module Piston
  class WorkingCopy
    class UnhandledWorkingCopy < RuntimeError; end
 
    class << self
      def logger
        @@logger ||= Log4r::Logger["handler"]
      end
 
      def guess(path)
        path = path.kind_of?(Pathname) ? path : Pathname.new(path.to_s)
        logger.info {"Guessing the working copy type of #{path.inspect}"}
        handler = handlers.detect do |handler|
          logger.debug {"Asking #{handler.name} if it understands #{path}"}
          handler.understands_dir?(path)
        end
 
        raise UnhandledWorkingCopy, "Don't know what working copy type #{path} is." if handler.nil?
        handler.new(path)
      end
 
      @@handlers = Array.new
      def add_handler(handler)
        @@handlers << handler
      end
 
      def handlers
        @@handlers
      end
      private :handlers
    end
 
    attr_reader :path
 
    def initialize(path)
      @path = path.kind_of?(Pathname) ? path : Pathname.new(path)
      logger.debug {"Initialized on #{@path}"}
    end
 
    def logger
      self.class.logger
    end
 
    def to_s
      "Piston::WorkingCopy(#{@path})"
    end
 
    def exist?
    end
 
    # Creates the initial working copy for pistonizing a new repository.
    def create
      logger.debug {"Creating working copy at #{path}"}
    end
 
    # Copy files from +revision+.  +revision+ must
    # #respond_to?(:each), and return each file that is to be copied.
    # Only files must be returned.
    #
    # Each item yielded by Revision#each must be a relative path.
    #
    # WorkingCopy will call Revision#copy_to with the full path to where the
    # file needs to be copied.
    def copy_from(revision)
      revision.each do |relpath|
        target = path + relpath
        target.dirname.mkdir rescue nil
 
        logger.debug {"Copying #{relpath} to #{target}"}
        revision.copy_to(relpath, target)
      end
    end
 
    # Stores a Hash of values that can be retrieved later.
    def remember(values, handler_values)
      values["format"] = 1
 
      # Stringify keys
      values.keys.each do |key|
        values[key.to_s] = values.delete(key)
      end
 
      logger.debug {"Remembering #{values.inspect} as well as #{handler_values.inspect}"}
      File.open(yaml_path, "wb") do |f|
        f.write(values.merge("handler" => handler_values).to_yaml)
      end
 
      logger.debug {"Calling \#after_remember on #{yaml_path}"}
      after_remember(yaml_path)
    end
 
    # Callback after #remember is done, to do whatever the
    # working copy needs to do with the file.
    def after_remember(path)
    end
 
    # Recalls a Hash of values from the working copy.
    def recall
      YAML.load(File.read(yaml_path))
    end
 
    def finalize
      logger.debug {"Finalizing #{path}"}
    end
 
    protected
    # The path to the piston YAML file.
    def yaml_path
      path + ".piston.yml"
    end
  end
end