module Buildr

  class Filter < Rake::Task

    # The target directory.
    attr_accessor :target
    # Filter to use. 
    attr_accessor :filter

    def initialize(*args)
      super
      enhance do |task|
        fail "No target directory specified" if !target || (File.exist?(target) && !File.directory?(target))
        unless copy_map.empty?
          verbose(Rake.application.options.trace || false) do
            copy_map do |dest, src|
              mkpath File.dirname(dest) rescue nil
              case filter
              when Proc, Method
                filtered = filter.call(File.read(src))
                File.open(dest, "w") { |file| file.write filtered }
              when Hash
                filtered = File.read(src).gsub(/\$\{.*\}/) { |str| filter[str[2..-2]] || str }
                File.open(dest, "w") { |file| file.write filtered }
              when nil
                cp src, dest
              else
                fail "Filter can be a hash (key=>value), or a proc/method; I don't understand #{filter}"
              end
            end
            touch target if File.exist?(target)
          end
        end 
      end
    end

    def include(*files)
      prerequisites.include *files
      self
    end
    alias :add :include 

    def exclude(*files)
      prerequisites.exclude *files
      self
    end

    def into(dir)
      self.target = dir
      self
    end

    def using(filter, &block)
      self.filter = filter || block
      self
    end

  protected

    # Return a copy map of all the files that need copying: the key is
    # the file to copy to, the value is the source file. If called with
    # a block, yields with each dest/source pair.
    def copy_map(&block)
      # Create a map between the source file and the similarly named
      # file in the target directory, including all files nested inside
      # directories.
      @copy_map ||= prerequisites.map(&:to_s).inject({}) do |map, path|
        if File.directory?(path)
          Dir[File.join(path, "**", "*")].each do |file|
            map[file.sub(File.dirname(path), target)] = file unless
              File.directory?(file) || prerequisites.exclude?(file)
          end
        elsif File.exist?(path)
          map[File.join(target, File.basename(path))] = path
        end
        map
      end.reject do |dest, src|
        # ... while ignoring that which does not need updating.
        File.exist?(dest) && File.stat(dest).mtime > File.stat(src).mtime
      end
      if block_given?
        @copy_map.each(&block)
      else
        @copy_map
      end
    end

  end

  def filter(*files)
    task = nil
    namespace { task = Filter.define_task("filter").include *files }
    task
  end

end