// 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 fnv::FnvHashMap;
use std::borrow::Cow;
use std::collections::hash_map::Entry;
use std::error;
use std::fmt;
use std::hash::{Hash, Hasher};
use std::sync::Arc;
use std::sync::Mutex;

use OomError;
use buffer::BufferAccess;
use command_buffer::CommandBufferExecError;
use command_buffer::pool::CommandPool;
use command_buffer::pool::CommandPoolAlloc;
use command_buffer::pool::CommandPoolBuilderAlloc;
use command_buffer::sys::Flags;
use command_buffer::sys::Kind;
use command_buffer::sys::UnsafeCommandBuffer;
use command_buffer::sys::UnsafeCommandBufferBuilder;
use command_buffer::sys::UnsafeCommandBufferBuilderPipelineBarrier;
use device::Device;
use device::DeviceOwned;
use device::Queue;
use framebuffer::FramebufferAbstract;
use framebuffer::RenderPassAbstract;
use image::ImageAccess;
use image::ImageLayout;
use sync::AccessCheckError;
use sync::AccessError;
use sync::AccessFlagBits;
use sync::GpuFuture;
use sync::PipelineStages;

/// Wrapper around `UnsafeCommandBufferBuilder` that handles synchronization for you.
///
/// Each method of the `UnsafeCommandBufferBuilder` has an equivalent in this wrapper, except
/// for `pipeline_layout` which is automatically handled. This wrapper automatically builds
/// pipeline barriers, keeps used resources alive and implements the `CommandBuffer` trait.
///
/// Since the implementation needs to cache commands in a `Vec`, most methods have additional
/// `Send + Sync + 'static` trait requirements on their generics.
///
/// If this builder finds out that a command isn't valid because of synchronization reasons (eg.
/// trying to copy from a buffer to an image which share the same memory), then an error is
/// returned.
/// Note that all methods are still unsafe, because this builder doesn't check the validity of
/// the commands except for synchronization purposes. The builder may panic if you pass invalid
/// commands.
///
/// The `P` generic is the same as `UnsafeCommandBufferBuilder`.
pub struct SyncCommandBufferBuilder<P> {
    // The actual Vulkan command buffer builder.
    inner: UnsafeCommandBufferBuilder<P>,

    // Stores the current state of all resources (buffers and images) that are in use by the
    // command buffer.
    resources: FnvHashMap<BuilderKey<P>, ResourceState>,

    // Prototype for the pipeline barrier that must be submitted before flushing the commands
    // in `commands`.
    pending_barrier: UnsafeCommandBufferBuilderPipelineBarrier,

    // Stores all the commands that were added to the sync builder. Some of them are maybe not
    // submitted to the inner builder yet. A copy of this `Arc` is stored in each `BuilderKey`.
    commands: Arc<Mutex<Commands<P>>>,

    // True if we're a secondary command buffer.
    is_secondary: bool,
}

// # How pipeline stages work in Vulkan
//
// Imagine you create a command buffer that contains 10 dispatch commands, and submit that command
// buffer. According to the Vulkan specs, the implementation is free to execute the 10 commands
// simultaneously.
//
// Now imagine that the command buffer contains 10 draw commands instead. Contrary to the dispatch
// commands, the draw pipeline contains multiple stages: draw indirect, vertex input, vertex shader,
// ..., fragment shader, late fragment test, color output. When there are multiple stages, the
// implementations must start and end the stages in order. In other words it can start the draw
// indirect stage of all 10 commands, then start the vertex input stage of all 10 commands, and so
// on. But it can't for example start the fragment shader stage of a command before starting the
// vertex shader stage of another command. Same thing for ending the stages in the right order.
//
// Depending on the type of the command, the pipeline stages are different. Compute shaders use the
// compute stage, while transfer commands use the transfer stage. The compute and transfer stages
// aren't ordered.
//
// When you submit multiple command buffers to a queue, the implementation doesn't do anything in
// particular and behaves as if the command buffers were appended to one another. Therefore if you
// submit a command buffer with 10 dispatch commands, followed with another command buffer with 5
// dispatch commands, then the implementation can perform the 15 commands simultaneously.
//
// ## Introducing barriers
//
// In some situations this is not the desired behaviour. If you add a command that writes to a
// buffer followed with another command that reads that buffer, you don't want them to execute
// simultaneously. Instead you want the second one to wait until the first one is finished. This
// is done by adding a pipeline barrier between the two commands.
//
// A pipeline barriers has a source stage and a destination stage (plus various other things).
// A barrier represents a split in the list of commands. When you add it, the stages of the commands
// before the barrier corresponding to the source stage of the barrier, must finish before the
// stages of the commands after the barrier corresponding to the destination stage of the barrier
// can start.
//
// For example if you add a barrier that transitions from the compute stage to the compute stage,
// then the compute stage of all the commands before the barrier must end before the compute stage
// of all the commands after the barrier can start. This is appropriate for the example about
// writing then reading the same buffer.
//
// ## Batching barriers
//
// Since barriers are "expensive" (as the queue must block), vulkano attempts to group as many
// pipeline barriers as possible into one.
//
// Adding a command to a sync command buffer builder does not immediately add it to the underlying
// command buffer builder. Instead the command is added to a queue, and the builder keeps a
// prototype of a barrier that must be added before the commands in the queue are flushed.
//
// Whenever you add a command, the builder will find out whether a barrier is needed before the
// command. If so, it will try to merge this barrier with the prototype and add the command to the
// queue. If not possible, the queue will be entirely flushed and the command added to a fresh new
// queue with a fresh new barrier prototype.

