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    //! High performance buffer writes.

    use std::ops::{Deref, DerefMut};
    use futures::{Future, Poll};
    use core::{self, OclPrm, MemMap as MemMapCore,
        MemFlags, MapFlags, ClNullEventPtr};
    use standard::{Event, EventList, Queue, Buffer, ClWaitListPtrEnum, ClNullEventPtrEnum};
    use async::{OrderLock, FutureGuard, ReadGuard, WriteGuard};
    use error::{Error as OclError, Result as OclResult};

    #[must_use = "futures do nothing unless polled"]
    #[derive(Debug)]
    pub struct FutureFlush<T: OclPrm> {
        future_guard: FutureGuard<Inner<T>, ReadGuard<Inner<T>>>,
    }

    impl<T: OclPrm> FutureFlush<T> {
        fn new(future_guard: FutureGuard<Inner<T>, ReadGuard<Inner<T>>>) -> FutureFlush<T> {
            FutureFlush { future_guard: future_guard }
        }

        /// Returns a mutable reference to the contained `FutureGuard`.
        pub fn future_guard(&mut self) -> &mut FutureGuard<Inner<T>, ReadGuard<Inner<T>>> {
            &mut self.future_guard
        }
    }

    impl<T: OclPrm> Future for FutureFlush<T> {
        type Item = ();
        type Error = OclError;

        #[inline]
        fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
            self.future_guard.poll().map(|res| res.map(|_read_guard| ()))
        }
    }

    /// A flush command builder.
    ///
    #[must_use = "commands do nothing unless enqueued"]
    #[derive(Debug)]
    pub struct FlushCmd<'c, T> where T: 'c + OclPrm {
        queue: Option<&'c Queue>,
        sink: BufferSink<T>,
        ewait: Option<ClWaitListPtrEnum<'c>>,
        enew: Option<ClNullEventPtrEnum<'c>>,
    }

    impl<'c, T> FlushCmd<'c, T> where T: OclPrm {
        /// Returns a new flush command builder.
        fn new(sink: BufferSink<T>) -> FlushCmd<'c, T> {
            FlushCmd {
                queue: None,
                sink: sink,
                ewait: None,
                enew: None,
            }
        }

        /// Specifies a queue to use for this call only.
        pub fn queue<'q, Q>(mut self, queue: &'q Q) -> FlushCmd<'c, T>
            where 'q: 'c, Q: 'q + AsRef<Queue>
        {
            self.queue = Some(queue.as_ref());
            self
        }

        /// Specifies an event or list of events to wait on before the command
        /// will run.
        ///
        /// When events generated using the `::enew` method of **other**,
        /// previously enqueued commands are passed here (either individually or
        /// as part of an [`EventList`]), this command will not execute until
        /// those commands have completed.
        ///
        /// Using events can compliment the use of queues to order commands by
        /// creating temporal dependencies between them (where commands in one
        /// queue must wait for the completion of commands in another). Events can
        /// also supplant queues altogether when, for example, using out-of-order
        /// queues.
        ///
        /// # Example
        ///
        /// ```rust,ignore
        /// // Create an event list:
        /// let mut event_list = EventList::new();
        /// // Enqueue a kernel on `queue_1`, creating an event representing the kernel
        /// // command in our list:
        /// kernel.cmd().queue(&queue_1).enew(&mut event_list).enq()?;
        /// // Read from a buffer using `queue_2`, ensuring the read does not begin until
        /// // after the kernel command has completed:
        /// buffer.read(rwvec.clone()).queue(&queue_2).ewait(&event_list).enq_async()?;
        /// ```
        ///
        /// [`EventList`]: struct.EventList.html
        pub fn ewait<Ewl>(mut self, ewait: Ewl) -> FlushCmd<'c, T>
                where Ewl: Into<ClWaitListPtrEnum<'c>> {
            self.ewait = Some(ewait.into());
            self
        }

