use std::rc::Rc;

use ::util::ResultExt;
use anyhow::Context as _;
use windows::{
    Win32::{
        Foundation::*,
        Graphics::Gdi::*,
        System::SystemServices::*,
        UI::{
            Controls::*,
            HiDpi::*,
            Input::{Ime::*, KeyboardAndMouse::*},
            WindowsAndMessaging::*,
        },
    },
    core::PCWSTR,
};

use crate::*;

pub(crate) const WM_GPUI_CURSOR_STYLE_CHANGED: u32 = WM_USER + 1;
pub(crate) const WM_GPUI_CLOSE_ONE_WINDOW: u32 = WM_USER + 2;
pub(crate) const WM_GPUI_TASK_DISPATCHED_ON_MAIN_THREAD: u32 = WM_USER + 3;
pub(crate) const WM_GPUI_DOCK_MENU_ACTION: u32 = WM_USER + 4;

const SIZE_MOVE_LOOP_TIMER_ID: usize = 1;
const AUTO_HIDE_TASKBAR_THICKNESS_PX: i32 = 1;

pub(crate) fn handle_msg(
    handle: HWND,
    msg: u32,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> LRESULT {
    let handled = match msg {
        WM_ACTIVATE => handle_activate_msg(wparam, state_ptr),
        WM_CREATE => handle_create_msg(handle, state_ptr),
        WM_MOVE => handle_move_msg(handle, lparam, state_ptr),
        WM_SIZE => handle_size_msg(wparam, lparam, state_ptr),
        WM_GETMINMAXINFO => handle_get_min_max_info_msg(lparam, state_ptr),
        WM_ENTERSIZEMOVE | WM_ENTERMENULOOP => handle_size_move_loop(handle),
        WM_EXITSIZEMOVE | WM_EXITMENULOOP => handle_size_move_loop_exit(handle),
        WM_TIMER => handle_timer_msg(handle, wparam, state_ptr),
        WM_NCCALCSIZE => handle_calc_client_size(handle, wparam, lparam, state_ptr),
        WM_DPICHANGED => handle_dpi_changed_msg(handle, wparam, lparam, state_ptr),
        WM_DISPLAYCHANGE => handle_display_change_msg(handle, state_ptr),
        WM_NCHITTEST => handle_hit_test_msg(handle, msg, wparam, lparam, state_ptr),
        WM_PAINT => handle_paint_msg(handle, state_ptr),
        WM_CLOSE => handle_close_msg(handle, state_ptr),
        WM_DESTROY => handle_destroy_msg(handle, state_ptr),
        WM_MOUSEMOVE => handle_mouse_move_msg(handle, lparam, wparam, state_ptr),
        WM_MOUSELEAVE | WM_NCMOUSELEAVE => handle_mouse_leave_msg(state_ptr),
        WM_NCMOUSEMOVE => handle_nc_mouse_move_msg(handle, lparam, state_ptr),
        WM_NCLBUTTONDOWN => {
            handle_nc_mouse_down_msg(handle, MouseButton::Left, wparam, lparam, state_ptr)
        }
        WM_NCRBUTTONDOWN => {
            handle_nc_mouse_down_msg(handle, MouseButton::Right, wparam, lparam, state_ptr)
        }
        WM_NCMBUTTONDOWN => {
            handle_nc_mouse_down_msg(handle, MouseButton::Middle, wparam, lparam, state_ptr)
        }
        WM_NCLBUTTONUP => {
            handle_nc_mouse_up_msg(handle, MouseButton::Left, wparam, lparam, state_ptr)
        }
        WM_NCRBUTTONUP => {
            handle_nc_mouse_up_msg(handle, MouseButton::Right, wparam, lparam, state_ptr)
        }
        WM_NCMBUTTONUP => {
            handle_nc_mouse_up_msg(handle, MouseButton::Middle, wparam, lparam, state_ptr)
        }
        WM_LBUTTONDOWN => handle_mouse_down_msg(handle, MouseButton::Left, lparam, state_ptr),
        WM_RBUTTONDOWN => handle_mouse_down_msg(handle, MouseButton::Right, lparam, state_ptr),
        WM_MBUTTONDOWN => handle_mouse_down_msg(handle, MouseButton::Middle, lparam, state_ptr),
        WM_XBUTTONDOWN => {
            handle_xbutton_msg(handle, wparam, lparam, handle_mouse_down_msg, state_ptr)
        }
        WM_LBUTTONUP => handle_mouse_up_msg(handle, MouseButton::Left, lparam, state_ptr),
        WM_RBUTTONUP => handle_mouse_up_msg(handle, MouseButton::Right, lparam, state_ptr),
        WM_MBUTTONUP => handle_mouse_up_msg(handle, MouseButton::Middle, lparam, state_ptr),
        WM_XBUTTONUP => handle_xbutton_msg(handle, wparam, lparam, handle_mouse_up_msg, state_ptr),
        WM_MOUSEWHEEL => handle_mouse_wheel_msg(handle, wparam, lparam, state_ptr),
        WM_MOUSEHWHEEL => handle_mouse_horizontal_wheel_msg(handle, wparam, lparam, state_ptr),
        WM_SYSKEYDOWN => handle_syskeydown_msg(handle, wparam, lparam, state_ptr),
        WM_SYSKEYUP => handle_syskeyup_msg(handle, wparam, lparam, state_ptr),
        WM_SYSCOMMAND => handle_system_command(wparam, state_ptr),
        WM_KEYDOWN => handle_keydown_msg(handle, wparam, lparam, state_ptr),
        WM_KEYUP => handle_keyup_msg(handle, wparam, lparam, state_ptr),
        WM_CHAR => handle_char_msg(wparam, state_ptr),
        WM_DEADCHAR => handle_dead_char_msg(wparam, state_ptr),
        WM_IME_STARTCOMPOSITION => handle_ime_position(handle, state_ptr),
        WM_IME_COMPOSITION => handle_ime_composition(handle, lparam, state_ptr),
        WM_SETCURSOR => handle_set_cursor(handle, lparam, state_ptr),
        WM_SETTINGCHANGE => handle_system_settings_changed(handle, wparam, lparam, state_ptr),
        WM_INPUTLANGCHANGE => handle_input_language_changed(lparam, state_ptr),
        WM_GPUI_CURSOR_STYLE_CHANGED => handle_cursor_changed(lparam, state_ptr),
        _ => None,
    };
    if let Some(n) = handled {
        LRESULT(n)
    } else {
        unsafe { DefWindowProcW(handle, msg, wparam, lparam) }
    }
}