impl<P> fmt::Debug for SyncCommandBufferBuilder<P> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Debug::fmt(&self.inner, f)
    }
}

/// Error returned if the builder detects that there's an unsolvable conflict.
#[derive(Debug, Clone)]
pub enum SyncCommandBufferBuilderError {
    /// Unsolvable conflict.
    Conflict {
        command1_name: &'static str,
        command1_param: Cow<'static, str>,
        command1_offset: usize,

        command2_name: &'static str,
        command2_param: Cow<'static, str>,
        command2_offset: usize,
    },
}

impl error::Error for SyncCommandBufferBuilderError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            SyncCommandBufferBuilderError::Conflict { .. } => {
                "unsolvable conflict"
            },
        }
    }
}

impl fmt::Display for SyncCommandBufferBuilderError {
    #[inline]
    fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        write!(fmt, "{}", error::Error::description(self))
    }
}

// List of commands stored inside a `SyncCommandBufferBuilder`.
struct Commands<P> {
    // Only the commands before `first_unflushed` have already been sent to the inner
    // `UnsafeCommandBufferBuilder`.
    first_unflushed: usize,

    // If we're currently inside a render pass, contains the index of the `CmdBeginRenderPass`
    // command.
    latest_render_pass_enter: Option<usize>,

    // The actual list.
    commands: Vec<Box<Command<P> + Send + Sync>>,
}

// Trait for single commands within the list of commands.
pub trait Command<P> {
    // Returns a user-friendly name for the command, for error reporting purposes.
    fn name(&self) -> &'static str;

    // Sends the command to the `UnsafeCommandBufferBuilder`. Calling this method twice on the same
    // object will likely lead to a panic.
    unsafe fn send(&mut self, out: &mut UnsafeCommandBufferBuilder<P>);

    // Turns this command into a `FinalCommand`.
    fn into_final_command(self: Box<Self>) -> Box<FinalCommand + Send + Sync>;

    // Gives access to the `num`th buffer used by the command.
    fn buffer(&self, _num: usize) -> &BufferAccess {
        panic!()
    }

    // Gives access to the `num`th image used by the command.
    fn image(&self, _num: usize) -> &ImageAccess {
        panic!()
    }

    // Returns a user-friendly name for the `num`th buffer used by the command, for error
    // reporting purposes.
    fn buffer_name(&self, _num: usize) -> Cow<'static, str> {
        panic!()
    }

    // Returns a user-friendly name for the `num`th image used by the command, for error
    // reporting purposes.
    fn image_name(&self, _num: usize) -> Cow<'static, str> {
        panic!()
    }
}

/// Type of resource whose state is to be tracked.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum KeyTy {
    Buffer,
    Image,
}

// Key that identifies a resource. Implements `PartialEq`, `Eq` and `Hash` so that two resources
// that conflict with each other compare equal.
//
// This works by holding an Arc to the list of commands and the index of the command that holds
// the resource.
struct BuilderKey<P> {
    // Same `Arc` as in the `SyncCommandBufferBuilder`.
    commands: Arc<Mutex<Commands<P>>>,
    // Index of the command that holds the resource within `commands`.
    command_id: usize,
    // Type of the resource.
    resource_ty: KeyTy,
    // Index of the resource within the command.
    resource_index: usize,
}

impl<P> BuilderKey<P> {
    // Turns this key used by the builder into a key used by the final command buffer.
    // Called when the command buffer is being built.
    fn into_cb_key(self, final_commands: Arc<Mutex<Vec<Box<FinalCommand + Send + Sync>>>>)
                   -> CbKey<'static> {
        CbKey::Command {
            commands: final_commands,
            command_id: self.command_id,
            resource_ty: self.resource_ty,
            resource_index: self.resource_index,
        }
    }

    #[inline]
    fn conflicts_buffer(&self, commands_lock: &Commands<P>, buf: &BufferAccess) -> bool {
        // TODO: put the conflicts_* methods directly on the Command trait to avoid an indirect call?
        match self.resource_ty {
            KeyTy::Buffer => {
                let c = &commands_lock.commands[self.command_id];
                c.buffer(self.resource_index).conflicts_buffer(buf)
            },
            KeyTy::Image => {
                let c = &commands_lock.commands[self.command_id];
                c.image(self.resource_index).conflicts_buffer(buf)
            },
        }
    }

