BASE32 = "0123456789bcdefghjkmnpqrstuvwxyz"

# 邻居查找表（纬度和经度交替变化）
NEIGHBORS = {
    "even": {
        "N": "p0r21436x8zb9dcf5h7kjnmqesgutwvy",
        "S": "14365h7k9dcfesgujnmqp0r2twvyx8zb",
        "E": "bc01fg45238967deuvhjyznpkmstqrwx",
        "W": "238967debc01fg45kmstqrwxuvhjyznp"
    },
    "odd": {
        "N": "bc01fg45238967deuvhjyznpkmstqrwx",
        "S": "238967debc01fg45kmstqrwxuvhjyznp",
        "E": "p0r21436x8zb9dcf5h7kjnmqesgutwvy",
        "W": "14365h7k9dcfesgujnmqp0r2twvyx8zb"
    }
}

# 边界字符（用于计算超出边界的情况）
BORDERS = {
    "even": {"N": "prxz", "S": "028b", "E": "bcfguvyz", "W": "0145hjnp"},
    "odd":  {"N": "bcfguvyz", "S": "0145hjnp", "E": "prxz", "W": "028b"}
}

def encode_geohash(lat, lng, precision=7):
    """手动实现 GeoHash 编码"""
    lat_range = [-90.0, 90.0]
    lng_range = [-180.0, 180.0]
    
    binary = ""
    is_even = True  # 纬度和经度交替编码
    
    while len(binary) < precision * 5:
        mid = (lng_range[0] + lng_range[1]) / 2 if is_even else (lat_range[0] + lat_range[1]) / 2
        if (lng if is_even else lat) >= mid:
            binary += "1"
            if is_even:
                lng_range[0] = mid
            else:
                lat_range[0] = mid
        else:
            binary += "0"
            if is_even:
                lng_range[1] = mid
            else:
                lat_range[1] = mid
        is_even = not is_even
    
    # 5 位二进制转 Base32
    return "".join(BASE32[int(binary[i:i+5], 2)] for i in range(0, len(binary), 5))

def decode_geohash(geohash):
    """解码 GeoHash 到 (lat, lng)"""
    lat_range = [-90.0, 90.0]
    lng_range = [-180.0, 180.0]
    
    binary = "".join(f"{BASE32.index(c):05b}" for c in geohash)
    
    is_even = True
    for bit in binary:
        if is_even:
            mid = (lng_range[0] + lng_range[1]) / 2
            lng_range = [mid, lng_range[1]] if bit == "1" else [lng_range[0], mid]
        else:
            mid = (lat_range[0] + lat_range[1]) / 2
            lat_range = [mid, lat_range[1]] if bit == "1" else [lat_range[0], mid]
        is_even = not is_even
    
    return (sum(lat_range) / 2, sum(lng_range) / 2)

def get_neighbor(geohash, direction):
    """计算 GeoHash 的单个方向邻居"""
    if not geohash:
        return None
    
    precision = len(geohash)
    last_char = geohash[-1]  # 取最后一个字符
    geohash_prefix = geohash[:-1]  # 除去最后一个字符

    is_even = (precision % 2) == 0  # 判断奇偶精度
    type_key = "even" if is_even else "odd"

    # 如果当前 GeoHash 位于边界，需要递归调整前缀
    if last_char in BORDERS[type_key][direction] and geohash_prefix:
        geohash_prefix = get_neighbor(geohash_prefix, direction)
    
    # 计算相邻 GeoHash
    new_last_char = BASE32[NEIGHBORS[type_key][direction].index(last_char)]
    return geohash_prefix + new_last_char

def get_all_neighbors(geohash):
    """计算 GeoHash 的 8 个相邻格子"""
    return {
        "N": get_neighbor(geohash, "N"),
        "S": get_neighbor(geohash, "S"),
        "E": get_neighbor(geohash, "E"),
        "W": get_neighbor(geohash, "W"),
        "NE": get_neighbor(get_neighbor(geohash, "N"), "E"),
        "NW": get_neighbor(get_neighbor(geohash, "N"), "W"),
        "SE": get_neighbor(get_neighbor(geohash, "S"), "E"),
        "SW": get_neighbor(get_neighbor(geohash, "S"), "W")
    }

if __name__ ==  '__main__':
    # 示例：计算北京天安门广场（39.9087, 116.3975）的邻居
    gh = encode_geohash(39.9087, 116.3975, precision=7)
    neighbors = get_all_neighbors(gh)

    print(f"中心 GeoHash: {gh}, {decode_geohash(gh)}")
    print("相邻 GeoHash:")
    for direction, neighbor in neighbors.items():
        print(f"{direction}: {neighbor}, {decode_geohash(neighbor)}")