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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::cmp;
    use std::ops::Range;
    use std::sync::Arc;
    use std::sync::Mutex;

    use device::Device;
    use instance::Instance;
    use instance::MemoryType;
    use memory::DeviceMemory;
    use memory::DeviceMemoryAllocError;
    use memory::MappedDeviceMemory;

    /// Memory pool that operates on a given memory type.
    #[derive(Debug)]
    pub struct StdHostVisibleMemoryTypePool {
        device: Arc<Device>,
        memory_type: u32,
        // TODO: obviously very inefficient
        occupied: Mutex<Vec<(Arc<MappedDeviceMemory>, Vec<Range<usize>>)>>,
    }

    impl StdHostVisibleMemoryTypePool {
        /// Creates a new pool that will operate on the given memory type.
        ///
        /// # Panic
        ///
        /// - Panics if the `device` and `memory_type` don't belong to the same physical device.
        /// - Panics if the memory type is not host-visible.
        ///
        #[inline]
        pub fn new(device: Arc<Device>, memory_type: MemoryType) -> Arc<StdHostVisibleMemoryTypePool> {
            assert_eq!(&**device.physical_device().instance() as *const Instance,
                       &**memory_type.physical_device().instance() as *const Instance);
            assert_eq!(device.physical_device().index(),
                       memory_type.physical_device().index());
            assert!(memory_type.is_host_visible());

            Arc::new(StdHostVisibleMemoryTypePool {
                         device: device.clone(),
                         memory_type: memory_type.id(),
                         occupied: Mutex::new(Vec::new()),
                     })
        }

        /// Allocates memory from the pool.
        ///
        /// # Panic
        ///
        /// - Panics if `size` is 0.
        /// - Panics if `alignment` is 0.
        ///
        pub fn alloc(me: &Arc<Self>, size: usize, alignment: usize)
                     -> Result<StdHostVisibleMemoryTypePoolAlloc, DeviceMemoryAllocError> {
            assert!(size != 0);
            assert!(alignment != 0);

            #[inline]
            fn align(val: usize, al: usize) -> usize {
                al * (1 + (val - 1) / al)
            }

            // Find a location.
            let mut occupied = me.occupied.lock().unwrap();

            // Try finding an entry in already-allocated chunks.
            for &mut (ref dev_mem, ref mut entries) in occupied.iter_mut() {
                // Try find some free space in-between two entries.
                for i in 0 .. entries.len().saturating_sub(1) {
                    let entry1 = entries[i].clone();
                    let entry1_end = align(entry1.end, alignment);
                    let entry2 = entries[i + 1].clone();
                    if entry1_end + size <= entry2.start {
                        entries.insert(i + 1, entry1_end .. entry1_end + size);
                        return Ok(StdHostVisibleMemoryTypePoolAlloc {
                                      pool: me.clone(),
                                      memory: dev_mem.clone(),
                                      offset: entry1_end,
                                      size: size,
                                  });
                    }
                }

                // Try append at the end.
                let last_end = entries.last().map(|e| align(e.end, alignment)).unwrap_or(0);
                if last_end + size <= (**dev_mem).as_ref().size() {
                    entries.push(last_end .. last_end + size);
                    return Ok(StdHostVisibleMemoryTypePoolAlloc {
                                  pool: me.clone(),
                                  memory: dev_mem.clone(),
                                  offset: last_end,
                                  size: size,
                              });
                }
            }

            // We need to allocate a new block.
            let new_block = {
                const MIN_BLOCK_SIZE: usize = 8 * 1024 * 1024; // 8 MB
                let to_alloc = cmp::max(MIN_BLOCK_SIZE, size.next_power_of_two());
                let new_block =
                    DeviceMemory::alloc_and_map(me.device.clone(), me.memory_type(), to_alloc)?;
                Arc::new(new_block)
            };

            occupied.push((new_block.clone(), vec![0 .. size]));
            Ok(StdHostVisibleMemoryTypePoolAlloc {
                   pool: me.clone(),
                   memory: new_block,
                   offset: 0,
                   size: size,
               })
        }

        /// Returns the device this pool operates on.
        #[inline]
        pub fn device(&self) -> &Arc<Device> {
            &self.device
        }

        /// Returns the memory type this pool operates on.
        #[inline]
        pub fn memory_type(&self) -> MemoryType {
            self.device
                .physical_device()
                .memory_type_by_id(self.memory_type)
                .unwrap()
        }
    }

    #[derive(Debug)]
    pub struct StdHostVisibleMemoryTypePoolAlloc {
        pool: Arc<StdHostVisibleMemoryTypePool>,
        memory: Arc<MappedDeviceMemory>,
        offset: usize,
        size: usize,
    }

    impl StdHostVisibleMemoryTypePoolAlloc {
        #[inline]
        pub fn memory(&self) -> &MappedDeviceMemory {
            &self.memory
        }

        #[inline]
        pub fn offset(&self) -> usize {
            self.offset
        }

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

    impl Drop for StdHostVisibleMemoryTypePoolAlloc {
        fn drop(&mut self) {
            let mut occupied = self.pool.occupied.lock().unwrap();

            let entries = occupied
                .iter_mut()
                .find(|e| &*e.0 as *const MappedDeviceMemory == &*self.memory)
                .unwrap();

            entries.1.retain(|e| e.start != self.offset);
        }
    }

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