# REMARK   1 CREATED WITH OPENMM 8.2, 2025-04-07
# HETATM    1  O       A   1       0.428   0.562  -0.006  1.00  0.00           O
# HETATM    2  H1      A   1       1.257   1.041  -0.006  1.00  0.00           H
# HETATM    3  H2      A   1      -0.243   1.245  -0.006  1.00  0.00           H
# TER       4          A   1
# CONECT    1    2    3
# CONECT    2    1
# CONECT    3    1
# END

from math import acos, sqrt, pi


def calc_hoh_angle(h1: tuple[float], h2: tuple[float], o: tuple[float]) -> float:
    x1 = h1[0] - o[0]
    y1 = h1[1] - o[1]
    z1 = h1[2] - o[2]

    x2 = h2[0] - o[0]
    y2 = h2[1] - o[1]
    z2 = h2[2] - o[2]

    xyz12 = (x1 * x2) + (y1 * y2) + (z1 * z2)

    angle = acos(xyz12 / (sqrt(x1**2 + y1**2 + z1**2) * sqrt(x2**2 + y2**2 + z2**2)))

    return angle * 180 / pi


# OpenMM

# Gaussian
print(
    calc_hoh_angle(
        h1=(0.694, 0.998, 0.000), h2=(-0.859, 1.209, 0.000), o=(-0.157, 0.554, 0.000)
    )
)
print(
    calc_hoh_angle(
        h1=(0.000, 0.781, -0.456), h2=(0.000, -0.781, -0.456), o=(0.000, 0.000, 0.114)
    )
)