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    // Copyright (c) 2016 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.

    //! Buffer whose content is read-written by the GPU only.
    //!
    //! Each access from the CPU or from the GPU locks the whole buffer for either reading or writing.
    //! You can read the buffer multiple times simultaneously from multiple queues. Trying to read and
    //! write simultaneously, or write and write simultaneously will block with a semaphore.

    use smallvec::SmallVec;
    use std::marker::PhantomData;
    use std::mem;
    use std::sync::Arc;
    use std::sync::Mutex;

    use buffer::BufferUsage;
    use buffer::sys::BufferCreationError;
    use buffer::sys::SparseLevel;
    use buffer::sys::UnsafeBuffer;
    use buffer::traits::BufferAccess;
    use buffer::traits::BufferInner;
    use buffer::traits::TypedBufferAccess;
    use device::Device;
    use device::DeviceOwned;
    use device::Queue;
    use image::ImageAccess;
    use instance::QueueFamily;
    use memory::DedicatedAlloc;
    use memory::DeviceMemoryAllocError;
    use memory::pool::AllocFromRequirementsFilter;
    use memory::pool::AllocLayout;
    use memory::pool::MappingRequirement;
    use memory::pool::MemoryPool;
    use memory::pool::MemoryPoolAlloc;
    use memory::pool::PotentialDedicatedAllocation;
    use memory::pool::StdMemoryPoolAlloc;
    use sync::AccessError;
    use sync::Sharing;

    /// Buffer whose content is in device-local memory.
    ///
    /// This buffer type is useful in order to store intermediary data. For example you execute a
    /// compute shader that writes to this buffer, then read the content of the buffer in a following
    /// compute or graphics pipeline.
    ///
    /// The `DeviceLocalBuffer` will be in device-local memory, unless the device doesn't provide any
    /// device-local memory.
    #[derive(Debug)]
    pub struct DeviceLocalBuffer<T: ?Sized, A = PotentialDedicatedAllocation<StdMemoryPoolAlloc>> {
        // Inner content.
        inner: UnsafeBuffer,

        // The memory held by the buffer.
        memory: A,

        // Queue families allowed to access this buffer.
        queue_families: SmallVec<[u32; 4]>,

        // Number of times this buffer is locked on the GPU side.
        gpu_lock: Mutex<GpuAccess>,

        // Necessary to make it compile.
        marker: PhantomData<Box<T>>,
    }

    #[derive(Debug, Copy, Clone)]
    enum GpuAccess {
        None,
        NonExclusive { num: u32 },
        Exclusive { num: u32 },
    }

    impl<T> DeviceLocalBuffer<T> {
        /// Builds a new buffer. Only allowed for sized data.
        // TODO: unsafe because uninitialized data
        #[inline]
        pub fn new<'a, I>(device: Arc<Device>, usage: BufferUsage, queue_families: I)
                          -> Result<Arc<DeviceLocalBuffer<T>>, DeviceMemoryAllocError>
            where I: IntoIterator<Item = QueueFamily<'a>>
        {
            unsafe { DeviceLocalBuffer::raw(device, mem::size_of::<T>(), usage, queue_families) }
        }
    }

    impl<T> DeviceLocalBuffer<[T]> {
        /// Builds a new buffer. Can be used for arrays.
        // TODO: unsafe because uninitialized data
        #[inline]
        pub fn array<'a, I>(device: Arc<Device>, len: usize, usage: BufferUsage, queue_families: I)
                            -> Result<Arc<DeviceLocalBuffer<[T]>>, DeviceMemoryAllocError>
            where I: IntoIterator<Item = QueueFamily<'a>>
        {
            unsafe { DeviceLocalBuffer::raw(device, len * mem::size_of::<T>(), usage, queue_families) }
        }
    }

    impl<T: ?Sized> DeviceLocalBuffer<T> {
        /// Builds a new buffer without checking the size.
        ///
        /// # Safety
        ///
        /// You must ensure that the size that you pass is correct for `T`.
        ///
        pub unsafe fn raw<'a, I>(device: Arc<Device>, size: usize, usage: BufferUsage,
                                 queue_families: I)
                                 -> Result<Arc<DeviceLocalBuffer<T>>, DeviceMemoryAllocError>
            where I: IntoIterator<Item = QueueFamily<'a>>
        {
            let queue_families = queue_families
                .into_iter()
                .map(|f| f.id())
                .collect::<SmallVec<[u32; 4]>>();

            let (buffer, mem_reqs) = {
                let sharing = if queue_families.len() >= 2 {
                    Sharing::Concurrent(queue_families.iter().cloned())
                } else {
                    Sharing::Exclusive
                };

