//! Glium compatibility module

use backend::graphics::egl::{
    error::Result as EGLResult,
    wayland::{EGLDisplay, EGLWaylandExtensions},
    EGLGraphicsBackend, SwapBuffersError,
};
use glium::{
    backend::{Backend, Context, Facade},
    debug::DebugCallbackBehavior,
    Frame, SwapBuffersError as GliumSwapBuffersError,
};
use std::{
    cell::{Ref, RefCell, RefMut},
    os::raw::c_void,
    rc::Rc,
};
use wayland_server::Display;

impl From<SwapBuffersError> for GliumSwapBuffersError {
    fn from(error: SwapBuffersError) -> Self {
        match error {
            SwapBuffersError::ContextLost => GliumSwapBuffersError::ContextLost,
            SwapBuffersError::AlreadySwapped => GliumSwapBuffersError::AlreadySwapped,
            SwapBuffersError::Unknown(_) => GliumSwapBuffersError::ContextLost, // TODO
        }
    }
}

/// Wrapper to expose `Glium` compatibility
pub struct GliumGraphicsBackend<T: EGLGraphicsBackend> {
    context: Rc<Context>,
    backend: Rc<InternalBackend<T>>,
}

struct InternalBackend<T: EGLGraphicsBackend>(RefCell<T>);

impl<T: EGLGraphicsBackend + 'static> GliumGraphicsBackend<T> {
    fn new(backend: T) -> GliumGraphicsBackend<T> {
        let internal = Rc::new(InternalBackend(RefCell::new(backend)));

        GliumGraphicsBackend {
            // cannot fail
            context: unsafe {
                Context::new(internal.clone(), true, DebugCallbackBehavior::default()).unwrap()
            },
            backend: internal,
        }
    }

    /// Start drawing on the backbuffer.
    ///
    /// This function returns a `Frame`, which can be used to draw on it. When the `Frame` is
    /// destroyed, the buffers are swapped.
    ///
    /// Note that destroying a `Frame` is immediate, even if vsync is enabled.
    #[inline]
    pub fn draw(&self) -> Frame {
        Frame::new(self.context.clone(), self.backend.get_framebuffer_dimensions())
    }

    /// Borrow the underlying backend.
    ///
    /// This follows the same semantics as `std::cell:RefCell`.
    /// Multiple read-only borrows are possible. Borrowing the
    /// backend while there is a mutable reference will panic.
    pub fn borrow(&self) -> Ref<T> {
        self.backend.0.borrow()
    }

    /// Borrow the underlying backend mutably.
    ///
    /// This follows the same semantics as `std::cell:RefCell`.
    /// Holding any other borrow while trying to borrow the backend
    /// mutably will panic. Note that Glium will borrow the backend
    /// (not mutably) during rendering.
    pub fn borrow_mut(&self) -> RefMut<T> {
        self.backend.0.borrow_mut()
    }
}

impl<T: EGLGraphicsBackend> Facade for GliumGraphicsBackend<T> {
    fn get_context(&self) -> &Rc<Context> {
        &self.context
    }
}

impl<T: EGLGraphicsBackend + 'static> From<T> for GliumGraphicsBackend<T> {
    fn from(backend: T) -> Self {
        GliumGraphicsBackend::new(backend)
    }
}

impl<T: EGLGraphicsBackend + EGLWaylandExtensions + 'static> EGLWaylandExtensions
    for GliumGraphicsBackend<T>
{
    fn bind_wl_display(&self, display: &Display) -> EGLResult<EGLDisplay> {
        (*self.backend).0.borrow().bind_wl_display(display)
    }
}

unsafe impl<T: EGLGraphicsBackend> Backend for InternalBackend<T> {
    fn swap_buffers(&self) -> Result<(), GliumSwapBuffersError> {
        self.0.borrow().swap_buffers().map_err(Into::into)
    }

    unsafe fn get_proc_address(&self, symbol: &str) -> *const c_void {
        self.0.borrow().get_proc_address(symbol) as *const c_void
    }

    fn get_framebuffer_dimensions(&self) -> (u32, u32) {
        self.0.borrow().get_framebuffer_dimensions()
    }

    fn is_current(&self) -> bool {
        self.0.borrow().is_current()
    }

    unsafe fn make_current(&self) {
        self.0.borrow().make_current().expect("Context was lost")
    }
}