This progression uses parallelism
with minor seventh chords moving through distantly-related keys for its "A" section where the melody is chromatic. The "B" bridge section is diatonic. The form is AAB.
It is tricky and fun to vamp over the chords as they change through the keys. It is cyclic, Am - Gm - Fm - Gm, however, there is a hint of Aeolian mode in each key instance because of the motion from the previous chord.
The bridge is fun because it tonally centers in on G, then uses a cadential trick with E as dominant to move back to Am and renew the cycle.