var l5 = ee.ImageCollection("LANDSAT/LT05/C01/T1_SR"),
    roi = /* color: #d63000 */ee.Geometry.Polygon(
        [[[77.68018052033392, 31.0091863423649],
          [80.36084458283392, 29.5863837026937],
          [80.98706528595892, 30.233944725529557],
          [78.85571762970892, 31.57247908795104]]]),
    elevation = ee.Image("USGS/SRTMGL1_003"),
    l7 = ee.ImageCollection("LANDSAT/LE07/C01/T1_RT_TOA");

// Defining a filter that gives results for months September to November
var mf = ee.Filter.calendarRange(9, 11, 'month');

Map.centerObject(roi, 9);

// Definig the image collections
var img1 = ee.ImageCollection(l5
            .filterDate('1984-01-01','1999-12-31')
            .filterBounds(roi)
            .filter(mf));
var img2 = ee.ImageCollection(l7
            .filterDate('2000-01-01','2018-12-31')
            .filterBounds(roi)
            .filter(mf));

// add NDWI band function
var addNDWI = function(image) {
  return image
    // NDWI
    .addBands(image.normalizedDifference(['B2', 'B4']).rename('NDWI'))
};

// map add ndwi function to both image collections
var image1 = img1.map(addNDWI);
var image2 = img2.map(addNDWI);

var test2 = image2.median();
Map.addLayer(test2.clip(roi), {}, 'image2');

// masking function for elevation
var mask = function(image) {
  var elevMask = elevation.updateMask(elevation.gt(1500));
  return image.updateMask(elevMask);
};

// masking function for NDWI
var mask1 = function(image){
  var ndwiMask = image.select('NDWI').gte(0.4);
  return image.updateMask(ndwiMask);
};

// map masking functions
var maskedImg = image1.map(mask).map(mask1);     //For 1984-1999
var maskedImg2 = image2.map(mask).map(mask1);    //For 2000-2018

// getting rid of bad pixels
function trimImage(image){
  return image.clip(image.geometry().buffer(-5000));
}

maskedImg2 = maskedImg2.map(trimImage);
print(maskedImg);
print(maskedImg2);

//set up params to view NDWI band
var ndwiViz = {bands: 'NDWI',min: 0.3, palette: ['00FFFF', '0000FF']};

var test = maskedImg.median();
var test1 = maskedImg2.median();

Map.addLayer(test.clip(roi), ndwiViz, 'NDWI 1984-1999');
Map.addLayer(test1.clip(roi), ndwiViz, 'NDWI 2000-2018');