/** 
 * Example GEE Script for Exploring Global Land Cover mapping and Estimation (GLANCE) 
 * Catalog -- Example 1: Loading datasets for a time range
 * 
 * Preliminary citation: 
 * 
 * Friedl, M.A., Woodcock, C.E., Olofsson, P., Zhu, Z., Loveland, T., 
 * Stanimirova, R., Arévalo, P., Bullock, E., Hu, K.-T., Zhang, Y., Turlej, K., 
 * Tarrio, K., McAvoy, K., Gorelick, N., Wang, J.A., Barber, C.P., Souza, C., 2022. 
 * Medium Spatial Resolution Mapping of Global Land Cover and Land Cover Change 
 * Across Multiple Decades From Landsat. Frontiers in Remote Sensing 3. 
 * https://doi.org/10.3389/frsen.2022.894571
 * 
 * User guide: https://lpdaac.usgs.gov/documents/1567/GLanCE_User_Guide_v1.pdf 
 * 
 * Authors: 
 *         Yingtong Zhang | zhangyt@bu.edu
 *         Paulo Arévalo  | parevalo@bu.edu 
 */


var GLANCE = ee.ImageCollection("projects/GLANCE/DATASETS/V001")
var palettes = require('users/gena/packages:palettes')

// -------------- SET GLOBAL VIZ PROPERTIES
Map.setOptions('HYBRID')
// Land cover Palette
var LCPalette = ['#386cb0', 'white', 'red', '#68666B', '#336600', '#28A765', '#ffff99']
var classes = ['Water', 'Snow/Ice', 'Developed', 'Bare', 'Forest', 'Shrub', 'Herbaceous']
var LCpal = {min: 1, max: 7, palette: LCPalette}

// EVI Palette
var eviPal = {palette: palettes.matplotlib.viridis[7], min:-100, max: 4000}
var eviRatePal = {palette: palettes.matplotlib.viridis[7], min:-700, max: 700}
// Change Palette
var doyPal = {palette: palettes.matplotlib.viridis[7], min:1, max: 365}


// Load the data for a certain year; can also be filtered by other properties
var filtered = GLANCE.filterDate('2015-01-01', '2016-01-01').mosaic()

// -------------- LAND COVER --------------
Map.addLayer(filtered.select('LC'), LCpal,'LC')

// -------------- EVI2--------------
Map.addLayer(filtered.select('EVI2median'), eviPal, "EVI2median",0)
Map.addLayer(filtered.select('EVI2amplitude'), eviPal, "EVI2amplitude",0)
Map.addLayer(filtered.select('EVI2rate'), eviRatePal, "EVI2rate",0)

// -------------- CHANGE --------------
Map.addLayer(filtered.select('changeDate'), doyPal, "Change day",0)
Map.addLayer(filtered.select('changeMag'), eviPal, "Change magnitude",0)
Map.addLayer(filtered.select('prevClass'), LCpal, "Previous class",0)

Map.setCenter(-52.9496, -6.1690, 11)

/** 
 * Example GEE Script for Exploring Global Land Cover mapping and Estimation (GLANCE) 
 * Catalog -- Example 2: Year of change and EVI2 change  
 * 
 * Preliminary citation: 
 * 
 * Friedl, M.A., Woodcock, C.E., Olofsson, P., Zhu, Z., Loveland, T., 
 * Stanimirova, R., Arévalo, P., Bullock, E., Hu, K.-T., Zhang, Y., Turlej, K., 
 * Tarrio, K., McAvoy, K., Gorelick, N., Wang, J.A., Barber, C.P., Souza, C., 2022. 
 * Medium Spatial Resolution Mapping of Global Land Cover and Land Cover Change 
 * Across Multiple Decades From Landsat. Frontiers in Remote Sensing 3. 
 * https://doi.org/10.3389/frsen.2022.894571
 * 
 * User guide: https://lpdaac.usgs.gov/documents/1567/GLanCE_User_Guide_v1.pdf 
 * 
 * Authors: 
 *         Yingtong Zhang | zhangyt@bu.edu
 *         Paulo Arévalo  | parevalo@bu.edu
 */

var GLANCE = ee.ImageCollection("projects/GLANCE/DATASETS/V001")
var palettes = require('users/gena/packages:palettes')


