// ------This code is used to calculate the FVC in GEE
// ------Author: Yu Feng, E-mail: fengyu263@163.com
// ------Set study area
var roi = ee.FeatureCollection(muru);
// ------Set start date
var startDate = ee.Date('2000-01-01'); 
// ------Set end date 
var endDate = ee.Date('2000-12-31'); 
// ------Set display parameters
var colorizedVis = {
  min: 0.0,
  max: 1.0,
  palette: ['FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901',
            '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01',
            '012E01', '011D01', '011301'],
};
Map.addLayer(roi, {color: "black"}, "roi",false);
Map.centerObject(roi, 13);
Map.setOptions("SATELLITE");
// ------Landsat image cloud processing
function maskLsr(image) {
  var cloudShadowBitMask = 1 << 4;
  var cloudsBitMask = 1 << 3;
  var qa = image.select('QA_PIXEL');
  var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0)
      .and(qa.bitwiseAnd(cloudsBitMask).eq(0));
  return image.updateMask(mask)
      .select("SR_B[1-7]*")
      .copyProperties(image, ["system:time_start"]);
}
// ------Applies scaling factors(L5/L7)
function applyScaleFactors_L5(image) {
  var opticalBands = image.select('SR_B.').multiply(0.0000275).add(-0.2);
  var thermalBands = image.select('ST_B.*').multiply(0.00341802).add(149.0);
  return image.addBands(opticalBands, null, true)
              .addBands(thermalBands, null, true);
}
// ------Applies scaling factors(L8)
function applyScaleFactors_L8(image) {
  var opticalBands = image.select('SR_B.').multiply(0.0000275).add(-0.2);
  var thermalBands = image.select('ST_B.*').multiply(0.00341802).add(149.0);
  return image.addBands(opticalBands, null, true)
              .addBands(thermalBands, null, true);
}
// ------Filter images
var imageCol = ee.ImageCollection('LANDSAT/LT05/C02/T1_L2')  // 2000-2011 (L5)
                   //    ee.ImageCollection('LANDSAT/LE07/C02/T1_L2')  // 2013 (L7) 
                   //    ee.ImageCollection('LANDSAT/LC08/C02/T1_L2') // 2013-2020 (L8)
                  .filterDate(startDate, endDate)
                  .map(applyScaleFactors_L5)  //  L5 and L7
              // .map(applyScaleFactors_L8)  // L8
                  .map(maskLsr)
                  .filterBounds(roi);
var image = imageCol.median().clip(roi.geometry());
// ------Calculate NDVI
var NDVI = image.normalizedDifference(["SR_B4","SR_B3"]).rename("NDVI");  // L5 and L7
//var NDVI = image.normalizedDifference(["SR_B5","SR_B4"]).rename("NDVI"); //  L8
Map.addLayer(NDVI,colorizedVis,'NDVI');
// ------Calculate FVC
function calFVC(BestVI,region,scale){
    var num = BestVI.reduceRegion({
      reducer:ee.Reducer.percentile([5,95]),
      geometry:region,
      scale:scale,
      maxPixels:1e13
    });
    var min = ee.Number(num.get("NDVI_p5"));
    var max = ee.Number(num.get("NDVI_p95"));
    print(min);
    print(max);
    var greaterPart = BestVI.gt(max);
    var lessPart = BestVI.lt(min);
    var middlePart =ee.Image(1).subtract(greaterPart).subtract(lessPart);
    var tempf1=BestVI.subtract(min).divide(max.subtract(min));
    var FVC=ee.Image(1).multiply(greaterPart).add(ee.Image(0).multiply(lessPart))
                      .add(tempf1.multiply(middlePart))
    return FVC.rename('FVC');
}
var FVC = calFVC(NDVI,roi,30);
// ------Export FVC
Export.image.toDrive({
  image: FVC,
  description: "fvc",
  scale: 30,
  region: roi.geometry(),
  maxPixels: 1e13
});
// ------Calculate the mean FVC
var FVCmean = FVC.reduceRegion({  
  reducer: ee.Reducer.mean(),  
  geometry: roi,   
  scale: 30  
}); 
print("FVC mean value is: ", FVCmean);