// ------------------------------------------------------------------------------------------------------------------------------------------------------
// Extract Satellite Records Thom Brade 2019_12_13
// > For the drone areas - in this case converted to raster for the purpose of uploading and managing
// > Aim is monthly averages (climatologies) for all instruments and for all bands for each drone survey area
// https://developers.google.com/earth-engine/sentinel1
// ------------------------------------------------------------------------------------------------------------------------------------------------------

// ######################################################################################################################################################
// Load in drone raster (coded by id)
// ######################################################################################################################################################

Map.setCenter(34.67, -18.97, 12);

// ######################################################################################################################################################
// Date variables
// https://developers.google.com/earth-engine/sentinel1
// ######################################################################################################################################################

var s1Start = ee.Date("2014-01-01"); var s1End = ee.Date("2019-10-31");

// ######################################################################################################################################################
// Sentinel 1 2014-present
// ######################################################################################################################################################

// ------------------------------------------------------------------------------------------------------------------------------------------------------
// BAND RATIO FUNCTION
// ------------------------------------------------------------------------------------------------------------------------------------------------------

var addBandRatio = function(image){

  var ratio_dB = image.addBands(image.select('VV').divide(image.select('VH')).rename('Ratio_dB'));
  var ratio_natural = image.addBands(image.select('VV_natural').divide(image.select('VH_natural')).rename('Ratio_natural'));

  return image.addBands(ratio_dB.addBands(ratio_natural));

};


var addNaturalUnits = function(image){

  var natural_VV = ((image.select('VV').lt(0).multiply(10)).pow(image.select('VV').divide(10))).rename('VV_natural');
  var natural_VH = ((image.select('VH').lt(0).multiply(10)).pow(image.select('VH').divide(10))).rename('VH_natural');

  return(image.addBands(natural_VV).addBands(natural_VH));
};

// ------------------------------------------------------------------------------------------------------------------------------------------------------
// MAKE COLLECTION
// ------------------------------------------------------------------------------------------------------------------------------------------------------

var s1coll = ee.ImageCollection("COPERNICUS/S1_GRD")
  .filterBounds(sa)
  .filterDate(s1Start,s1End)
  .filter(ee.Filter.eq('instrumentMode', 'IW'))
   // Filter to get images with VV and VH dual polarization.
  .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
  .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))

//print(addNaturalUnits(s1coll.first()))
s1coll = s1coll.map(addNaturalUnits);
s1coll = s1coll.map(addBandRatio);

print(s1coll.first());

// ------------------------------------------------------------------------------------------------------------------------------------------------------
// map a function that adds a band for day of year and year

var addDates = function(image){
  var doy = image.date().getRelative('day', 'year');
  var doyBand = ee.Image.constant(doy).uint16().rename('doy');
  var mon = image.date().get('month');
  var monBand = ee.Image.constant(mon).uint16().rename('month');
  var year = image.date().get('year');
  var yearBand = ee.Image.constant(year).uint16().rename('year');
 return image.addBands(doyBand).addBands(monBand).addBands(yearBand);
};

s1coll = s1coll.map(addDates);
print(s1coll,10);

// ------------------------------------------------------------------------------------------------------------------------------------------------------
// Period of interest?

// var series1 = ui.Chart.image.doySeriesByYear(
//     s1coll,'Ratio' ,sa, ee.Reducer.median(), 500);
// print(series1);

// ------------------------------------------------------------------------------------------------------------------------------------------------------
// GET STATISTICS
// ------------------------------------------------------------------------------------------------------------------------------------------------------

// ------------------------------------------------------------------------------------------------------------------------------------------------------
// Combine reducers for single pass (can add as many as needed here)
var reducer = ee.Reducer.percentile([50,70,90])
  .combine({reducer2: ee.Reducer.stdDev(), sharedInputs: true});

// ------------------------------------------------------------------------------------------------------------------------------------------------------
// Function to iterate reduceRegions on collection
var statsfun = function(image,list){
  var newimg = image.reduceRegions({
    collection: zones,
    reducer: reducer,
    scale: 30
  });
  return ee.List(list).add(newimg);
};

var list = ee.List([]);

var stats = ee.List(s1coll.iterate(statsfun,list));

var statsOut = ee.FeatureCollection(stats).flatten();


// ------------------------------------------------------------------------------------------------------------------------------------------------------
// Export the processed  FeatureCollection.
// ------------------------------------------------------------------------------------------------------------------------------------------------------

Export.table.toDrive({
  collection: statsOut,
  description: 's1result',
  fileFormat: 'CSV'
});


Map.addLayer(s1coll.select('Ratio_natural').median(), {min:0,max:5}, 'Ratio')

Map.addLayer(s1coll.select('Ratio_natural').median().gt(5), {palette:['yellow','red']}, 'Damage')