metadata: add ability to search exif metadata.

Usage:

* https://danbooru.donmai.us/media_metadata?search[has_metadata]=true
* https://danbooru.donmai.us/media_metadata?search[has_metadata]=false
* https://danbooru.donmai.us/media_metadata?search[metadata_has_key]=GIF:GIFVersion
* https://danbooru.donmai.us/media_metadata?search[metadata][GIF:GIFVersion]=89a
* https://danbooru.donmai.us/media_metadata?search[metadata][GIF:GIFVersion]&search[metadata][GIF:BackgroundColor]=0

app/models/media_asset.rb

@@ -1,20 +1,20 @@
 class MediaAsset < ApplicationRecord
   has_one :media_metadata, dependent: :destroy
 
-  def self.create_from_media_file!(media_file)
-    create!(
-      md5: media_file.md5,
-      file_ext: media_file.file_ext,
-      file_size: media_file.file_size,
-      image_width: media_file.width,
-      image_height: media_file.height,
-      media_metadata: MediaMetadata.new(metadata: media_file.metadata),
-    )
-  end
-
   def self.search(params)
     q = search_attributes(params, :id, :created_at, :updated_at, :md5, :file_ext, :file_size, :image_width, :image_height)
     q = q.apply_default_order(params)
     q
   end
+
+  def file=(file_or_path)
+    media_file = file_or_path.is_a?(MediaFile) ? file_or_path : MediaFile.open(file_or_path)
+
+    self.md5 = media_file.md5
+    self.file_ext = media_file.file_ext
+    self.file_size = media_file.file_size
+    self.image_width = media_file.width
+    self.image_height = media_file.height
+    self.media_metadata = MediaMetadata.new(file: media_file)
+  end
 end

app/models/media_metadata.rb

@@ -15,8 +15,12 @@ class MediaMetadata < ApplicationRecord
   belongs_to :media_asset
 
   def self.search(params)
-    q = search_attributes(params, :id, :created_at, :updated_at, :media_asset_id)
+    q = search_attributes(params, :id, :created_at, :updated_at, :media_asset, :metadata)
     q = q.apply_default_order(params)
     q
   end
+
+  def file=(file_or_path)
+    self.metadata = MediaFile.open(file_or_path).metadata
+  end
 end