Is "he takes extreme measures to ensure that he is seen by no one" a complex sentence?

• He takes extreme measures to ensure that he is seen by no one

Let's take it apart, shall we?

First, insert the missing clause marker in order for the purpose infinitive, and identify auxiliary verbs (in this case, only is).

• He takes extreme measures in order to ensure that he is seen by no one

Next, identify and count the remaining main verbs. This is the number of clauses.

• He takes extreme measures to ensure that he is seen by no one
  Present tense takes, infinitive ensure, present passive seen. Three verbs, three clauses.

Next, identify the type of each clause.

• [He takes extreme measures [in order to ensure [that he is seen by no one]]]
• He takes extreme measures [in order to S] : main clause, present tense, subject He
• [in order to] ensure [that S] : purpose infinitive sentence adverb clause, no subject
• [that] he is seen by no one : passive present tensed direct object complement of ensure

Finally, identify missing subjects -- he is the subject of ensure in the purpose infinitive, under identity with the subject of takes -- and unwind rules, in this case only Passive in the complement clause, which produces

• [He takes extreme measures [in order for him to ensure [that no one sees him]]]

So, since it has one main clause and two dependent clauses, I guess this is a complex sentence. Though that's not important; most sentences are complex; simple sentences only occur in grade school and on TV news.