#! /usr/bin/python3
# ==================================================================
# calculate the angle between two vectors (line segments)
# based on: www.adamsmith.haus/python/answers/
#       how-to-get-the-angle-between-two-vectors-in-python
# -------------------------------------------------------------------
# Note: this code finds the smallest angle between two vectors.
#       it does not know clockwise/counterclockwise.
# -------------------------------------------------------------------
# v1 - vector 1
# v2 - vector 2
# uv - display unit vectors (debug)
# ===================================================================

import numpy as np

def two_vector_angle(v1,v2,uv=False):

    # ---- vector norm

    unit_v1 = v1 / np.linalg.norm(v1)

    unit_v2 = v2/np.linalg.norm(v2)

    if uv:
        print(f'unit_v1 = {unit_v1}')
        print(f'unit_v2 = {unit_v2}')

    #---- dot product of two vectors

    dot_product = np.dot(unit_v1, unit_v2)

    # --- generate the angle between v1 and v2

    a_rad = np.arccos(dot_product)

    return a_rad

# -------------------------------------------------------------------
# ---- main
# -------------------------------------------------------------------

if __name__ == '__main__':

    # ---- Y axis

    v1 = (0.0,100.0)           # Y axis

    # ---- simulated fold line vector

    deg = 30.0
    rad = np.deg2rad(deg)

    v2 = [100.0 * np.cos(rad), 100.0 * np.sin(rad)]

    ang_rad = two_vector_angle(v1,v2)

    ang_deg = np.rad2deg(ang_rad)

    print(f'# test-deg={deg:3} ' + 
          f'calc-rad={ang_rad:.3f} ' +
          f'calc-deg={ang_deg:.3f}')