grid.py

import numpy as np
import random


class Grid:
    """
    2D occupancy grid map for rover navigation.

    Cells are represented as integers:
        0 = free
        1 = obstacle
    """

    def __init__(self, width: int = 20, height: int = 20, obstacle_ratio: float = 0.25):
        """
        Args:
            width: Number of columns.
            height: Number of rows.
            obstacle_ratio: Fraction of cells randomly set as obstacles (0.0-1.0).
        """
        self.width = width
        self.height = height
        self.grid = np.zeros((height, width), dtype=int)
        self._place_obstacles(obstacle_ratio)

    def _place_obstacles(self, ratio: float):
        """Randomly populate obstacles, ensuring start (0,0) and goal are always free."""
        for y in range(self.height):
            for x in range(self.width):
                if random.random() < ratio:
                    self.grid[y][x] = 1
        self.grid[0][0] = 0
        self.grid[self.height - 1][self.width - 1] = 0

    def is_free(self, x: int, y: int) -> bool:
        """Return True if (x, y) is within bounds and not an obstacle."""
        return 0 <= x < self.width and 0 <= y < self.height and self.grid[y][x] == 0

    def get_neighbors(self, x: int, y: int) -> list:
        """Return free 4-connected neighbors of (x, y)."""
        directions = [(0, 1), (1, 0), (0, -1), (-1, 0)]
        return [(x+dx, y+dy) for dx, dy in directions if self.is_free(x+dx, y+dy)]