    #[inline]
    fn conflicts_image(&self, commands_lock: &Commands<P>, img: &ImageAccess) -> bool {
        // TODO: put the conflicts_* methods directly on the Command trait to avoid an indirect call?
        match self.resource_ty {
            KeyTy::Buffer => {
                let c = &commands_lock.commands[self.command_id];
                c.buffer(self.resource_index).conflicts_image(img)
            },
            KeyTy::Image => {
                let c = &commands_lock.commands[self.command_id];
                c.image(self.resource_index).conflicts_image(img)
            },
        }
    }
}

impl<P> PartialEq for BuilderKey<P> {
    #[inline]
    fn eq(&self, other: &BuilderKey<P>) -> bool {
        debug_assert!(Arc::ptr_eq(&self.commands, &other.commands));
        let commands_lock = self.commands.lock().unwrap();

        match other.resource_ty {
            KeyTy::Buffer => {
                let c = &commands_lock.commands[other.command_id];
                self.conflicts_buffer(&commands_lock, c.buffer(other.resource_index))
            },
            KeyTy::Image => {
                let c = &commands_lock.commands[other.command_id];
                self.conflicts_image(&commands_lock, c.image(other.resource_index))
            },
        }
    }
}

impl<P> Eq for BuilderKey<P> {
}

impl<P> Hash for BuilderKey<P> {
    #[inline]
    fn hash<H: Hasher>(&self, state: &mut H) {
        let commands_lock = self.commands.lock().unwrap();

        match self.resource_ty {
            KeyTy::Buffer => {
                let c = &commands_lock.commands[self.command_id];
                c.buffer(self.resource_index).conflict_key().hash(state)
            },
            KeyTy::Image => {
                let c = &commands_lock.commands[self.command_id];
                c.image(self.resource_index).conflict_key().hash(state)
            },
        }
    }
}

// State of a resource during the building of the command buffer.
#[derive(Debug, Clone)]
struct ResourceState {
    // Stage of the command that last used this resource.
    stages: PipelineStages,
    // Access for the command that last used this resource.
    access: AccessFlagBits,

    // True if the resource was used in exclusive mode at any point during the building of the
    // command buffer. Also true if an image layout transition or queue transfer has been performed.
    exclusive_any: bool,

    // True if the last command that used this resource used it in exclusive mode.
    exclusive: bool,

    // Layout at the first use of the resource by the command buffer. Can be `Undefined` if we
    // don't care.
    initial_layout: ImageLayout,

    // Current layout at this stage of the building.
    current_layout: ImageLayout,
}

impl ResourceState {
    // Turns this `ResourceState` into a `ResourceFinalState`. Called when the command buffer is
    // being built.
    #[inline]
    fn finalize(self) -> ResourceFinalState {
        ResourceFinalState {
            final_stages: self.stages,
            final_access: self.access,
            exclusive: self.exclusive_any,
            initial_layout: self.initial_layout,
            final_layout: self.current_layout,
        }
    }
}

impl<P> SyncCommandBufferBuilder<P> {
    /// Builds a new `SyncCommandBufferBuilder`. The parameters are the same as the
    /// `UnsafeCommandBufferBuilder::new` function.
    ///
    /// # Safety
    ///
    /// See `UnsafeCommandBufferBuilder::new()` and `SyncCommandBufferBuilder`.
    pub unsafe fn new<Pool, R, F, A>(pool: &Pool, kind: Kind<R, F>, flags: Flags)
                                     -> Result<SyncCommandBufferBuilder<P>, OomError>
        where Pool: CommandPool<Builder = P, Alloc = A>,
              P: CommandPoolBuilderAlloc<Alloc = A>,
              A: CommandPoolAlloc,
              R: RenderPassAbstract,
              F: FramebufferAbstract
    {
        let (is_secondary, inside_render_pass) = match kind {
            Kind::Primary => (false, false),
            Kind::Secondary { ref render_pass, .. } => (true, render_pass.is_some()),
        };

        let cmd = UnsafeCommandBufferBuilder::new(pool, kind, flags)?;
        Ok(SyncCommandBufferBuilder::from_unsafe_cmd(cmd, is_secondary, inside_render_pass))
    }

    /// Builds a `SyncCommandBufferBuilder` from an existing `UnsafeCommandBufferBuilder`.
    ///
    /// # Safety
    ///
    /// See `UnsafeCommandBufferBuilder::new()` and `SyncCommandBufferBuilder`.
    ///
    /// In addition to this, the `UnsafeCommandBufferBuilder` should be empty. If it isn't, then
    /// you must take into account the fact that the `SyncCommandBufferBuilder` won't be aware of
    /// any existing resource usage.
    #[inline]
    pub unsafe fn from_unsafe_cmd(cmd: UnsafeCommandBufferBuilder<P>, is_secondary: bool,
                                  inside_render_pass: bool)
                                  -> SyncCommandBufferBuilder<P> {
        let latest_render_pass_enter = if inside_render_pass { Some(0) } else { None };

        SyncCommandBufferBuilder {
            inner: cmd,
            resources: FnvHashMap::default(),
            pending_barrier: UnsafeCommandBufferBuilderPipelineBarrier::new(),
            commands: Arc::new(Mutex::new(Commands {
                                              first_unflushed: 0,
                                              latest_render_pass_enter,
                                              commands: Vec::new(),
                                          })),
            is_secondary,
        }
    }

    // Adds a command to be processed by the builder.
    //
    // After this method has been called, call `prev_cmd_resource` for each buffer or image used
    // by the command.
    #[inline]
    pub(super) fn append_command<C>(&mut self, command: C)
        where C: Command<P> + Send + Sync + 'static
    {
        // Note that we don't submit the command to the inner command buffer yet.
        self.commands
            .lock()
            .unwrap()
            .commands
            .push(Box::new(command));
    }

    // Call this when the previous command entered a render pass.
    #[inline]
    pub(super) fn prev_cmd_entered_render_pass(&mut self) {
        let mut cmd_lock = self.commands.lock().unwrap();
        cmd_lock.latest_render_pass_enter = Some(cmd_lock.commands.len() - 1);
    }

