from typing import Any
from typing import Optional

"""
same convention as SVG
           W
(0,0)┌───────────► x
     │                
  H  │                
     │                
     │                
     ▼                
     y
grid G store list of rows
to get G(x,y), must first extract row y and then col y => G[y][x]
"""

def grid_geom(G:list[list[Any]]) -> tuple[int,int]:
    H = len(G)
    W = len(G[0])
    return W, H

def in_grid(G:list[list[Any]], x:int, y:int) -> bool:
    W, H = grid_geom(G)
    return x>=0 and x<W and y>=0 and y<H

def get_in_grid(G:list[list[Any]], x:int, y:int) -> Optional[Any]:
    if in_grid(G, x,y):
        return G[y][x]

UP = (0,-1) ; RIGHT = (1,0) ; DOWN = (0,1) ; LEFT = (-1,0)

MOVE4 = [ UP, RIGHT, DOWN, LEFT ]
DIAG4 = [(1,1),(-1,-1),(1,-1),(-1,1)]
MOVE8 = MOVE4 + DIAG4