PluginWrapper

        # @param [String, Symbol, Module, Class] plugin
        def initialize(plugin)
          case plugin
          when Module
            @canonical_name = plugin.name || plugin.object_id
            @plugin = plugin
          when Symbol, String
            @canonical_name, @gem_name = plugin.to_s.split('.').reverse
            @plugin = nil
          else
            @canonical_name = plugin.object_id
            @plugin = plugin
          end
        end

        # @return [String]
        attr_reader :canonical_name

        # @return [Class<Plugin>]
        def plugin
          @plugin ||= require_plugin
        end

        # Returns the given plugin if it is already a PluginWrapper.
        def self.new(plugin)
          if plugin.is_a?(self)
            plugin
          else
            super
          end
        end

        # @return [Boolean]
        # @api private
        def eql? other
          canonical_name == other.canonical_name
        end

        # @return [String]
        # @api private
        def hash
          canonical_name.hash
        end

        private

        # @return [Class<Plugin>]
        def require_plugin
          require(@gem_name) if @gem_name
          plugin_class = Kernel
          @canonical_name.split('::').each do |const_name|
            plugin_class = plugin_class.const_get(const_name)
          end
          plugin_class
        end

      end
    end
  end
end