fn handle_move_msg(
    handle: HWND,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    let origin = logical_point(
        lparam.signed_loword() as f32,
        lparam.signed_hiword() as f32,
        lock.scale_factor,
    );
    lock.origin = origin;
    let size = lock.logical_size;
    let center_x = origin.x.0 + size.width.0 / 2.;
    let center_y = origin.y.0 + size.height.0 / 2.;
    let monitor_bounds = lock.display.bounds();
    if center_x < monitor_bounds.left().0
        || center_x > monitor_bounds.right().0
        || center_y < monitor_bounds.top().0
        || center_y > monitor_bounds.bottom().0
    {
        // center of the window may have moved to another monitor
        let monitor = unsafe { MonitorFromWindow(handle, MONITOR_DEFAULTTONULL) };
        // minimize the window can trigger this event too, in this case,
        // monitor is invalid, we do nothing.
        if !monitor.is_invalid() && lock.display.handle != monitor {
            // we will get the same monitor if we only have one
            lock.display = WindowsDisplay::new_with_handle(monitor);
        }
    }
    if let Some(mut callback) = lock.callbacks.moved.take() {
        drop(lock);
        callback();
        state_ptr.state.borrow_mut().callbacks.moved = Some(callback);
    }
    Some(0)
}

fn handle_get_min_max_info_msg(
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let lock = state_ptr.state.borrow();
    let min_size = lock.min_size?;
    let scale_factor = lock.scale_factor;
    let boarder_offset = lock.border_offset;
    drop(lock);
    unsafe {
        let minmax_info = &mut *(lparam.0 as *mut MINMAXINFO);
        minmax_info.ptMinTrackSize.x =
            min_size.width.scale(scale_factor).0 as i32 + boarder_offset.width_offset;
        minmax_info.ptMinTrackSize.y =
            min_size.height.scale(scale_factor).0 as i32 + boarder_offset.height_offset;
    }
    Some(0)
}

fn handle_size_msg(
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();

    // Don't resize the renderer when the window is minimized, but record that it was minimized so
    // that on restore the swap chain can be recreated via `update_drawable_size_even_if_unchanged`.
    if wparam.0 == SIZE_MINIMIZED as usize {
        lock.restore_from_minimized = lock.callbacks.request_frame.take();
        return Some(0);
    }

    let width = lparam.loword().max(1) as i32;
    let height = lparam.hiword().max(1) as i32;
    let new_size = size(DevicePixels(width), DevicePixels(height));
    let scale_factor = lock.scale_factor;
    if lock.restore_from_minimized.is_some() {
        lock.renderer
            .update_drawable_size_even_if_unchanged(new_size);
        lock.callbacks.request_frame = lock.restore_from_minimized.take();
    } else {
        lock.renderer.update_drawable_size(new_size);
    }
    let new_size = new_size.to_pixels(scale_factor);
    lock.logical_size = new_size;
    if let Some(mut callback) = lock.callbacks.resize.take() {
        drop(lock);
        callback(new_size, scale_factor);
        state_ptr.state.borrow_mut().callbacks.resize = Some(callback);
    }
    Some(0)
}

fn handle_size_move_loop(handle: HWND) -> Option<isize> {
    unsafe {
        let ret = SetTimer(
            Some(handle),
            SIZE_MOVE_LOOP_TIMER_ID,
            USER_TIMER_MINIMUM,
            None,
        );
        if ret == 0 {
            log::error!(
                "unable to create timer: {}",
                std::io::Error::last_os_error()
            );
        }
    }
    None
}

fn handle_size_move_loop_exit(handle: HWND) -> Option<isize> {
    unsafe {
        KillTimer(Some(handle), SIZE_MOVE_LOOP_TIMER_ID).log_err();
    }
    None
}

fn handle_timer_msg(
    handle: HWND,
    wparam: WPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    if wparam.0 == SIZE_MOVE_LOOP_TIMER_ID {
        for runnable in state_ptr.main_receiver.drain() {
            runnable.run();
        }
        handle_paint_msg(handle, state_ptr)
    } else {
        None
    }
}

fn handle_paint_msg(handle: HWND, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    if let Some(mut request_frame) = lock.callbacks.request_frame.take() {
        drop(lock);
        request_frame(Default::default());
        state_ptr.state.borrow_mut().callbacks.request_frame = Some(request_frame);
    }
    unsafe { ValidateRect(Some(handle), None).ok().log_err() };
    Some(0)
}

fn handle_close_msg(handle: HWND, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    let output = if let Some(mut callback) = lock.callbacks.should_close.take() {
        drop(lock);
        let should_close = callback();
        state_ptr.state.borrow_mut().callbacks.should_close = Some(callback);
        if should_close { None } else { Some(0) }
    } else {
        None
    };

    // Workaround as window close animation is not played with `WS_EX_LAYERED` enabled.
    if output.is_none() {
        unsafe {
            let current_style = get_window_long(handle, GWL_EXSTYLE);
            set_window_long(
                handle,
                GWL_EXSTYLE,
                current_style & !WS_EX_LAYERED.0 as isize,
            );
        }
    }

    output
}

fn handle_destroy_msg(handle: HWND, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let callback = {
        let mut lock = state_ptr.state.borrow_mut();
        lock.callbacks.close.take()
    };
    if let Some(callback) = callback {
        callback();
    }
    unsafe {
        PostThreadMessageW(
            state_ptr.main_thread_id_win32,
            WM_GPUI_CLOSE_ONE_WINDOW,
            WPARAM(state_ptr.validation_number),
            LPARAM(handle.0 as isize),
        )
        .log_err();
    }
    Some(0)
}

fn handle_mouse_move_msg(
    handle: HWND,
    lparam: LPARAM,
    wparam: WPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    start_tracking_mouse(handle, &state_ptr, TME_LEAVE);

    let mut lock = state_ptr.state.borrow_mut();
    let Some(mut func) = lock.callbacks.input.take() else {
        return Some(1);
    };
    let scale_factor = lock.scale_factor;
    drop(lock);

    let pressed_button = match MODIFIERKEYS_FLAGS(wparam.loword() as u32) {
        flags if flags.contains(MK_LBUTTON) => Some(MouseButton::Left),
        flags if flags.contains(MK_RBUTTON) => Some(MouseButton::Right),
        flags if flags.contains(MK_MBUTTON) => Some(MouseButton::Middle),
        flags if flags.contains(MK_XBUTTON1) => {
            Some(MouseButton::Navigate(NavigationDirection::Back))
        }
        flags if flags.contains(MK_XBUTTON2) => {
            Some(MouseButton::Navigate(NavigationDirection::Forward))
        }
        _ => None,
    };
    let x = lparam.signed_loword() as f32;
    let y = lparam.signed_hiword() as f32;
    let input = PlatformInput::MouseMove(MouseMoveEvent {
        position: logical_point(x, y, scale_factor),
        pressed_button,
        modifiers: current_modifiers(),
    });
    let handled = !func(input).propagate;
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled { Some(0) } else { Some(1) }
}

fn handle_mouse_leave_msg(state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    lock.hovered = false;
    if let Some(mut callback) = lock.callbacks.hovered_status_change.take() {
        drop(lock);
        callback(false);
        state_ptr.state.borrow_mut().callbacks.hovered_status_change = Some(callback);
    }

