This sentence is complex because it contains both a dependant and an independent clause. Do not be fooled by the addition of "however" or the length of the sentence.
If you need reasoning, here you are:
Simple: has one independent clause
Compound: has two independent clauses (either joined by a coordinating conjunction or a semicolon)
Complex: contains a dependant and an independent clause
Compound-Complex: Contains at least two independent clauses and one dependent clause
Hope this helps! If you have any questions about what any of the words that I used in my explanation mean (such as an independent clause and a dependent clause), feel free to ask.
