#include "countdown.h"

Countdown::Countdown(qint64 durationMs)
    : m_duration(qMax<qint64>(0, durationMs)), m_remainingAtStart(m_duration)
{
}

bool Countdown::setDuration(qint64 durationMs)
{
    if (m_state == State::Running || m_state == State::Paused || durationMs < 0)
        return false;
    m_duration = durationMs;
    reset();
    return true;
}

void Countdown::start(qint64 nowMs)
{
    if (m_state == State::Running || m_duration <= 0)
        return;
    if (m_state != State::Paused)
        m_remainingAtStart = m_duration;
    m_segmentStarted = nowMs;
    m_state = State::Running;
}

qint64 Countdown::remaining(qint64 nowMs) const
{
    if (m_state == State::Finished)
        return 0;
    if (m_state != State::Running)
        return m_remainingAtStart;
    const qint64 elapsed = qMax<qint64>(0, nowMs - m_segmentStarted);
    return qMax<qint64>(0, m_remainingAtStart - elapsed);
}

void Countdown::update(qint64 nowMs)
{
    if (m_state == State::Running && remaining(nowMs) == 0) {
        m_remainingAtStart = 0;
        m_state = State::Finished;
    }
}

void Countdown::pause(qint64 nowMs)
{
    update(nowMs);
    if (m_state != State::Running)
        return;
    // 先保存这一刻的剩余时间，再切换状态，暂停期间不继续扣减。
    m_remainingAtStart = remaining(nowMs);
    m_state = State::Paused;
}

void Countdown::reset()
{
    m_remainingAtStart = m_duration;
    m_segmentStarted = 0;
    m_state = State::Ready;
}