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    // Copyright (c) 2017 The vulkano developers
    // Licensed under the Apache License, Version 2.0
    // <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT
    // license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
    // at your option. All files in the project carrying such
    // notice may not be copied, modified, or distributed except
    // according to those terms.

    use std::mem;
    use std::sync::Arc;
    use std::sync::Mutex;
    use std::sync::MutexGuard;
    use std::time::Duration;

    use buffer::BufferAccess;
    use command_buffer::submit::SubmitAnyBuilder;
    use command_buffer::submit::SubmitCommandBufferBuilder;
    use device::Device;
    use device::DeviceOwned;
    use device::Queue;
    use image::ImageAccess;
    use image::ImageLayout;
    use sync::AccessCheckError;
    use sync::AccessFlagBits;
    use sync::Fence;
    use sync::FlushError;
    use sync::GpuFuture;
    use sync::PipelineStages;

    /// Builds a new fence signal future.
    #[inline]
    pub fn then_signal_fence<F>(future: F, behavior: FenceSignalFutureBehavior) -> FenceSignalFuture<F>
        where F: GpuFuture
    {
        let device = future.device().clone();

        assert!(future.queue().is_some()); // TODO: document

        let fence = Fence::from_pool(device.clone()).unwrap();
        FenceSignalFuture {
            device: device,
            state: Mutex::new(FenceSignalFutureState::Pending(future, fence)),
            behavior: behavior,
        }
    }

    /// Describes the behavior of the future if you submit something after it.
    #[derive(Debug, Copy, Clone, PartialEq, Eq)]
    pub enum FenceSignalFutureBehavior {
        /// Continue execution on the same queue.
        Continue,
        /// Wait for the fence to be signalled before submitting any further operation.
        Block {
            /// How long to block the current thread.
            timeout: Option<Duration>,
        },
    }

    /// Represents a fence being signaled after a previous event.
    ///
    /// Contrary to most other future types, it is possible to block the current thread until the event
    /// happens. This is done by calling the `wait()` function.
    ///
    /// Also note that the `GpuFuture` trait is implemented on `Arc<FenceSignalFuture<_>>`.
    /// This means that you can put this future in an `Arc` and keep a copy of it somewhere in order
    /// to know when the execution reached that point.
    ///
    /// ```
    /// use std::sync::Arc;
    /// use vulkano::sync::GpuFuture;
    ///
    /// # let future: Box<GpuFuture> = return;
    /// // Assuming you have a chain of operations, like this:
    /// // let future = ...
    /// //      .then_execute(foo)
    /// //      .then_execute(bar)
    ///
    /// // You can signal a fence at this point of the chain, and put the future in an `Arc`.
    /// let fence_signal = Arc::new(future.then_signal_fence());
    ///
    /// // And then continue the chain:
    /// // fence_signal.clone()
    /// //      .then_execute(baz)
    /// //      .then_execute(qux)
    ///
    /// // Later you can wait until you reach the point of `fence_signal`:
    /// fence_signal.wait(None).unwrap();
    /// ```
    #[must_use = "Dropping this object will immediately block the thread until the GPU has finished \
                  processing the submission"]
    pub struct FenceSignalFuture<F>
        where F: GpuFuture
    {
        // Current state. See the docs of `FenceSignalFutureState`.
        state: Mutex<FenceSignalFutureState<F>>,
        // The device of the future.
        device: Arc<Device>,
        behavior: FenceSignalFutureBehavior,
    }

    // This future can be in three different states: pending (ie. newly-created), submitted (ie. the
    // command that submits the fence has been submitted), or cleaned (ie. the previous future has
    // been dropped).
    enum FenceSignalFutureState<F> {
        // Newly-created. Not submitted yet.
        Pending(F, Fence),

        // Partially submitted to the queue. Only happens in situations where submitting requires two
        // steps, and when the first step succeeded while the second step failed.
        //
        // Note that if there's ever a submit operation that needs three steps we will need to rework
        // this code, as it was designed for two-step operations only.
        PartiallyFlushed(F, Fence),

        // Submitted to the queue.
        Flushed(F, Fence),

        // The submission is finished. The previous future and the fence have been cleaned.
        Cleaned,

