ai tags: add autotagger API client.

Add API client for https://github.com/danbooru/autotagger service.

app/logical/autotagger_client.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+# API client for the Danbooru Autotagger service. Used for the AI tagging feature.
+#
+# @see https://autotagger.donmai.us
+# @see https://github.com/danbooru/autotagger
+class AutotaggerClient
+  attr_reader :autotagger_url, :http
+
+  def initialize(autotagger_url: Danbooru.config.autotagger_url.to_s, http: Danbooru::Http.new)
+    @autotagger_url = autotagger_url.chomp("/")
+    @http = http
+  end
+
+  def evaluate(file, limit: 50, confidence: 0.01)
+    return {} if autotagger_url.blank?
+
+    response = http.post("#{autotagger_url}/evaluate", form: { file: HTTP::FormData::File.new(file), threshold: confidence, format: "json" })
+    return {} if !response.status.success?
+
+    tag_names_with_scores = response.parse.first["tags"]
+    tags = Tag.where(name: tag_names_with_scores.keys).index_by(&:name)
+    tag_names_with_scores.transform_keys(&tags)
+  end
+end