    // Call this when the previous command left a render pass.
    #[inline]
    pub(super) fn prev_cmd_left_render_pass(&mut self) {
        let mut cmd_lock = self.commands.lock().unwrap();
        debug_assert!(cmd_lock.latest_render_pass_enter.is_some());
        cmd_lock.latest_render_pass_enter = None;
    }

    // After a command is added to the list of pending commands, this function must be called for
    // each resource used by the command that has just been added.
    // The function will take care of handling the pipeline barrier or flushing.
    //
    // `resource_ty` and `resource_index` designate the resource in the previous command (accessed
    // through `Command::buffer(..)` or `Command::image(..)`.
    //
    // `exclusive`, `stages` and `access` must match the way the resource has been used.
    //
    // `start_layout` and `end_layout` designate the image layout that the image is expected to be
    // in when the command starts, and the image layout that the image will be transitioned to
    // during the command. When it comes to buffers, you should pass `Undefined` for both.
    pub(super) fn prev_cmd_resource(&mut self, resource_ty: KeyTy, resource_index: usize,
                                    exclusive: bool, stages: PipelineStages,
                                    access: AccessFlagBits, start_layout: ImageLayout,
                                    end_layout: ImageLayout)
                                    -> Result<(), SyncCommandBufferBuilderError> {
        // Anti-dumbness checks.
        debug_assert!(exclusive || start_layout == end_layout);
        debug_assert!(access.is_compatible_with(&stages));
        debug_assert!(resource_ty != KeyTy::Image || end_layout != ImageLayout::Undefined);
        debug_assert!(resource_ty != KeyTy::Buffer || start_layout == ImageLayout::Undefined);
        debug_assert!(resource_ty != KeyTy::Buffer || end_layout == ImageLayout::Undefined);
        debug_assert_ne!(end_layout, ImageLayout::Preinitialized);

        let (first_unflushed_cmd_id, latest_command_id) = {
            let commands_lock = self.commands.lock().unwrap();
            debug_assert!(commands_lock.commands.len() >= 1);
            (commands_lock.first_unflushed, commands_lock.commands.len() - 1)
        };

        let key = BuilderKey {
            commands: self.commands.clone(),
            command_id: latest_command_id,
            resource_ty,
            resource_index,
        };

        // Note that the call to `entry()` will lock the mutex, so we can't keep it locked
        // throughout the function.
        match self.resources.entry(key) {

            // Situation where this resource was used before in this command buffer.
            Entry::Occupied(entry) => {
                // `collision_cmd_id` contains the ID of the command that we are potentially
                // colliding with.
                let collision_cmd_id = entry.key().command_id;
                debug_assert!(collision_cmd_id <= latest_command_id);

                let entry_key_resource_index = entry.key().resource_index;
                let entry_key_resource_ty = entry.key().resource_ty;
                let entry = entry.into_mut();

                // Find out if we have a collision with the pending commands.
                if exclusive || entry.exclusive || entry.current_layout != start_layout {
                    // Collision found between `latest_command_id` and `collision_cmd_id`.

                    // We now want to modify the current pipeline barrier in order to handle the
                    // collision. But since the pipeline barrier is going to be submitted before
                    // the flushed commands, it would be a mistake if `collision_cmd_id` hasn't
                    // been flushed yet.
                    if collision_cmd_id >= first_unflushed_cmd_id {
                        unsafe {
                            // Flush the pending barrier.
                            self.inner.pipeline_barrier(&self.pending_barrier);
                            self.pending_barrier = UnsafeCommandBufferBuilderPipelineBarrier::new();

                            // Flush the commands if possible, or return an error if not possible.
                            {
                                let mut commands_lock = self.commands.lock().unwrap();
                                let start = commands_lock.first_unflushed;
                                let end = if let Some(rp_enter) = commands_lock
                                    .latest_render_pass_enter
                                {
                                    rp_enter
                                } else {
                                    latest_command_id
                                };
                                if collision_cmd_id >= end {
                                    let cmd1 = &commands_lock.commands[collision_cmd_id];
                                    let cmd2 = &commands_lock.commands[latest_command_id];
                                    return Err(SyncCommandBufferBuilderError::Conflict {
                                                   command1_name: cmd1.name(),
                                                   command1_param: match entry_key_resource_ty {
                                                       KeyTy::Buffer => cmd1.buffer_name(entry_key_resource_index),
                                                       KeyTy::Image =>
                                                           cmd1.image_name(entry_key_resource_index),
                                                   },
                                                   command1_offset: collision_cmd_id,

                                                   command2_name: cmd2.name(),
                                                   command2_param: match resource_ty {
                                                       KeyTy::Buffer =>
                                                           cmd2.buffer_name(resource_index),
                                                       KeyTy::Image =>
                                                           cmd2.image_name(resource_index),
                                                   },
                                                   command2_offset: latest_command_id,
                                               });
                                }
                                for command in &mut commands_lock.commands[start .. end] {
                                    command.send(&mut self.inner);
                                }
                                commands_lock.first_unflushed = end;
                            }
                        }
                    }

                    // Modify the pipeline barrier to handle the collision.
                    unsafe {
                        let commands_lock = self.commands.lock().unwrap();
                        match resource_ty {
                            KeyTy::Buffer => {
                                let buf = commands_lock.commands[latest_command_id]
                                    .buffer(resource_index);

