module Rails
  module Paths
    # This object is an extended hash that behaves as root of the <tt>Rails::Paths</tt> system.
    # It allows you to collect information about how you want to structure your application
    # paths by a Hash like API. It requires you to give a physical path on initialization.
    #
    #   root = Root.new "/rails"
    #   root.add "app/controllers", eager_load: true
    #
    # The command above creates a new root object and add "app/controllers" as a path.
    # This means we can get a <tt>Rails::Paths::Path</tt> object back like below:
    #
    #   path = root["app/controllers"]
    #   path.eager_load?               # => true
    #   path.is_a?(Rails::Paths::Path) # => true
    #
    # The +Path+ object is simply an enumerable and allows you to easily add extra paths:
    #
    #   path.is_a?(Enumerable) # => true
    #   path.to_ary.inspect    # => ["app/controllers"]
    #
    #   path << "lib/controllers"
    #   path.to_ary.inspect    # => ["app/controllers", "lib/controllers"]
    #
    # Notice that when you add a path using +add+, the path object created already
    # contains the path with the same path value given to +add+. In some situations,
    # you may not want this behavior, so you can give :with as option.
    #
    #   root.add "config/routes", with: "config/routes.rb"
    #   root["config/routes"].inspect # => ["config/routes.rb"]
    #
    # The +add+ method accepts the following options as arguments:
    # eager_load, autoload, autoload_once and glob.
    #
    # Finally, the +Path+ object also provides a few helpers:
    #
    #   root = Root.new "/rails"
    #   root.add "app/controllers"
    #
    #   root["app/controllers"].expanded # => ["/rails/app/controllers"]
    #   root["app/controllers"].existent # => ["/rails/app/controllers"]
    #
    # Check the <tt>Rails::Paths::Path</tt> documentation for more information.
    class Root
      attr_accessor :path

      def initialize(path)
        @current = nil
        @path = path
        @root = {}
      end

      def []=(path, value)
        glob = self[path] ? self[path].glob : nil
        add(path, with: value, glob: glob)
      end

      def add(path, options = {})
        with = Array(options.fetch(:with, path))
        @root[path] = Path.new(self, path, with, options)
      end

      def [](path)
        @root[path]
      end

      def values
        @root.values
      end

      def keys
        @root.keys
      end

      def values_at(*list)
        @root.values_at(*list)
      end

      def all_paths
        values.tap { |v| v.uniq! }
      end

      def autoload_once
        filter_by { |p| p.autoload_once? }
      end

      def eager_load
        filter_by { |p| p.eager_load? }
      end

      def autoload_paths
        filter_by { |p| p.autoload? }
      end

      def load_paths
        filter_by { |p| p.load_path? }
      end

    private

      def filter_by(&block)
        all_paths.find_all(&block).flat_map { |path|
          paths = path.existent
          paths - path.children.map { |p| yield(p) ? [] : p.existent }.flatten
        }.uniq
      end
    end

    class Path
      include Enumerable

      attr_accessor :glob

      def initialize(root, current, paths, options = {})
        @paths    = paths
        @current  = current
        @root     = root
        @glob     = options[:glob]

        options[:autoload_once] ? autoload_once! : skip_autoload_once!
        options[:eager_load]    ? eager_load!    : skip_eager_load!
        options[:autoload]      ? autoload!      : skip_autoload!
        options[:load_path]     ? load_path!     : skip_load_path!
      end

      def children
        keys = @root.keys.find_all { |k|
          k.start_with?(@current) && k != @current
        }
        @root.values_at(*keys.sort)
      end

      def first
        expanded.first
      end

      def last
        expanded.last
      end

      %w(autoload_once eager_load autoload load_path).each do |m|
        class_eval <<-RUBY, __FILE__, __LINE__ + 1
          def #{m}!        # def eager_load!
            @#{m} = true   #   @eager_load = true
          end              # end
                           #
          def skip_#{m}!   # def skip_eager_load!
            @#{m} = false  #   @eager_load = false
          end              # end
                           #
          def #{m}?        # def eager_load?
            @#{m}          #   @eager_load
          end              # end
        RUBY
      end

      def each(&block)
        @paths.each(&block)
      end

      def <<(path)
        @paths << path
      end
      alias :push :<<

      def concat(paths)
        @paths.concat paths
      end

      def unshift(path)
        @paths.unshift path
      end

      def to_ary
        @paths
      end

      # Expands all paths against the root and return all unique values.
      def expanded
        raise "You need to set a path root" unless @root.path
        result = []

        each do |p|
          path = File.expand_path(p, @root.path)

          if @glob && File.directory?(path)
            Dir.chdir(path) do
              result.concat(Dir.glob(@glob).map { |file| File.join path, file }.sort)
            end
          else
            result << path
          end
        end

        result.uniq!
        result
      end

      # Returns all expanded paths but only if they exist in the filesystem.
      def existent
        expanded.select { |f| File.exists?(f) }
      end

      def existent_directories
        expanded.select { |d| File.directory?(d) }
      end

      alias to_a expanded
    end
  end
end