#![cfg_attr(not(feature = "rt"), allow(dead_code))]

//! Source of time abstraction.

//!

//! By default, `std::time::Instant::now()` is used. However, when the

//! `test-util` feature flag is enabled, the values returned for `now()` are

//! configurable.

cfg_not_test_util! {

    use crate::time::{Instant};

    #[derive(Debug, Clone)]

    pub(crate) struct Clock {}

    pub(crate) fn now() -> Instant {

        Instant::from_std(std::time::Instant::now())

    }

    impl Clock {

        pub(crate) fn new(_enable_pausing: bool, _start_paused: bool) -> Clock {

            Clock {}

        }

        pub(crate) fn now(&self) -> Instant {

            now()

        }

    }

}

cfg_test_util! {

    use crate::time::{Duration, Instant};

    use crate::loom::sync::Mutex;

    use crate::loom::sync::atomic::Ordering;

    use std::sync::atomic::AtomicBool as StdAtomicBool;

    cfg_rt! {

        #[track_caller]

        fn with_clock<R>(f: impl FnOnce(Option<&Clock>) -> Result<R, &'static str>) -> R {

            use crate::runtime::Handle;

            let res = match Handle::try_current() {

                Ok(handle) => f(Some(handle.inner.driver().clock())),

                Err(ref e) if e.is_missing_context() => f(None),

                Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),

            };

            match res {

                Ok(ret) => ret,

                Err(msg) => panic!("{}", msg),

            }

        }

Unexecuted instantiation: tokio::time::clock::with_clock::<tokio::time::instant::Instant, tokio::time::clock::now::{closure#0}>

Unexecuted instantiation: tokio::time::clock::with_clock::<(), tokio::time::clock::pause::{closure#0}>

Unexecuted instantiation: tokio::time::clock::with_clock::<(), tokio::time::clock::resume::{closure#0}>

    }

    cfg_not_rt! {

        #[track_caller]

        fn with_clock<R>(f: impl FnOnce(Option<&Clock>) -> Result<R, &'static str>) -> R {

            match f(None) {

                Ok(ret) => ret,

                Err(msg) => panic!("{}", msg),

            }

        }

    }

    /// A handle to a source of time.

    #[derive(Debug)]

    pub(crate) struct Clock {

        inner: Mutex<Inner>,

    }

    // Used to track if the clock was ever paused. This is an optimization to

    // avoid touching the mutex if `test-util` was accidentally enabled in

    // release mode.

    //

    // A static is used so we can avoid accessing the thread-local as well. The

    // `std` AtomicBool is used directly because loom does not support static

    // atomics.

    static DID_PAUSE_CLOCK: StdAtomicBool = StdAtomicBool::new(false);

    #[derive(Debug)]

    struct Inner {

        /// True if the ability to pause time is enabled.

        enable_pausing: bool,

        /// Instant to use as the clock's base instant.

        base: std::time::Instant,

        /// Instant at which the clock was last unfrozen.

        unfrozen: Option<std::time::Instant>,

        /// Number of `inhibit_auto_advance` calls still in effect.

        auto_advance_inhibit_count: usize,

    }

    /// Pauses time.

    ///

    /// The current value of `Instant::now()` is saved and all subsequent calls

    /// to `Instant::now()` will return the saved value. The saved value can be

    /// changed by [`advance`] or by the time auto-advancing once the runtime

    /// has no work to do. This only affects the `Instant` type in Tokio, and

    /// the `Instant` in std continues to work as normal.

    ///

    /// Pausing time requires the `current_thread` Tokio runtime. This is the

    /// default runtime used by `#[tokio::test]`. The runtime can be initialized

    /// with time in a paused state using the `Builder::start_paused` method.

    ///

    /// For cases where time is immediately paused, it is better to pause

    /// the time using the `main` or `test` macro:

    /// ```

    /// #[tokio::main(flavor = "current_thread", start_paused = true)]

    /// async fn main() {

    ///    println!("Hello world");

    /// }

    /// ```

    ///

    /// # Panics

    ///

    /// Panics if time is already frozen or if called from outside of a

    /// `current_thread` Tokio runtime.

    ///

    /// # Auto-advance

    ///

    /// If time is paused and the runtime has no work to do, the clock is

    /// auto-advanced to the next pending timer. This means that [`Sleep`] or

    /// other timer-backed primitives can cause the runtime to advance the

    /// current time when awaited.

    ///

    /// [`Sleep`]: crate::time::Sleep

    /// [`advance`]: crate::time::advance

    #[track_caller]

    pub fn pause() {

        with_clock(|maybe_clock| {

            match maybe_clock {

                Some(clock) => clock.pause(),

                None => Err("time cannot be frozen from outside the Tokio runtime"),

            }

        });

    }

    /// Resumes time.

    ///

    /// Clears the saved `Instant::now()` value. Subsequent calls to

    /// `Instant::now()` will return the value returned by the system call.

    ///

    /// # Panics

    ///

    /// Panics if time is not frozen or if called from outside of the Tokio

    /// runtime.

