// surfman/surfman/src/platform/windows/angle/context.rs
//
//! Wrapper for EGL contexts managed by ANGLE using Direct3D 11 as a backend on Windows.

use super::device::Device;
use super::surface::{Surface, Synchronization, Win32Objects};
use crate::context::{ContextID, CREATE_CONTEXT_MUTEX};
use crate::egl;
use crate::egl::types::{EGLConfig, EGLContext, EGLint};
use crate::platform::generic::egl::context::{self, CurrentContextGuard};
use crate::platform::generic::egl::device::EGL_FUNCTIONS;
use crate::platform::generic::egl::error::ToWindowingApiError;
use crate::platform::generic::egl::surface::ExternalEGLSurfaces;
use crate::surface::Framebuffer;
use crate::{ContextAttributes, Error, Gl, SurfaceInfo};
use euclid::default::Size2D;

use glow::HasContext;
use std::mem;
use std::os::raw::c_void;
use std::thread;
use winapi::shared::winerror::S_OK;
use winapi::um::winbase::INFINITE;

pub use crate::platform::generic::egl::context::{ContextDescriptor, NativeContext};

/// Represents an OpenGL rendering context.
///
/// A context allows you to issue rendering commands to a surface. When initially created, a
/// context has no attached surface, so rendering commands will fail or be ignored. Typically, you
/// attach a surface to the context before rendering.
///
/// Contexts take ownership of the surfaces attached to them. In order to mutate a surface in any
/// way other than rendering to it (e.g. presenting it to a window, which causes a buffer swap), it
/// must first be detached from its context. Each surface is associated with a single context upon
/// creation and may not be rendered to from any other context. However, you can wrap a surface in
/// a surface texture, which allows the surface to be read from another context.
///
/// OpenGL objects may not be shared across contexts directly, but surface textures effectively
/// allow for sharing of texture data. Contexts are local to a single thread and device.
///
/// A context must be explicitly destroyed with `destroy_context()`, or a panic will occur.
pub struct Context {
    pub(crate) egl_context: EGLContext,
    pub(crate) id: ContextID,
    framebuffer: Framebuffer<Surface, ExternalEGLSurfaces>,
    context_is_owned: bool,
    pub(crate) gl: Gl,
}

impl Drop for Context {
    #[inline]
    fn drop(&mut self) {
        if self.egl_context != egl::NO_CONTEXT && !thread::panicking() {
            panic!("Contexts must be destroyed explicitly with `destroy_context`!")
        }
    }
}

impl Device {
    /// Creates a context descriptor with the given attributes.
    ///
    /// Context descriptors are local to this device.
    #[inline]
    pub fn create_context_descriptor(
        &self,
        attributes: &ContextAttributes,
    ) -> Result<ContextDescriptor, Error> {
        unsafe {
            ContextDescriptor::new(
                self.egl_display,
                attributes,
                &[
                    egl::BIND_TO_TEXTURE_RGBA as EGLint,
                    1 as EGLint,
                    egl::SURFACE_TYPE as EGLint,
                    egl::PBUFFER_BIT as EGLint,
                    egl::RENDERABLE_TYPE as EGLint,
                    egl::OPENGL_ES2_BIT as EGLint,
                ],
            )
        }
    }

    /// Creates a new OpenGL context.
    ///
    /// The context initially has no surface attached. Until a surface is bound to it, rendering
    /// commands will fail or have no effect.
    pub fn create_context(
        &self,
        descriptor: &ContextDescriptor,
        share_with: Option<&Context>,
    ) -> Result<Context, Error> {
        let (egl_context, id) = {
            let mut next_context_id_lock = CREATE_CONTEXT_MUTEX.lock().unwrap();
            let egl_context = unsafe {
                context::create_context(
                    self.egl_display,
                    descriptor,
                    share_with.map_or(egl::NO_CONTEXT, |ctx| ctx.egl_context),
                    self.gl_api(),
                )?
            };
            next_context_id_lock.0 += 1;
            (egl_context, *next_context_id_lock)
        };

        unsafe {
            EGL_FUNCTIONS.with(|egl| {
                let result = egl.MakeCurrent(
                    self.egl_display,
                    egl::NO_SURFACE,
                    egl::NO_SURFACE,
                    egl_context,
                );
                if result == egl::FALSE {
                    return Err(Error::MakeCurrentFailed(
                        egl.GetError().to_windowing_api_error(),
                    ));
                }
                Ok(())
            })?;
        }

        let context = Context {
            egl_context,
            id,
            framebuffer: Framebuffer::None,
            context_is_owned: true,
            gl: unsafe { Gl::from_loader_function(context::get_proc_address) },
        };
        Ok(context)
    }

