First Commit

Projects/02_ClassroomTimer/countdown.cpp

@@ -0,0 +1,61 @@
+#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;
+}
+