#306

backend/app/services/material_thumbnail_generator.rb

@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+require 'mini_magick'
+require 'open3'
+require 'tempfile'
+
+
+class MaterialThumbnailGenerator
+  SIZE = '180x180'
+
+  class << self
+    def generate! material
+      new(material).generate!
+    rescue ActiveStorage::FileNotFoundError, ArgumentError, MiniMagick::Error => e
+      Rails.logger.warn("Material thumbnail generation skipped: #{ e.class }: #{ e.message }")
+      nil
+    end
+  end
+
+  def initialize material
+    @material = material
+  end
+
+  def generate!
+    @material.thumbnail.purge if @material.thumbnail.attached?
+    return unless @material.file.attached?
+    return unless image? || video?
+
+    @material.file.blob.open do |file|
+      thumbnail = image? ? image_thumbnail(file.path) : video_thumbnail(file.path)
+      attach_thumbnail(thumbnail) if thumbnail
+    end
+  end
+
+  private
+
+  def image? = content_type.start_with?('image/')
+
+  def video? = content_type.start_with?('video/')
+
+  def content_type = @material.file.blob.content_type.to_s
+
+  def image_thumbnail path
+    image = MiniMagick::Image.open(path)
+    image.resize(SIZE)
+    image.format('jpg')
+    image
+  end
+
+  def video_thumbnail path
+    [1, 0].each do |seconds|
+      tempfile = Tempfile.new(['material-thumbnail', '.jpg'])
+      tempfile.close
+      ok = extract_video_frame(path, tempfile.path, seconds)
+      next unless ok && File.size?(tempfile.path)
+
+      return image_thumbnail(tempfile.path)
+    ensure
+      tempfile&.unlink
+    end
+
+    nil
+  end
+
+  def extract_video_frame input_path, output_path, seconds
+    _stdout, stderr, status =
+        Open3.capture3('ffmpeg',
+                       '-y',
+                       '-ss', seconds.to_s,
+                       '-i', input_path,
+                       '-frames:v', '1',
+                       '-f', 'image2',
+                       output_path)
+    Rails.logger.warn("ffmpeg thumbnail failed: #{ stderr }") unless status.success?
+    status.success?
+  rescue Errno::ENOENT => e
+    Rails.logger.warn("ffmpeg unavailable for material thumbnail: #{ e.message }")
+    false
+  end
+
+  def attach_thumbnail image
+    @material.thumbnail.attach(io: File.open(image.path),
+                               filename: 'material-thumbnail.jpg',
+                               content_type: 'image/jpeg')
+  end
+end