        /// Specifies the destination to store a new, optionally created event
        /// associated with this command.
        ///
        /// The destination can be a mutable reference to an empty event (created
        /// using [`Event::empty`]) or a mutable reference to an event list.
        ///
        /// After this command is enqueued, the event in the destination can be
        /// passed to the `::ewait` method of another command. Doing so will cause
        /// the other command to wait until this command has completed before
        /// executing.
        ///
        /// Using events can compliment the use of queues to order commands by
        /// creating temporal dependencies between them (where commands in one
        /// queue must wait for the completion of commands in another). Events can
        /// also supplant queues altogether when, for example, using out-of-order
        /// queues.
        ///
        /// # Example
        ///
        /// ```rust,ignore
        /// // Create an event list:
        /// let mut event = Event::empty();
        /// // Enqueue a kernel on `queue_1`, creating an event representing the kernel
        /// // command in our list:
        /// kernel.cmd().queue(&queue_1).enew(&mut event).enq()?;
        /// // Read from a buffer using `queue_2`, ensuring the read does not begin until
        /// // after the kernel command has completed:
        /// buffer.read(rwvec.clone()).queue(&queue_2).ewait(&event).enq_async()?;
        /// ```
        ///
        /// [`Event::empty`]: struct.Event.html#method.empty
        pub fn enew<En>(mut self, enew: En) -> FlushCmd<'c, T>
                where En: Into<ClNullEventPtrEnum<'c>> {
            self.enew = Some(enew.into());
            self
        }

        /// Enqueues this command.
        pub fn enq(mut self) -> OclResult<FutureFlush<T>> {
            let inner = unsafe { &*self.sink.lock.as_ptr() };

            let buffer = inner.buffer.as_core();

            let queue = match self.queue {
                Some(q) => q,
                None => inner.buffer.default_queue().unwrap(),
            };

            let mut future_read = self.sink.lock.read();
            if let Some(wl) = self.ewait {
                future_read.set_lock_wait_events(wl);
            }

            future_read.create_lock_event(queue.context_ptr()?)?;

            let mut unmap_event = Event::empty();
            let mut map_event = Event::empty();

            unsafe {
                core::enqueue_unmap_mem_object::<T, _, _, _>(queue, buffer, &inner.memory,
                    future_read.lock_event(), Some(&mut unmap_event))?;

                let memory = core::enqueue_map_buffer::<T, _, _, _>(queue, buffer, false,
                    MapFlags::new().write_invalidate_region(), inner.default_offset, inner.default_len,
                    Some(&unmap_event), Some(&mut map_event))?;
                debug_assert!(memory.as_ptr() == inner.memory.as_ptr());

                // Copy the tail/conclusion event.
                if let Some(ref mut enew) = self.enew {
                    enew.clone_from(&map_event);
                }
            }

            // Ensure that the unmap and (re)map finish before the future resolves.
            future_read.set_command_wait_event(map_event);

            Ok(FutureFlush::new(future_read))
        }
    }

    #[derive(Debug)]
    pub struct Inner<T: OclPrm> {
        buffer: Buffer<T>,
        memory: MemMapCore<T>,
        default_offset: usize,
        default_len: usize,
    }

    impl<T: OclPrm> Inner<T> {
        /// Returns the internal buffer.
        pub fn buffer(self: &Inner<T>) -> &Buffer<T> {
            &self.buffer
        }

        /// Returns the internal memory mapping.
        pub fn memory(self: &Inner<T>) -> &MemMapCore<T> {
            &self.memory
        }

        /// Returns the default offset.
        pub fn default_offset(self: &Inner<T>) -> usize {
            self.default_offset
        }
    }

    impl<T: OclPrm> Deref for Inner<T> {
        type Target = [T];

        #[inline]
        fn deref(&self) -> &[T] {
            unsafe { self.memory.as_slice(self.default_len) }
        }
    }

    impl<T: OclPrm> DerefMut for Inner<T> {
        #[inline]
        fn deref_mut(&mut self) -> &mut [T] {
            unsafe { self.memory.as_slice_mut(self.default_len) }
        }
    }

    impl<T: OclPrm> Drop for Inner<T> {
        /// Drops the `Inner` enqueuing an unmap and blocking until it
        /// completes.
        fn drop(&mut self) {
            let mut new_event = Event::empty();
            core::enqueue_unmap_mem_object::<T, _, _, _>(self.buffer.default_queue().unwrap(),
                &self.buffer, &self.memory, None::<&EventList>, Some(&mut new_event)).unwrap();
            new_event.wait_for().unwrap();
        }
    }

