use std::{
    char,
    os::raw::c_int,
    ptr,
    sync::atomic::{AtomicBool, AtomicPtr, Ordering},
};

use crate::event::{ModifiersState, ScanCode, VirtualKeyCode};

use winapi::{
    shared::minwindef::{HKL, HKL__, LPARAM, UINT, WPARAM},
    um::winuser,
};

fn key_pressed(vkey: c_int) -> bool {
    unsafe { (winuser::GetKeyState(vkey) & (1 << 15)) == (1 << 15) }
}

pub fn get_key_mods() -> ModifiersState {
    let mut mods = ModifiersState::default();
    let filter_out_altgr = layout_uses_altgr() && key_pressed(winuser::VK_RMENU);

    mods.shift = key_pressed(winuser::VK_SHIFT);
    mods.ctrl = key_pressed(winuser::VK_CONTROL) && !filter_out_altgr;
    mods.alt = key_pressed(winuser::VK_MENU) && !filter_out_altgr;
    mods.logo = key_pressed(winuser::VK_LWIN) || key_pressed(winuser::VK_RWIN);
    mods
}

unsafe fn get_char(keyboard_state: &[u8; 256], v_key: u32, hkl: HKL) -> Option<char> {
    let mut unicode_bytes = [0u16; 5];
    let len = winuser::ToUnicodeEx(
        v_key,
        0,
        keyboard_state.as_ptr(),
        unicode_bytes.as_mut_ptr(),
        unicode_bytes.len() as _,
        0,
        hkl,
    );
    if len >= 1 {
        char::decode_utf16(unicode_bytes.into_iter().cloned())
            .next()
            .and_then(|c| c.ok())
    } else {
        None
    }
}

/// Figures out if the keyboard layout has an AltGr key instead of an Alt key.
///
/// Unfortunately, the Windows API doesn't give a way for us to conveniently figure that out. So,
/// we use a technique blatantly stolen from [the Firefox source code][source]: iterate over every
/// possible virtual key and compare the `char` output when AltGr is pressed vs when it isn't. If
/// pressing AltGr outputs characters that are different from the standard characters, the layout
/// uses AltGr. Otherwise, it doesn't.
///
/// [source]: https://github.com/mozilla/gecko-dev/blob/265e6721798a455604328ed5262f430cfcc37c2f/widget/windows/KeyboardLayout.cpp#L4356-L4416
fn layout_uses_altgr() -> bool {
    unsafe {
        static ACTIVE_LAYOUT: AtomicPtr<HKL__> = AtomicPtr::new(ptr::null_mut());
        static USES_ALTGR: AtomicBool = AtomicBool::new(false);

        let hkl = winuser::GetKeyboardLayout(0);
        let old_hkl = ACTIVE_LAYOUT.swap(hkl, Ordering::SeqCst);

        if hkl == old_hkl {
            return USES_ALTGR.load(Ordering::SeqCst);
        }

        let mut keyboard_state_altgr = [0u8; 256];
        // AltGr is an alias for Ctrl+Alt for... some reason. Whatever it is, those are the keypresses
        // we have to emulate to do an AltGr test.
        keyboard_state_altgr[winuser::VK_MENU as usize] = 0x80;
        keyboard_state_altgr[winuser::VK_CONTROL as usize] = 0x80;

        let keyboard_state_empty = [0u8; 256];

        for v_key in 0..=255 {
            let key_noaltgr = get_char(&keyboard_state_empty, v_key, hkl);
            let key_altgr = get_char(&keyboard_state_altgr, v_key, hkl);
            if let (Some(noaltgr), Some(altgr)) = (key_noaltgr, key_altgr) {
                if noaltgr != altgr {
                    USES_ALTGR.store(true, Ordering::SeqCst);
                    return true;
                }
            }
        }

