1 files changed, 59 insertions, 0 deletions
diff --git a/lib/gitlab/search/recent_items.rb b/lib/gitlab/search/recent_items.rb
new file mode 100644
index 00000000000..40d96ded275
--- /dev/null
+++ b/lib/gitlab/search/recent_items.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Search
+    # This is an abstract class used for storing/searching recently viewed
+    # items. The #type and #finder methods are the only ones needed to be
+    # implemented by classes inheriting from this.
+    class RecentItems
+      ITEMS_LIMIT = 100
+      EXPIRES_AFTER = 7.days
+
+      def initialize(user:, items_limit: ITEMS_LIMIT, expires_after: EXPIRES_AFTER)
+        @user = user
+        @items_limit = items_limit
+        @expires_after = expires_after
+      end
+
+      def log_view(item)
+        with_redis do |redis|
+          redis.zadd(key, Time.now.to_f, item.id)
+          redis.expire(key, @expires_after)
+
+          # There is a race condition here where we could end up removing an
+          # item from 2 places concurrently but this is fine since worst case
+          # scenario we remove an extra item from the end of the list.
+          if redis.zcard(key) > @items_limit
+            redis.zremrangebyrank(key, 0, 0) # Remove least recent
+          end
+        end
+      end
+
+      def search(term)
+        ids = with_redis do |redis|
+          redis.zrevrange(key, 0, @items_limit - 1)
+        end.map(&:to_i)
+
+        finder.new(@user, search: term, in: 'title').execute.reorder(nil).id_in_ordered(ids) # rubocop: disable CodeReuse/ActiveRecord
+      end
+
+      private
+
+      def with_redis(&blk)
+        Gitlab::Redis::SharedState.with(&blk) # rubocop: disable CodeReuse/ActiveRecord
+      end
+
+      def key
+        "recent_items:#{type.name.downcase}:#{@user.id}"
+      end
+
+      def type
+        raise NotImplementedError
+      end
+
+      def finder
+        raise NotImplementedError
+      end
+    end
+  end
+end