# -*- coding: utf-8 -*-
import numpy as np
# ---------------
# User settings
# --------------
def staircase_from_line(i0, i1, j0, j1):
    """Make an optimal staircase polyline given the end points"""

    swapXY = False
    if abs(i1-i0) < abs(j0-j1):  # Mostly vertical
        i0, i1, j0, j1 = j0, j1, i0, i1
        swapXY = True

    # Find integer points X0 and Y0 on line
    if i0 < i1:
        X0 = list(range(i0, i1+1))
    elif i0 > i1:
        X0 = list(range(i0, i1-1, -1))
    else:  # i0 = i1 and j0 = j1
        raise ValueError("Section reduced to a point")
    slope = float(j1-j0) / (i1-i0)
    Y0 = [j0 + slope*(x-i0) for x in X0]

    # sign = -1 if Y0 is decreasing, otherwise sign = 1
    sign = 1
    if Y0[-1] < Y0[0]:     # Decreasing Y
        sign = -1

    # Make lists of positions along staircase
    X, Y = [i0], [j0]

    for i in range(len(X0)-1):
        y = Y[-1]                    # Last point on list so far
        x0, y0 = X0[i], Y0[i]        # Present point along line
        x1, y1 = X0[i+1], Y0[i+1]    # Next point along line
        if abs(y-y0) + abs(y-y1) > abs(y+sign-y0) + abs(y+sign-y1):
            # jump
            X.append(x0)
            Y.append(y+sign)
            X.append(x1)
            Y.append(y+sign)
        else:                        # Ordinary append
            X.append(x1)
            Y.append(y)
    # Possible jump to last point
    # Assumes Y0[-1]
    if Y[-1] != j1:
        X.append(i1)
        Y.append(j1)

    if swapXY:
        X, Y = Y, X

    return np.array(X), np.array(Y)

# --------------------------------