require 'multi_json'
require 'time'

module Sprockets
  # The Manifest logs the contents of assets compiled to a single
  # directory. It records basic attributes about the asset for fast
  # lookup without having to compile. A pointer from each logical path
  # indicates with fingerprinted asset is the current one.
  #
  # The JSON is part of the public API and should be considered
  # stable. This should make it easy to read from other programming
  # languages and processes that don't have sprockets loaded. See
  # `#assets` and `#files` for more infomation about the structure.
  class Manifest
    attr_reader :environment, :path, :dir

    # Create new Manifest associated with an `environment`. `path` is
    # a full path to the manifest json file. The file may or may not
    # already exist. The dirname of the `path` will be used to write
    # compiled assets to. Otherwise, if the path is a directory, the
    # filename will default to "manifest.json" in that directory.
    #
    #   Manifest.new(environment, "./public/assets/manifest.json")
    #
    def initialize(environment, path)
      @environment = environment

      if File.extname(path) == ""
        @dir  = File.expand_path(path)
        @path = File.join(@dir, 'manifest.json')
      else
        @path = File.expand_path(path)
        @dir  = File.dirname(path)
      end

      data = nil

      begin
        if File.exist?(@path)
          data = MultiJson.decode(File.read(@path))
        end
      rescue MultiJson::DecodeError => e
        logger.error "#{@path} is invalid: #{e.class} #{e.message}"
      end

      @data = data.is_a?(Hash) ? data : {}
    end

    # Returns internal assets mapping. Keys are logical paths which
    # map to the latest fingerprinted filename.
    #
    #   Logical path (String): Fingerprint path (String)
    #
    #   { "application.js" => "application-2e8e9a7c6b0aafa0c9bdeec90ea30213.js",
    #     "jquery.js"      => "jquery-ae0908555a245f8266f77df5a8edca2e.js" }
    #
    def assets
      @data['assets'] ||= {}
    end

    # Returns internal file directory listing. Keys are filenames
    # which map to an attributes array.
    #
    #   Fingerprint path (String):
    #     logical_path: Logical path (String)
    #     mtime: ISO8601 mtime (String)
    #     digest: Base64 hex digest (String)
    #
    #  { "application-2e8e9a7c6b0aafa0c9bdeec90ea30213.js" =>
    #      { 'logical_path' => "application.js",
    #        'mtime' => "2011-12-13T21:47:08-06:00",
    #        'digest' => "2e8e9a7c6b0aafa0c9bdeec90ea30213" } }
    #
    def files
      @data['files'] ||= {}
    end

    # Compile and write asset to directory. The asset is written to a
    # fingerprinted filename like
    # `application-2e8e9a7c6b0aafa0c9bdeec90ea30213.js`. An entry is
    # also inserted into the manifest file.
    #
    #   compile("application.js")
    #
    def compile(*args)
      paths = environment.each_logical_path(*args).to_a +
        args.flatten.select { |fn| Pathname.new(fn).absolute? }

      paths.each do |path|
        if asset = find_asset(path)
          files[asset.digest_path] = {
            'logical_path' => asset.logical_path,
            'mtime'        => asset.mtime.iso8601,
            'digest'       => asset.digest
          }
          assets[asset.logical_path] = asset.digest_path

          target = File.join(dir, asset.digest_path)

          if File.exist?(target)
            logger.debug "Skipping #{target}, already exists"
          else
            logger.info "Writing #{target}"
            asset.write_to target
          end

          save
          asset
        end
      end
    end

    # Removes file from directory and from manifest. `filename` must
    # be the name with any directory path.
    #
    #   manifest.remove("application-2e8e9a7c6b0aafa0c9bdeec90ea30213.js")
    #
    def remove(filename)
      path = File.join(dir, filename)
      logical_path = files[filename]['logical_path']

      if assets[logical_path] == filename
        assets.delete(logical_path)
      end

      files.delete(filename)
      FileUtils.rm(path) if File.exist?(path)

      save

      logger.warn "Removed #{filename}"

      nil
    end

    # Cleanup old assets in the compile directory. By default it will
    # keep the latest version plus 2 backups.
    def clean(keep = 2)
      self.assets.keys.each do |logical_path|
        # Get assets sorted by ctime, newest first
        assets = backups_for(logical_path)

        # Keep the last N backups
        assets = assets[keep..-1] || []

        # Remove old assets
        assets.each { |path, _| remove(path) }
      end
    end

    # Wipe directive
    def clobber
      FileUtils.rm_r(@dir) if File.exist?(@dir)
      logger.warn "Removed #{@dir}"
      nil
    end

    protected
      # Finds all the backup assets for a logical path. The latest
      # version is always excluded. The return array is sorted by the
      # assets mtime in descending order (Newest to oldest).
      def backups_for(logical_path)
        files.select { |filename, attrs|
          # Matching logical paths
          attrs['logical_path'] == logical_path &&
            # Excluding whatever asset is the current
            assets[logical_path] != filename
        }.sort_by { |filename, attrs|
          # Sort by timestamp
          Time.parse(attrs['mtime'])
        }.reverse
      end

      # Basic wrapper around Environment#find_asset. Logs compile time.
      def find_asset(logical_path)
        asset = nil
        ms = benchmark do
          asset = environment.find_asset(logical_path)
        end
        logger.warn "Compiled #{logical_path}  (#{ms}ms)"
        asset
      end

      # Persist manfiest back to FS
      def save
        FileUtils.mkdir_p dir
        File.open(path, 'w') do |f|
          f.write MultiJson.encode(@data)
        end
      end

    private
      def logger
        environment.logger
      end

      def benchmark
        start_time = Time.now.to_f
        yield
        ((Time.now.to_f - start_time) * 1000).to_i
      end
  end
end