    Some(0)
}

fn handle_syskeydown_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    let input = handle_key_event(handle, wparam, lparam, &mut lock, |keystroke| {
        PlatformInput::KeyDown(KeyDownEvent {
            keystroke,
            is_held: lparam.0 & (0x1 << 30) > 0,
        })
    })?;
    let mut func = lock.callbacks.input.take()?;
    drop(lock);

    let handled = !func(input).propagate;

    let mut lock = state_ptr.state.borrow_mut();
    lock.callbacks.input = Some(func);

    if handled {
        lock.system_key_handled = true;
        Some(0)
    } else {
        // we need to call `DefWindowProcW`, or we will lose the system-wide `Alt+F4`, `Alt+{other keys}`
        // shortcuts.
        None
    }
}

fn handle_syskeyup_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    let input = handle_key_event(handle, wparam, lparam, &mut lock, |keystroke| {
        PlatformInput::KeyUp(KeyUpEvent { keystroke })
    })?;
    let mut func = lock.callbacks.input.take()?;
    drop(lock);
    func(input);
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    // Always return 0 to indicate that the message was handled, so we could properly handle `ModifiersChanged` event.
    Some(0)
}

// It's a known bug that you can't trigger `ctrl-shift-0`. See:
// https://superuser.com/questions/1455762/ctrl-shift-number-key-combination-has-stopped-working-for-a-few-numbers
fn handle_keydown_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    let Some(input) = handle_key_event(handle, wparam, lparam, &mut lock, |keystroke| {
        PlatformInput::KeyDown(KeyDownEvent {
            keystroke,
            is_held: lparam.0 & (0x1 << 30) > 0,
        })
    }) else {
        return Some(1);
    };
    drop(lock);

    let is_composing = with_input_handler(&state_ptr, |input_handler| {
        input_handler.marked_text_range()
    })
    .flatten()
    .is_some();
    if is_composing {
        translate_message(handle, wparam, lparam);
        return Some(0);
    }

    let Some(mut func) = state_ptr.state.borrow_mut().callbacks.input.take() else {
        return Some(1);
    };

    let handled = !func(input).propagate;

    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled {
        Some(0)
    } else {
        translate_message(handle, wparam, lparam);
        Some(1)
    }
}

fn handle_keyup_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    let Some(input) = handle_key_event(handle, wparam, lparam, &mut lock, |keystroke| {
        PlatformInput::KeyUp(KeyUpEvent { keystroke })
    }) else {
        return Some(1);
    };

    let Some(mut func) = lock.callbacks.input.take() else {
        return Some(1);
    };
    drop(lock);

    let handled = !func(input).propagate;
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled { Some(0) } else { Some(1) }
}

fn handle_char_msg(wparam: WPARAM, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let input = parse_char_message(wparam, &state_ptr)?;
    with_input_handler(&state_ptr, |input_handler| {
        input_handler.replace_text_in_range(None, &input);
    });

    Some(0)
}

fn handle_dead_char_msg(wparam: WPARAM, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let ch = char::from_u32(wparam.0 as u32)?.to_string();
    with_input_handler(&state_ptr, |input_handler| {
        input_handler.replace_and_mark_text_in_range(None, &ch, None);
    });
    None
}

fn handle_mouse_down_msg(
    handle: HWND,
    button: MouseButton,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    unsafe { SetCapture(handle) };
    let mut lock = state_ptr.state.borrow_mut();
    let Some(mut func) = lock.callbacks.input.take() else {
        return Some(1);
    };
    let x = lparam.signed_loword();
    let y = lparam.signed_hiword();
    let physical_point = point(DevicePixels(x as i32), DevicePixels(y as i32));
    let click_count = lock.click_state.update(button, physical_point);
    let scale_factor = lock.scale_factor;
    drop(lock);

    let input = PlatformInput::MouseDown(MouseDownEvent {
        button,
        position: logical_point(x as f32, y as f32, scale_factor),
        modifiers: current_modifiers(),
        click_count,
        first_mouse: false,
    });
    let handled = !func(input).propagate;
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled { Some(0) } else { Some(1) }
}

fn handle_mouse_up_msg(
    _handle: HWND,
    button: MouseButton,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    unsafe { ReleaseCapture().log_err() };
    let mut lock = state_ptr.state.borrow_mut();
    let Some(mut func) = lock.callbacks.input.take() else {
        return Some(1);
    };
    let x = lparam.signed_loword() as f32;
    let y = lparam.signed_hiword() as f32;
    let click_count = lock.click_state.current_count;
    let scale_factor = lock.scale_factor;
    drop(lock);

    let input = PlatformInput::MouseUp(MouseUpEvent {
        button,
        position: logical_point(x, y, scale_factor),
        modifiers: current_modifiers(),
        click_count,
    });
    let handled = !func(input).propagate;
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled { Some(0) } else { Some(1) }
}

fn handle_xbutton_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    handler: impl Fn(HWND, MouseButton, LPARAM, Rc<WindowsWindowStatePtr>) -> Option<isize>,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let nav_dir = match wparam.hiword() {
        XBUTTON1 => NavigationDirection::Back,
        XBUTTON2 => NavigationDirection::Forward,
        _ => return Some(1),
    };
    handler(handle, MouseButton::Navigate(nav_dir), lparam, state_ptr)
}

