import xarray as xr


def generate_grid_file_from_netcdf(input_file, output_grid_file, resolution):
    """
    從 NetCDF 檔案自動生成目標網格文件。

    :param input_file: NetCDF 檔案路徑
    :param output_grid_file: 目標網格文件名
    :param resolution: 目標網格解析度（度）
    """
    # 載入 NetCDF 檔案
    dataset = xr.open_dataset(input_file) # .nc檔案
    lat = dataset["XLAT"] #緯度
    lon = dataset["XLONG"] #經度

    # 獲取經緯度範圍
    lat_min, lat_max = lat.min().item(), lat.max().item()
    lon_min, lon_max = lon.min().item(), lon.max().item()
    print(f"Latitude range: {lat_min} to {lat_max}")
    print(f"Longitude range: {lon_min} to {lon_max}")

    # 計算網格點數
    x_size = int((lon_max - lon_min) / resolution) + 1
    y_size = int((lat_max - lat_min) / resolution) + 1

    # 生成網格文件
    with open(output_grid_file, "w") as f:
        f.write("gridtype = latlon\n")
        f.write(f"xsize    = {x_size}\n")
        f.write(f"ysize    = {y_size}\n")
        f.write(f"xfirst   = {lon_min}\n")
        f.write(f"xinc     = {resolution}\n")
        f.write(f"yfirst   = {lat_min}\n")
        f.write(f"yinc     = {resolution}\n")
    print(f"Grid file '{output_grid_file}' has been created.")


input_nc_file = "input.nc"  # 原始 NetCDF 檔案
grid_file = "grid_2km.txt"  # 目標網格文件
resolution = 0.018  # 2km ≈ 0.018度

generate_grid_file_from_netcdf(input_nc_file, grid_file, resolution)