    /// Wraps a native `EGLContext` in a context object.
    ///
    /// The underlying `EGLContext` is not retained, as there is no way to do this in the EGL API.
    /// Therefore, it is the caller's responsibility to keep it alive as long as this `Context`
    /// remains alive.
    pub unsafe fn create_context_from_native_context(
        &self,
        native_context: NativeContext,
    ) -> Result<Context, Error> {
        let mut next_context_id = CREATE_CONTEXT_MUTEX.lock().unwrap();

        // Create the context.
        let context = Context {
            egl_context: native_context.egl_context,
            id: *next_context_id,
            framebuffer: Framebuffer::External(ExternalEGLSurfaces {
                draw: native_context.egl_draw_surface,
                read: native_context.egl_read_surface,
            }),
            context_is_owned: false,
            gl: Gl::from_loader_function(context::get_proc_address),
        };
        next_context_id.0 += 1;

        Ok(context)
    }

    /// Destroys a context.
    ///
    /// The context must have been created on this device.
    pub fn destroy_context(&self, context: &mut Context) -> Result<(), Error> {
        if context.egl_context == egl::NO_CONTEXT {
            return Ok(());
        }

        if let Ok(Some(mut surface)) = self.unbind_surface_from_context(context) {
            self.destroy_surface(context, &mut surface)?;
        }

        EGL_FUNCTIONS.with(|egl| unsafe {
            egl.MakeCurrent(
                self.egl_display,
                egl::NO_SURFACE,
                egl::NO_SURFACE,
                egl::NO_CONTEXT,
            );

            if context.context_is_owned {
                let result = egl.DestroyContext(self.egl_display, context.egl_context);
                assert_ne!(result, egl::FALSE);
            }

            context.egl_context = egl::NO_CONTEXT;
        });

        Ok(())
    }

    /// Returns the descriptor that this context was created with.
    pub fn context_descriptor(&self, context: &Context) -> ContextDescriptor {
        unsafe {
            ContextDescriptor::from_egl_context(&context.gl, self.egl_display, context.egl_context)
        }
    }

    /// Makes the context the current OpenGL context for this thread.
    ///
    /// After calling this function, it is valid to use OpenGL rendering commands.
    pub fn make_context_current(&self, context: &Context) -> Result<(), Error> {
        unsafe {
            let (egl_draw_surface, egl_read_surface) = match context.framebuffer {
                Framebuffer::Surface(ref surface) => (surface.egl_surface, surface.egl_surface),
                Framebuffer::None => (egl::NO_SURFACE, egl::NO_SURFACE),
                Framebuffer::External(ref surfaces) => (surfaces.draw, surfaces.read),
            };

            EGL_FUNCTIONS.with(|egl| {
                let result = egl.MakeCurrent(
                    self.egl_display,
                    egl_draw_surface,
                    egl_read_surface,
                    context.egl_context,
                );
                if result == egl::FALSE {
                    let err = egl.GetError().to_windowing_api_error();
                    return Err(Error::MakeCurrentFailed(err));
                }
                Ok(())
            })
        }
    }

    /// Removes the current OpenGL context from this thread.
    ///
    /// After calling this function, OpenGL rendering commands will fail until a new context is
    /// made current.
    pub fn make_no_context_current(&self) -> Result<(), Error> {
        unsafe { context::make_no_context_current(self.egl_display) }
    }

    pub(crate) fn temporarily_make_context_current(
        &self,
        context: &Context,
    ) -> Result<CurrentContextGuard, Error> {
        let guard = CurrentContextGuard::new();
        self.make_context_current(context)?;
        Ok(guard)
    }

    pub(crate) fn context_is_current(&self, context: &Context) -> bool {
        EGL_FUNCTIONS.with(|egl| unsafe { egl.GetCurrentContext() == context.egl_context })
    }

    /// Returns the attributes that the context descriptor was created with.
    #[inline]
    pub fn context_descriptor_attributes(
        &self,
        context_descriptor: &ContextDescriptor,
    ) -> ContextAttributes {
        unsafe { context_descriptor.attributes(self.egl_display) }
    }

    /// Fetches the address of an OpenGL function associated with this context.
    ///
    /// OpenGL functions are local to a context. You should not use OpenGL functions on one context
    /// with any other context.
    ///
    /// This method is typically used with a function like `gl::load_with()` from the `gl` crate to
    /// load OpenGL function pointers.
    #[inline]
    pub fn get_proc_address(&self, _: &Context, symbol_name: &str) -> *const c_void {
        context::get_proc_address(symbol_name)
    }

    #[inline]
    pub(crate) fn context_descriptor_to_egl_config(
        &self,
        context_descriptor: &ContextDescriptor,
    ) -> EGLConfig {
        unsafe { context::egl_config_from_id(self.egl_display, context_descriptor.egl_config_id) }
    }