fn handle_mouse_wheel_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let modifiers = current_modifiers();
    let mut lock = state_ptr.state.borrow_mut();
    let Some(mut func) = lock.callbacks.input.take() else {
        return Some(1);
    };
    let scale_factor = lock.scale_factor;
    let wheel_scroll_amount = match modifiers.shift {
        true => lock.system_settings.mouse_wheel_settings.wheel_scroll_chars,
        false => lock.system_settings.mouse_wheel_settings.wheel_scroll_lines,
    };
    drop(lock);

    let wheel_distance =
        (wparam.signed_hiword() as f32 / WHEEL_DELTA as f32) * wheel_scroll_amount as f32;
    let mut cursor_point = POINT {
        x: lparam.signed_loword().into(),
        y: lparam.signed_hiword().into(),
    };
    unsafe { ScreenToClient(handle, &mut cursor_point).ok().log_err() };
    let input = PlatformInput::ScrollWheel(ScrollWheelEvent {
        position: logical_point(cursor_point.x as f32, cursor_point.y as f32, scale_factor),
        delta: ScrollDelta::Lines(match modifiers.shift {
            true => Point {
                x: wheel_distance,
                y: 0.0,
            },
            false => Point {
                y: wheel_distance,
                x: 0.0,
            },
        }),
        modifiers,
        touch_phase: TouchPhase::Moved,
    });
    let handled = !func(input).propagate;
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled { Some(0) } else { Some(1) }
}

fn handle_mouse_horizontal_wheel_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    let Some(mut func) = lock.callbacks.input.take() else {
        return Some(1);
    };
    let scale_factor = lock.scale_factor;
    let wheel_scroll_chars = lock.system_settings.mouse_wheel_settings.wheel_scroll_chars;
    drop(lock);

    let wheel_distance =
        (-wparam.signed_hiword() as f32 / WHEEL_DELTA as f32) * wheel_scroll_chars as f32;
    let mut cursor_point = POINT {
        x: lparam.signed_loword().into(),
        y: lparam.signed_hiword().into(),
    };
    unsafe { ScreenToClient(handle, &mut cursor_point).ok().log_err() };
    let event = PlatformInput::ScrollWheel(ScrollWheelEvent {
        position: logical_point(cursor_point.x as f32, cursor_point.y as f32, scale_factor),
        delta: ScrollDelta::Lines(Point {
            x: wheel_distance,
            y: 0.0,
        }),
        modifiers: current_modifiers(),
        touch_phase: TouchPhase::Moved,
    });
    let handled = !func(event).propagate;
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled { Some(0) } else { Some(1) }
}

fn retrieve_caret_position(state_ptr: &Rc<WindowsWindowStatePtr>) -> Option<POINT> {
    with_input_handler_and_scale_factor(state_ptr, |input_handler, scale_factor| {
        let caret_range = input_handler.selected_text_range(false)?;
        let caret_position = input_handler.bounds_for_range(caret_range.range)?;
        Some(POINT {
            // logical to physical
            x: (caret_position.origin.x.0 * scale_factor) as i32,
            y: (caret_position.origin.y.0 * scale_factor) as i32
                + ((caret_position.size.height.0 * scale_factor) as i32 / 2),
        })
    })
}

fn handle_ime_position(handle: HWND, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    unsafe {
        let ctx = ImmGetContext(handle);

        let Some(caret_position) = retrieve_caret_position(&state_ptr) else {
            return Some(0);
        };
        {
            let config = COMPOSITIONFORM {
                dwStyle: CFS_POINT,
                ptCurrentPos: caret_position,
                ..Default::default()
            };
            ImmSetCompositionWindow(ctx, &config as _).ok().log_err();
        }
        {
            let config = CANDIDATEFORM {
                dwStyle: CFS_CANDIDATEPOS,
                ptCurrentPos: caret_position,
                ..Default::default()
            };
            ImmSetCandidateWindow(ctx, &config as _).ok().log_err();
        }
        ImmReleaseContext(handle, ctx).ok().log_err();
        Some(0)
    }
}

fn handle_ime_composition(
    handle: HWND,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let ctx = unsafe { ImmGetContext(handle) };
    let result = handle_ime_composition_inner(ctx, lparam, state_ptr);
    unsafe { ImmReleaseContext(handle, ctx).ok().log_err() };
    result
}

fn handle_ime_composition_inner(
    ctx: HIMC,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let lparam = lparam.0 as u32;
    if lparam == 0 {
        // Japanese IME may send this message with lparam = 0, which indicates that
        // there is no composition string.
        with_input_handler(&state_ptr, |input_handler| {
            input_handler.replace_text_in_range(None, "");
        })?;
        Some(0)
    } else {
        if lparam & GCS_COMPSTR.0 > 0 {
            let comp_string = parse_ime_composition_string(ctx, GCS_COMPSTR)?;
            let caret_pos = (!comp_string.is_empty() && lparam & GCS_CURSORPOS.0 > 0).then(|| {
                let pos = retrieve_composition_cursor_position(ctx);
                pos..pos
            });
            with_input_handler(&state_ptr, |input_handler| {
                input_handler.replace_and_mark_text_in_range(None, &comp_string, caret_pos);
            })?;
        }
        if lparam & GCS_RESULTSTR.0 > 0 {
            let comp_result = parse_ime_composition_string(ctx, GCS_RESULTSTR)?;
            with_input_handler(&state_ptr, |input_handler| {
                input_handler.replace_text_in_range(None, &comp_result);
            })?;
            return Some(0);
        }

        // currently, we don't care other stuff
        None
    }
}

/// SEE: https://learn.microsoft.com/en-us/windows/win32/winmsg/wm-nccalcsize
fn handle_calc_client_size(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    if !state_ptr.hide_title_bar || state_ptr.state.borrow().is_fullscreen() || wparam.0 == 0 {
        return None;
    }

    let is_maximized = state_ptr.state.borrow().is_maximized();
    let insets = get_client_area_insets(handle, is_maximized, state_ptr.windows_version);
    // wparam is TRUE so lparam points to an NCCALCSIZE_PARAMS structure
    let mut params = lparam.0 as *mut NCCALCSIZE_PARAMS;
    let mut requested_client_rect = unsafe { &mut ((*params).rgrc) };

    requested_client_rect[0].left += insets.left;
    requested_client_rect[0].top += insets.top;
    requested_client_rect[0].right -= insets.right;
    requested_client_rect[0].bottom -= insets.bottom;