                                let b = &mut self.pending_barrier;
                                b.add_buffer_memory_barrier(buf,
                                                            entry.stages,
                                                            entry.access,
                                                            stages,
                                                            access,
                                                            true,
                                                            None,
                                                            0,
                                                            buf.size());
                            },

                            KeyTy::Image => {
                                let img = commands_lock.commands[latest_command_id]
                                    .image(resource_index);

                                let b = &mut self.pending_barrier;
                                b.add_image_memory_barrier(img,
                                                           0 .. img.mipmap_levels(),
                                                           0 .. img.dimensions().array_layers(),
                                                           entry.stages,
                                                           entry.access,
                                                           stages,
                                                           access,
                                                           true,
                                                           None,
                                                           entry.current_layout,
                                                           start_layout);
                            },
                        };
                    }

                    // Update state.
                    entry.stages = stages;
                    entry.access = access;
                    entry.exclusive_any = true;
                    entry.exclusive = exclusive;
                    if exclusive || end_layout != ImageLayout::Undefined {
                        // Only modify the layout in case of a write, because buffer operations
                        // pass `Undefined` for the layout. While a buffer write *must* set the
                        // layout to `Undefined`, a buffer read must not touch it.
                        entry.current_layout = end_layout;
                    }

                } else {
                    // There is no collision. Simply merge the stages and accesses.
                    // TODO: what about simplifying the newly-constructed stages/accesses?
                    //       this would simplify the job of the driver, but is it worth it?
                    entry.stages = entry.stages | stages;
                    entry.access = entry.access | access;
                }
            },

            // Situation where this is the first time we use this resource in this command buffer.
            Entry::Vacant(entry) => {
                // We need to perform some tweaks if the initial layout requirement of the image
                // is different from the first layout usage.
                let mut actually_exclusive = exclusive;
                let mut actual_start_layout = start_layout;

                if !self.is_secondary && resource_ty == KeyTy::Image &&
                    start_layout != ImageLayout::Undefined &&
                    start_layout != ImageLayout::Preinitialized
                {
                    let commands_lock = self.commands.lock().unwrap();
                    let img = commands_lock.commands[latest_command_id].image(resource_index);
                    let initial_layout_requirement = img.initial_layout_requirement();

                    if initial_layout_requirement != start_layout {
                        actually_exclusive = true;
                        actual_start_layout = initial_layout_requirement;

                        // Note that we transition from `bottom_of_pipe`, which means that we
                        // wait for all the previous commands to be entirely finished. This is
                        // suboptimal, but:
                        //
                        // - If we're at the start of the command buffer we have no choice anyway,
                        //   because we have no knowledge about what comes before.
                        // - If we're in the middle of the command buffer, this pipeline is going
                        //   to be merged with an existing barrier. While it may still be
                        //   suboptimal in some cases, in the general situation it will be ok.
                        //
                        unsafe {
                            let b = &mut self.pending_barrier;
                            b.add_image_memory_barrier(img,
                                                       0 .. img.mipmap_levels(),
                                                       0 .. img.dimensions().array_layers(),
                                                       PipelineStages {
                                                           bottom_of_pipe: true,
                                                           ..PipelineStages::none()
                                                       },
                                                       AccessFlagBits::none(),
                                                       stages,
                                                       access,
                                                       true,
                                                       None,
                                                       initial_layout_requirement,
                                                       start_layout);
                        }
                    }
                }

                entry.insert(ResourceState {
                    stages: stages,
                    access: access,
                    exclusive_any: actually_exclusive,
                    exclusive: actually_exclusive,
                    initial_layout: actual_start_layout,
                    current_layout: end_layout,     // TODO: what if we reach the end with Undefined? that's not correct?
                });
            },
        }


        Ok(())
    }

    /// Builds the command buffer and turns it into a `SyncCommandBuffer`.
    #[inline]
    pub fn build(mut self) -> Result<SyncCommandBuffer<P::Alloc>, OomError>
        where P: CommandPoolBuilderAlloc
    {
        let mut commands_lock = self.commands.lock().unwrap();
        debug_assert!(commands_lock.latest_render_pass_enter.is_none() ||
                          self.pending_barrier.is_empty());

        // The commands that haven't been sent to the inner command buffer yet need to be sent.
        unsafe {
            self.inner.pipeline_barrier(&self.pending_barrier);
            let f = commands_lock.first_unflushed;
            for command in &mut commands_lock.commands[f ..] {
                command.send(&mut self.inner);
            }
        }

        // Transition images to their desired final layout.
        if !self.is_secondary {
            unsafe {
                // TODO: this could be optimized by merging the barrier with the barrier above?
                let mut barrier = UnsafeCommandBufferBuilderPipelineBarrier::new();

                for (key, state) in &mut self.resources {
                    if key.resource_ty != KeyTy::Image {
                        continue;
                    }

                    let img = commands_lock.commands[key.command_id].image(key.resource_index);
                    let requested_layout = img.final_layout_requirement();
                    if requested_layout == state.current_layout {
                        continue;
                    }

                    barrier.add_image_memory_barrier(img,
                                                     0 .. img.mipmap_levels(),
                                                     0 .. img.dimensions().array_layers(),
                                                     state.stages,
                                                     state.access,
                                                     PipelineStages {
                                                         top_of_pipe: true,
                                                         ..PipelineStages::none()
                                                     },
                                                     AccessFlagBits::none(),
                                                     true,
                                                     None, // TODO: queue transfers?
                                                     state.current_layout,
                                                     requested_layout);

                    state.exclusive_any = true;
                    state.current_layout = requested_layout;
                }

                self.inner.pipeline_barrier(&barrier);
            }
        }

        // Turns the commands into a list of "final commands" that are slimmer.
        let final_commands = {
            let mut final_commands = Vec::with_capacity(commands_lock.commands.len());
            for command in commands_lock.commands.drain(..) {
                final_commands.push(command.into_final_command());
            }
            Arc::new(Mutex::new(final_commands))
        };

