// 核心協(xié)程依賴
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.3"
// 可選：ViewModel + StateFlow 擴展
implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.6.2"
implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.6.2"

import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch
class CounterViewModel : ViewModel() {
    // 1. 私有可變 StateFlow（生產(chǎn)者），初始化默認值 0
    private val _counterState = MutableStateFlow(0)
    // 2. 對外暴露只讀 StateFlow（消費者）
    val counterState: StateFlow<Int> = _counterState.asStateFlow()
    // 3. 同步更新狀態(tài)（主線程/協(xié)程均可）
    fun incrementCounter() {
        _counterState.value += 1
    }
    // 4. 異步更新狀態(tài)（模擬網(wǎng)絡(luò)/耗時操作）
    fun incrementCounterAsync() {
        viewModelScope.launch {
            delay(1000) // 模擬耗時操作
            _counterState.value += 1
        }
    }
    // 5. 重置狀態(tài)
    fun resetCounter() {
        _counterState.value = 0
    }
}

import android.os.Bundle
import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.lifecycleScope
import androidx.lifecycle.repeatOnLifecycle
import kotlinx.coroutines.launch
import com.example.stateflow.databinding.ActivityCounterBinding
class CounterActivity : AppCompatActivity() {
    // 視圖綁定
    private lateinit var binding: ActivityCounterBinding
    // ViewModel 實例
    private val viewModel: CounterViewModel by viewModels()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityCounterBinding.inflate(layoutInflater)
        setContentView(binding.root)
        // 綁定點擊事件
        binding.btnIncrement.setOnClickListener {
            viewModel.incrementCounter()
        }
        binding.btnIncrementAsync.setOnClickListener {
            viewModel.incrementCounterAsync()
        }
        binding.btnReset.setOnClickListener {
            viewModel.resetCounter()
        }
        // 收集 StateFlow 狀態(tài)（生命周期感知）
        collectCounterState()
    }
    private fun collectCounterState() {
        // repeatOnLifecycle：僅在 RESUMED 狀態(tài)收集，PAUSED 時暫停，DESTROYED 時取消
        lifecycleScope.launch {
            repeatOnLifecycle(androidx.lifecycle.Lifecycle.State.RESUMED) {
                // 收集狀態(tài)更新
                viewModel.counterState.collect { count ->
                    // 更新 UI
                    binding.tvCounter.text = "當前計數(shù)：$count"
                }
            }
        }
    }
}

// 在 ViewModel 中擴展狀態(tài)
val counterTextState: StateFlow<String> = _counterState
    .map { count -> "轉(zhuǎn)換后的計數(shù)：$count" } // 狀態(tài)轉(zhuǎn)換
    .filter { it.isNotEmpty() } // 過濾空值
    .stateIn(
        scope = viewModelScope,
        started = androidx.lifecycle.WhileSubscribed(5000), // 5 秒無訂閱則停止
        initialValue = "轉(zhuǎn)換后的計數(shù)：0"
    )

// 定義第二個狀態(tài)
private val _isLoading = MutableStateFlow(false)
val isLoading: StateFlow<Boolean> = _isLoading.asStateFlow()
// 合并計數(shù)和加載狀態(tài)
val combinedState: StateFlow<Pair<Int, Boolean>> = combine(
    _counterState,
    _isLoading
) { count, loading ->
    count to loading
}.stateIn(
    scope = viewModelScope,
    started = WhileSubscribed(5000),
    initialValue = 0 to false
)
// 異步操作中更新加載狀態(tài)
fun incrementCounterWithLoading() {
    viewModelScope.launch {
        _isLoading.value = true
        delay(1000)
        _counterState.value += 1
        _isLoading.value = false
    }
}

// 搜索框輸入狀態(tài)
private val _searchText = MutableStateFlow("")
val searchText: StateFlow<String> = _searchText.asStateFlow()
// 防抖后的搜索狀態(tài)（500ms 無輸入才發(fā)射）
val debouncedSearchText: StateFlow<String> = _searchText
    .debounce(500)
    .stateIn(
        scope = viewModelScope,
        started = WhileSubscribed(5000),
        initialValue = ""
    )

// 初始化 DataStore
private val Context.dataStore by preferencesDataStore(name = "counter_prefs")
private val COUNTER_KEY = intPreferencesKey("counter")
// 從 DataStore 加載初始狀態(tài)
private suspend fun loadCounterFromDataStore(): Int {
    return dataStore.data.map { prefs ->
        prefs[COUNTER_KEY] ?: 0
    }.first()
}
// 更新狀態(tài)時持久化
fun incrementCounter() {
    viewModelScope.launch {
        _counterState.value += 1
        dataStore.edit { prefs ->
            prefs[COUNTER_KEY] = _counterState.value
        }
    }
}