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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 std::sync::Arc;
    use std::sync::Mutex;

    use OomError;
    use descriptor::descriptor_set::DescriptorPool;
    use descriptor::descriptor_set::DescriptorPoolAlloc;
    use descriptor::descriptor_set::DescriptorPoolAllocError;
    use descriptor::descriptor_set::DescriptorsCount;
    use descriptor::descriptor_set::UnsafeDescriptorPool;
    use descriptor::descriptor_set::UnsafeDescriptorSet;
    use descriptor::descriptor_set::UnsafeDescriptorSetLayout;
    use device::Device;
    use device::DeviceOwned;

    /// Standard implementation of a descriptor pool.
    ///
    /// It is guaranteed that the `Arc<StdDescriptorPool>` is kept alive by its allocations. This is
    /// desirable so that we can store a `Weak<StdDescriptorPool>`.
    ///
    /// Whenever a set is allocated, this implementation will try to find a pool that has some space
    /// for it. If there is one, allocate from it. If there is none, create a new pool whose capacity
    /// is 40 sets and 40 times the requested descriptors. This number is arbitrary.
    pub struct StdDescriptorPool {
        device: Arc<Device>,
        pools: Mutex<Vec<Arc<Mutex<Pool>>>>,
    }

    struct Pool {
        pool: UnsafeDescriptorPool,
        remaining_capacity: DescriptorsCount,
        remaining_sets_count: u32,
    }

    impl StdDescriptorPool {
        /// Builds a new `StdDescriptorPool`.
        pub fn new(device: Arc<Device>) -> StdDescriptorPool {
            StdDescriptorPool {
                device: device,
                pools: Mutex::new(Vec::new()),
            }
        }
    }

    /// A descriptor set allocated from a `StdDescriptorPool`.
    pub struct StdDescriptorPoolAlloc {
        pool: Arc<Mutex<Pool>>,
        // The set. Inside an option so that we can extract it in the destructor.
        set: Option<UnsafeDescriptorSet>,
        // We need to keep track of this count in order to add it back to the capacity when freeing.
        descriptors: DescriptorsCount,
        // We keep the parent of the pool alive, otherwise it would be destroyed.
        pool_parent: Arc<StdDescriptorPool>,
    }

    unsafe impl DescriptorPool for Arc<StdDescriptorPool> {
        type Alloc = StdDescriptorPoolAlloc;

        // TODO: eventually use a lock-free algorithm?
        fn alloc(&mut self, layout: &UnsafeDescriptorSetLayout)
                 -> Result<StdDescriptorPoolAlloc, OomError> {
            let mut pools = self.pools.lock().unwrap();

            // Try find an existing pool with some free space.
            for pool_arc in pools.iter_mut() {
                let mut pool = pool_arc.lock().unwrap();

                if pool.remaining_sets_count == 0 {
                    continue;
                }

                if !(pool.remaining_capacity >= *layout.descriptors_count()) {
                    continue;
                }

                // Note that we decrease these values *before* trying to allocate from the pool.
                // If allocating from the pool results in an error, we just ignore it. In order to
                // avoid trying the same failing pool every time, we "pollute" it by reducing the
                // available space.
                pool.remaining_sets_count -= 1;
                pool.remaining_capacity -= *layout.descriptors_count();

                let alloc = unsafe {
                    match pool.pool.alloc(Some(layout)) {
                        Ok(mut sets) => sets.next().unwrap(),
                        // An error can happen if we're out of memory, or if the pool is fragmented.
                        // We handle these errors by just ignoring this pool and trying the next ones.
                        Err(_) => continue,
                    }
                };

                return Ok(StdDescriptorPoolAlloc {
                              pool: pool_arc.clone(),
                              set: Some(alloc),
                              descriptors: *layout.descriptors_count(),
                              pool_parent: self.clone(),
                          });
            }

            // No existing pool can be used. Create a new one.
            // We use an arbitrary number of 40 sets and 40 times the requested descriptors.
            let count = layout.descriptors_count().clone() * 40;
            // Failure to allocate a new pool results in an error for the whole function because
            // there's no way we can recover from that.
            let mut new_pool = UnsafeDescriptorPool::new(self.device.clone(), &count, 40, true)?;

            let alloc = unsafe {
                match new_pool.alloc(Some(layout)) {
                    Ok(mut sets) => sets.next().unwrap(),
                    Err(DescriptorPoolAllocError::OutOfHostMemory) => {
                        return Err(OomError::OutOfHostMemory);
                    },
                    Err(DescriptorPoolAllocError::OutOfDeviceMemory) => {
                        return Err(OomError::OutOfDeviceMemory);
                    },
                    // A fragmented pool error can't happen at the first ever allocation.
                    Err(DescriptorPoolAllocError::FragmentedPool) => unreachable!(),
                    // Out of pool memory cannot happen at the first ever allocation.
                    Err(DescriptorPoolAllocError::OutOfPoolMemory) => unreachable!(),
                }
            };

            let pool_obj = Arc::new(Mutex::new(Pool {
                                                   pool: new_pool,
                                                   remaining_capacity: count -
                                                       *layout.descriptors_count(),
                                                   remaining_sets_count: 40 - 1,
                                               }));

            pools.push(pool_obj.clone());

            Ok(StdDescriptorPoolAlloc {
                   pool: pool_obj,
                   set: Some(alloc),
                   descriptors: *layout.descriptors_count(),
                   pool_parent: self.clone(),
               })
        }
    }

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

    impl DescriptorPoolAlloc for StdDescriptorPoolAlloc {
        #[inline]
        fn inner(&self) -> &UnsafeDescriptorSet {
            self.set.as_ref().unwrap()
        }

        #[inline]
        fn inner_mut(&mut self) -> &mut UnsafeDescriptorSet {
            self.set.as_mut().unwrap()
        }
    }

    impl Drop for StdDescriptorPoolAlloc {
        // This is the destructor of a single allocation (not of the whole pool).
        fn drop(&mut self) {
            unsafe {
                let mut pool = self.pool.lock().unwrap();
                pool.pool.free(self.set.take()).unwrap();
                // Add back the capacity only after freeing, in case of a panic during the free.
                pool.remaining_sets_count += 1;
                pool.remaining_capacity += self.descriptors;
            }
        }
    }

    #[cfg(test)]
    mod tests {
        use descriptor::descriptor::DescriptorDesc;
        use descriptor::descriptor::DescriptorDescTy;
        use descriptor::descriptor::ShaderStages;
        use descriptor::descriptor_set::DescriptorPool;
        use descriptor::descriptor_set::StdDescriptorPool;
        use descriptor::descriptor_set::UnsafeDescriptorSetLayout;
        use std::iter;
        use std::sync::Arc;

        #[test]
        fn desc_pool_kept_alive() {
            // Test that the `StdDescriptorPool` is kept alive by its allocations.
            let (device, _) = gfx_dev_and_queue!();

            let desc = DescriptorDesc {
                ty: DescriptorDescTy::Sampler,
                array_count: 1,
                stages: ShaderStages::all(),
                readonly: false,
            };
            let layout = UnsafeDescriptorSetLayout::new(device.clone(), iter::once(Some(desc)))
                .unwrap();

            let mut pool = Arc::new(StdDescriptorPool::new(device));
            let pool_weak = Arc::downgrade(&pool);
            let alloc = pool.alloc(&layout);
            drop(pool);
            assert!(pool_weak.upgrade().is_some());
        }
    }

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