        // Build the final resources states.
        let final_resources_states: FnvHashMap<_, _> = {
            self.resources
                .into_iter()
                .map(|(resource, state)| {
                         (resource.into_cb_key(final_commands.clone()), state.finalize())
                     })
                .collect()
        };

        Ok(SyncCommandBuffer {
               inner: self.inner.build()?,
               resources: final_resources_states,
               commands: final_commands,
           })
    }
}

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

/// Command buffer built from a `SyncCommandBufferBuilder` that provides utilities to handle
/// synchronization.
pub struct SyncCommandBuffer<P> {
    // The actual Vulkan command buffer.
    inner: UnsafeCommandBuffer<P>,

    // State of all the resources used by this command buffer.
    resources: FnvHashMap<CbKey<'static>, ResourceFinalState>,

    // List of commands used by the command buffer. Used to hold the various resources that are
    // being used. Each element of `resources` has a copy of this `Arc`, but we need to keep one
    // here in case `resources` is empty.
    commands: Arc<Mutex<Vec<Box<FinalCommand + Send + Sync>>>>,
}

// Usage of a resource in a finished command buffer.
#[derive(Debug, Clone)]
struct ResourceFinalState {
    // Stages of the last command that uses the resource.
    final_stages: PipelineStages,
    // Access for the last command that uses the resource.
    final_access: AccessFlagBits,

    // True if the resource is used in exclusive mode.
    exclusive: bool,

    // Layout that an image must be in at the start of the command buffer. Can be `Undefined` if we
    // don't care.
    initial_layout: ImageLayout,

    // Layout the image will be in at the end of the command buffer.
    final_layout: ImageLayout, // TODO: maybe wrap in an Option to mean that the layout doesn't change? because of buffers?
}

/// Equivalent to `Command`, but with less methods. Typically contains less things than the
/// `Command` it comes from.
pub trait FinalCommand {
    // Returns a user-friendly name for the command, for error reporting purposes.
    fn name(&self) -> &'static str;

    // Gives access to the `num`th buffer used by the command.
    fn buffer(&self, _num: usize) -> &BufferAccess {
        panic!()
    }

    // Gives access to the `num`th image used by the command.
    fn image(&self, _num: usize) -> &ImageAccess {
        panic!()
    }

    // Returns a user-friendly name for the `num`th buffer used by the command, for error
    // reporting purposes.
    fn buffer_name(&self, _num: usize) -> Cow<'static, str> {
        panic!()
    }

    // Returns a user-friendly name for the `num`th image used by the command, for error
    // reporting purposes.
    fn image_name(&self, _num: usize) -> Cow<'static, str> {
        panic!()
    }
}

impl FinalCommand for &'static str {
    fn name(&self) -> &'static str {
        *self
    }
}

// Equivalent of `BuilderKey` for a finished command buffer.
//
// In addition to this, it also add two other variants which are `BufferRef` and `ImageRef`. These
// variants are used in order to make it possible to compare a `CbKey` stored in the
// `SyncCommandBuffer` with a temporarily-created `CbKey`. The Rust HashMap doesn't allow us to do
// that otherwise.
//
// You should never store a `BufferRef` or a `ImageRef` inside the `SyncCommandBuffer`.
enum CbKey<'a> {
    // The resource is held in the list of commands.
    Command {
        // Same `Arc` as in the `SyncCommandBufferBuilder`.
        commands: Arc<Mutex<Vec<Box<FinalCommand + Send + Sync>>>>,
        // Index of the command that holds the resource within `commands`.
        command_id: usize,
        // Type of the resource.
        resource_ty: KeyTy,
        // Index of the resource within the command.
        resource_index: usize,
    },

    // Temporary key that holds a reference to a buffer. Should never be stored in the list of
    // resources of `SyncCommandBuffer`.
    BufferRef(&'a BufferAccess),

    // Temporary key that holds a reference to an image. Should never be stored in the list of
    // resources of `SyncCommandBuffer`.
    ImageRef(&'a ImageAccess),
}

// The `CbKey::Command` variants implements `Send` and `Sync`, but the other two variants don't
// because it would be too constraining.
//
// Since only `CbKey::Command` must be stored in the resources hashmap, we force-implement `Send`
// and `Sync` so that the hashmap itself implements `Send` and `Sync`.
unsafe impl<'a> Send for CbKey<'a> {
}
unsafe impl<'a> Sync for CbKey<'a> {
}

impl<'a> CbKey<'a> {
    #[inline]
    fn conflicts_buffer(&self, commands_lock: Option<&Vec<Box<FinalCommand + Send + Sync>>>,
                        buf: &BufferAccess)
                        -> bool {
        match *self {
            CbKey::Command {
                ref commands,
                command_id,
                resource_ty,
                resource_index,
            } => {
                let lock = if commands_lock.is_none() {
                    Some(commands.lock().unwrap())
                } else {
                    None
                };
                let commands_lock = commands_lock.unwrap_or_else(|| lock.as_ref().unwrap());

