sh.shardCollection = function(fullName, key, unique, options) {
  sh._checkFullName(fullName);
  assert(key, "need a key");
  assert(typeof (key) == "object", "key needs to be an object");

  var calculateInitialShardingStats = function (fullName, key) {
    const CHUNK_SIZE_DEFAULT = 64;
    const BSON_MAX_SIZE      = 16777216;

    var chunkSizeDoc = db.getSiblingDB("config").settings.findOne({ _id: "chunksize" });
    var chunkSize = (chunkSizeDoc !== null) ? chunkSizeDoc.value : CHUNK_SIZE_DEFAULT;

    // collection size prior to sharding
    var namespace = fullName.split('.');
    var collection = db.getSiblingDB(namespace[0]).getCollection(namespace.slice(1).join('.'));
    var stats = collection.stats();
    var collectionSize = stats.shards[stats.primary].size;

    // retrieve a sample document and project only the values defined by the shard key
    var projection = Object.assign({}, key);
    if (!Object.hasOwnProperty("_id"))
        projection["_id"] = 0;
    var sample = collection.aggregate([ { $sample: { size: 1 } }, { $project: projection } ]).toArray()

    var avgKeyValueSize = Object.bsonsize(sample);
    var maxSplits = BSON_MAX_SIZE / avgKeyValueSize;
    var maxCollectionSizeMB = maxSplits * (chunkSize / 2);
 
    return {
      shardKey: key,
      sampleDocumentValues: sample,
      averageShardKeyValueSize: avgKeyValueSize,
      chunkSizeMB: chunkSize,
      maxSplitNum: parseInt(maxSplits),
      collectionSize: collectionSize,
      maxCollectionSize: maxCollectionSizeMB * 1048576 // convert from MB to bytes
    }
  }
  
  var bypassCollectionSizeValidation = false;
  var cmd = { shardCollection: fullName, key: key };

  if (unique) {
    cmd.unique = true;
  }
  if (options) {
    if (typeof (options) !== "object") {
      throw new Error("options must be an object");
    }
    if (options.hasOwnProperty("bypassCollectionSizeValidation") && typeof (options.bypassCollectionSizeValidation) == "boolean") {
      bypassCollectionSizeValidation = options.bypassCollectionSizeValidation;
      delete options.bypassCollectionSizeValidation;
    }
    Object.extend(cmd, options);
  }

  var collectionShardingStats = calculateInitialShardingStats(fullName, key);
  printjson(collectionShardingStats)
  print("The theoretical maximum collection size to shard is: " + collectionShardingStats.maxCollectionSize);
  print("The current collection size is: " + collectionShardingStats.collectionSize);
  if (!bypassCollectionSizeValidation && (collectionShardingStats.collectionSize > collectionShardingStats.maxCollectionSize)) {
    print("Sharding collection aborted due to theoretical maximum collection size being exceeded.")
    print("Set 'options.bypassCollectionSizeValidation' = true to shard anyway");
  }

  return sh._adminCommand(cmd);
}

function setup() {
    use test;
    sh.enableSharding("test");
    db.foo.drop();
    function generate_random_data(size){
        var chars = 'abcdefghijklmnopqrstuvwxyz'.split('');
        var len = chars.length;
        var random_data = [];
    
        while (size--) {
            random_data.push(chars[Math.random()*len | 0]);
        }
    
        return random_data.join('');
    }
    for (var i = 0; i < 100; i++) { db.foo.insert({ d: new Date(), data: generate_random_data(1024) }); }
}

setup();
db.foo.createIndex({ data: 1, d: 1 })
sh.shardCollection("test.foo", { data: 1, d: 1 })

/*
{
	"shardKey" : {
		"data" : 1,
		"d" : 1
	},
	"sampleDocumentValues" : [
		{
			"d" : ISODate("2020-07-02T11:04:00.145Z"),
			"data" : "ycxzwsiybchmdfvllyxwbzasqcoonbyupgudqlwunpspvdmlqmlhguzpgwkhpypukfydvmrlpefasyepnfdioikcbdisynxifdzbargahylffevbsshibbwoaskqzvmfgxyvsvwhbdbrbosshrvtoqbjqsahphcekjhxiseaqdqjzvgiqiszdsbvamjliavgqybljwefwdntcmddoiuhvjbfhsjpnttatgxjsumlkjifjwssudzcydngpsesqudkmxxdruhhbwfsojtrdvgkrwajsfktgyezgnxzjboejioxjhernhaefdxgubiotvikerqilqlselzrttfjmcuiwlkfqhradxmtazzaghxlmaiyiwzyxdvlcetpzrbzhhapfhfctxsshuxcnqmyyuisrhwvfxxanufuxwcskoutxeaiertjpntqcsnwvaeqioiybtoxfmdswecjlmnmhaayvhadjrzanmvjxopnwakkdafcvtllmjxpisijafcdwbzokxxdnyvpovuldoqceiyaxjudewbjidispedpmlfpglokahjycjpyhrqpbzicuecuiivdylcrzwtbkqtthkifjevywtctsrrzuvmdoazffxniertktbwsyzqxkknwxciaircmogydbgvqoisygeifjcvoezpuehjmxjmoivjpoecatyggdfstgiwlmvnxsnovrzvdoiwaftneeklvyjxbtmqfdtfdpqclapzuvryrnynaobpokvxcyiiqsxnjsiqjlliyekrrcvwnhwobcoyighfbmaggzbxivcoqmtiystheevbhcjuapayuybzeofilsbvzrpbklezsvomrarwdexrxyzzmjqnttqthneubffoqktqcxkuvjtyjkpdstatdlwbrjdpyavouteomobfqpmvjzspkoqvznfseqshkhdnpxowgxczzfvjjreaekuyihyulyojoyrvxshqkpuzhztxrdtckngwuvpnuvibpnamslyrpojpjwkgvssbwoxvf"
		}
	],
	"averageShardKeyValueSize" : 1059,
	"chunkSizeMB" : 64,
	"maxSplitNum" : 15842,
	"collectionSize" : 106800,
	"maxCollectionSize" : 531586358282.6365
}
The theoretical maximum collection size to shard is: 531586358282.6365
The current collection size is: 106800
{
	"collectionsharded" : "test.foo",
	"collectionUUID" : UUID("85f43966-69a5-4f37-ae5f-68c0292b512b"),
	"ok" : 1,
	"operationTime" : Timestamp(1593687856, 9),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1593687856, 9),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}
*/