require 'rbconfig'
require 'digest/sha1'

module Guard

  autoload :Darwin,  'guard/listeners/darwin'
  autoload :Linux,   'guard/listeners/linux'
  autoload :Windows, 'guard/listeners/windows'
  autoload :Polling, 'guard/listeners/polling'

  class Listener

    DefaultIgnorePaths = %w[. .. .bundle .git log tmp vendor]
    attr_accessor :changed_files
    attr_reader :directory, :ignore_paths, :locked

    def self.select_and_init(*a)
      if mac? && Darwin.usable?
        Darwin.new(*a)
      elsif linux? && Linux.usable?
        Linux.new(*a)
      elsif windows? && Windows.usable?
        Windows.new(*a)
      else
        UI.info "Using polling (Please help us to support your system better than that.)"
        Polling.new(*a)
      end
    end

    def initialize(directory = Dir.pwd, options = {})
      @directory           = directory.to_s
      @sha1_checksums_hash = {}
      @file_timestamp_hash = {}
      @relativize_paths    = options.fetch(:relativize_paths, true)
      @watch_deletions     = options.fetch(:deletions, false)
      @changed_files       = []
      @locked              = false
      @ignore_paths        = DefaultIgnorePaths
      @ignore_paths        |= options[:ignore_paths] if options[:ignore_paths]

      update_last_event
      start_reactor
    end

    def start_reactor
      return if ENV["GUARD_ENV"] == 'test'
      Thread.new do
        loop do
          if @changed_files != [] && !@locked
            changed_files = @changed_files.dup
            clear_changed_files
            ::Guard.run_on_change(changed_files)
          else
            sleep 0.1
          end
        end
      end
    end

    def start
      watch(@directory)
      timestamp_files
    end

    def stop
    end

    def lock
      @locked = true
    end

    def unlock
      @locked = false
    end

    def clear_changed_files
      @changed_files.clear
    end

    def on_change(&callback)
      @callback = callback
    end

    def update_last_event
      @last_event = Time.now
    end

    def modified_files(dirs, options={})
      last_event = @last_event
      files = []
      if @watch_deletions
        deleted_files = @file_timestamp_hash.collect do |path, ts|
          unless File.exists?(path)
            @sha1_checksums_hash.delete(path)
            @file_timestamp_hash.delete(path)
            "!#{path}"
          end
        end
        files.concat(deleted_files.compact)
      end
      update_last_event
      files.concat(potentially_modified_files(dirs, options).select { |path| file_modified?(path, last_event) })
      relativize_paths(files)
    end

    def worker
      raise NotImplementedError, "should respond to #watch"
    end

    # register a directory to watch. must be implemented by the subclasses
    def watch(directory)
      raise NotImplementedError, "do whatever you want here, given the directory as only argument"
    end

    def all_files
      potentially_modified_files([@directory], :all => true)
    end

    # scopes all given paths to the current #directory
    def relativize_paths(paths)
      return paths unless relativize_paths?
      paths.map do |path|
        path.gsub(%r{#{@directory}/}, '')
      end
    end

    def relativize_paths?
      !!@relativize_paths
    end

    # populate initial timestamp file hash to watch for deleted or moved files
    def timestamp_files
      all_files.each {|path| set_file_timestamp_hash(path, file_timestamp(path)) } if @watch_deletions
    end

    # return children of the passed dirs that are not in the ignore_paths list
    def exclude_ignored_paths(dirs, ignore_paths = self.ignore_paths)
      Dir.glob(dirs.map { |d| "#{d.sub(%r{/+$}, '')}/*" }, File::FNM_DOTMATCH).reject do |path|
        ignore_paths.include?(File.basename(path))
      end
    end

  private

    def potentially_modified_files(dirs, options={})
      paths = exclude_ignored_paths(dirs)

      if options[:all]
        paths.inject([]) do |array, path|
          if File.file?(path)
            array << path
          else
            array += Dir.glob("#{path}/**/*", File::FNM_DOTMATCH).select { |p| File.file?(p) }
          end
          array
        end
      else
        paths.select { |path| File.file?(path) }
      end
    end

    # Depending on the filesystem, mtime/ctime is probably only precise to the second, so round
    # both values down to the second for the comparison.
    # ctime is used only on == comparison to always catches Rails 3.1 Assets pipelined on Mac OSX
    def file_modified?(path, last_event)
      ctime = File.ctime(path).to_i
      mtime = File.mtime(path).to_i
      if [mtime, ctime].max == last_event.to_i
        file_content_modified?(path, sha1_checksum(path))
      elsif mtime > last_event.to_i
        set_sha1_checksums_hash(path, sha1_checksum(path))
        true
      elsif @watch_deletions
        ts = file_timestamp(path)
        if ts != @file_timestamp_hash[path]
          set_file_timestamp_hash(path, ts)
          true
        end
      else
        false
      end
    rescue
      false
    end

    def file_content_modified?(path, sha1_checksum)
      if @sha1_checksums_hash[path] != sha1_checksum
        set_sha1_checksums_hash(path, sha1_checksum)
        true
      else
        false
      end
    end

    def set_file_timestamp_hash(path, file_timestamp)
        @file_timestamp_hash[path] = file_timestamp
    end

    def set_sha1_checksums_hash(path, sha1_checksum)
      @sha1_checksums_hash[path] = sha1_checksum
    end

    def file_timestamp(path)
      File.mtime(path).to_i
    end

    def sha1_checksum(path)
      Digest::SHA1.file(path).to_s
    end

    def self.mac?
      RbConfig::CONFIG['target_os'] =~ /darwin/i
    end

    def self.linux?
      RbConfig::CONFIG['target_os'] =~ /linux/i
    end

    def self.windows?
      RbConfig::CONFIG['target_os'] =~ /mswin|mingw/i
    end

  end
end