    // Fix auto hide taskbar not showing. This solution is based on the approach
    // used by Chrome. However, it may result in one row of pixels being obscured
    // in our client area. But as Chrome says, "there seems to be no better solution."
    if is_maximized {
        if let Some(ref taskbar_position) = state_ptr
            .state
            .borrow()
            .system_settings
            .auto_hide_taskbar_position
        {
            // Fot the auto-hide taskbar, adjust in by 1 pixel on taskbar edge,
            // so the window isn't treated as a "fullscreen app", which would cause
            // the taskbar to disappear.
            match taskbar_position {
                AutoHideTaskbarPosition::Left => {
                    requested_client_rect[0].left += AUTO_HIDE_TASKBAR_THICKNESS_PX
                }
                AutoHideTaskbarPosition::Top => {
                    requested_client_rect[0].top += AUTO_HIDE_TASKBAR_THICKNESS_PX
                }
                AutoHideTaskbarPosition::Right => {
                    requested_client_rect[0].right -= AUTO_HIDE_TASKBAR_THICKNESS_PX
                }
                AutoHideTaskbarPosition::Bottom => {
                    requested_client_rect[0].bottom -= AUTO_HIDE_TASKBAR_THICKNESS_PX
                }
            }
        }
    }

    Some(0)
}

fn handle_activate_msg(wparam: WPARAM, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let activated = wparam.loword() > 0;
    let this = state_ptr.clone();
    state_ptr
        .executor
        .spawn(async move {
            let mut lock = this.state.borrow_mut();
            if let Some(mut func) = lock.callbacks.active_status_change.take() {
                drop(lock);
                func(activated);
                this.state.borrow_mut().callbacks.active_status_change = Some(func);
            }
        })
        .detach();

    None
}

fn handle_create_msg(handle: HWND, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    if state_ptr.hide_title_bar {
        notify_frame_changed(handle);
        Some(0)
    } else {
        None
    }
}

fn handle_dpi_changed_msg(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let new_dpi = wparam.loword() as f32;
    let mut lock = state_ptr.state.borrow_mut();
    lock.scale_factor = new_dpi / USER_DEFAULT_SCREEN_DPI as f32;
    lock.border_offset.update(handle).log_err();
    drop(lock);

    let rect = unsafe { &*(lparam.0 as *const RECT) };
    let width = rect.right - rect.left;
    let height = rect.bottom - rect.top;
    // this will emit `WM_SIZE` and `WM_MOVE` right here
    // even before this function returns
    // the new size is handled in `WM_SIZE`
    unsafe {
        SetWindowPos(
            handle,
            None,
            rect.left,
            rect.top,
            width,
            height,
            SWP_NOZORDER | SWP_NOACTIVATE,
        )
        .context("unable to set window position after dpi has changed")
        .log_err();
    }

    Some(0)
}

/// The following conditions will trigger this event:
/// 1. The monitor on which the window is located goes offline or changes resolution.
/// 2. Another monitor goes offline, is plugged in, or changes resolution.
///
/// In either case, the window will only receive information from the monitor on which
/// it is located.
///
/// For example, in the case of condition 2, where the monitor on which the window is
/// located has actually changed nothing, it will still receive this event.
fn handle_display_change_msg(handle: HWND, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    // NOTE:
    // Even the `lParam` holds the resolution of the screen, we just ignore it.
    // Because WM_DPICHANGED, WM_MOVE, WM_SIZE will come first, window reposition and resize
    // are handled there.
    // So we only care about if monitor is disconnected.
    let previous_monitor = state_ptr.state.borrow().display;
    if WindowsDisplay::is_connected(previous_monitor.handle) {
        // we are fine, other display changed
        return None;
    }
    // display disconnected
    // in this case, the OS will move our window to another monitor, and minimize it.
    // we deminimize the window and query the monitor after moving
    unsafe {
        let _ = ShowWindow(handle, SW_SHOWNORMAL);
    };
    let new_monitor = unsafe { MonitorFromWindow(handle, MONITOR_DEFAULTTONULL) };
    // all monitors disconnected
    if new_monitor.is_invalid() {
        log::error!("No monitor detected!");
        return None;
    }
    let new_display = WindowsDisplay::new_with_handle(new_monitor);
    state_ptr.state.borrow_mut().display = new_display;
    Some(0)
}

fn handle_hit_test_msg(
    handle: HWND,
    msg: u32,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    if !state_ptr.is_movable || state_ptr.state.borrow().is_fullscreen() {
        return None;
    }

    let mut lock = state_ptr.state.borrow_mut();
    if let Some(mut callback) = lock.callbacks.hit_test_window_control.take() {
        drop(lock);
        let area = callback();
        state_ptr
            .state
            .borrow_mut()
            .callbacks
            .hit_test_window_control = Some(callback);
        if let Some(area) = area {
            return match area {
                WindowControlArea::Drag => Some(HTCAPTION as _),
                WindowControlArea::Close => Some(HTCLOSE as _),
                WindowControlArea::Max => Some(HTMAXBUTTON as _),
                WindowControlArea::Min => Some(HTMINBUTTON as _),
            };
        }
    } else {
        drop(lock);
    }

    if !state_ptr.hide_title_bar {
        // If the OS draws the title bar, we don't need to handle hit test messages.
        return None;
    }

    // default handler for resize areas
    let hit = unsafe { DefWindowProcW(handle, msg, wparam, lparam) };
    if matches!(
        hit.0 as u32,
        HTNOWHERE
            | HTRIGHT
            | HTLEFT
            | HTTOPLEFT
            | HTTOP
            | HTTOPRIGHT
            | HTBOTTOMRIGHT
            | HTBOTTOM
            | HTBOTTOMLEFT
    ) {
        return Some(hit.0);
    }

    if state_ptr.state.borrow().is_fullscreen() {
        return Some(HTCLIENT as _);
    }

    let dpi = unsafe { GetDpiForWindow(handle) };
    let frame_y = unsafe { GetSystemMetricsForDpi(SM_CYFRAME, dpi) };

    let mut cursor_point = POINT {
        x: lparam.signed_loword().into(),
        y: lparam.signed_hiword().into(),
    };
    unsafe { ScreenToClient(handle, &mut cursor_point).ok().log_err() };
    if !state_ptr.state.borrow().is_maximized() && cursor_point.y >= 0 && cursor_point.y <= frame_y
    {
        return Some(HTTOP as _);
    }