                // TODO: put the conflicts_* methods directly on the FinalCommand trait to avoid an indirect call?
                match resource_ty {
                    KeyTy::Buffer => {
                        let c = &commands_lock[command_id];
                        c.buffer(resource_index).conflicts_buffer(buf)
                    },
                    KeyTy::Image => {
                        let c = &commands_lock[command_id];
                        c.image(resource_index).conflicts_buffer(buf)
                    },
                }
            },

            CbKey::BufferRef(b) => b.conflicts_buffer(buf),
            CbKey::ImageRef(i) => i.conflicts_buffer(buf),
        }
    }

    #[inline]
    fn conflicts_image(&self, commands_lock: Option<&Vec<Box<FinalCommand + Send + Sync>>>,
                       img: &ImageAccess)
                       -> bool {
        match *self {
            CbKey::Command {
                ref commands,
                command_id,
                resource_ty,
                resource_index,
            } => {
                let lock = if commands_lock.is_none() {
                    Some(commands.lock().unwrap())
                } else {
                    None
                };
                let commands_lock = commands_lock.unwrap_or_else(|| lock.as_ref().unwrap());

                // TODO: put the conflicts_* methods directly on the Command trait to avoid an indirect call?
                match resource_ty {
                    KeyTy::Buffer => {
                        let c = &commands_lock[command_id];
                        c.buffer(resource_index).conflicts_image(img)
                    },
                    KeyTy::Image => {
                        let c = &commands_lock[command_id];
                        c.image(resource_index).conflicts_image(img)
                    },
                }
            },

            CbKey::BufferRef(b) => b.conflicts_image(img),
            CbKey::ImageRef(i) => i.conflicts_image(img),
        }
    }
}

impl<'a> PartialEq for CbKey<'a> {
    #[inline]
    fn eq(&self, other: &CbKey) -> bool {
        match *self {
            CbKey::BufferRef(a) => {
                other.conflicts_buffer(None, a)
            },
            CbKey::ImageRef(a) => {
                other.conflicts_image(None, a)
            },
            CbKey::Command {
                ref commands,
                command_id,
                resource_ty,
                resource_index,
            } => {
                let commands_lock = commands.lock().unwrap();

                match resource_ty {
                    KeyTy::Buffer => {
                        let c = &commands_lock[command_id];
                        other.conflicts_buffer(Some(&commands_lock), c.buffer(resource_index))
                    },
                    KeyTy::Image => {
                        let c = &commands_lock[command_id];
                        other.conflicts_image(Some(&commands_lock), c.image(resource_index))
                    },
                }
            },
        }
    }
}

impl<'a> Eq for CbKey<'a> {
}

impl<'a> Hash for CbKey<'a> {
    #[inline]
    fn hash<H: Hasher>(&self, state: &mut H) {
        match *self {
            CbKey::Command {
                ref commands,
                command_id,
                resource_ty,
                resource_index,
            } => {
                let commands_lock = commands.lock().unwrap();

                match resource_ty {
                    KeyTy::Buffer => {
                        let c = &commands_lock[command_id];
                        c.buffer(resource_index).conflict_key().hash(state)
                    },
                    KeyTy::Image => {
                        let c = &commands_lock[command_id];
                        c.image(resource_index).conflict_key().hash(state)
                    },
                }
            },

            CbKey::BufferRef(buf) => buf.conflict_key().hash(state),
            CbKey::ImageRef(img) => img.conflict_key().hash(state),
        }
    }
}

impl<P> AsRef<UnsafeCommandBuffer<P>> for SyncCommandBuffer<P> {
    #[inline]
    fn as_ref(&self) -> &UnsafeCommandBuffer<P> {
        &self.inner
    }
}

impl<P> SyncCommandBuffer<P> {
    /// Tries to lock the resources used by the command buffer.
    ///
    /// > **Note**: You should call this in the implementation of the `CommandBuffer` trait.
    pub fn lock_submit(&self, future: &GpuFuture, queue: &Queue)
                       -> Result<(), CommandBufferExecError> {

        let commands_lock = self.commands.lock().unwrap();

        // Number of resources in `self.resources` that have been successfully locked.
        let mut locked_resources = 0;
        // Final return value of this function.
        let mut ret_value = Ok(());

        // Try locking resources. Updates `locked_resources` and `ret_value`, and break if an error
        // happens.
        for (key, entry) in self.resources.iter() {
            let (command_id, resource_ty, resource_index) = match *key {
                CbKey::Command {
                    command_id,
                    resource_ty,
                    resource_index,
                    ..
                } => {
                    (command_id, resource_ty, resource_index)
                },
                _ => unreachable!(),
            };

            match resource_ty {
                KeyTy::Buffer => {
                    let cmd = &commands_lock[command_id];
                    let buf = cmd.buffer(resource_index);

