I have seen this blog https://medium.com/androiddevelopers/datastore-and-data-migration-fdca806eb1aa, but it is not quite detail. It does not show how to do data migration of proto datastore plus how you do it using Dagger Hilt.

This is what I have done so far.
I have a AppSettings (like AppPreferences)

@Serializable
data class AppSettings(
    val prepareSeconds: Long = 10L,
    val workSeconds: Long = 90L,
    val restSeconds: Long = 30L,
    val totalSets: Int = 3
) {
    companion object {
        fun getDefaultInstance() = AppSettings()
    }
}

Serialiser (I don’t use .proto file, I have a Preferences Data Class & deserialize and serialize it)

object AppSettingsSerializer : Serializer<AppSettings> {

    override val defaultValue: AppSettings
        get() = AppSettings()

    override suspend fun readFrom(input: InputStream): AppSettings {
        return try {
            Json.decodeFromString(
                deserializer = AppSettings.serializer(),
                string = input.readBytes().decodeToString()
            )
        } catch (e: SerializationException) {
            throw CorruptionException("Unable to read AppSettingsPrefs", e)
        }
    }

    @Suppress("BlockingMethodInNonBlockingContext")
    override suspend fun writeTo(t: AppSettings, output: OutputStream) {
        output.write(
            Json.encodeToString(
                serializer = AppSettings.serializer(),
                value = t
            ).encodeToByteArray()
        )
    }
}

Dagger Hilt Module finally

@Module
@InstallIn(SingletonComponent::class)
object AppModule {

    @Singleton
    @Provides
    fun provideAppSettingsDataStore(
        @ApplicationContext appContext: Context,
        coroutineScope: CoroutineScope,
    ): DataStore<AppSettings> {
        return DataStoreFactory.create(
            serializer = AppSettingsSerializer,
            corruptionHandler = ReplaceFileCorruptionHandler {
                AppSettings.getDefaultInstance()
            },
            scope = coroutineScope,
            produceFile = {
                appContext.dataStoreFile(DATA_STORE_FILE_NAME)
            },
            migrations = listOf(object : DataMigration<AppSettings> {

                // Specify your condition for whether the migration should happen
                override suspend fun shouldMigrate(currentData: AppSettings) = true

                // Instruction on how exactly the old data is transformed into new data
                // I DO NOT THINK THIS IS RIGHT WAY TO DO IT, HOW SHOULD IT BE DONE??
                override suspend fun migrate(currentData: AppSettings): AppSettings =
                       AppSettings(
                        prepareSeconds = currentData.prepareSeconds,
                        workSeconds = currentData.workSeconds,
                        restSeconds = currentData.restSeconds,
                        totalSets = currentData.totalSets,
                    )
           

                // Once the migration is over, clean up the old storage
                override suspend fun cleanUp() = Unit
            })
        )
    }

When I update AppSettings (Preferences) with new field/update existing field name/ delete some field. Then DataStore not do migration but re-intialise with default value.

What I am doing wrong. Can anyone give me any resources/blog or code on how to do data migration of proto datastore using Dagger Hilt.