        // A function panicked while the state was being modified. Should never happen.
        Poisoned,
    }

    impl<F> FenceSignalFuture<F>
        where F: GpuFuture
    {
        /// Blocks the current thread until the fence is signaled by the GPU. Performs a flush if
        /// necessary.
        ///
        /// If `timeout` is `None`, then the wait is infinite. Otherwise the thread will unblock after
        /// the specified timeout has elapsed and an error will be returned.
        ///
        /// If the wait is successful, this function also cleans any resource locked by previous
        /// submissions.
        pub fn wait(&self, timeout: Option<Duration>) -> Result<(), FlushError> {
            let mut state = self.state.lock().unwrap();

            self.flush_impl(&mut state)?;

            match mem::replace(&mut *state, FenceSignalFutureState::Cleaned) {
                FenceSignalFutureState::Flushed(previous, fence) => {
                    fence.wait(timeout)?;
                    unsafe {
                        previous.signal_finished();
                    }
                    Ok(())
                },
                FenceSignalFutureState::Cleaned => Ok(()),
                _ => unreachable!(),
            }
        }
    }

    impl<F> FenceSignalFuture<F>
        where F: GpuFuture
    {
        // Implementation of `cleanup_finished`, but takes a `&self` instead of a `&mut self`.
        // This is an external function so that we can also call it from an `Arc<FenceSignalFuture>`.
        #[inline]
        fn cleanup_finished_impl(&self) {
            let mut state = self.state.lock().unwrap();

            match *state {
                FenceSignalFutureState::Flushed(ref mut prev, ref fence) => {
                    match fence.wait(Some(Duration::from_secs(0))) {
                        Ok(()) => unsafe {
                            prev.signal_finished()
                        },
                        Err(_) => {
                            prev.cleanup_finished();
                            return;
                        },
                    }
                },
                FenceSignalFutureState::Pending(ref mut prev, _) => {
                    prev.cleanup_finished();
                    return;
                },
                FenceSignalFutureState::PartiallyFlushed(ref mut prev, _) => {
                    prev.cleanup_finished();
                    return;
                },
                _ => return,
            };

            // This code can only be reached if we're already flushed and waiting on the fence
            // succeeded.
            *state = FenceSignalFutureState::Cleaned;
        }

        // Implementation of `flush`. You must lock the state and pass the mutex guard here.
        fn flush_impl(&self, state: &mut MutexGuard<FenceSignalFutureState<F>>)
                      -> Result<(), FlushError> {
            unsafe {
                // In this function we temporarily replace the current state with `Poisoned` at the
                // beginning, and we take care to always put back a value into `state` before
                // returning (even in case of error).
                let old_state = mem::replace(&mut **state, FenceSignalFutureState::Poisoned);

                let (previous, fence, partially_flushed) = match old_state {
                    FenceSignalFutureState::Pending(prev, fence) => {
                        (prev, fence, false)
                    },
                    FenceSignalFutureState::PartiallyFlushed(prev, fence) => {
                        (prev, fence, true)
                    },
                    other => {
                        // We were already flushed in the past, or we're already poisoned. Don't do
                        // anything.
                        **state = other;
                        return Ok(());
                    },
                };

                // TODO: meh for unwrap
                let queue = previous.queue().unwrap().clone();

