/**** Start of imports. If edited, may not auto-convert in the playground. ****/
var imgcol_gpp = ee.ImageCollection("MODIS/006/MOD17A2H"),
    imgcol_PMLV1 = ee.ImageCollection("projects/pml_evapotranspiration/PML/OUTPUT/PML_V1_8day");
/***** End of imports. If edited, may not auto-convert in the playground. *****/
var pkg_export = require('users/kongdd/public:pkg_export.js');

// var pkg_modis   = require('users/kongdd/public:pkg_modis.js');
/**
 * This function is used to convert 8-day product into monthly
 */ 

var pkg_modis  = {};

pkg_modis.duration = function(dateRange, unit){
    unit = unit || 'day';
    dateRange = ee.DateRange(dateRange);
    return dateRange.end().difference(dateRange.start(), unit);
};


/**
 * Sum 8-day images into monthly by weights, which are generated by overlapping 
 * days with current month.  
 */
pkg_modis.d8_to_monthly_img = function(imgcol, date_month){
    var bandnames = imgcol.first().bandNames();

    // 1. filter images
    var monthDate_start = ee.Date(date_month);
    var monthDate_end   = monthDate_start.advance(1, 'month')
        .advance(-1, 'day');
    var monthDate_range = ee.DateRange(monthDate_start, monthDate_end);
    var monthdays = monthDate_end.difference(monthDate_start, 'day').add(1);
    
    var filter = ee.Filter.or(
        ee.Filter.dateRangeContains({
            leftValue: monthDate_range,
            rightField:'system:time_start'
        }), 
        ee.Filter.dateRangeContains({
            leftValue: monthDate_range,
            rightField:'date_end'
        })
    );
    
    var imgcol_i = imgcol.filter(filter)
        // .aside(print)
        .map(function(img){
            var date_start = ee.Date(img.get('system:time_start'));
            var date_end   = ee.Date(img.get('system:time_end'));
            
            var range_sect = monthDate_range.intersection(ee.DateRange(date_start, date_end));
            var days = pkg_modis.duration(range_sect);
            // print(range_sect);
            return img
                .set('range_sect', range_sect)
                .set('duration_day', days)
                .set('duration_month', days.divide(monthdays))
                .set('date_start', date_start)
                .set('date_end' , date_end);
        });
    // 2. get weights
    // print(imgcol_i);
    var mask = imgcol_i.first().mask();
    
    imgcol_i = imgcol_i.map(function(img){
        return img.unmask(-999.0);
    });
    
    var array  = imgcol_i.toArray(); // [ntime, 1]
    var weight = imgcol_i.aggregate_array('duration_month');
    weight = ee.Image(ee.Array([weight]));    // [1, ntime]
    // weight = weight.updateMask(mask.select(0));
    
    // x_month = x_daily * monthDays
    var res = ee.Image(weight).matrixMultiply(array).multiply(monthdays)
        .arrayProject([1]).arrayFlatten([bandnames])  // 2d to bands
        .set('system:time_start', monthDate_start.millis())
        .set('system:index', monthDate_start.format('yyyy_MM_dd'))
        .updateMask(mask);
    res = res.set('images', imgcol_i.toList(100));
    
    
    // pkg_export.ExportImg(res, 'test2', range, cellsize, type, folder);
    // Map.addLayer(array, {}, 'array');
    // Map.addLayer(weight, {}, 'weight');
    // Map.addLayer(imgcol_i, {}, 'raw x');
    // Map.addLayer(res, {}, 'x');

    return ee.Image(res);
};


pkg_modis.d8_to_monthly = function(imgcol){
    imgcol = ee.ImageCollection(imgcol);
    
    // First, subtract 1sec for date_end to fix DateRange
    imgcol = imgcol.map(function(img){
        var date_start = ee.Date(img.get('system:time_start'));
        var date_end   = ee.Date(img.get('system:time_end')).advance(-1, 'second');
        
        var date_month = ee.Date.fromYMD(date_start.get('year'), date_start.get('month'), 1);
        return img
            .set('date_start', date_start)
            .set('date_end'  , date_end)
            .set('date_month', date_month); 
    });
    // print(imgcol.limit(3));
    
    var months = ee.Dictionary(imgcol.aggregate_histogram('date_month')).keys();
    var res    = months.map(function(date_month){
        return pkg_modis.d8_to_monthly_img(imgcol, date_month);
    });
    
    // var x = pkg_modis.d8_to_monthly_img(imgcol, months.get(0));
    
    res = ee.ImageCollection(res);
    return res;
};


var debug = true;
if (debug){
    var filter = ee.Filter.calendarRange(2016, 2016, 'year');
    var imgcol = imgcol_PMLV1.select([0, 1, 2, 3]) //(['Gpp', 'PsnNet'])
        .filter(filter)
        .map(function(img){
            var date = ee.Date(img.get('system:time_start'));
            return img.set('system:time_end', date.advance(8, 'day'));
        });
    // print(imgcol);
    
    var res = pkg_modis.d8_to_monthly(imgcol);
    var img = res.first().expression('b(0) + b(1) + b(2)');
    var pkg_vis  = require('users/kongdd/public:pkg_vis.js');
    var vis_vi   = {min: 0, max: 1500, palette:pkg_vis.colors.RdYlGn[11]};
    
    var lg_vi    = pkg_vis.grad_legend(vis_vi  , 'ET');
    Map.addLayer(img, vis_vi, 'ET');
    
    var range = [-180, -60, 180, 90], 
        cellsize = 1/4, 
        type = 'drive',
        folder = 'PML', 
        crs = 'EPSG:4326';
    // pkg_export.ExportImgCol(res, undefined, range, cellsize, type, folder, crs, undefined, 'PMLV1_monthly_');
    
    // print(res);
    Map.addLayer(imgcol, {}, 'imgcol raw');   
    Map.addLayer(res   , {}, 'imgcol monthly');    
}