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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.

    use crossbeam::queue::SegQueue;
    use fnv::FnvHashMap;
    use std::collections::hash_map::Entry;
    use std::marker::PhantomData;
    use std::mem::ManuallyDrop;
    use std::ptr;
    use std::sync::Arc;
    use std::sync::Mutex;
    use std::sync::Weak;
    use std::thread;
    use std::vec::IntoIter as VecIntoIter;

    use command_buffer::pool::CommandPool;
    use command_buffer::pool::CommandPoolAlloc;
    use command_buffer::pool::CommandPoolBuilderAlloc;
    use command_buffer::pool::UnsafeCommandPool;
    use command_buffer::pool::UnsafeCommandPoolAlloc;
    use instance::QueueFamily;

    use OomError;
    use VulkanObject;
    use device::Device;
    use device::DeviceOwned;

    /// Standard implementation of a command pool.
    ///
    /// It is guaranteed that the allocated command buffers keep the `Arc<StandardCommandPool>` alive.
    /// This is desirable so that we can store a `Weak<StandardCommandPool>`.
    ///
    /// Will use one Vulkan pool per thread in order to avoid locking. Will try to reuse command
    /// buffers. Command buffers can't be moved between threads during the building process, but
    /// finished command buffers can.
    pub struct StandardCommandPool {
        // The device.
        device: Arc<Device>,

        // Identifier of the queue family.
        queue_family: u32,

        // For each thread, we store thread-specific info.
        per_thread: Mutex<FnvHashMap<thread::ThreadId, Weak<StandardCommandPoolPerThread>>>,
    }

    unsafe impl Send for StandardCommandPool {
    }
    unsafe impl Sync for StandardCommandPool {
    }

    struct StandardCommandPoolPerThread {
        // The Vulkan pool of this thread.
        pool: Mutex<UnsafeCommandPool>,
        // List of existing primary command buffers that are available for reuse.
        available_primary_command_buffers: SegQueue<UnsafeCommandPoolAlloc>,
        // List of existing secondary command buffers that are available for reuse.
        available_secondary_command_buffers: SegQueue<UnsafeCommandPoolAlloc>,
    }

    impl StandardCommandPool {
        /// Builds a new pool.
        ///
        /// # Panic
        ///
        /// - Panics if the device and the queue family don't belong to the same physical device.
        ///
        pub fn new(device: Arc<Device>, queue_family: QueueFamily) -> StandardCommandPool {
            assert_eq!(device.physical_device().internal_object(),
                       queue_family.physical_device().internal_object());

            StandardCommandPool {
                device: device,
                queue_family: queue_family.id(),
                per_thread: Mutex::new(Default::default()),
            }
        }
    }

    unsafe impl CommandPool for Arc<StandardCommandPool> {
        type Iter = VecIntoIter<StandardCommandPoolBuilder>;
        type Builder = StandardCommandPoolBuilder;
        type Alloc = StandardCommandPoolAlloc;

        fn alloc(&self, secondary: bool, count: u32) -> Result<Self::Iter, OomError> {
            // Find the correct `StandardCommandPoolPerThread` structure.
            let mut hashmap = self.per_thread.lock().unwrap();
            // TODO: meh for iterating everything every time
            hashmap.retain(|_, w| w.upgrade().is_some());

            // Get an appropriate `Arc<StandardCommandPoolPerThread>`.
            let per_thread = match hashmap.entry(thread::current().id()) {
                Entry::Occupied(entry) => {
                    // The `unwrap()` can't fail, since we retained only valid members earlier.
                    entry.get().upgrade().unwrap()
                },
                Entry::Vacant(entry) => {
                    let new_pool =
                        UnsafeCommandPool::new(self.device.clone(), self.queue_family(), false, true)?;
                    let pt = Arc::new(StandardCommandPoolPerThread {
                                          pool: Mutex::new(new_pool),
                                          available_primary_command_buffers: SegQueue::new(),
                                          available_secondary_command_buffers: SegQueue::new(),
                                      });

                    entry.insert(Arc::downgrade(&pt));
                    pt
                },
            };

            // The final output.
            let mut output = Vec::with_capacity(count as usize);

            // First, pick from already-existing command buffers.
            {
                let existing = if secondary {
                    &per_thread.available_secondary_command_buffers
                } else {
                    &per_thread.available_primary_command_buffers
                };

                for _ in 0 .. count as usize {
                    if let Ok(cmd) = existing.pop() {
                        output.push(StandardCommandPoolBuilder {
                                        inner: StandardCommandPoolAlloc {
                                            cmd: ManuallyDrop::new(cmd),
                                            pool: per_thread.clone(),
                                            pool_parent: self.clone(),
                                            secondary: secondary,
                                            device: self.device.clone(),
                                        },
                                        dummy_avoid_send_sync: PhantomData,
                                    });
                    } else {
                        break;
                    }
                }
            };