    Some(HTCLIENT as _)
}

fn handle_nc_mouse_move_msg(
    handle: HWND,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    start_tracking_mouse(handle, &state_ptr, TME_LEAVE | TME_NONCLIENT);

    let mut lock = state_ptr.state.borrow_mut();
    let mut func = lock.callbacks.input.take()?;
    let scale_factor = lock.scale_factor;
    drop(lock);

    let mut cursor_point = POINT {
        x: lparam.signed_loword().into(),
        y: lparam.signed_hiword().into(),
    };
    unsafe { ScreenToClient(handle, &mut cursor_point).ok().log_err() };
    let input = PlatformInput::MouseMove(MouseMoveEvent {
        position: logical_point(cursor_point.x as f32, cursor_point.y as f32, scale_factor),
        pressed_button: None,
        modifiers: current_modifiers(),
    });
    let handled = !func(input).propagate;
    state_ptr.state.borrow_mut().callbacks.input = Some(func);

    if handled { Some(0) } else { None }
}

fn handle_nc_mouse_down_msg(
    handle: HWND,
    button: MouseButton,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    if let Some(mut func) = lock.callbacks.input.take() {
        let scale_factor = lock.scale_factor;
        let mut cursor_point = POINT {
            x: lparam.signed_loword().into(),
            y: lparam.signed_hiword().into(),
        };
        unsafe { ScreenToClient(handle, &mut cursor_point).ok().log_err() };
        let physical_point = point(DevicePixels(cursor_point.x), DevicePixels(cursor_point.y));
        let click_count = lock.click_state.update(button, physical_point);
        drop(lock);

        let input = PlatformInput::MouseDown(MouseDownEvent {
            button,
            position: logical_point(cursor_point.x as f32, cursor_point.y as f32, scale_factor),
            modifiers: current_modifiers(),
            click_count,
            first_mouse: false,
        });
        let result = func(input.clone());
        let handled = !result.propagate || result.default_prevented;
        state_ptr.state.borrow_mut().callbacks.input = Some(func);

        if handled {
            return Some(0);
        }
    } else {
        drop(lock);
    };

    // Since these are handled in handle_nc_mouse_up_msg we must prevent the default window proc
    if button == MouseButton::Left {
        match wparam.0 as u32 {
            HTMINBUTTON => state_ptr.state.borrow_mut().nc_button_pressed = Some(HTMINBUTTON),
            HTMAXBUTTON => state_ptr.state.borrow_mut().nc_button_pressed = Some(HTMAXBUTTON),
            HTCLOSE => state_ptr.state.borrow_mut().nc_button_pressed = Some(HTCLOSE),
            _ => return None,
        };
        Some(0)
    } else {
        None
    }
}

fn handle_nc_mouse_up_msg(
    handle: HWND,
    button: MouseButton,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let mut lock = state_ptr.state.borrow_mut();
    if let Some(mut func) = lock.callbacks.input.take() {
        let scale_factor = lock.scale_factor;
        drop(lock);

        let mut cursor_point = POINT {
            x: lparam.signed_loword().into(),
            y: lparam.signed_hiword().into(),
        };
        unsafe { ScreenToClient(handle, &mut cursor_point).ok().log_err() };
        let input = PlatformInput::MouseUp(MouseUpEvent {
            button,
            position: logical_point(cursor_point.x as f32, cursor_point.y as f32, scale_factor),
            modifiers: current_modifiers(),
            click_count: 1,
        });
        let handled = !func(input).propagate;
        state_ptr.state.borrow_mut().callbacks.input = Some(func);

        if handled {
            return Some(0);
        }
    } else {
        drop(lock);
    }

    let last_pressed = state_ptr.state.borrow_mut().nc_button_pressed.take();
    if button == MouseButton::Left
        && let Some(last_pressed) = last_pressed
    {
        let handled = match (wparam.0 as u32, last_pressed) {
            (HTMINBUTTON, HTMINBUTTON) => {
                unsafe { ShowWindowAsync(handle, SW_MINIMIZE).ok().log_err() };
                true
            }
            (HTMAXBUTTON, HTMAXBUTTON) => {
                if state_ptr.state.borrow().is_maximized() {
                    unsafe { ShowWindowAsync(handle, SW_NORMAL).ok().log_err() };
                } else {
                    unsafe { ShowWindowAsync(handle, SW_MAXIMIZE).ok().log_err() };
                }
                true
            }
            (HTCLOSE, HTCLOSE) => {
                unsafe {
                    PostMessageW(Some(handle), WM_CLOSE, WPARAM::default(), LPARAM::default())
                        .log_err()
                };
                true
            }
            _ => false,
        };
        if handled {
            return Some(0);
        }
    }

    None
}

fn handle_cursor_changed(lparam: LPARAM, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    let mut state = state_ptr.state.borrow_mut();
    let had_cursor = state.current_cursor.is_some();

    state.current_cursor = if lparam.0 == 0 {
        None
    } else {
        Some(HCURSOR(lparam.0 as _))
    };

    if had_cursor != state.current_cursor.is_some() {
        unsafe { SetCursor(state.current_cursor) };
    }

    Some(0)
}

fn handle_set_cursor(
    handle: HWND,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    if unsafe { !IsWindowEnabled(handle).as_bool() }
        || matches!(
            lparam.loword() as u32,
            HTLEFT
                | HTRIGHT
                | HTTOP
                | HTTOPLEFT
                | HTTOPRIGHT
                | HTBOTTOM
                | HTBOTTOMLEFT
                | HTBOTTOMRIGHT
        )
    {
        return None;
    }
    unsafe {
        SetCursor(state_ptr.state.borrow().current_cursor);
    };
    Some(1)
}

fn handle_system_settings_changed(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    if wparam.0 != 0 {
        let mut lock = state_ptr.state.borrow_mut();
        let display = lock.display;
        lock.system_settings.update(display, wparam.0);
        lock.click_state.system_update(wparam.0);
        lock.border_offset.update(handle).log_err();
    } else {
        handle_system_theme_changed(handle, lparam, state_ptr)?;
    };
    // Force to trigger WM_NCCALCSIZE event to ensure that we handle auto hide
    // taskbar correctly.
    notify_frame_changed(handle);

