import numpy as np


def lic_flow(vectors, len_pix=10):
    vectors = np.asarray(vectors)
    m, n, two = vectors.shape
    if two != 2:
        raise ValueError

    result = np.zeros((2 * len_pix + 1, m, n, 2), dtype=np.int32)  # FIXME: int16?
    center = len_pix
    result[center, :, :, 0] = np.arange(m)[:, np.newaxis]
    result[center, :, :, 1] = np.arange(n)[np.newaxis, :]

    for i in range(m):
        for j in range(n):
            y = i
            x = j
            fx = 0.5
            fy = 0.5
            for k in range(len_pix):
                vx, vy = vectors[y, x]
                print(x, y, vx, vy)
                if vx >= 0:
                    tx = (1 - fx) / vx
                else:
                    tx = -fx / vx
                if vy >= 0:
                    ty = (1 - fy) / vy
                else:
                    ty = -fy / vy
                if tx < ty:
                    print("x step")
                    if vx > 0:
                        x += 1
                        fy += vy * tx
                        fx = 0.0
                    else:
                        x -= 1
                        fy += vy * tx
                        fx = 1.0
                else:
                    print("y step")
                    if vy > 0:
                        y += 1
                        fx += vx * ty
                        fy = 0.0
                    else:
                        y -= 1
                        fx += vx * ty
                        fy = 1.0
                if x < 0:
                    x = 0
                if y < 0:
                    y = 0
                if x >= n:
                    x = n - 1
                if y >= m:
                    y = m - 1
                result[center + k + 1, i, j, :] = y, x

    return result