src/derails/passive_hoarding/analyzer/video_analyzer.rb
# frozen_string_literal: true

module PassiveHoarding
  # = Active Storage Video \Analyzer
  #
  # Extracts the following from a video blob:
  #
  # * Width (pixels)
  # * Height (pixels)
  # * Duration (seconds)
  # * Angle (degrees)
  # * Display aspect ratio
  # * Audio (true if file has an audio channel, false if not)
  # * Video (true if file has an video channel, false if not)
  #
  # Example:
  #
  #   PassiveHoarding::Analyzer::VideoAnalyzer.new(blob).metadata
  #   # => { width: 640.0, height: 480.0, duration: 5.0, angle: 0, display_aspect_ratio: [4, 3], audio: true, video: true }
  #
  # When a video's angle is 90, -90, 270 or -270 degrees, its width and height are automatically swapped for convenience.
  #
  # This analyzer requires the {FFmpeg}[https://www.ffmpeg.org] system library, which is not provided by \Rails.
  class Analyzer::VideoAnalyzer < Analyzer
    def self.accept?(blob)
      blob.video?
    end

    def metadata
      { width: width, height: height, duration: duration, angle: angle, display_aspect_ratio: display_aspect_ratio, audio: audio?, video: video? }.compact
    end

    private
      def width
        if rotated?
          computed_height || encoded_height
        else
          encoded_width
        end
      end

      def height
        if rotated?
          encoded_width
        else
          computed_height || encoded_height
        end
      end

      def duration
        duration = video_stream["duration"] || container["duration"]
        Float(duration) if duration
      end

      def angle
        if tags["rotate"]
          Integer(tags["rotate"])
        elsif display_matrix && display_matrix["rotation"]
          Integer(display_matrix["rotation"])
        end
      end

      def display_matrix
        side_data.detect { |data| data["side_data_type"] == "Display Matrix" }
      end

      def display_aspect_ratio
        if descriptor = video_stream["display_aspect_ratio"]
          if terms = descriptor.split(":", 2)
            numerator   = Integer(terms[0])
            denominator = Integer(terms[1])

            [numerator, denominator] unless numerator == 0
          end
        end
      end

      def rotated?
        angle == 90 || angle == 270 || angle == -90 || angle == -270
      end

      def audio?
        audio_stream.present?
      end

      def video?
        video_stream.present?
      end

      def computed_height
        if encoded_width && display_height_scale
          encoded_width * display_height_scale
        end
      end

      def encoded_width
        @encoded_width ||= Float(video_stream["width"]) if video_stream["width"]
      end

      def encoded_height
        @encoded_height ||= Float(video_stream["height"]) if video_stream["height"]
      end

      def display_height_scale
        @display_height_scale ||= Float(display_aspect_ratio.last) / display_aspect_ratio.first if display_aspect_ratio
      end

      def tags
        @tags ||= video_stream["tags"] || {}
      end

      def side_data
        @side_data ||= video_stream["side_data_list"] || {}
      end

      def video_stream
        @video_stream ||= streams.detect { |stream| stream["codec_type"] == "video" } || {}
      end

      def audio_stream
        @audio_stream ||= streams.detect { |stream| stream["codec_type"] == "audio" } || {}
      end

      def streams
        probe["streams"] || []
      end

      def container
        probe["format"] || {}
      end

      def probe
        @probe ||= download_blob_to_tempfile { |file| probe_from(file) }
      end

      def probe_from(file)
        instrument(File.basename(ffprobe_path)) do
          IO.popen([ ffprobe_path,
            "-print_format", "json",
            "-show_streams",
            "-show_format",
            "-v", "error",
            file.path
          ]) do |output|
            JSON.parse(output.read)
          end
        end
      rescue Errno::ENOENT
        logger.info "Skipping video analysis because ffprobe isn't installed"
        {}
      end

      def ffprobe_path
        PassiveHoarding.paths[:ffprobe] || "ffprobe"
      end
  end
end
