/**
 * 气象数据下载 —— 以年平均气温与年总降雨量处理下载为例
 *
 * @author CVEO Team
 * @date 2026-01-15
 *
 * 1. 加载 ERA5-Land 数据
 * 2. 合成年度平均气温数据, 年度总降雨量数据
 * 3. 导出 COG 云优化并填补缺失值的 GeoTIFF 影像 (大区域 GEE 自动分块下载)
 */

// 加载研究区域和影像
// var region_name = "应城市";
// var region_name_en = "Yingcheng";
// var region = Yingcheng;
// var target_crs = "EPSG:4526";
var region_name = "保康县";
var region_name_en = "Baokang";
var region = Baokang;
var target_crs = "EPSG:4525";
var target_res = 30;
var start_year = 2021;
var end_year = 2025;
var start_date = start_year + "-01-01";
var end_date = end_year + "-12-31";
var ERA5Bands = ["temperature_2m", "total_precipitation_sum"];
var commonBands = ["temperature", "total_precipitation_sum"];

var region_geo = region.geometry();
var bounds = region_geo.bounds();
var common_filter = ee.Filter.and(
  ee.Filter.bounds(bounds),
  ee.Filter.date(start_date, end_date)
);

/**
 * 开尔文转摄氏度
 * @param {ee.Image} image Landsat LST image
 * @returns {ee.Image} Landsat LST image in Celsius
 */
function kelvinToCelsius(image) {
  return ee.Image(image.expression("B1 - 273.15", { B1: image.select("temperature") }))
    .copyProperties(image)
    .copyProperties(image, ["system:time_start", "system:index", "system:id"]);
}

// 加载 ERA5-Land 数据
var ERA5dataset = ee.ImageCollection("ECMWF/ERA5_LAND/MONTHLY_AGGR")
  .filter(common_filter)
  .select(ERA5Bands, commonBands);
print(start_date + " - " + end_date + " ERA5-Land dataset", ERA5dataset);
var ERA5Tempdataset = ERA5dataset.select("temperature").map(kelvinToCelsius);
var ERA5Raindataset = ERA5dataset.select("total_precipitation_sum");

// 合成年度平均 ERA5-Land 气温数据
var years = ee.List.sequence(start_year, end_year);
var yearlyTemp = ee.ImageCollection.fromImages(
  years.map(function (y) {
    return ERA5Tempdataset.filter(ee.Filter.calendarRange(y, y, "year"))
      .mean()
      .set("year", y);
  })
);
var yearlyRain = ee.ImageCollection.fromImages(
  years.map(function (y) {
    return ERA5Raindataset.filter(ee.Filter.calendarRange(y, y, "year"))
      .sum()
      .set("year", y);
  })
);
if (start_year == end_year) {
  var year_str = start_year;
} else {
  var year_str = start_year + "-" + end_year;
}
print(year_str + " Annual Mean ERA5-Land Temperature dataset", yearlyTemp);
print(year_str + " Annual Mean ERA5-Land Precipitation dataset", yearlyRain);

// 合成处理后会丢失投影信息, 需要重新设置投影
var proj = ERA5dataset.first().select(1).projection();
var annual_mean_temperature = ee.Image(yearlyTemp.mean()).setDefaultProjection(proj);
print(year_str + " Annual Mean ERA5-Land Temperature Histogram", ui.Chart.image.histogram(annual_mean_temperature, region, 10000, 258));

var annual_mean_precipitation = ee.Image(yearlyRain.mean()).setDefaultProjection(proj);
print(year_str + " Annual Mean ERA5-Land Precipitation Histogram", ui.Chart.image.histogram(annual_mean_precipitation, region, 10000, 258));

var annual_mean_temp_1km = annual_mean_temperature.clip(bounds).resample("bicubic").reproject({
  crs: "EPSG:4526",
  scale: 30,
});
var annual_mean_precipitation_1km = annual_mean_precipitation.clip(bounds).resample("bicubic").reproject({
  crs: "EPSG:4526",
  scale: 30,
});

var temperature_vis = {
  min: -20,
  max: 30,
  palette: [
    '040274', '040281', '0502a3', '0502b8', '0502ce', '0502e6',
    '0602ff', '235cb1', '307ef3', '269db1', '30c8e2', '32d3ef',
    '3be285', '3ff38f', '86e26f', '3ae237', 'b5e22e', 'd6e21f',
    'fff705', 'ffd611', 'ffb613', 'ff8b13', 'ff6e08', 'ff500d',
    'ff0000', 'de0101', 'c21301', 'a71001', '911003'
  ],
};

var precipitation_vis = {
  min: 0,
  max: 2,
  palette: [
    '000096', '0064ff', '00b4ff', '33db80', '9beb4a',
    'ffeb00', 'ffb300', 'ff6400', 'eb1e00', 'af0000'
  ],
};

var styling = {
  color: "blue",
  fillColor: "00000000",
};

Map.centerObject(region, 7);
Map.addLayer(annual_mean_temperature, temperature_vis, year_str + " Annual Mean Temperature 0.1 degree");
Map.addLayer(annual_mean_precipitation, precipitation_vis, year_str + " Annual Mean Precipitation 0.1 degree");
Map.addLayer(annual_mean_temp_1km, temperature_vis, year_str + " Annual Mean Temperature " + target_res + "m");
Map.addLayer(annual_mean_precipitation_1km, precipitation_vis, year_str + " Annual Mean Precipitation " + target_res + "m");
Map.addLayer(region.style(styling), {}, region_name);

// 导出合并后的影像
// 明确设置数据类型为Float32, 否则默认类型为Float64, 会占用更多内存
// 并对缺失值进行填充, 否则默认为nan不便于后续本地处理
function exportCOG(image, description, folder, region, scale, crs) {
  image = image.toFloat().unmask(-9999.0);
  // 默认为 EPSG:4526 投影
  crs = crs || "EPSG:4526";
  Export.image.toDrive({
    image: image,
    description: description,
    folder: folder,
    region: region, // 添加后会自动裁剪
    scale: scale,
    crs: crs,
    maxPixels: 1e13, // GEE 最多支持 1e8 像素, 当超过时会自动分块
    fileFormat: "GeoTIFF",
    // 导出COG云优化的GeoTIFF影像, 并明确设置缺失值为-9999.0
    formatOptions: {
      cloudOptimized: true,
      noData: -9999.0,
    },
  });
}

print("Start exporting " + year_str + " Yearly Mean ERA5-Land Temperature (" + target_crs + " " + target_res + "m)", annual_mean_temperature);
exportCOG(
  annual_mean_temperature,
  region_name_en + "_ERA5_Temperature_" + year_str + "_" + target_res + "m",
  "Temperature",
  region,
  target_res,
  target_crs
);
print("Start exporting " + year_str + " Yearly Mean ERA5-Land Precipitation (" + target_crs + " " + target_res + "m)", annual_mean_precipitation);
exportCOG(
  annual_mean_precipitation,
  region_name_en + "_ERA5_Precipitation_" + year_str + "_" + target_res + "m",
  "Precipitation",
  region,
  target_res,
  target_crs
);