from typing import Optional, Dict, Tuple

from util.PathDefinitions import WeightedGraph, Location
from util.PriorityQueue import PriorityQueue


def heuristic(a: Tuple[int, int], b: Tuple[int, int]) -> float:
    (x1, y1) = a

    (x2, y2) = b
    return abs(x1 - x2) + abs(y1 - y2)


def a_star_search(graph: WeightedGraph, start: Tuple[int, int], goal: Tuple[int, int]):
    frontier = PriorityQueue()
    frontier.put(start, 0)
    came_from: Dict[Location, Optional[Location]] = {}
    cost_so_far: Dict[Location, float] = {}
    came_from[start] = None
    cost_so_far[start] = 0

    while not frontier.empty():
        current: Location = frontier.get()

        if current == goal:
            break

        for next in graph.neighbors(current):
            new_cost = cost_so_far[current] + graph.cost(current, next)
            if next not in cost_so_far or new_cost < cost_so_far[next]:
                cost_so_far[next] = new_cost
                priority = new_cost + heuristic(next, goal)
                frontier.put(next, priority)
                came_from[next] = current

    return came_from, cost_so_far.keys()