// Copyright (c) 2017 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::error;
use std::fmt;

use VulkanObject;
use buffer::BufferAccess;
use device::DeviceOwned;
use pipeline::vertex::VertexSource;

/// Checks whether vertex buffers can be bound.
///
/// # Panic
///
/// - Panics if one of the vertex buffers was not created with the same device as `pipeline`.
///
pub fn check_vertex_buffers<P, V>(pipeline: &P, vertex_buffers: V)
                                  -> Result<CheckVertexBuffer, CheckVertexBufferError>
    where P: DeviceOwned + VertexSource<V>
{
    let (vertex_buffers, vertex_count, instance_count) = pipeline.decode(vertex_buffers);

    for (num, buf) in vertex_buffers.iter().enumerate() {
        assert_eq!(buf.inner().buffer.device().internal_object(),
                   pipeline.device().internal_object());

        if !buf.inner().buffer.usage_vertex_buffer() {
            return Err(CheckVertexBufferError::BufferMissingUsage { num_buffer: num });
        }
    }

    Ok(CheckVertexBuffer {
           vertex_buffers,
           vertex_count: vertex_count as u32,
           instance_count: instance_count as u32,
       })
}

/// Information returned if `check_vertex_buffer` succeeds.
pub struct CheckVertexBuffer {
    /// The list of vertex buffers.
    pub vertex_buffers: Vec<Box<dyn BufferAccess + Send + Sync>>,
    /// Number of vertices available in the intersection of the buffers.
    pub vertex_count: u32,
    /// Number of instances available in the intersection of the buffers.
    pub instance_count: u32,
}

/// Error that can happen when checking whether the vertex buffers are valid.
#[derive(Debug, Copy, Clone)]
pub enum CheckVertexBufferError {
    /// The "vertex buffer" usage must be enabled on the buffer.
    BufferMissingUsage {
        /// Index of the buffer that is missing usage.
        num_buffer: usize,
    },
}

impl error::Error for CheckVertexBufferError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            CheckVertexBufferError::BufferMissingUsage { .. } => {
                "the vertex buffer usage is missing on a vertex buffer"
            },
        }
    }
}

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