// Production code
public class TaskScheduler {
    private final Clock clock;

    public TaskScheduler(Clock clock) {
        this.clock = clock;
    }

    public Task scheduleNext(Duration after) {
        return new Task(Instant.now(clock).plus(after));
    }
}

// Wire-up
TaskScheduler prodScheduler = new TaskScheduler(Clock.systemDefaultZone());

@Test
void scheduleNext() {
    Clock fixed = Clock.fixed(
        Instant.parse("2026-05-20T14:30:00Z"),
        ZoneId.of("America/New_York")
    );
    TaskScheduler scheduler = new TaskScheduler(fixed);

    Task task = scheduler.scheduleNext(Duration.ofMinutes(5));

    assertEquals(
        Instant.parse("2026-05-20T14:35:00Z"),
        task.getScheduledAt()
    );
}

Clock realPlus10 = Clock.offset(Clock.systemDefaultZone(), Duration.ofMinutes(10));
// Code reading this clock sees real-time + 10 minutes

// Custom: a Clock that can be advanced manually
public class MutableClock extends Clock {
    private Instant instant;
    private final ZoneId zone;

    public MutableClock(Instant instant, ZoneId zone) {
        this.instant = instant;
        this.zone = zone;
    }

    public void setInstant(Instant i) { this.instant = i; }
    public void advance(Duration d) { instant = instant.plus(d); }

    @Override public Clock withZone(ZoneId z) { return new MutableClock(instant, z); }
    @Override public ZoneId getZone() { return zone; }
    @Override public Instant instant() { return instant; }
}

public class Logger {
    private final InstantSource source;
    public Logger(InstantSource source) { this.source = source; }
    public void log(String msg) {
        System.out.println(source.instant() + " " + msg);
    }
}

// Test
InstantSource fake = () -> Instant.parse("2026-05-20T14:30:00Z");
new Logger(fake).log("hi");

@Configuration
public class ClockConfig {
    @Bean
    public Clock clock() {
        return Clock.systemDefaultZone();
    }
}

// Test
@TestConfiguration
public class TestClockConfig {
    @Bean public Clock clock() {
        return Clock.fixed(Instant.parse("2026-05-20T14:30:00Z"), ZoneOffset.UTC);
    }
}

@Test
void springForwardLocalTime() {
    Clock fixed = Clock.fixed(
        Instant.parse("2026-03-08T07:30:00Z"),  // 02:30 EDT - invalid local
        ZoneId.of("America/New_York")
    );

    // ZonedDateTime resolution depends on resolver
    ZonedDateTime zdt = ZonedDateTime.ofInstant(fixed.instant(), fixed.getZone());
    // Per dst-transition-reference: assert the behaviour matches docs
}

mvn test
gradle test

jobs:
  jvm-tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - uses: actions/setup-java@v4
        with: { java-version: '21', distribution: 'temurin' }
      - run: mvn test