    Some(0)
}

fn handle_system_command(wparam: WPARAM, state_ptr: Rc<WindowsWindowStatePtr>) -> Option<isize> {
    if wparam.0 == SC_KEYMENU as usize {
        let mut lock = state_ptr.state.borrow_mut();
        if lock.system_key_handled {
            lock.system_key_handled = false;
            return Some(0);
        }
    }
    None
}

fn handle_system_theme_changed(
    handle: HWND,
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    // lParam is a pointer to a string that indicates the area containing the system parameter
    // that was changed.
    let parameter = PCWSTR::from_raw(lparam.0 as _);
    if unsafe { !parameter.is_null() && !parameter.is_empty() } {
        if let Some(parameter_string) = unsafe { parameter.to_string() }.log_err() {
            log::info!("System settings changed: {}", parameter_string);
            match parameter_string.as_str() {
                "ImmersiveColorSet" => {
                    let new_appearance = system_appearance()
                        .context("unable to get system appearance when handling ImmersiveColorSet")
                        .log_err()?;
                    let mut lock = state_ptr.state.borrow_mut();
                    if new_appearance != lock.appearance {
                        lock.appearance = new_appearance;
                        let mut callback = lock.callbacks.appearance_changed.take()?;
                        drop(lock);
                        callback();
                        state_ptr.state.borrow_mut().callbacks.appearance_changed = Some(callback);
                        configure_dwm_dark_mode(handle, new_appearance);
                    }
                }
                _ => {}
            }
        }
    }
    Some(0)
}

fn handle_input_language_changed(
    lparam: LPARAM,
    state_ptr: Rc<WindowsWindowStatePtr>,
) -> Option<isize> {
    let thread = state_ptr.main_thread_id_win32;
    let validation = state_ptr.validation_number;
    unsafe {
        PostThreadMessageW(thread, WM_INPUTLANGCHANGE, WPARAM(validation), lparam).log_err();
    }
    Some(0)
}

#[inline]
fn parse_char_message(wparam: WPARAM, state_ptr: &Rc<WindowsWindowStatePtr>) -> Option<String> {
    let code_point = wparam.loword();
    let mut lock = state_ptr.state.borrow_mut();
    // https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-3/#G2630
    match code_point {
        0xD800..=0xDBFF => {
            // High surrogate, wait for low surrogate
            lock.pending_surrogate = Some(code_point);
            None
        }
        0xDC00..=0xDFFF => {
            if let Some(high_surrogate) = lock.pending_surrogate.take() {
                // Low surrogate, combine with pending high surrogate
                String::from_utf16(&[high_surrogate, code_point]).ok()
            } else {
                // Invalid low surrogate without a preceding high surrogate
                log::warn!(
                    "Received low surrogate without a preceding high surrogate: {code_point:x}"
                );
                None
            }
        }
        _ => {
            lock.pending_surrogate = None;
            char::from_u32(code_point as u32)
                .filter(|c| !c.is_control())
                .map(|c| c.to_string())
        }
    }
}

#[inline]
fn translate_message(handle: HWND, wparam: WPARAM, lparam: LPARAM) {
    let msg = MSG {
        hwnd: handle,
        message: WM_KEYDOWN,
        wParam: wparam,
        lParam: lparam,
        // It seems like leaving the following two parameters empty doesn't break key events, they still work as expected.
        // But if any bugs pop up after this PR, this is probably the place to look first.
        time: 0,
        pt: POINT::default(),
    };
    unsafe { TranslateMessage(&msg).ok().log_err() };
}

fn handle_key_event<F>(
    handle: HWND,
    wparam: WPARAM,
    lparam: LPARAM,
    state: &mut WindowsWindowState,
    f: F,
) -> Option<PlatformInput>
where
    F: FnOnce(Keystroke) -> PlatformInput,
{
    let virtual_key = VIRTUAL_KEY(wparam.loword());
    let mut modifiers = current_modifiers();

    match virtual_key {
        VK_SHIFT | VK_CONTROL | VK_MENU | VK_LWIN | VK_RWIN => {
            if state
                .last_reported_modifiers
                .is_some_and(|prev_modifiers| prev_modifiers == modifiers)
            {
                return None;
            }
            state.last_reported_modifiers = Some(modifiers);
            Some(PlatformInput::ModifiersChanged(ModifiersChangedEvent {
                modifiers,
                capslock: current_capslock(),
            }))
        }
        VK_PACKET => {
            translate_message(handle, wparam, lparam);
            None
        }
        VK_CAPITAL => {
            let capslock = current_capslock();
            if state
                .last_reported_capslock
                .is_some_and(|prev_capslock| prev_capslock == capslock)
            {
                return None;
            }
            state.last_reported_capslock = Some(capslock);
            Some(PlatformInput::ModifiersChanged(ModifiersChangedEvent {
                modifiers,
                capslock,
            }))
        }
        vkey => {
            let vkey = if vkey == VK_PROCESSKEY {
                VIRTUAL_KEY(unsafe { ImmGetVirtualKey(handle) } as u16)
            } else {
                vkey
            };
            let keystroke = parse_normal_key(vkey, lparam, modifiers)?;
            Some(f(keystroke))
        }
    }
}

fn parse_immutable(vkey: VIRTUAL_KEY) -> Option<String> {
    Some(
        match vkey {
            VK_SPACE => "space",
            VK_BACK => "backspace",
            VK_RETURN => "enter",
            VK_TAB => "tab",
            VK_UP => "up",
            VK_DOWN => "down",
            VK_RIGHT => "right",
            VK_LEFT => "left",
            VK_HOME => "home",
            VK_END => "end",
            VK_PRIOR => "pageup",
            VK_NEXT => "pagedown",
            VK_BROWSER_BACK => "back",
            VK_BROWSER_FORWARD => "forward",
            VK_ESCAPE => "escape",
            VK_INSERT => "insert",
            VK_DELETE => "delete",
            VK_APPS => "menu",
            VK_F1 => "f1",
            VK_F2 => "f2",
            VK_F3 => "f3",
            VK_F4 => "f4",
            VK_F5 => "f5",
            VK_F6 => "f6",
            VK_F7 => "f7",
            VK_F8 => "f8",
            VK_F9 => "f9",
            VK_F10 => "f10",
            VK_F11 => "f11",
            VK_F12 => "f12",
            VK_F13 => "f13",
            VK_F14 => "f14",
            VK_F15 => "f15",
            VK_F16 => "f16",
            VK_F17 => "f17",
            VK_F18 => "f18",
            VK_F19 => "f19",
            VK_F20 => "f20",
            VK_F21 => "f21",
            VK_F22 => "f22",
            VK_F23 => "f23",
            VK_F24 => "f24",
            _ => return None,
        }
        .to_string(),
    )
}

