User settings management

Lobby needs to be able to save user's game and engine settings, including hotkeys. Some requirements:

User settings should stay consistent between lobby, game and engine updates
User settings should always be automatically migrated to latest versions
When possible, user settings should be backed up to Teiserver
User settings should override sensible defaults at an indivdual setting basis (instead of being an entire file replacement)

A possible way I see this working could be as follows:

lobby-default-settings.json:

{
    "fullscreen": true
    "displayIndex": 0,
    "skipIntro": false,
    "sfxVolume": 5,
    "musicVolume": 5,
    "loginAutomatically": true,
}

user-settings.json:

[
    {
        "accountId": 1234,
        "lobby": {
            "skipIntro": true,
            "musicVolume": 0
        },
        "engine": {},
        "game": {},
        "hotkeys": {}
    }
]

An interface would need to be written for all the different parts of infra to be able to read and write their relevant settings to this file.

Random ramblings:

Migrations

When a particular setting format is changed, the interface will need to either invalidate the previous setting or migrate it in some way. Some examples of how a setting's format might change:

Key rename (e.g. skipIntro: boolean -> introEnabled: boolean)
Data format change (e.g. skipIntro: boolean -> skipIntro: string)

For key renames, this could simply be a map lookup from old names to new names. This gets slightly more complicated however if old setting names get reused for other purposes later on. For data format changes, logic would need to be written to convert the old format to the new format. Migrations would need to be written for specific versions and all run sequentially when jumping from one version to another. Things could also get messy when watching old replays.

The easiest solution would be to invalidate any changed settings when moving from one version to another where the setting format differs. So long as we keep format changes to the absolute minimum, and account for future possibilities where we can, I think this is ok.

Setting definitions

We already have definitions very similar to this in certain places, but it should follow a standard and be the same everywhere. Recommend following JSONSchema.

[
    {
        "id": "lobby_volume_music",
        "name": "Music Volume",
        "description": "The volume level for the music played in the lobby",
        "type": "integer",
        "min": 0,
        "max": 100,
        "step": 1,
        "default": 5
    }
]

Validation

Both default and user settings should be validated against their relevant definitions. Actions can be taken depending on the type of invalidation found, e.g.

user setting has an id not found in definitions -> remove it from user settings
user number setting value is greater than the allowed maximum value -> cap it at the max
user number setting value is not divisible by the step amount -> round it to the nearest step amount
user number setting value is a float, but the definition requires an integer ->round it to nearest int etc

Similar to migrations, it may just be easiest to clear settings if they're not valid, needs discussion.

Cloud backup

If we're backing settings up to Teiserver, they'll probably need to be timestamped with last modified date, e.g. in case users change them offline and don't want their settings in the cloud to override their changes, or vice-versa if they change them on one PC and then log into their account on another.

beyond-all-reason / bar-lobby