                    // Because try_gpu_lock needs to be called first,
                    // this should never return Ok without first returning Err
                    let prev_err = match future.check_buffer_access(&buf, entry.exclusive, queue) {
                        Ok(_) => {
                            unsafe {
                                buf.increase_gpu_lock();
                            }
                            locked_resources += 1;
                            continue;
                        },
                        Err(err) => err,
                    };

                    match (buf.try_gpu_lock(entry.exclusive, queue), prev_err) {
                        (Ok(_), _) => (),
                        (Err(err), AccessCheckError::Unknown) |
                        (_, AccessCheckError::Denied(err)) => {
                            ret_value = Err(CommandBufferExecError::AccessError {
                                                error: err,
                                                command_name: cmd.name().into(),
                                                command_param: cmd.buffer_name(resource_index),
                                                command_offset: command_id,
                                            });
                            break;
                        },
                    };

                    locked_resources += 1;
                },

                KeyTy::Image => {
                    let cmd = &commands_lock[command_id];
                    let img = cmd.image(resource_index);

                    let prev_err = match future.check_image_access(img, entry.initial_layout,
                                                                   entry.exclusive, queue)
                    {
                        Ok(_) => {
                            unsafe { img.increase_gpu_lock(); }
                            locked_resources += 1;
                            continue;
                        },
                        Err(err) => err
                    };

                    match (img.try_gpu_lock(entry.exclusive, entry.initial_layout), prev_err) {
                        (Ok(_), _) => (),
                        (Err(err), AccessCheckError::Unknown) |
                        (_, AccessCheckError::Denied(err)) => {
                            ret_value = Err(CommandBufferExecError::AccessError {
                                                error: err,
                                                command_name: cmd.name().into(),
                                                command_param: cmd.image_name(resource_index),
                                                command_offset: command_id,
                                            });
                            break;
                        },
                    };

                    locked_resources += 1;
                },
            }
        }

        // If we are going to return an error, we have to unlock all the resources we locked above.
        if let Err(_) = ret_value {
            for key in self.resources.keys().take(locked_resources) {
                let (command_id, resource_ty, resource_index) = match *key {
                    CbKey::Command {
                        command_id,
                        resource_ty,
                        resource_index,
                        ..
                    } => {
                        (command_id, resource_ty, resource_index)
                    },
                    _ => unreachable!(),
                };

                match resource_ty {
                    KeyTy::Buffer => {
                        let cmd = &commands_lock[command_id];
                        let buf = cmd.buffer(resource_index);
                        unsafe {
                            buf.unlock();
                        }
                    },

                    KeyTy::Image => {
                        let cmd = &commands_lock[command_id];
                        let img = cmd.image(resource_index);
                        unsafe {
                            img.unlock(None);
                        }
                    },
                }
            }
        }

        // TODO: pipeline barriers if necessary?

        ret_value
    }

    /// Unlocks the resources used by the command buffer.
    ///
    /// > **Note**: You should call this in the implementation of the `CommandBuffer` trait.
    ///
    /// # Safety
    ///
    /// The command buffer must have been successfully locked with `lock_submit()`.
    ///
    pub unsafe fn unlock(&self) {
        let commands_lock = self.commands.lock().unwrap();

        for (key, val) in self.resources.iter() {
            let (command_id, resource_ty, resource_index) = match *key {
                CbKey::Command {
                    command_id,
                    resource_ty,
                    resource_index,
                    ..
                } => {
                    (command_id, resource_ty, resource_index)
                },
                _ => unreachable!(),
            };

            match resource_ty {
                KeyTy::Buffer => {
                    let cmd = &commands_lock[command_id];
                    let buf = cmd.buffer(resource_index);
                    buf.unlock();
                },
                KeyTy::Image => {
                    let cmd = &commands_lock[command_id];
                    let img = cmd.image(resource_index);
                    let trans = if val.final_layout != val.initial_layout {
                        Some(val.final_layout)
                    } else {
                        None
                    };
                    img.unlock(trans);
                },
            }
        }
    }

    /// Checks whether this command buffer has access to a buffer.
    ///
    /// > **Note**: Suitable when implementing the `CommandBuffer` trait.
    #[inline]
    pub fn check_buffer_access(
        &self, buffer: &BufferAccess, exclusive: bool, queue: &Queue)
        -> Result<Option<(PipelineStages, AccessFlagBits)>, AccessCheckError> {
        // TODO: check the queue family

        if let Some(value) = self.resources.get(&CbKey::BufferRef(buffer)) {
            if !value.exclusive && exclusive {
                return Err(AccessCheckError::Unknown);
            }

            return Ok(Some((value.final_stages, value.final_access)));
        }

        Err(AccessCheckError::Unknown)
    }

    /// Checks whether this command buffer has access to an image.
    ///
    /// > **Note**: Suitable when implementing the `CommandBuffer` trait.
    #[inline]
    pub fn check_image_access(
        &self, image: &ImageAccess, layout: ImageLayout, exclusive: bool, queue: &Queue)
        -> Result<Option<(PipelineStages, AccessFlagBits)>, AccessCheckError> {
        // TODO: check the queue family

        if let Some(value) = self.resources.get(&CbKey::ImageRef(image)) {
            if layout != ImageLayout::Undefined && value.final_layout != layout {
                return Err(AccessCheckError::Denied(AccessError::UnexpectedImageLayout {
                                                        allowed: value.final_layout,
                                                        requested: layout,
                                                    }));
            }

            if !value.exclusive && exclusive {
                return Err(AccessCheckError::Unknown);
            }

            return Ok(Some((value.final_stages, value.final_access)));
        }

        Err(AccessCheckError::Unknown)
    }
}

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