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class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding
    private var current = 0L

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

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class CustomView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    @AttrRes defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {

    private var periodMs = 0L
    private var currentMs = 0L
    private var color = 0
    private var style = FILL

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<resources>
    <declare-styleable name="CustomView">
        <attr name="custom_color" format="color" />
        <attr name="custom_style" format="enum">
            <enum name="fill" value="0" />
            <enum name="stroke" value="1" />
        </attr>
    </declare-styleable>
</resources>

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class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    private val stopwatchAdapter = StopwatchAdapter()
    private val stopwatches = mutableListOf<Stopwatch>()
    private var nextId = 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

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class StopwatchViewHolder(
    private val binding: StopwatchItemBinding,
    private val listener: StopwatchListener,
    private val resources: Resources
) : RecyclerView.ViewHolder(binding.root) {

    private var timer: CountDownTimer? = null

    fun bind(stopwatch: Stopwatch) {
        binding.stopwatchTimer.text = stopwatch.currentMs.displayTime()

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/*...*/
override fun start(id: Int) {
        changeStopwatch(id, null, true)
    }

    override fun stop(id: Int, currentMs: Long) {
        changeStopwatch(id, currentMs, false)
    }

    override fun reset(id: Int) {

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interface StopwatchListener {

    fun start(id: Int)

    fun stop(id: Int, currentMs: Long)

    fun reset(id: Int)

    fun delete(id: Int)
}

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class StopwatchViewHolder(
    private val binding: StopwatchItemBinding
): RecyclerView.ViewHolder(binding.root) {

    private var timer: CountDownTimer? = null

    fun bind(stopwatch: Stopwatch) {
        binding.stopwatchTimer.text = stopwatch.currentMs.displayTime()

        if (stopwatch.isStarted) {

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class StopwatchAdapter: ListAdapter<Stopwatch, StopwatchViewHolder>(itemComparator) {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): StopwatchViewHolder {
        val layoutInflater = LayoutInflater.from(parent.context)
        val binding = StopwatchItemBinding.inflate(layoutInflater, parent, false)
        return StopwatchViewHolder(binding)
    }

    override fun onBindViewHolder(holder: StopwatchViewHolder, position: Int) {
        holder.bind(getItem(position))

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class StopwatchViewHolder(
    private val binding: StopwatchItemBinding
): RecyclerView.ViewHolder(binding.root) {

    fun bind(stopwatch: Stopwatch) {
        binding.stopwatchTimer.text = stopwatch.currentMs.displayTime()
    }

    private fun Long.displayTime(): String {
        if (this <= 0L) {