settings_migrator.js

const DefaultSettings = {
    "shakeEnabled": true,
    "shakePower": 1.0,
    "shakeSpeed": 1.0,
    "fovEnabled": false,
    "fovValue": 71.0,
    "distanceEnabled": false,
    "distanceValue": 170.0,
}

module.exports = function MigrateSettings(from_ver, to_ver, settings) {
    if (from_ver === undefined) {
        // Migrate legacy config file
        return Object.assign(Object.assign({}, DefaultSettings), settings);
    } else if (from_ver === null) {
        // No config file exists, use default settings
        return DefaultSettings;
    } else {
        // Migrate from older version (using the new system) to latest one
        if (from_ver + 1 < to_ver) {
            // Recursively upgrade in one-version steps
            settings = MigrateSettings(from_ver, from_ver + 1, settings);
            return MigrateSettings(from_ver + 1, to_ver, settings);
        }

        // If we reach this point it's guaranteed that from_ver === to_ver - 1, so we can implement
        // a switch for each version step that upgrades to the next version. This enables us to
        // upgrade from any version to the latest version without additional effort!
        switch (to_ver) {
            case 2:
                settings.shakeEnabled = settings.enabled;
                delete settings.enabled;

                settings.shakePower = settings.power;
                delete settings.power;

                settings.shakeSpeed = settings.speed;
                delete settings.speed;

                settings.fovEnabled = DefaultSettings.fovEnabled;
                settings.fovValue = DefaultSettings.fovValue;
                settings.distanceEnabled = DefaultSettings.distanceEnabled;
                settings.distanceValue = DefaultSettings.distanceValue;
                break;
        }

        return settings;
    }
}