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// Copyright 2016 The Gfx-rs Developers.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Memory buffers

use std::error::Error;
use std::sync::{Weak, Mutex, MutexGuard};
use std::{mem, fmt, cmp, hash};
use {memory, mapping, handle};
use {Resources};

/// Untyped buffer
#[derive(Debug)]
pub struct Raw<R: Resources> {
    resource: R::Buffer,
    info: Info,
    mapping: Mutex<Option<Weak<mapping::Raw<R>>>>,
}

impl<R: Resources> Raw<R> {
    #[doc(hidden)]
    pub fn new(resource: R::Buffer, info: Info) -> Self {
        Raw {
            resource: resource,
            info: info,
            mapping: Mutex::new(None),
        }
    }

    #[doc(hidden)]
    pub fn resource(&self) -> &R::Buffer { &self.resource }

    /// Get buffer info
    pub fn get_info(&self) -> &Info { &self.info }

    fn mapping_opt(&self) -> MutexGuard<Option<Weak<mapping::Raw<R>>>> {
        self.mapping.lock().unwrap()
    }

    /// Get the current buffer mapping
    #[doc(hidden)]
    pub fn mapping(&self) -> Option<handle::RawMapping<R>> {
        let weak_opt = self.mapping_opt();
        weak_opt.as_ref().map(|w| handle::RawMapping::upgrade(w))
    }

    /// Needs to be called internally after the buffer is mapped
    #[doc(hidden)]
    pub fn was_mapped(&self, raw: &handle::RawMapping<R>) {
        let mut weak_opt = self.mapping_opt();
        *weak_opt = Some(raw.downgrade());
    }

    /// Needs to be called internally after the buffer is unmapped
    #[doc(hidden)]
    pub fn was_unmapped(&self) {
        let mut weak_opt = self.mapping_opt();
        *weak_opt = None;
    }

    /// Get the number of elements in the buffer.
    ///
    /// Fails if `T` is zero-sized.
    #[doc(hidden)]
    pub unsafe fn len<T>(&self) -> usize {
        assert!(mem::size_of::<T>() != 0, "Cannot determine the length of zero-sized buffers.");
        self.get_info().size / mem::size_of::<T>()
    }
}

impl<R: Resources + cmp::PartialEq> cmp::PartialEq for Raw<R> {
    fn eq(&self, other: &Self) -> bool {
        self.resource().eq(other.resource())
    }
}

impl<R: Resources + cmp::Eq> cmp::Eq for Raw<R> {}

impl<R: Resources + hash::Hash> hash::Hash for Raw<R> {
    fn hash<H: hash::Hasher>(&self, state: &mut H) {
        self.resource().hash(state);
    }
}

/// Role of the memory buffer. GLES doesn't allow chaning bind points for buffers.
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
#[repr(u8)]
pub enum Role {
    /// Generic vertex buffer
    Vertex,
    /// Index buffer
    Index,
    /// Constant buffer
    Constant,
}

/// An information block that is immutable and associated to each buffer.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub struct Info {
    /// Role
    pub role: Role,
    /// Usage hint
    pub usage: memory::Usage,
    /// Bind flags
    pub bind: memory::Bind,
    /// Size in bytes
    pub size: usize,
    /// Stride of a single element, in bytes. Only used for structured buffers
    /// that you use via shader resource / unordered access views.
    pub stride: usize,
}

/// Error creating a buffer.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum CreationError {
    /// Some of the bind flags are not supported.
    UnsupportedBind(memory::Bind),
    /// Unknown other error.
    Other,
    // TODO: unsupported role
}

impl fmt::Display for CreationError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        if let CreationError::UnsupportedBind(ref bind) = *self {
            write!(f, "{}: {:?}", self.description(), bind)
        } else {
            write!(f, "{}", self.description())
        }
    }
}

impl Error for CreationError {
    fn description(&self) -> &str {
        match *self {
            CreationError::UnsupportedBind(_) => "Bind flags are not supported",
            CreationError::Other => "An unknown error occurred",
        }
    }
}

/// An error happening on buffer updates.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum UpdateError {
    /// Trying to change the contents outside of the allocation.
    OutOfBounds,
}

impl fmt::Display for UpdateError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.description())
    }
}

impl Error for UpdateError {
    fn description(&self) -> &str {
        match *self {
            UpdateError::OutOfBounds =>
                "Tried to change the buffer contents outside of the allocation",
        }
    }
}