    /// Attaches a surface to a context for rendering.
    ///
    /// This function takes ownership of the surface. The surface must have been created with this
    /// context, or an `IncompatibleSurface` error is returned.
    ///
    /// If this function is called with a surface already bound, a `SurfaceAlreadyBound` error is
    /// returned. To avoid this error, first unbind the existing surface with
    /// `unbind_surface_from_context`.
    ///
    /// If an error is returned, the surface is returned alongside it.
    pub fn bind_surface_to_context(
        &self,
        context: &mut Context,
        surface: Surface,
    ) -> Result<(), (Error, Surface)> {
        if context.id != surface.context_id {
            return Err((Error::IncompatibleSurface, surface));
        }

        match context.framebuffer {
            Framebuffer::None => {}
            Framebuffer::External(_) => return Err((Error::ExternalRenderTarget, surface)),
            Framebuffer::Surface(_) => return Err((Error::SurfaceAlreadyBound, surface)),
        }

        // If the surface is synchronized with GLFinish, then finish.
        // FIXME(pcwalton): Is this necessary and sufficient?
        if surface.uses_gl_finish() {
            if let Ok(_guard) = self.temporarily_make_context_current(context) {
                unsafe {
                    context.gl.finish();
                }
            }
        }

        let is_current = self.context_is_current(context);

        match surface.win32_objects {
            Win32Objects::Pbuffer {
                synchronization: Synchronization::KeyedMutex(ref keyed_mutex),
                ..
            } => unsafe {
                let result = keyed_mutex.AcquireSync(0, INFINITE);
                assert_eq!(result, S_OK);
            },
            _ => {}
        }

        context.framebuffer = Framebuffer::Surface(surface);

        if is_current {
            // We need to make ourselves current again, because the surface changed.
            drop(self.make_context_current(context));
        }

        Ok(())
    }

    /// Removes and returns any attached surface from this context.
    ///
    /// Any pending OpenGL commands targeting this surface will be automatically flushed, so the
    /// surface is safe to read from immediately when this function returns.
    pub fn unbind_surface_from_context(
        &self,
        context: &mut Context,
    ) -> Result<Option<Surface>, Error> {
        match context.framebuffer {
            Framebuffer::None => return Ok(None),
            Framebuffer::External(_) => return Err(Error::ExternalRenderTarget),
            Framebuffer::Surface(_) => {}
        }

        let surface = match mem::replace(&mut context.framebuffer, Framebuffer::None) {
            Framebuffer::Surface(surface) => surface,
            Framebuffer::None | Framebuffer::External(_) => unreachable!(),
        };

        match surface.win32_objects {
            Win32Objects::Pbuffer {
                synchronization: Synchronization::KeyedMutex(ref keyed_mutex),
                ..
            } => unsafe {
                let result = keyed_mutex.ReleaseSync(0);
                assert_eq!(result, S_OK);
            },
            _ => {}
        }

        Ok(Some(surface))
    }

    /// Displays the contents of the currently bound surface to the screen, if
    /// it is a widget surface.
    ///
    /// Widget surfaces are internally double-buffered, so changes to them don't
    /// show up in their associated widgets until this method is called.
    pub fn present_bound_surface(&self, context: &mut Context) -> Result<(), Error> {
        match &context.framebuffer {
            Framebuffer::Surface(surface) => surface.present(self),
            _ => Ok(()),
        }
    }

    /// If the currently bound surface is a widget surface, resize it,
    pub fn resize_bound_surface(
        &self,
        context: &mut Context,
        size: Size2D<i32>,
    ) -> Result<(), Error> {
        if let Framebuffer::Surface(surface) = &mut context.framebuffer {
            surface.resize(size);
        }
        Ok(())
    }

    /// Returns a unique ID representing a context.
    ///
    /// This ID is unique to all currently-allocated contexts. If you destroy a context and create
    /// a new one, the new context might have the same ID as the destroyed one.
    #[inline]
    pub fn context_id(&self, context: &Context) -> ContextID {
        context.id
    }

    /// Returns various information about the surface attached to a context.
    ///
    /// This includes, most notably, the OpenGL framebuffer object needed to render to the surface.
    pub fn context_surface_info(&self, context: &Context) -> Result<Option<SurfaceInfo>, Error> {
        match context.framebuffer {
            Framebuffer::None => Ok(None),
            Framebuffer::External(_) => Err(Error::ExternalRenderTarget),
            Framebuffer::Surface(ref surface) => Ok(Some(self.surface_info(surface))),
        }
    }

    /// Given a context, returns its underlying EGL context and attached surfaces.
    pub fn native_context(&self, context: &Context) -> NativeContext {
        let (egl_draw_surface, egl_read_surface) = match context.framebuffer {
            Framebuffer::Surface(Surface { egl_surface, .. }) => (egl_surface, egl_surface),
            Framebuffer::External(ExternalEGLSurfaces { draw, read }) => (draw, read),
            Framebuffer::None => (egl::NO_SURFACE, egl::NO_SURFACE),
        };

        NativeContext {
            egl_context: context.egl_context,
            egl_draw_surface,
            egl_read_surface,
        }
    }
}
