Who is who?

Imagine that you came to settle in a small but promising company. The director decides to introduce you to his team. He calls three employees: a designer, a programmer and an admin.

The first one comes in and from the threshold cheerfully declares: “I am a designer”. Following the second, smiling mysteriously: "I am not a designer." After a minute, the third one enters, looking tired and, shaking his head, excuses himself: "I am not a programmer."

The director, leaning back in his chair and stretching in a sly smile, remarks: “Only one told the truth! How can you guess who is who? ”
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But it is possible! There is only one solution. I repeat briefly the condition:
1. designer
2. not a designer
3. not a programmer
One of the answers of the staff is truthful, two false. It is required to determine who is who.

This is a school problem in mathematics (I hope you have not forgotten it yet?), I added only a small literary digression and changed professions. We write the answers, as always, in white and white. I wish you success!