fn parse_normal_key(
    vkey: VIRTUAL_KEY,
    lparam: LPARAM,
    mut modifiers: Modifiers,
) -> Option<Keystroke> {
    let mut key_char = None;
    let key = parse_immutable(vkey).or_else(|| {
        let scan_code = lparam.hiword() & 0xFF;
        key_char = generate_key_char(
            vkey,
            scan_code as u32,
            modifiers.control,
            modifiers.shift,
            modifiers.alt,
        );
        get_keystroke_key(vkey, scan_code as u32, &mut modifiers)
    })?;
    Some(Keystroke {
        modifiers,
        key,
        key_char,
    })
}

fn parse_ime_composition_string(ctx: HIMC, comp_type: IME_COMPOSITION_STRING) -> Option<String> {
    unsafe {
        let string_len = ImmGetCompositionStringW(ctx, comp_type, None, 0);
        if string_len >= 0 {
            let mut buffer = vec![0u8; string_len as usize + 2];
            ImmGetCompositionStringW(
                ctx,
                comp_type,
                Some(buffer.as_mut_ptr() as _),
                string_len as _,
            );
            let wstring = std::slice::from_raw_parts::<u16>(
                buffer.as_mut_ptr().cast::<u16>(),
                string_len as usize / 2,
            );
            Some(String::from_utf16_lossy(wstring))
        } else {
            None
        }
    }
}

#[inline]
fn retrieve_composition_cursor_position(ctx: HIMC) -> usize {
    unsafe { ImmGetCompositionStringW(ctx, GCS_CURSORPOS, None, 0) as usize }
}

#[inline]
fn is_virtual_key_pressed(vkey: VIRTUAL_KEY) -> bool {
    unsafe { GetKeyState(vkey.0 as i32) < 0 }
}

#[inline]
pub(crate) fn current_modifiers() -> Modifiers {
    Modifiers {
        control: is_virtual_key_pressed(VK_CONTROL),
        alt: is_virtual_key_pressed(VK_MENU),
        shift: is_virtual_key_pressed(VK_SHIFT),
        platform: is_virtual_key_pressed(VK_LWIN) || is_virtual_key_pressed(VK_RWIN),
        function: false,
    }
}

#[inline]
pub(crate) fn current_capslock() -> Capslock {
    let on = unsafe { GetKeyState(VK_CAPITAL.0 as i32) & 1 } > 0;
    Capslock { on: on }
}

fn get_client_area_insets(
    handle: HWND,
    is_maximized: bool,
    windows_version: WindowsVersion,
) -> RECT {
    // For maximized windows, Windows outdents the window rect from the screen's client rect
    // by `frame_thickness` on each edge, meaning `insets` must contain `frame_thickness`
    // on all sides (including the top) to avoid the client area extending onto adjacent
    // monitors.
    //
    // For non-maximized windows, things become complicated:
    //
    // - On Windows 10
    // The top inset must be zero, since if there is any nonclient area, Windows will draw
    // a full native titlebar outside the client area. (This doesn't occur in the maximized
    // case.)
    //
    // - On Windows 11
    // The top inset is calculated using an empirical formula that I derived through various
    // tests. Without this, the top 1-2 rows of pixels in our window would be obscured.
    let dpi = unsafe { GetDpiForWindow(handle) };
    let frame_thickness = get_frame_thickness(dpi);
    let top_insets = if is_maximized {
        frame_thickness
    } else {
        match windows_version {
            WindowsVersion::Win10 => 0,
            WindowsVersion::Win11 => (dpi as f32 / USER_DEFAULT_SCREEN_DPI as f32).round() as i32,
        }
    };
    RECT {
        left: frame_thickness,
        top: top_insets,
        right: frame_thickness,
        bottom: frame_thickness,
    }
}

// there is some additional non-visible space when talking about window
// borders on Windows:
// - SM_CXSIZEFRAME: The resize handle.
// - SM_CXPADDEDBORDER: Additional border space that isn't part of the resize handle.
fn get_frame_thickness(dpi: u32) -> i32 {
    let resize_frame_thickness = unsafe { GetSystemMetricsForDpi(SM_CXSIZEFRAME, dpi) };
    let padding_thickness = unsafe { GetSystemMetricsForDpi(SM_CXPADDEDBORDER, dpi) };
    resize_frame_thickness + padding_thickness
}

fn notify_frame_changed(handle: HWND) {
    unsafe {
        SetWindowPos(
            handle,
            None,
            0,
            0,
            0,
            0,
            SWP_FRAMECHANGED
                | SWP_NOACTIVATE
                | SWP_NOCOPYBITS
                | SWP_NOMOVE
                | SWP_NOOWNERZORDER
                | SWP_NOREPOSITION
                | SWP_NOSENDCHANGING
                | SWP_NOSIZE
                | SWP_NOZORDER,
        )
        .log_err();
    }
}

fn start_tracking_mouse(
    handle: HWND,
    state_ptr: &Rc<WindowsWindowStatePtr>,
    flags: TRACKMOUSEEVENT_FLAGS,
) {
    let mut lock = state_ptr.state.borrow_mut();
    if !lock.hovered {
        lock.hovered = true;
        unsafe {
            TrackMouseEvent(&mut TRACKMOUSEEVENT {
                cbSize: std::mem::size_of::<TRACKMOUSEEVENT>() as u32,
                dwFlags: flags,
                hwndTrack: handle,
                dwHoverTime: HOVER_DEFAULT,
            })
            .log_err()
        };
        if let Some(mut callback) = lock.callbacks.hovered_status_change.take() {
            drop(lock);
            callback(true);
            state_ptr.state.borrow_mut().callbacks.hovered_status_change = Some(callback);
        }
    }
}

fn with_input_handler<F, R>(state_ptr: &Rc<WindowsWindowStatePtr>, f: F) -> Option<R>
where
    F: FnOnce(&mut PlatformInputHandler) -> R,
{
    let mut input_handler = state_ptr.state.borrow_mut().input_handler.take()?;
    let result = f(&mut input_handler);
    state_ptr.state.borrow_mut().input_handler = Some(input_handler);
    Some(result)
}

fn with_input_handler_and_scale_factor<F, R>(
    state_ptr: &Rc<WindowsWindowStatePtr>,
    f: F,
) -> Option<R>
where
    F: FnOnce(&mut PlatformInputHandler, f32) -> Option<R>,
{
    let mut lock = state_ptr.state.borrow_mut();
    let mut input_handler = lock.input_handler.take()?;
    let scale_factor = lock.scale_factor;
    drop(lock);
    let result = f(&mut input_handler, scale_factor);
    state_ptr.state.borrow_mut().input_handler = Some(input_handler);
    result
}
