// Javascript

var Berlin = ee.Geometry.Point([13.40619231451105, 52.51970379595016]);

// add Landsat footprint for point marker
var wrs2_descending = ee.FeatureCollection('users/gaertnerp/Blog/WRS2_descending');
var wrs2_filtered = wrs2_descending.filterBounds(Berlin); // filter footprint to aoi

Map.addLayer(wrs2_filtered, {},'Landsat footprint', true, 0.3);  // add layer to map


Map.setOptions('TERRAIN');      // change basemap
Map.centerObject(Berlin, 7);    // center map to Berlin

var now = Date.now();
var eeNow = ee.Date(now);

// Javascript

// #### Landsat 8 ####

var L8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
.filterBounds(Berlin)
.filterDate('2015-06-23', eeNow)
.map(function(image) {
  var date = ee.Date(image.get('system:time_start')).format("YYYY-MM-dd");
  date = ee.Date(date);
    return image.set('date', date);
  })
  .map(function(image) {
  var ID = ee.String(image.get('system:index'));
    return image.set('ID', ID);
  })
  .map(function(image) {
  var date = ee.Date(image.get('system:time_start'));
    return image.set('date_time', date);
  });


// ### Sentinel 2 ####

var S2 = ee.ImageCollection('COPERNICUS/S2')
.filterBounds(Berlin)
.map(function(image) {
  var date = ee.Date(image.get('system:time_start')).format("YYYY-MM-dd");
    return image.set('date', ee.Date(date));
  })
  .map(function(image) {
  var ID = ee.String(image.get('system:index'));
    return image.set('ID', ID);
  })
  .map(function(image) {
  var date = ee.Date(image.get('system:time_start'));
    return image.set('date_time', date);
  });
  

// Javascript

// Get FeatureCollection from ImageCollection
var L8_FC = ee.FeatureCollection(L8).select([
  'ID','date','date_time','CLOUD_COVER','SATELLITE','system:index'
]);

var S2_FC = ee.FeatureCollection(S2).select([
  'ID','date','date_time','CLOUDY_PIXEL_PERCENTAGE','SPACECRAFT_NAME','system:index'],
 ['ID','date','date_time','CLOUD_COVER'            ,'SATELLITE'      ,'system:index']);

// Get all matches between the 'date' 
// elements of two collections

// the equals filter specifies how the collections match ('date')
var toyFilter = ee.Filter.equals({ leftField: 'date', rightField: 'date'});

// define the join.
var innerJoin = ee.Join.inner('primary', 'secondary');

// apply the join.
var joined = innerJoin.apply(L8_FC, S2_FC, toyFilter);


// #### Select Matches for 

var flattener = function(feat){
  return ee.Feature(ee.Feature(feat).get('primary'));
};
var sel_primary = joined.map(flattener);


var flattener = function(feat){
  return ee.Feature(ee.Feature(feat).get('secondary'));
};
var sel_secondary = joined.map(flattener);


// Merge & Sort by Date
var merged_selection = sel_secondary.merge(sel_primary).sort('date');

// get unique matching dates
var distinct_dates = sel_primary.select('date').distinct(['date']).sort('date');

// Javascript


// Create a new property with default dates but original times for the x-axis.
var all_dates_to_default_date = function(feature) {
  
  var xx         = feature.get('date_time');
  var equal_time = ee.Date(xx).update({year: 2000, month: 1, day:1});
  var add_3h     = ee.Date(equal_time).advance({delta:3,unit:'hour'}); // add 3 hours
  
  return feature.set({time_default: add_3h});
  
};

merged_selection = merged_selection.map(all_dates_to_default_date);

// Create a ScatterChart witch all dates when L8 & S2 where at the same location

var chart_date = ui.Chart.feature.groups(merged_selection, 'time_default', 'date', 'SATELLITE')
    .setChartType('ScatterChart')
    .setOptions({
      width: 600,
      height: 400,
      crosshair: { 
        trigger: 'both' ,
        opacity: 0.5 ,
        orientation: 'both'
      },
      title: 'When Landsat-8 (almost) meets the Sentinels',
      hAxis: {title: 'Time',
        gridlines: {
            count: -1,
            units: {
              hours: {format: ['HH:mm']}
            }
          }
      },
      vAxis: {title: 'Date'},
      tooltip: {isHtml: true},
    });

print(chart_date);

// Javascript


var flattener_get_diff = function(feat){
  
  feat             = ee.Feature(feat);
  var primary_f    = ee.Feature(feat.get('primary')); // primary is L8
  var L8_date_time = primary_f.get('date_time');

  var secondary_f  = ee.Feature(feat.get('secondary')); // primary is S2
  var S2_ID        = secondary_f.get('ID');             // image ID
  var S2_date_time = secondary_f.get('date_time');
  var date_str     = secondary_f.get('date');
  date_str         = ee.Date(date_str).format("YYYY-MM-dd");
  
  // absolute difference between the S2 & L8 sensing times in minutes
  var time_diff    = ee.Date(S2_date_time).difference(L8_date_time, 'minute').abs(); 
  
  return primary_f.set('date_str', date_str).set('S2/L8', time_diff).set('S2_ID', S2_ID);

};

var primary_f = joined.map(flattener_get_diff)
primary_f = primary_f.sort('S2/L8').limit(5) // Select the Top 5 with the smallest difference

// Make BarChart with the Top 5.
var chart1 = ui.Chart.feature.byProperty({features: primary_f,xProperties: ['S2/L8'], seriesProperty: 'date_str'})
    .setChartType('BarChart')
    .setOptions({
      title: 'Top 5: Days with the smallest time difference between Landsat and Sentinel scenes',
      hAxis: { title: 'Time difference between Landsat 8 and Sentinel (Minutes)',
               minValue: 0},
      vAxis: { title: 'Top 5 Days' }
});
print(chart1);

//Javascript

// #### Load Images with the smallest difference to the Map. ####

// #LANDSAT-8

var L8_ID = primary_f.first().get('ID'); // get the L8 image ID

var srCollection = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
  .filterBounds(Berlin) 
  .filterMetadata('system:index','equals' ,L8_ID);

var L8_vizParams = {
  bands: ['B5', 'B4', 'B3'],
  min: 0,
  max: 4000,
  gamma: [0.95, 1.1, 1]
};

var L8_img = ee.Image(srCollection.first());
Map.addLayer(L8_img, L8_vizParams, 'Landsat8');

// Sentinel 2

var S2_ID = primary_f.first().get('S2_ID'); // get the S2 image ID

var srCollection_S2 = ee.ImageCollection('COPERNICUS/S2')
  .filterBounds(Berlin) 
  .filterMetadata('system:index','equals' ,S2_ID);

var S2_vizParams = {
  bands: ['B8', 'B4', 'B3'],
  min: 0,
  max: 4000,
  gamma: [0.95, 1.1, 1]
};

var S2_img = ee.Image(srCollection_S2.first());
Map.addLayer(S2_img, S2_vizParams, 'Sentinel', 0.7, true);