    #[track_caller]

    pub fn resume() {

        with_clock(|maybe_clock| {

            let clock = match maybe_clock {

                Some(clock) => clock,

                None => return Err("time cannot be frozen from outside the Tokio runtime"),

            };

            let mut inner = clock.inner.lock();

            if inner.unfrozen.is_some() {

                return Err("time is not frozen");

            }

            inner.unfrozen = Some(std::time::Instant::now());

            Ok(())

        });

    }

    /// Advances time.

    ///

    /// Increments the saved `Instant::now()` value by `duration`. Subsequent

    /// calls to `Instant::now()` will return the result of the increment.

    ///

    /// This function will make the current time jump forward by the given

    /// duration in one jump. This means that all `sleep` calls with a deadline

    /// before the new time will immediately complete "at the same time", and

    /// the runtime is free to poll them in any order.  Additionally, this

    /// method will not wait for the `sleep` calls it advanced past to complete.

    /// If you want to do that, you should instead call [`sleep`] and rely on

    /// the runtime's auto-advance feature.

    ///

    /// Note that calls to `sleep` are not guaranteed to complete the first time

    /// they are polled after a call to `advance`. For example, this can happen

    /// if the runtime has not yet touched the timer driver after the call to

    /// `advance`. However if they don't, the runtime will poll the task again

    /// shortly.

    ///

    /// # Panics

    ///

    /// Panics if any of the following conditions are met:

    ///

    /// - The clock is not frozen, which means that you must

    ///   call [`pause`] before calling this method.

    /// - If called outside of the Tokio runtime.

    /// - If the input `duration` is too large (such as [`Duration::MAX`])

    ///   to be safely added to the current time without causing an overflow.

    ///

    /// # Caveats

    ///

    /// Using a very large `duration` is not recommended,

    /// as it may cause panicking due to overflow.

    ///

    /// # Auto-advance

    ///

    /// If the time is paused and there is no work to do, the runtime advances

    /// time to the next timer. See [`pause`](pause#auto-advance) for more

    /// details.

    ///

    /// [`sleep`]: fn@crate::time::sleep

    pub async fn advance(duration: Duration) {

        with_clock(|maybe_clock| {

            let clock = match maybe_clock {

                Some(clock) => clock,

                None => return Err("time cannot be frozen from outside the Tokio runtime"),

            };

            clock.advance(duration)

        });

        crate::task::yield_now().await;

    }

    /// Returns the current instant, factoring in frozen time.

    pub(crate) fn now() -> Instant {

        if !DID_PAUSE_CLOCK.load(Ordering::Acquire) {

            return Instant::from_std(std::time::Instant::now());

        }

        with_clock(|maybe_clock| {

            Ok(if let Some(clock) = maybe_clock {

                clock.now()

            } else {

                Instant::from_std(std::time::Instant::now())

            })

        })

    }

    impl Clock {

        /// Returns a new `Clock` instance that uses the current execution context's

        /// source of time.

        pub(crate) fn new(enable_pausing: bool, start_paused: bool) -> Clock {

            let now = std::time::Instant::now();

            let clock = Clock {

                inner: Mutex::new(Inner {

                    enable_pausing,

                    base: now,

                    unfrozen: Some(now),

                    auto_advance_inhibit_count: 0,

                }),

            };

            if start_paused {

                if let Err(msg) = clock.pause() {

                    panic!("{}", msg);

                }

            }

            clock

        }

        pub(crate) fn pause(&self) -> Result<(), &'static str> {

            let mut inner = self.inner.lock();

            if !inner.enable_pausing {

                return Err("`time::pause()` requires the `current_thread` Tokio runtime. \

                        This is the default Runtime used by `#[tokio::test].");

            }

            // Track that we paused the clock

            DID_PAUSE_CLOCK.store(true, Ordering::Release);

            let elapsed = match inner.unfrozen.as_ref() {

                Some(v) => v.elapsed(),

                None => return Err("time is already frozen")

            };

            inner.base += elapsed;

            inner.unfrozen = None;

            Ok(())

        }

        /// Temporarily stop auto-advancing the clock (see `tokio::time::pause`).

        pub(crate) fn inhibit_auto_advance(&self) {

            let mut inner = self.inner.lock();

            inner.auto_advance_inhibit_count += 1;

        }

        pub(crate) fn allow_auto_advance(&self) {

            let mut inner = self.inner.lock();

            inner.auto_advance_inhibit_count -= 1;

        }

        pub(crate) fn can_auto_advance(&self) -> bool {

            let inner = self.inner.lock();

            inner.unfrozen.is_none() && inner.auto_advance_inhibit_count == 0

        }

        pub(crate) fn advance(&self, duration: Duration) -> Result<(), &'static str> {

            let mut inner = self.inner.lock();

            if inner.unfrozen.is_some() {

                return Err("time is not frozen");

            }

            inner.base += duration;

            Ok(())

        }

        pub(crate) fn now(&self) -> Instant {

            let inner = self.inner.lock();

            let mut ret = inner.base;

            if let Some(unfrozen) = inner.unfrozen {

                ret += unfrozen.elapsed();

            }

            Instant::from_std(ret)

        }

    }

}