                // There are three possible outcomes for the flush operation: success, partial success
                // in which case `result` will contain `Err(OutcomeErr::Partial)`, or total failure
                // in which case `result` will contain `Err(OutcomeErr::Full)`.
                enum OutcomeErr<E> {
                    Partial(E),
                    Full(E),
                }
                let result = match previous.build_submission()? {
                    SubmitAnyBuilder::Empty => {
                        debug_assert!(!partially_flushed);
                        let mut b = SubmitCommandBufferBuilder::new();
                        b.set_fence_signal(&fence);
                        b.submit(&queue).map_err(|err| OutcomeErr::Full(err.into()))
                    },
                    SubmitAnyBuilder::SemaphoresWait(sem) => {
                        debug_assert!(!partially_flushed);
                        let b: SubmitCommandBufferBuilder = sem.into();
                        debug_assert!(!b.has_fence());
                        b.submit(&queue).map_err(|err| OutcomeErr::Full(err.into()))
                    },
                    SubmitAnyBuilder::CommandBuffer(mut cb_builder) => {
                        debug_assert!(!partially_flushed);
                        // The assert below could technically be a debug assertion as it is part of the
                        // safety contract of the trait. However it is easy to get this wrong if you
                        // write a custom implementation, and if so the consequences would be
                        // disastrous and hard to debug. Therefore we prefer to just use a regular
                        // assertion.
                        assert!(!cb_builder.has_fence());
                        cb_builder.set_fence_signal(&fence);
                        cb_builder
                            .submit(&queue)
                            .map_err(|err| OutcomeErr::Full(err.into()))
                    },
                    SubmitAnyBuilder::BindSparse(mut sparse) => {
                        debug_assert!(!partially_flushed);
                        // Same remark as `CommandBuffer`.
                        assert!(!sparse.has_fence());
                        sparse.set_fence_signal(&fence);
                        sparse
                            .submit(&queue)
                            .map_err(|err| OutcomeErr::Full(err.into()))
                    },
                    SubmitAnyBuilder::QueuePresent(present) => {
                        let intermediary_result = if partially_flushed {
                            Ok(())
                        } else {
                            present.submit(&queue)
                        };
                        match intermediary_result {
                            Ok(()) => {
                                let mut b = SubmitCommandBufferBuilder::new();
                                b.set_fence_signal(&fence);
                                b.submit(&queue).map_err(|err| OutcomeErr::Partial(err.into()))
                            },
                            Err(err) => {
                                Err(OutcomeErr::Full(err.into()))
                            },
                        }
                    },
                };

                // Restore the state before returning.
                match result {
                    Ok(()) => {
                        **state = FenceSignalFutureState::Flushed(previous, fence);
                        Ok(())
                    },
                    Err(OutcomeErr::Partial(err)) => {
                        **state = FenceSignalFutureState::PartiallyFlushed(previous, fence);
                        Err(err)
                    },
                    Err(OutcomeErr::Full(err)) => {
                        **state = FenceSignalFutureState::Pending(previous, fence);
                        Err(err)
                    },
                }
            }
        }
    }

    impl<F> FenceSignalFutureState<F> {
        #[inline]
        fn get_prev(&self) -> Option<&F> {
            match *self {
                FenceSignalFutureState::Pending(ref prev, _) => Some(prev),
                FenceSignalFutureState::PartiallyFlushed(ref prev, _) => Some(prev),
                FenceSignalFutureState::Flushed(ref prev, _) => Some(prev),
                FenceSignalFutureState::Cleaned => None,
                FenceSignalFutureState::Poisoned => None,
            }
        }
    }

    unsafe impl<F> GpuFuture for FenceSignalFuture<F>
        where F: GpuFuture
    {
        #[inline]
        fn cleanup_finished(&mut self) {
            self.cleanup_finished_impl()
        }

        #[inline]
        unsafe fn build_submission(&self) -> Result<SubmitAnyBuilder, FlushError> {
            let mut state = self.state.lock().unwrap();
            self.flush_impl(&mut state)?;

            match *state {
                FenceSignalFutureState::Flushed(_, ref fence) => {
                    match self.behavior {
                        FenceSignalFutureBehavior::Block { timeout } => {
                            fence.wait(timeout)?;
                        },
                        FenceSignalFutureBehavior::Continue => (),
                    }
                },
                FenceSignalFutureState::Cleaned |
                FenceSignalFutureState::Poisoned => (),
                FenceSignalFutureState::Pending(_, _) => unreachable!(),
                FenceSignalFutureState::PartiallyFlushed(_, _) => unreachable!(),
            }

            Ok(SubmitAnyBuilder::Empty)
        }

        #[inline]
        fn flush(&self) -> Result<(), FlushError> {
            let mut state = self.state.lock().unwrap();
            self.flush_impl(&mut state)
        }

        #[inline]
        unsafe fn signal_finished(&self) {
            let state = self.state.lock().unwrap();
            match *state {
                FenceSignalFutureState::Flushed(ref prev, _) => {
                    prev.signal_finished();
                },
                FenceSignalFutureState::Cleaned |
                FenceSignalFutureState::Poisoned => (),
                _ => unreachable!(),
            }
        }

        #[inline]
        fn queue_change_allowed(&self) -> bool {
            match self.behavior {
                FenceSignalFutureBehavior::Continue => {
                    let state = self.state.lock().unwrap();
                    if state.get_prev().is_some() {
                        false
                    } else {
                        true
                    }
                },
                FenceSignalFutureBehavior::Block { .. } => {
                    true
                },
            }
        }

