const val FROM_DB  = "FROM_DB"
const val FROM_API = "FROM_API"

class MainActivity : AppCompatActivity(), CoroutineScope {

    //region Coroutines initialization
    private val job = Job()
    override val coroutineContext: CoroutineContext = Dispatchers.Main + job
    //endregion

    //region variable declaration
    private val todos = ArrayList<Todo>()
    private var adapter: TodoAdapter? = null
    //endregion

    //region livedata variables
    private val progressLiveData = MutableLiveData<Boolean>()
    private val todoListLiveData = MutableLiveData<Result.ResultWrapper<List<Todo>, String>>()
    //endregion


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        initAdapter()
        initRealm()
        setListeners()
        getLocalTodos()
        getRemoteTodos()
    }


    /**
    * Adapter is initialized here. Called once from [onCreate()]
    */
    private fun initAdapter() {
        adapter = TodoAdapter(this, todos)
        rvTodos.layoutManager = LinearLayoutManager(this)
        rvTodos.adapter = adapter
    }

    /**
    * Realm instance is initialized here. Called once from [onCreate()]
    */
    private fun initRealm() {
        Realm.init(this)
        val config = RealmConfiguration
            .Builder()
            .name("simplified_caching.realm")
            .schemaVersion(1)
            .deleteRealmIfMigrationNeeded()
            .build()
        Realm.setDefaultConfiguration(config)
    }

    /**
    * LiveData observers are set here
    * [todoListLiveData] observes for changes to [todo] which is the data source for our [adapter]
    * [progressLiveData] observes a boolean which is responsible for flipping our [vfMain]
    */
    private fun setListeners() {
        progressLiveData.observe(this, Observer { isLoading ->
            vfMain.displayedChild = if(isLoading) 0 else 1
        })

        todoListLiveData.observe(this, Observer { result ->
            val isFromDb = result.message == FROM_DB
            if(!isFromDb) {
                //presist data if changes observered are not from DB
                result.data.saveAll()
            }
            //for any change to [todos] clear list, add new data to list, notifiy adapter
            clearAndAllToList(result.data)
            adapter?.notifyDataSetChanged()
        })
    }

    private fun clearAndAllToList(todosToAdd: List<Todo>?) {
        todos.clear()
        todosToAdd?.let { todos.addAll(it) }
    }

    /**
    * Get cached data from Realm
    */
    private fun getLocalTodos() {
        progressLiveData.value = false
        val todosFromDb = Todo().queryAll()
        todoListLiveData.value = Result.ResultWrapper(todosFromDb, FROM_DB)
    }

    /**
    * Get remote data from API using Retrofit
    */
    private fun getRemoteTodos() {
        launch {
            if(todos.isEmpty()) {
                progressLiveData.value = true
            }
            val todosFromApi = ApiController.retrofit.create<ApiInterface>().getTodos().await()
            progressLiveData.value = false
            todoListLiveData.value = Result.ResultWrapper(todosFromApi, FROM_API)
        }
    }
}