Utilizing the provided musical theme and letter-based structure, compose a piece of music.
X:1
L:1/8
M:4/4
K:D
['AG FDFA', 'g2 fg', 'ecAG FDFA d2 fd']  
X:1
L:1/8
M:4/4
K:D
 AG ||"D" FDFA d2 fd | d2 fd"A" ecAG |"D" FDFA d2 fd | dcAF"G" G2 :: de |"D" f3 f"G" g2 fg | 
"D" abag fdde |"D" f3 f"G" g2 fg |"D" abaf"G" g2 fg |"D" agfa"G" gfeg |"D" fedf"A" ecAG | 
"D" FDFA d2 fd | dcAF"G" G2 :|  