        #[inline]
        fn queue(&self) -> Option<Arc<Queue>> {
            let state = self.state.lock().unwrap();
            if let Some(prev) = state.get_prev() {
                prev.queue()
            } else {
                None
            }
        }

        #[inline]
        fn check_buffer_access(
            &self, buffer: &dyn BufferAccess, exclusive: bool, queue: &Queue)
            -> Result<Option<(PipelineStages, AccessFlagBits)>, AccessCheckError> {
            let state = self.state.lock().unwrap();
            if let Some(previous) = state.get_prev() {
                previous.check_buffer_access(buffer, exclusive, queue)
            } else {
                Err(AccessCheckError::Unknown)
            }
        }

        #[inline]
        fn check_image_access(&self, image: &dyn ImageAccess, layout: ImageLayout, exclusive: bool,
                              queue: &Queue)
                              -> Result<Option<(PipelineStages, AccessFlagBits)>, AccessCheckError> {
            let state = self.state.lock().unwrap();
            if let Some(previous) = state.get_prev() {
                previous.check_image_access(image, layout, exclusive, queue)
            } else {
                Err(AccessCheckError::Unknown)
            }
        }
    }

    unsafe impl<F> DeviceOwned for FenceSignalFuture<F>
        where F: GpuFuture
    {
        #[inline]
        fn device(&self) -> &Arc<Device> {
            &self.device
        }
    }

    impl<F> Drop for FenceSignalFuture<F>
        where F: GpuFuture
    {
        fn drop(&mut self) {
            let mut state = self.state.lock().unwrap();

            // We ignore any possible error while submitting for now. Problems are handled below.
            let _ = self.flush_impl(&mut state);

            match mem::replace(&mut *state, FenceSignalFutureState::Cleaned) {
                FenceSignalFutureState::Flushed(previous, fence) => {
                    // This is a normal situation. Submitting worked.
                    // TODO: handle errors?
                    fence.wait(None).unwrap();
                    unsafe {
                        previous.signal_finished();
                    }
                },
                FenceSignalFutureState::Cleaned => {
                    // Also a normal situation. The user called `cleanup_finished()` before dropping.
                },
                FenceSignalFutureState::Poisoned => {
                    // The previous future was already dropped and blocked the current queue.
                },
                FenceSignalFutureState::Pending(_, _) |
                FenceSignalFutureState::PartiallyFlushed(_, _) => {
                    // Flushing produced an error. There's nothing more we can do except drop the
                    // previous future and let it block the current queue.
                },
            }
        }
    }

    unsafe impl<F> GpuFuture for Arc<FenceSignalFuture<F>>
        where F: GpuFuture
    {
        #[inline]
        fn cleanup_finished(&mut self) {
            self.cleanup_finished_impl()
        }

        #[inline]
        unsafe fn build_submission(&self) -> Result<SubmitAnyBuilder, FlushError> {
            // Note that this is sound because we always return `SubmitAnyBuilder::Empty`. See the
            // documentation of `build_submission`.
            (**self).build_submission()
        }

        #[inline]
        fn flush(&self) -> Result<(), FlushError> {
            (**self).flush()
        }

        #[inline]
        unsafe fn signal_finished(&self) {
            (**self).signal_finished()
        }

        #[inline]
        fn queue_change_allowed(&self) -> bool {
            (**self).queue_change_allowed()
        }

        #[inline]
        fn queue(&self) -> Option<Arc<Queue>> {
            (**self).queue()
        }

        #[inline]
        fn check_buffer_access(
            &self, buffer: &dyn BufferAccess, exclusive: bool, queue: &Queue)
            -> Result<Option<(PipelineStages, AccessFlagBits)>, AccessCheckError> {
            (**self).check_buffer_access(buffer, exclusive, queue)
        }

        #[inline]
        fn check_image_access(&self, image: &dyn ImageAccess, layout: ImageLayout, exclusive: bool,
                              queue: &Queue)
                              -> Result<Option<(PipelineStages, AccessFlagBits)>, AccessCheckError> {
            (**self).check_image_access(image, layout, exclusive, queue)
        }
    }

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