Factor polynomial a^7+b^7

/      /     /pi\      /pi\\\ /      /     2/pi\      2/pi\\\ /      /   2/pi\      2/pi\          /pi\    /pi\\\ /      /   /pi\    /2*pi\      /pi\    /2*pi\        /pi\    /2*pi\        /2*pi\    /pi\\\ /      /   /pi\    /2*pi\      /pi\    /2*pi\        /2*pi\    /pi\        /pi\    /2*pi\\\ /      /     /pi\    /3*pi\      /pi\    /3*pi\        /pi\    /3*pi\        /3*pi\    /pi\\\ /      /   /pi\    /3*pi\      /pi\    /3*pi\        /pi\    /3*pi\        /3*pi\    /pi\\\
|a - b*|I*sin|--| + cos|--|||*|a - b*|- cos |--| - sin |--|||*|a - b*|sin |--| - cos |--| - 2*I*cos|--|*sin|--|||*|a - b*|cos|--|*cos|----| - sin|--|*sin|----| + I*cos|--|*sin|----| + I*cos|----|*sin|--|||*|a - b*|cos|--|*cos|----| + sin|--|*sin|----| + I*cos|----|*sin|--| - I*cos|--|*sin|----|||*|a - b*|- cos|--|*cos|----| - sin|--|*sin|----| + I*cos|--|*sin|----| - I*cos|----|*sin|--|||*|a - b*|sin|--|*sin|----| - cos|--|*cos|----| - I*cos|--|*sin|----| - I*cos|----|*sin|--|||
\      \     \7 /      \7 /// \      \      \7 /       \7 /// \      \    \7 /       \7 /          \7 /    \7 /// \      \   \7 /    \ 7  /      \7 /    \ 7  /        \7 /    \ 7  /        \ 7  /    \7 /// \      \   \7 /    \ 7  /      \7 /    \ 7  /        \ 7  /    \7 /        \7 /    \ 7  /// \      \     \7 /    \ 7  /      \7 /    \ 7  /        \7 /    \ 7  /        \ 7  /    \7 /// \      \   \7 /    \ 7  /      \7 /    \ 7  /        \7 /    \ 7  /        \ 7  /    \7 ///

$$\left(a - b \left(\cos{\left(\frac{\pi}{7} \right)} + i \sin{\left(\frac{\pi}{7} \right)}\right)\right) \left(a - b \left(- \cos^{2}{\left(\frac{\pi}{7} \right)} - \sin^{2}{\left(\frac{\pi}{7} \right)}\right)\right) \left(a - b \left(- \cos^{2}{\left(\frac{\pi}{7} \right)} + \sin^{2}{\left(\frac{\pi}{7} \right)} - 2 i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)}\right)\right) \left(a - b \left(- \sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{2 \pi}{7} \right)} + \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)} + i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)} + i \sin{\left(\frac{2 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)}\right)\right) \left(a - b \left(\sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{2 \pi}{7} \right)} + \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)} - i \sin{\left(\frac{2 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)} + i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{2 \pi}{7} \right)}\right)\right) \left(a - b \left(- \sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{3 \pi}{7} \right)} - \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)} - i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)} + i \sin{\left(\frac{3 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)}\right)\right) \left(a - b \left(- \cos{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)} + \sin{\left(\frac{\pi}{7} \right)} \sin{\left(\frac{3 \pi}{7} \right)} - i \sin{\left(\frac{3 \pi}{7} \right)} \cos{\left(\frac{\pi}{7} \right)} - i \sin{\left(\frac{\pi}{7} \right)} \cos{\left(\frac{3 \pi}{7} \right)}\right)\right)$$

((((((a - b*(i*sin(pi/7) + cos(pi/7)))*(a - b*(-cos(pi/7)^2 - sin(pi/7)^2)))*(a - b*(sin(pi/7)^2 - cos(pi/7)^2 - 2*i*cos(pi/7)*sin(pi/7))))*(a - b*(cos(pi/7)*cos(2*pi/7) - sin(pi/7)*sin(2*pi/7) + i*cos(pi/7)*sin(2*pi/7) + i*cos(2*pi/7)*sin(pi/7))))*(a - b*(cos(pi/7)*cos(2*pi/7) + sin(pi/7)*sin(2*pi/7) + i*cos(2*pi/7)*sin(pi/7) - i*cos(pi/7)*sin(2*pi/7))))*(a - b*(-cos(pi/7)*cos(3*pi/7) - sin(pi/7)*sin(3*pi/7) + i*cos(pi/7)*sin(3*pi/7) - i*cos(3*pi/7)*sin(pi/7))))*(a - b*(sin(pi/7)*sin(3*pi/7) - cos(pi/7)*cos(3*pi/7) - i*cos(pi/7)*sin(3*pi/7) - i*cos(3*pi/7)*sin(pi/7)))