            // Then allocate the rest.
            if output.len() < count as usize {
                let pool_lock = per_thread.pool.lock().unwrap();
                let num_new = count as usize - output.len();

                for cmd in pool_lock.alloc_command_buffers(secondary, num_new)? {
                    output.push(StandardCommandPoolBuilder {
                                    inner: StandardCommandPoolAlloc {
                                        cmd: ManuallyDrop::new(cmd),
                                        pool: per_thread.clone(),
                                        pool_parent: self.clone(),
                                        secondary: secondary,
                                        device: self.device.clone(),
                                    },
                                    dummy_avoid_send_sync: PhantomData,
                                });
                }
            }

            // Final output.
            Ok(output.into_iter())
        }

        #[inline]
        fn queue_family(&self) -> QueueFamily {
            self.device
                .physical_device()
                .queue_family_by_id(self.queue_family)
                .unwrap()
        }
    }

    unsafe impl DeviceOwned for StandardCommandPool {
        #[inline]
        fn device(&self) -> &Arc<Device> {
            &self.device
        }
    }

    /// Command buffer allocated from a `StandardCommandPool` and that is currently being built.
    pub struct StandardCommandPoolBuilder {
        // The only difference between a `StandardCommandPoolBuilder` and a `StandardCommandPoolAlloc`
        // is that the former must not implement `Send` and `Sync`. Therefore we just share the structs.
        inner: StandardCommandPoolAlloc,
        // Unimplemented `Send` and `Sync` from the builder.
        dummy_avoid_send_sync: PhantomData<*const u8>,
    }

    unsafe impl CommandPoolBuilderAlloc for StandardCommandPoolBuilder {
        type Alloc = StandardCommandPoolAlloc;

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

        #[inline]
        fn into_alloc(self) -> Self::Alloc {
            self.inner
        }

        #[inline]
        fn queue_family(&self) -> QueueFamily {
            self.inner.queue_family()
        }
    }

    unsafe impl DeviceOwned for StandardCommandPoolBuilder {
        #[inline]
        fn device(&self) -> &Arc<Device> {
            self.inner.device()
        }
    }

    /// Command buffer allocated from a `StandardCommandPool`.
    pub struct StandardCommandPoolAlloc {
        // The actual command buffer. Extracted in the `Drop` implementation.
        cmd: ManuallyDrop<UnsafeCommandPoolAlloc>,
        // We hold a reference to the command pool for our destructor.
        pool: Arc<StandardCommandPoolPerThread>,
        // Keep alive the `StandardCommandPool`, otherwise it would be destroyed.
        pool_parent: Arc<StandardCommandPool>,
        // True if secondary command buffer.
        secondary: bool,
        // The device we belong to. Necessary because of the `DeviceOwned` trait implementation.
        device: Arc<Device>,
    }

    unsafe impl Send for StandardCommandPoolAlloc {
    }
    unsafe impl Sync for StandardCommandPoolAlloc {
    }

    unsafe impl CommandPoolAlloc for StandardCommandPoolAlloc {
        #[inline]
        fn inner(&self) -> &UnsafeCommandPoolAlloc {
            &*self.cmd
        }

        #[inline]
        fn queue_family(&self) -> QueueFamily {
            let queue_family_id = self.pool.pool.lock().unwrap().queue_family().id();

            self.device
                .physical_device()
                .queue_family_by_id(queue_family_id)
                .unwrap()
        }
    }

    unsafe impl DeviceOwned for StandardCommandPoolAlloc {
        #[inline]
        fn device(&self) -> &Arc<Device> {
            // Note that we could grab the device from `self.pool`. Unfortunately this requires a mutex
            // lock, so it isn't compatible with the API of `DeviceOwned`.
            &self.device
        }
    }

    impl Drop for StandardCommandPoolAlloc {
        fn drop(&mut self) {
            // Safe because `self.cmd` is wrapped in a `ManuallyDrop`.
            let cmd: UnsafeCommandPoolAlloc = unsafe { ptr::read(&*self.cmd) };

            if self.secondary {
                self.pool.available_secondary_command_buffers.push(cmd);
            } else {
                self.pool.available_primary_command_buffers.push(cmd);
            }
        }
    }

    #[cfg(test)]
    mod tests {
        use VulkanObject;
        use command_buffer::pool::CommandPool;
        use command_buffer::pool::CommandPoolBuilderAlloc;
        use command_buffer::pool::StandardCommandPool;
        use device::Device;
        use std::sync::Arc;

        #[test]
        fn reuse_command_buffers() {
            let (device, _) = gfx_dev_and_queue!();
            let queue_family = device.physical_device().queue_families().next().unwrap();

            let pool = Device::standard_command_pool(&device, queue_family);

            let cb = pool.alloc(false, 1).unwrap().next().unwrap();
            let raw = cb.inner().internal_object();
            drop(cb);

            let cb2 = pool.alloc(false, 1).unwrap().next().unwrap();
            assert_eq!(raw, cb2.inner().internal_object());
        }

        #[test]
        fn pool_kept_alive_by_allocs() {
            let (device, queue) = gfx_dev_and_queue!();

            let pool = Arc::new(StandardCommandPool::new(device, queue.family()));
            let pool_weak = Arc::downgrade(&pool);

            let cb = pool.alloc(false, 1).unwrap().next().unwrap();
            drop(pool);
            assert!(pool_weak.upgrade().is_some());

            drop(cb);
            assert!(pool_weak.upgrade().is_none());
        }
    }

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