uploads: move thumbnail generation code to MediaFile.

* Move image thumbnail generation code to MediaFile::Image.
* Move video thumbnail generation code to MediaFile::Video.
* Move ugoira->webm conversion code to MediaFile::Ugoira.

This separates thumbnail generation from the upload process so that it's
possible to generate thumbnails outside of uploads.

app/logical/media_file/ugoira.rb

@@ -1,13 +1,93 @@
 class MediaFile::Ugoira < MediaFile
-  def dimensions
-    tempfile = Tempfile.new
-    folder = Zip::File.new(file.path)
-    folder.first.extract(tempfile.path) { true }
+  extend Memoist
+  class Error < StandardError; end
+  attr_reader :frame_data
 
-    image_file = MediaFile.open(tempfile)
-    image_file.dimensions
-  ensure
-    image_file.close
-    tempfile.close!
+  def self.conversion_enabled?
+    system("ffmpeg -version > /dev/null") && system("mkvmerge --version > /dev/null")
   end
+
+  def initialize(file, frame_data: {}, **options)
+    super(file, **options)
+    @frame_data = frame_data
+  end
+
+  def close
+    file.close
+    zipfile.close
+    preview_frame.close
+  end
+
+  def dimensions
+    preview_frame.dimensions
+  end
+
+  def preview(width, height)
+    preview_frame.preview(width, height)
+  end
+
+  def crop(width, height)
+    preview_frame.crop(width, height)
+  end
+
+  # XXX should take width and height and resize image
+  def convert
+    raise NotImplementedError, "can't convert ugoira to webm: ffmpeg or mkvmerge not installed" unless self.class.conversion_enabled?
+
+    Dir.mktmpdir("ugoira-#{md5}") do |tmpdir|
+      output_file = Tempfile.new(["ugoira-conversion", ".webm"], binmode: true)
+
+      FileUtils.mkdir_p("#{tmpdir}/images")
+
+      zipfile.each do |entry|
+        path = File.join(tmpdir, "images", entry.name)
+        entry.extract(path)
+      end
+
+      # Duplicate last frame to avoid it being displayed only for a very short amount of time.
+      last_file_name = zipfile.entries.last.name
+      last_file_name =~ /\A(\d{6})(\.\w{,4})\Z/
+      new_last_index = $1.to_i + 1
+      file_ext = $2
+      new_last_filename = ("%06d" % new_last_index) + file_ext
+      path_from = File.join(tmpdir, "images", last_file_name)
+      path_to = File.join(tmpdir, "images", new_last_filename)
+      FileUtils.cp(path_from, path_to)
+
+      delay_sum = 0
+      timecodes_path = File.join(tmpdir, "timecodes.tc")
+      File.open(timecodes_path, "w+") do |f|
+        f.write("# timecode format v2\n")
+        frame_data.each do |img|
+          f.write("#{delay_sum}\n")
+          delay_sum += (img["delay"] || img["delay_msec"])
+        end
+        f.write("#{delay_sum}\n")
+        f.write("#{delay_sum}\n")
+      end
+
+      ext = zipfile.first.name.match(/\.(\w{,4})$/)[1]
+      ffmpeg_out, status = Open3.capture2e("ffmpeg -i #{tmpdir}/images/%06d.#{ext} -codec:v libvpx -crf 4 -b:v 5000k -an #{tmpdir}/tmp.webm")
+      raise Error, "ffmpeg failed: #{ffmpeg_out}" unless status.success?
+
+      mkvmerge_out, status = Open3.capture2e("mkvmerge -o #{output_file.path} --webm --timecodes 0:#{tmpdir}/timecodes.tc #{tmpdir}/tmp.webm")
+      raise Error, "mkvmerge failed: #{mkvmerge_out}" unless status.success?
+
+      MediaFile.open(output_file)
+    end
+  end
+
+  private
+
+  def zipfile
+    Zip::File.new(file.path)
+  end
+
+  def preview_frame
+    tempfile = Tempfile.new("ugoira-preview", binmode: true)
+    zipfile.entries.first.extract(tempfile.path) { true } #  'true' means overwrite the existing tempfile.
+    MediaFile.open(tempfile)
+  end
+
+  memoize :zipfile, :preview_frame
 end