Split Gmail thread and label by date in a google script - google-apps-script

Question

Hy,
I have a server sending me several log mails by day and I want to automaticly label this mails.
I can't touch the server configuration to adapt the mail subject, so the work must be done by "receiver".
The Subject is still same so gmail merge them in a thread of 100, but I want to split them by date. So One Date, one thread. In addition, I want label them whith a nested label: "Server1" -> "Date"
I've only found a way to add label to the thread in globality and no way to split them.
Is it even possible?
After a new look on my issue, perhaps add the date at the message subject can split threads.
Like:
function AddLogSubjectADate() {
var threads = GmailApp.search('from:sender#server.com has:nouserlabels');
threads.forEach(function(messages){
messages.getMessages().forEach(function(msg){
var date = msg.getDate();
var date_of_mail = Utilities.formatDate(date, "GMT+1", "yyyy/MM/dd")
var subj = msg.getSubject()
var newsubj = subj + date_of_mail
//A way to modify subject
});
});
}
But I didn't find a way to change the subject.
Post Scriptum
I don't think it's relevant, but here is my previous work. but it add label to the thread. Like I said I haven't find a way to split threads.
function AddLogLabelbyDate() {
var today = new Date();
var tomorrow = new Date();
var yesterday = new Date();
tomorrow.setDate(today.getDate()+1);
yesterday.setDate(today.getDate()-1);
var date_today = Utilities.formatDate(today, "GMT+1", "yyyy/MM/dd")
var date_tomorrow = Utilities.formatDate(tomorrow, "GMT+1", "yyyy/MM/dd")
var date_yesterday = Utilities.formatDate(yesterday, "GMT+1", "yyyy/MM/dd")
var threads = GmailApp.search('from:sender#server.com has:nouserlabels before:'+ date_tomorrow +' after:'+ date_yesterday +'');
label.addToThreads(threads);
}

Answer 1

Per the API documentation, Gmail follows some rules about thread grouping:
In order to be part of a thread, a message or draft must meet the following criteria:1. The requested threadId must be specified on the Message or Draft.Message you supply with your request.2. The References and In-Reply-To headers must be set in compliance with the RFC 2822 standard.3. The Subject headers must match.
So, you can prevent the automatic grouping into a given conversation thread by modifying any of those 3 parameters.
Alternately, you can apply per-message conversation labels, though this will not really help you if you use "Conversation View" UI.
Both of these methods require the use of the Gmail REST API, for which Apps Script provides an "advanced service" client library. The native GmailApp does not provide a method for per-message thread alteration, or for manipulating messages in the manner needed.
Thread Separation
If you wanted to disable the conversation grouping, in theory you could do this:
Message#get to obtain a full message representation
Modify one of the properties Gmail uses to perform thread grouping
Message#insert or import to create the new message on the server
Message#delete to remove the original
Message#get to get the inserted message metadata, after Gmail has given it a threadId.
Get the remaining messages that should share that new threadId, modify them appropriately, and insert.
Repeat.
I haven't tested that approach, hence my "in theory" comment.
Per-message labeling
The relevant API methods include Gmail.User.Labels.list, Gmail.User.Messages.list, Gmail.User.Messages.modify, and Gmail.User.Messages.batchModify. You'll probably want to use the list and messages.batchModify methods, since you seem to have a large number of messages for which you'd like to make alterations. Note, there are non-trivial rate limits in place, so working in small batches is liable to be most resource-efficient.
This is likely to be the simplest method to implement, since you don't have to actually create or delete messages - just search for messages that should have a given label, add (or create and add) it to them, and remove any non-desired labels. To start you off, here are some minimal examples that show how to work with the Gmail REST API. I expect you will need to refer to the API documentation when you use this information to construct your actual script.
An example Labels#list:
function getLabelsWithName(labelName) {
const search = Gmail.Users.Labels.list("me");
if (!search.labels || !search.labels.length)
return [];
const matches = search.labels.filter(function (label) {
// Return true to include the label, false to omit it.
return label.name === labelName;
});
return matches;
}
An example Messages#list:
function getPartialMessagesWithLabel(labelResource) {
const options = {
labelIds: [ labelResource.id ],
fields: "nextPageToken,messages(id,threadId,labelIds,internalDate)"
};
const results = [];
// Messages#list is paginated, so we must page through them to obtain all results.
do {
var search = Gmail.Users.Messages.list("me", options);
options.pageToken = search.nextPageToken;
if (search.messages && search.messages.length)
Array.prototype.push.apply(results, search.messages);
} while (options.pageToken);
return results;
}
An example Messages#batchModify:
function batchAddLabels(messageArray, labels) {
if (!messageArray || !messageArray.length || !messageArray[0].id)
throw new Error("Missing array of messages to update");
if (!labels || !labels.length || !labels[0].id)
throw new Error("Missing array of label resources to add to the given messages");
const requestMetaData = {
"addLabelIds": labels.map(function (label) { return label.id; }),
"ids": messageArray.map(function (msg) { return msg.id; }) // max 1000 per request!
};
Gmail.Users.Messages.batchModify(requestMetaData, "me");
}
Additional Resources:
Message Searches
"fields" parameter