uploads: allow searching uploads and media assets by metatag.

Allow searching the /uploads and /media_assets pages by the following metatags:

* id:
* md5:
* width:
* height:
* duration:
* mpixels:
* ratio:
* filesize:
* filetype:
* date:
* age:
* status:<processing|active|deleted|expunged|failed> (for /media_assets)
* status:<pending|processing|active|failed> (for /uploads)
* is:<filetype>, is:<status>
* exif:

Examples:

* https://betabooru.donmai.us/media_assets?search[ai_tags_match]=filetype:png
* https://betabooru.donmai.us/uploads?search[ai_tags_match]=filetype:png

Note that in /uploads search, the id:, date:, and age: metatags refer to the upload media asset, not
the upload itself.

Note also that uploads may contain multiple assets, so for example searching uploads by
`filetype:png` will return all uploads containing at least one PNG file, even if they contain other
non-PNG files.

app/logical/media_asset_query.rb

@@ -0,0 +1,89 @@
+# frozen_string_literal: true
+
+# A MediaAssetQuery is a tag search performed on media assets (or upload media assets) using AI tags.
+class MediaAssetQuery
+  extend Memoist
+
+  attr_reader :search_string
+  delegate :to_infix, :to_pretty_string, to: :ast
+  alias_method :to_s, :to_infix
+
+  def initialize(search_string)
+    @search_string = search_string.to_s.strip
+  end
+
+  def self.search(search_string, **options)
+    new(search_string).search(**options)
+  end
+
+  def ast
+    @ast ||= PostQuery::Parser.parse(search_string)
+  end
+
+  def normalized_ast
+    @normalized_ast ||= ast.to_cnf.rewrite_opts.trim
+  end
+
+  def search(relation: MediaAsset.all, foreign_key: :id, score_range: (50..))
+    normalized_ast.visit do |node, *children|
+      case node.type
+      in :all
+        relation.all
+      in :none
+        relation.none
+      in :tag
+        ai_tag = AITag.named(node.name).where(score: score_range)
+        relation.where(ai_tag.where(AITag.arel_table[:media_asset_id].eq(relation.arel_table[foreign_key])).arel.exists)
+      in :metatag
+        metatag_matches(node.name, node.value, relation)
+      in :wildcard
+        relation.none
+      in :not
+        children.first.negate_relation
+      in :and
+        joins = children.flat_map(&:joins_values)
+        orders = children.flat_map(&:order_values)
+        nodes = children.map { |child| child.joins(joins).order(orders) }
+        nodes.reduce(&:and)
+      in :or
+        joins = children.flat_map(&:joins_values)
+        orders = children.flat_map(&:order_values)
+        nodes = children.map { |child| child.joins(joins).order(orders) }
+        nodes.reduce(&:or)
+      end
+    end
+  end
+
+  def metatag_matches(name, value, relation)
+    case name
+    when "id"
+      relation.attribute_matches(value, :id)
+    when "md5"
+      relation.attribute_matches(value, "media_assets.md5", :md5)
+    when "width"
+      relation.attribute_matches(value, "media_assets.image_width")
+    when "height"
+      relation.attribute_matches(value, "media_assets.image_height")
+    when "duration"
+      relation.attribute_matches(value, "media_assets.duration", :float)
+    when "mpixels"
+      relation.attribute_matches(value, "(media_assets.image_width * media_assets.image_height) / 1000000.0", :float)
+    when "ratio"
+      relation.attribute_matches(value, "ROUND(media_assets.image_width::numeric / media_assets.image_height::numeric, 2)", :ratio)
+    when "filesize"
+      relation.attribute_matches(value, "media_assets.file_size", :filesize)
+    when "filetype"
+      relation.attribute_matches(value, "media_assets.file_ext", :enum)
+    when "date"
+      relation.attribute_matches(value, :created_at, :date)
+    when "age"
+      relation.attribute_matches(value, :created_at, :age)
+    when "status"
+      relation.attribute_matches(value, :status, :enum)
+    when "is"
+      relation.is_matches(value)
+    when "exif"
+      relation.exif_matches(value)
+    end
+  end
+end