CSV Import: Redo the logic for repeating timestamp

This way, it will re-import old imports just fine.
For new imports, the order of timestamps in the CSV files will have to
be  the same, always. So, either using the same dumps or enforcing order
on the CSV dump is required.

packages/rocketchat-importer-csv/server.js

@@ -286,7 +286,7 @@ Importer.CSV = class ImporterCSV extends Importer.Base {
 
 				const room = RocketChat.models.Rooms.findOneById(csvChannel.rocketId, { fields: { usernames: 1, t: 1, name: 1 } });
 				Meteor.runAsUser(startedByUserId, () => {
-					let roomCounter = 0;
+					const timestamps = {};
 					for (const [msgGroupData, msgs] of messagesMap.entries()) {
 						super.updateRecord({ 'messagesstatus': `${ ch }/${ msgGroupData }.${ msgs.messages.length }` });
 						for (const msg of msgs.messages) {
@@ -298,8 +298,15 @@ Importer.CSV = class ImporterCSV extends Importer.Base {
 
 							const creator = this.getUserFromUsername(msg.username);
 							if (creator) {
+								let suffix = '';
+								if (timestamps[msg.ts] === undefined) {
+									timestamps[msg.ts] = 1;
+								} else {
+									suffix = `-${ timestamps[msg.ts] }`;
+									timestamps[msg.ts] += 1;
+								}
 								const msgObj = {
-									_id: `csv-${ csvChannel.id }-${ roomCounter }-${ msg.ts }`,
+									_id: `csv-${ csvChannel.id }-${ msg.ts }${ suffix }`,
 									ts: new Date(parseInt(msg.ts)),
 									msg: msg.text,
 									rid: room._id,
@@ -310,7 +317,6 @@ Importer.CSV = class ImporterCSV extends Importer.Base {
 								};
 
 								RocketChat.sendMessage(creator, msgObj, room, true);
-								roomCounter += 1;
 							}
 
 							super.addCountCompleted(1);