    /// Represents mapped memory and allows frames of data to be 'flushed'
    /// (written) from host-accessible mapped memory region into its associated
    /// device-visible buffer in a repeated fashion.
    ///
    /// This represents the fastest possible method for continuously writing
    /// frames of data to a device.
    ///
    #[derive(Clone, Debug)]
    pub struct BufferSink<T: OclPrm> {
        lock: OrderLock<Inner<T>>,
    }

    impl<T: OclPrm> BufferSink<T> {
        /// Returns a new `BufferSink`.
        ///
        /// The current thread will be blocked while the buffer is initialized
        /// upon calling this function.
        pub fn new(queue: Queue, len: usize) -> OclResult<BufferSink<T>> {
            let buffer = Buffer::<T>::builder()
                .queue(queue.clone())
                .flags(MemFlags::new().alloc_host_ptr().host_write_only())
                .len(len)
                .fill_val(T::default())
                .build()?;

            unsafe { BufferSink::from_buffer(buffer, None, 0, len) }
        }

        /// Returns a new `BufferSink`.
        ///
        /// ## Safety
        ///
        /// `buffer` must not have the same region mapped more than once.
        ///
        pub unsafe fn from_buffer(mut buffer: Buffer<T>, queue: Option<Queue>, default_offset: usize,
                default_len: usize) -> OclResult<BufferSink<T>> {
            let buf_flags = buffer.flags()?;
            assert!(buf_flags.contains(MemFlags::new().alloc_host_ptr()) ||
                buf_flags.contains(MemFlags::new().use_host_ptr()),
                "A buffer sink must be created with a buffer that has either \
                the MEM_ALLOC_HOST_PTR` or `MEM_USE_HOST_PTR flag.");
            assert!(!buf_flags.contains(MemFlags::new().host_no_access()) &&
                !buf_flags.contains(MemFlags::new().host_read_only()),
                "A buffer sink may not be created with a buffer that has either the \
                `MEM_HOST_NO_ACCESS` or `MEM_HOST_READ_ONLY` flags.");
            assert!(default_offset + default_len <= buffer.len());

            match queue {
                Some(q) => { buffer.set_default_queue(q); },
                None => assert!(buffer.default_queue().is_some(),
                    "A buffer sink must be created with a queue."),
            }

            let map_flags = MapFlags::new().write_invalidate_region();

            let memory = core::enqueue_map_buffer::<T, _, _, _>(buffer.default_queue().unwrap(),
                buffer.as_core(), true, map_flags, default_offset, default_len, None::<&EventList>,
                    None::<&mut Event>)?;

            let inner = Inner {
                buffer,
                memory,
                default_offset,
                default_len
            };

            Ok(BufferSink {
                lock: OrderLock::new(inner),
            })
        }

        /// Returns a new `FutureGuard` which will resolve into a a `ReadGuard`.
        pub fn read(self) -> FutureGuard<Inner<T>, ReadGuard<Inner<T>>> {
            self.lock.read()

        }

        /// Returns a new `FutureGuard` which will resolve into a a `WriteGuard`.
        pub fn write(self) -> FutureGuard<Inner<T>, WriteGuard<Inner<T>>> {
            self.lock.write()
        }

        /// Returns a command builder which, once enqueued, will flush data from
        /// the mapped memory region to the device.
        pub fn flush<'c>(self) -> FlushCmd<'c, T> {
            FlushCmd::new(self)
        }

        /// Returns a reference to the internal buffer.
        #[inline]
        pub fn buffer(&self) -> &Buffer<T> {
            unsafe { &(*self.lock.as_mut_ptr()).buffer }
        }

        /// Returns a reference to the internal memory mapping.
        #[inline]
        pub fn memory(&self) -> &MemMapCore<T> {
            unsafe { &(*self.lock.as_mut_ptr()).memory }
        }

        /// Returns a reference to the internal offset.
        #[inline]
        pub fn default_offset(&self) -> usize {
            unsafe { (*self.lock.as_mut_ptr()).default_offset }
        }

        /// Returns the length of the memory region.
        #[inline]
        pub fn default_len(&self) -> usize {
            unsafe { (*self.lock.as_ptr()).default_len }
        }

        /// Returns a mutable slice into the contained memory region.
        ///
        /// Used by buffer command builders when preparing future read and write
        /// commands.
        ///
        /// Do not use unless you are 100% certain that there will be no other
        /// reads or writes for the entire access duration (only possible if
        /// manually manipulating the lock status).
        pub unsafe fn as_mut_slice(&self) -> &mut [T] {
            let ptr = (*self.lock.as_mut_ptr()).memory.as_mut_ptr();
            let default_len = (*self.lock.as_ptr()).default_len;
            ::std::slice::from_raw_parts_mut(ptr, default_len)
        }

        /// Returns a pointer address to the internal memory region, usable as a
        /// unique identifier.
        pub fn id(&self) -> usize {
            unsafe { (*self.lock.as_ptr()).memory.as_ptr() as usize }
        }
    }

    impl<T: OclPrm> From<OrderLock<Inner<T>>> for BufferSink<T> {
        fn from(order_lock: OrderLock<Inner<T>>) -> BufferSink<T> {
            BufferSink { lock: order_lock }
        }
    }

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