// -------------- SET GLOBAL VIZ PROPERTIES
Map.setOptions('HYBRID')

// EVI Palette
var eviChangePal = {palette: palettes.matplotlib.viridis[7], min:-1000, max: 1000}
var eviPal = {palette: palettes.matplotlib.viridis[7], min:2000, max: 3000}

// Change Palette
var changePalette = ['#ffffcc','#ffeda0','#fed976','#feb24c','#fd8d3c','#fc4e2a',
  '#e31a1c','#bd0026','#800026']
var changePal = {palette: changePalette, min:2005, max: 2020}


// -------------- FILTER AND SELECT DATASETS
var filteredCol = GLANCE.filterDate('2005-01-01', '2020-01-01')
var changeDate = filteredCol.select('changeDate')
var EVI2change = filteredCol.select('changeMag')
var EVI2median = filteredCol.select('EVI2median')

// --------------  CREATE ANNUAL MOSAICS

// Extract list of available years from image id. 
// Keep in mind change layers are only available from 2002
var imageIds = changeDate.aggregate_array('id')

var years = ee.List(imageIds.map(function(value){
  return ee.String(value).split("-").get(0)
})).distinct()

// Create constant image with years, useful for indexing
var dateDictImg = ee.Dictionary.fromLists(
  years, years.map(function(x){return ee.Number.parse(x)})).toImage()

// Function to retrieve annual mosaics per dataset
var getYearlyStack = function(imgCol, yearsStr){
  return ee.ImageCollection.fromImages(
    yearsStr.map(function(y) {
      // Get the list of image IDs for the current year
      return imgCol.filter(ee.Filter.stringContains('system:index', y)).mosaic()
    })
  ).toBands()
}

// Generate annual mosaics of change date, and retrieve year of first change
var changeYear = dateDictImg
  .updateMask(getYearlyStack(changeDate, years))
  .reduce(ee.Reducer.firstNonNull())

// Generate annual mosaics of EVI2 change, and retrieve value for year of first change
var EVI2firstChange = getYearlyStack(EVI2change, years)
  .updateMask(changeYear)
  .reduce(ee.Reducer.firstNonNull())

// --------------  VISUALIZE -------------- 

// Year of first change and magnitude of EVI2 change for that year
Map.addLayer(changeYear, changePal, "Change year")
Map.addLayer(EVI2firstChange, eviChangePal, "First EVI2 change", 0)


// Average EVI2 median 3 years before and after the first change
var EVI2medianStack = getYearlyStack(EVI2median, years)
var yearWindow = 3
var beforeChange = dateDictImg
  .lt(changeYear)
  .and(dateDictImg.gte(changeYear.subtract(yearWindow)))
var afterChange = dateDictImg
  .gt(changeYear)
  .and(dateDictImg.lte(changeYear.add(yearWindow)))

Map.addLayer(EVI2medianStack.updateMask(beforeChange).reduce(ee.Reducer.mean()), 
  eviPal, "EVI2 before change", 0)
Map.addLayer(EVI2medianStack.updateMask(afterChange).reduce(ee.Reducer.mean()),
  eviPal, "EVI2 after change", 0)


// Function to automate the creation of a legend
function createLegend(viz){
  var lon = ee.Image.pixelLonLat().select('longitude')
  var gradient = lon.multiply((viz.max-viz.min)/100.0).add(viz.min)
  var legendImage = gradient.visualize(viz)
  var params = {bbox:'0,0,100,10', dimensions:'200x10'}
  var thumbnail = ui.Thumbnail({
    image: legendImage,
    params: params,
  })
  
  var panel = ui.Panel([
    ui.Label(viz['min']), thumbnail,  ui.Label(viz['max']),
  ], ui.Panel.Layout.Flow('horizontal'))
  
  return panel
}

// Print legends to the console
print("Change Year", createLegend(changePal))
print("EVI2 Change Magnitude x10,000", createLegend(eviChangePal))
print("EVI2 median", createLegend(eviPal))

Map.setCenter(-61.9446, -21.6216, 11)