Move project saving to server to helper, allow external save action

[paulkaplan]

Resolves

What Github issue does this resolve (please include link)?

• Resolves Allow project saving method to be configured #4606

Proposed Changes

Describe what this Pull Request does

Move the current save code to a helper that can be eventually moved to WWW, and allow a GUI consumer to pass in a onUpdateProjectData method to handle project JSON saves.

Reason for Changes

Explain why these changes should be made

See linked issue.

[rschamp]

Inspecting the properties of the return value seems like it could lead to bugs... what do you think about this alternative?

[rschamp]

We should remove this eventually, although adding the default makes this PR seamless, so I think it's the way to go now.

[rschamp]

Can we rely on the supplier of onUpdateProjectData to ensure it returns a promise? If not, maybe we should wrap the entire thing in a promise that gets returned? Something like:

return new Promise((resolve, reject) => {
    try {
        const saveReturnValue = onUpdateProjectData(projectId, savedVMState, requestParams);
    } catch (e) {
        return reject(e);
    }
    // if saveReturnValue is a promise, this wrapper promise will resolve to what saveReturnValue resolves to
    return resolve(saveReturnValue); 
});

[paulkaplan]

Yeah i wasn't quite sure whether to enforce the promise requirement. That code block actually started as if (!returnValue.then) { throw new Error('You must return a promise'); } but then i realized i could just resolve at that point. Also you don't need to try/catch because it is already inside a promise chain, so throwing in that function would automatically go to the next .catch in the chain.

[paulkaplan]

Actually i think you can just return Promise.resolve(onUpdateProjectData(...)) since promises unwrap the resolve value from other promises

[rschamp]

That looks good to me.

[paulkaplan]

Oh wait, even simpler, it is in a promise chain, it doesn't matter if it is a promise or not, either way the next then will get the same result at the right time 00a4db1 🤦‍♂️