add sync API with swagger documentation at /api

app/controllers/api/base.rb

@@ -0,0 +1,58 @@
+require "grape"
+require "grape-swagger"
+require "ostruct"
+
+class Api::Base < Grape::API
+  format :json
+  content_type :json, "application/json"
+
+  helpers do
+    def parse_since_param(raw_since)
+      return nil if raw_since.blank?
+
+      Time.iso8601(raw_since)
+    rescue ArgumentError
+      error!({ error: "Invalid since parameter. Use ISO8601 timestamp." }, 400)
+    end
+  end
+
+  resource :entries do
+    desc "Return public entries in all languages",
+         attributes: OpenStruct.new(success: nil, produces: nil)
+    params do
+      optional :since,
+               type: String,
+               desc: "ISO8601 timestamp. Returns entries updated after this time."
+    end
+    get do
+      since_time = parse_since_param(params[:since])
+
+      entries_scope = Entry.active_entries
+      entries_scope = entries_scope.where("updated_at > ?", since_time) if since_time
+
+      entries_scope
+        .order(:updated_at, :id)
+        .select(
+          :id,
+          :category,
+          :fi,
+          :en,
+          :sv,
+          :no,
+          :ru,
+          :de,
+          :updated_at
+        )
+    end
+  end
+
+  add_swagger_documentation(
+    info: {
+      title: "Sanasto Wiki API",
+      description: "Public sync API for Sanasto Wiki glossary entries."
+    },
+    mount_path: "/swagger",
+    hide_documentation_path: true,
+    format: :json
+  )
+end