// Copyright (c) 2017 The vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or https://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::sync::atomic::AtomicBool;
use std::sync::atomic::Ordering;
use std::sync::Arc;
use std::sync::Mutex;

use crate::buffer::BufferAccess;
use crate::command_buffer::submit::SubmitAnyBuilder;
use crate::command_buffer::submit::SubmitCommandBufferBuilder;
use crate::command_buffer::submit::SubmitSemaphoresWaitBuilder;
use crate::device::Device;
use crate::device::DeviceOwned;
use crate::device::Queue;
use crate::image::ImageAccess;
use crate::image::ImageLayout;
use crate::sync::AccessCheckError;
use crate::sync::AccessFlags;
use crate::sync::FlushError;
use crate::sync::GpuFuture;
use crate::sync::PipelineStages;
use crate::sync::Semaphore;

/// Builds a new semaphore signal future.
#[inline]
pub fn then_signal_semaphore<F>(future: F) -> SemaphoreSignalFuture<F>
where
    F: GpuFuture,
{
    let device = future.device().clone();

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

    SemaphoreSignalFuture {
        previous: future,
        semaphore: Semaphore::from_pool(device).unwrap(),
        wait_submitted: Mutex::new(false),
        finished: AtomicBool::new(false),
    }
}

/// Represents a semaphore being signaled after a previous event.
#[must_use = "Dropping this object will immediately block the thread until the GPU has finished \
              processing the submission"]
pub struct SemaphoreSignalFuture<F>
where
    F: GpuFuture,
{
    previous: F,
    semaphore: Semaphore,
    // True if the signaling command has already been submitted.
    // If flush is called multiple times, we want to block so that only one flushing is executed.
    // Therefore we use a `Mutex<bool>` and not an `AtomicBool`.
    wait_submitted: Mutex<bool>,
    finished: AtomicBool,
}

unsafe impl<F> GpuFuture for SemaphoreSignalFuture<F>
where
    F: GpuFuture,
{
    #[inline]
    fn cleanup_finished(&mut self) {
        self.previous.cleanup_finished();
    }

    #[inline]
    unsafe fn build_submission(&self) -> Result<SubmitAnyBuilder, FlushError> {
        // Flushing the signaling part, since it must always be submitted before the waiting part.
        self.flush()?;

        let mut sem = SubmitSemaphoresWaitBuilder::new();
        sem.add_wait_semaphore(&self.semaphore);
        Ok(SubmitAnyBuilder::SemaphoresWait(sem))
    }

    fn flush(&self) -> Result<(), FlushError> {
        unsafe {
            let mut wait_submitted = self.wait_submitted.lock().unwrap();

            if *wait_submitted {
                return Ok(());
            }

            let queue = self.previous.queue().unwrap().clone();

            match self.previous.build_submission()? {
                SubmitAnyBuilder::Empty => {
                    let mut builder = SubmitCommandBufferBuilder::new();
                    builder.add_signal_semaphore(&self.semaphore);
                    builder.submit(&queue)?;
                }
                SubmitAnyBuilder::SemaphoresWait(sem) => {
                    let mut builder: SubmitCommandBufferBuilder = sem.into();
                    builder.add_signal_semaphore(&self.semaphore);
                    builder.submit(&queue)?;
                }
                SubmitAnyBuilder::CommandBuffer(mut builder) => {
                    debug_assert_eq!(builder.num_signal_semaphores(), 0);
                    builder.add_signal_semaphore(&self.semaphore);
                    builder.submit(&queue)?;
                }
                SubmitAnyBuilder::BindSparse(_) => {
                    unimplemented!() // TODO: how to do that?
                                     /*debug_assert_eq!(builder.num_signal_semaphores(), 0);
                                     builder.add_signal_semaphore(&self.semaphore);
                                     builder.submit(&queue)?;*/
                }
                SubmitAnyBuilder::QueuePresent(present) => {
                    present.submit(&queue)?;
                    let mut builder = SubmitCommandBufferBuilder::new();
                    builder.add_signal_semaphore(&self.semaphore);
                    builder.submit(&queue)?; // FIXME: problematic because if we return an error and flush() is called again, then we'll submit the present twice
                }
            };

            // Only write `true` here in order to try again next time if an error occurs.
            *wait_submitted = true;
            Ok(())
        }
    }

    #[inline]
    unsafe fn signal_finished(&self) {
        debug_assert!(*self.wait_submitted.lock().unwrap());
        self.finished.store(true, Ordering::SeqCst);
        self.previous.signal_finished();
    }

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

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

    #[inline]
    fn check_buffer_access(
        &self,
        buffer: &dyn BufferAccess,
        exclusive: bool,
        queue: &Queue,
    ) -> Result<Option<(PipelineStages, AccessFlags)>, AccessCheckError> {
        self.previous
            .check_buffer_access(buffer, exclusive, queue)
            .map(|_| None)
    }

    #[inline]
    fn check_image_access(
        &self,
        image: &dyn ImageAccess,
        layout: ImageLayout,
        exclusive: bool,
        queue: &Queue,
    ) -> Result<Option<(PipelineStages, AccessFlags)>, AccessCheckError> {
        self.previous
            .check_image_access(image, layout, exclusive, queue)
            .map(|_| None)
    }
}

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

impl<F> Drop for SemaphoreSignalFuture<F>
where
    F: GpuFuture,
{
    fn drop(&mut self) {
        unsafe {
            if !*self.finished.get_mut() {
                // TODO: handle errors?
                self.flush().unwrap();
                // Block until the queue finished.
                self.queue().unwrap().wait().unwrap();
                self.previous.signal_finished();
            }
        }
    }
}