baseview 0.1.3

Low-level windowing system geared towards making audio plugin UIs.
Documentation 
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use super::*;
use std::ptr::NonNull;
use std::rc::Rc;
use windows_sys::Win32::Foundation::{HWND, LPARAM, LRESULT, WPARAM};
use windows_sys::Win32::UI::WindowsAndMessaging::*;

/// The wndproc implementation wrapping a given [`WindowImpl`] type.
///
/// This handles all the lifecycle details of the window and its data created by [create_window].
pub unsafe extern "system" fn wnd_proc<W: WindowImpl>(
    window: HWND, message_code: u32, w_param: WPARAM, l_param: LPARAM,
) -> LRESULT {
    let handle_default = || unsafe { DefWindowProcW(window, message_code, w_param, l_param) };
    let window = unsafe { HWnd::from_raw(window) };

    match message_code {
        WM_CREATE => {
            let create = unsafe { &*(l_param as *const CREATESTRUCTW) };
            let inner_ptr = create.lpCreateParams as *mut WindowData<W>;

            let Some(inner_ptr) = NonNull::new(inner_ptr) else {
                // If the state pointer was null for some weird reason, we just abort.
                // TODO: log error
                return -1;
            };

            if let Err(_e) = window.set_userdata_ptr(inner_ptr.as_ptr()) {
                // The call to SetWindowLongPtrW failed for some reason, we cannot continue.

                // Recover and free the received pointer data.
                drop(Rc::from_raw(inner_ptr.as_ptr()));

                // TODO: log error
                return -1;
            }

            // Now the fun begins
            let result = {
                let inner = unsafe { inner_ptr.as_ref() };

                inner.initialize(window)
            };

            match result {
                // If successful, all good.
                // Ownership of the inner state has been passed to the window via the userdata ptr.
                Ok(()) => 0,

                // If initializer failed, abort.
                Err(_) => {
                    // First, revoke ownership from the window, we don't want it to be used by any subsequent messages.
                    let _ = window.set_userdata_ptr(core::ptr::null::<W>());

                    // Try to recover and free the received pointer data. But if this also fails, better to leak
                    // it than risk crashing
                    drop(Rc::from_raw(inner_ptr.as_ptr()));

                    // TODO: log error
                    -1
                }
            }
        }
        WM_DESTROY => {
            let Some(state_ptr) = window.get_userdata_ptr::<WindowData<W>>() else {
                // State pointer can be null if the WM_DESTROY message got sent before
                // the handling of WM_CREATE above finished, or if it failed.
                // If that's the case, we have nothing to destroy.
                return handle_default();
            };

            let state = unsafe { Rc::from_raw(state_ptr.as_ptr()) };
            state.destroy_started(window);
            let _ = window.set_userdata_ptr(core::ptr::null::<W>());
            drop(state);

            0
        }
        _ => {
            let Some(inner_ptr) = window.get_userdata_ptr::<WindowData<W>>() else {
                return handle_default();
            };

            // This guarantees WindowData remains valid until the end of this scope,
            // even if the event handler leads to the window being destroyed
            let inner = unsafe { WindowData::from_raw(inner_ptr) };

            let result = inner.handle_message(window, message_code, w_param, l_param);

            drop(inner);

            result.unwrap_or_else(handle_default)
        }
    }
}