                match UnsafeBuffer::new(device.clone(), size, usage, sharing, SparseLevel::none()) {
                    Ok(b) => b,
                    Err(BufferCreationError::AllocError(err)) => return Err(err),
                    Err(_) => unreachable!(),        // We don't use sparse binding, therefore the other
                    // errors can't happen
                }
            };

            let mem = MemoryPool::alloc_from_requirements(&Device::standard_pool(&device),
                                        &mem_reqs,
                                        AllocLayout::Linear,
                                        MappingRequirement::DoNotMap,
                                        DedicatedAlloc::Buffer(&buffer),
                                        |t| if t.is_device_local() {
                                            AllocFromRequirementsFilter::Preferred
                                        } else {
                                            AllocFromRequirementsFilter::Allowed
                                        })?;
            debug_assert!((mem.offset() % mem_reqs.alignment) == 0);
            buffer.bind_memory(mem.memory(), mem.offset())?;

            Ok(Arc::new(DeviceLocalBuffer {
                            inner: buffer,
                            memory: mem,
                            queue_families: queue_families,
                            gpu_lock: Mutex::new(GpuAccess::None),
                            marker: PhantomData,
                        }))
        }
    }

    impl<T: ?Sized, A> DeviceLocalBuffer<T, A> {
        /// Returns the queue families this buffer can be used on.
        // TODO: use a custom iterator
        #[inline]
        pub fn queue_families(&self) -> Vec<QueueFamily> {
            self.queue_families
                .iter()
                .map(|&num| {
                         self.device()
                             .physical_device()
                             .queue_family_by_id(num)
                             .unwrap()
                     })
                .collect()
        }
    }

    unsafe impl<T: ?Sized, A> DeviceOwned for DeviceLocalBuffer<T, A> {
        #[inline]
        fn device(&self) -> &Arc<Device> {
            self.inner.device()
        }
    }

    unsafe impl<T: ?Sized, A> BufferAccess for DeviceLocalBuffer<T, A>
        where T: 'static + Send + Sync
    {
        #[inline]
        fn inner(&self) -> BufferInner {
            BufferInner {
                buffer: &self.inner,
                offset: 0,
            }
        }

        #[inline]
        fn size(&self) -> usize {
            self.inner.size()
        }

        #[inline]
        fn conflicts_buffer(&self, other: &dyn BufferAccess) -> bool {
            self.conflict_key() == other.conflict_key() // TODO:
        }

        #[inline]
        fn conflicts_image(&self, other: &dyn ImageAccess) -> bool {
            false
        }

        #[inline]
        fn conflict_key(&self) -> (u64, usize) {
            (self.inner.key(), 0)
        }

        #[inline]
        fn try_gpu_lock(&self, exclusive: bool, _: &Queue) -> Result<(), AccessError> {
            let mut lock = self.gpu_lock.lock().unwrap();
            match &mut *lock {
                a @ &mut GpuAccess::None => {
                    if exclusive {
                        *a = GpuAccess::Exclusive { num: 1 };
                    } else {
                        *a = GpuAccess::NonExclusive { num: 1 };
                    }

                    Ok(())
                },
                &mut GpuAccess::NonExclusive { ref mut num } => {
                    if exclusive {
                        Err(AccessError::AlreadyInUse)
                    } else {
                        *num += 1;
                        Ok(())
                    }
                },
                &mut GpuAccess::Exclusive { .. } => {
                    Err(AccessError::AlreadyInUse)
                },
            }
        }

        #[inline]
        unsafe fn increase_gpu_lock(&self) {
            let mut lock = self.gpu_lock.lock().unwrap();
            match *lock {
                GpuAccess::None => panic!(),
                GpuAccess::NonExclusive { ref mut num } => {
                    debug_assert!(*num >= 1);
                    *num += 1;
                },
                GpuAccess::Exclusive { ref mut num } => {
                    debug_assert!(*num >= 1);
                    *num += 1;
                },
            }
        }

        #[inline]
        unsafe fn unlock(&self) {
            let mut lock = self.gpu_lock.lock().unwrap();

            match *lock {
                GpuAccess::None => panic!("Tried to unlock a buffer that isn't locked"),
                GpuAccess::NonExclusive { ref mut num } => {
                    assert!(*num >= 1);
                    *num -= 1;
                    if *num >= 1 {
                        return;
                    }
                },
                GpuAccess::Exclusive { ref mut num } => {
                    assert!(*num >= 1);
                    *num -= 1;
                    if *num >= 1 {
                        return;
                    }
                },
            };

            *lock = GpuAccess::None;
        }
    }

    unsafe impl<T: ?Sized, A> TypedBufferAccess for DeviceLocalBuffer<T, A>
        where T: 'static + Send + Sync
    {
        type Content = T;
    }

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