        USES_ALTGR.store(false, Ordering::SeqCst);
        false
    }
}

pub fn vkey_to_winit_vkey(vkey: c_int) -> Option<VirtualKeyCode> {
    // VK_* codes are documented here https://msdn.microsoft.com/en-us/library/windows/desktop/dd375731(v=vs.85).aspx
    match vkey {
        //winuser::VK_LBUTTON => Some(VirtualKeyCode::Lbutton),
        //winuser::VK_RBUTTON => Some(VirtualKeyCode::Rbutton),
        //winuser::VK_CANCEL => Some(VirtualKeyCode::Cancel),
        //winuser::VK_MBUTTON => Some(VirtualKeyCode::Mbutton),
        //winuser::VK_XBUTTON1 => Some(VirtualKeyCode::Xbutton1),
        //winuser::VK_XBUTTON2 => Some(VirtualKeyCode::Xbutton2),
        winuser::VK_BACK => Some(VirtualKeyCode::Back),
        winuser::VK_TAB => Some(VirtualKeyCode::Tab),
        //winuser::VK_CLEAR => Some(VirtualKeyCode::Clear),
        winuser::VK_RETURN => Some(VirtualKeyCode::Return),
        winuser::VK_LSHIFT => Some(VirtualKeyCode::LShift),
        winuser::VK_RSHIFT => Some(VirtualKeyCode::RShift),
        winuser::VK_LCONTROL => Some(VirtualKeyCode::LControl),
        winuser::VK_RCONTROL => Some(VirtualKeyCode::RControl),
        winuser::VK_LMENU => Some(VirtualKeyCode::LAlt),
        winuser::VK_RMENU => Some(VirtualKeyCode::RAlt),
        winuser::VK_PAUSE => Some(VirtualKeyCode::Pause),
        winuser::VK_CAPITAL => Some(VirtualKeyCode::Capital),
        winuser::VK_KANA => Some(VirtualKeyCode::Kana),
        //winuser::VK_HANGUEL => Some(VirtualKeyCode::Hanguel),
        //winuser::VK_HANGUL => Some(VirtualKeyCode::Hangul),
        //winuser::VK_JUNJA => Some(VirtualKeyCode::Junja),
        //winuser::VK_FINAL => Some(VirtualKeyCode::Final),
        //winuser::VK_HANJA => Some(VirtualKeyCode::Hanja),
        winuser::VK_KANJI => Some(VirtualKeyCode::Kanji),
        winuser::VK_ESCAPE => Some(VirtualKeyCode::Escape),
        winuser::VK_CONVERT => Some(VirtualKeyCode::Convert),
        winuser::VK_NONCONVERT => Some(VirtualKeyCode::NoConvert),
        //winuser::VK_ACCEPT => Some(VirtualKeyCode::Accept),
        //winuser::VK_MODECHANGE => Some(VirtualKeyCode::Modechange),
        winuser::VK_SPACE => Some(VirtualKeyCode::Space),
        winuser::VK_PRIOR => Some(VirtualKeyCode::PageUp),
        winuser::VK_NEXT => Some(VirtualKeyCode::PageDown),
        winuser::VK_END => Some(VirtualKeyCode::End),
        winuser::VK_HOME => Some(VirtualKeyCode::Home),
        winuser::VK_LEFT => Some(VirtualKeyCode::Left),
        winuser::VK_UP => Some(VirtualKeyCode::Up),
        winuser::VK_RIGHT => Some(VirtualKeyCode::Right),
        winuser::VK_DOWN => Some(VirtualKeyCode::Down),
        //winuser::VK_SELECT => Some(VirtualKeyCode::Select),
        //winuser::VK_PRINT => Some(VirtualKeyCode::Print),
        //winuser::VK_EXECUTE => Some(VirtualKeyCode::Execute),
        winuser::VK_SNAPSHOT => Some(VirtualKeyCode::Snapshot),
        winuser::VK_INSERT => Some(VirtualKeyCode::Insert),
        winuser::VK_DELETE => Some(VirtualKeyCode::Delete),
        //winuser::VK_HELP => Some(VirtualKeyCode::Help),
        0x30 => Some(VirtualKeyCode::Key0),
        0x31 => Some(VirtualKeyCode::Key1),
        0x32 => Some(VirtualKeyCode::Key2),
        0x33 => Some(VirtualKeyCode::Key3),
        0x34 => Some(VirtualKeyCode::Key4),
        0x35 => Some(VirtualKeyCode::Key5),
        0x36 => Some(VirtualKeyCode::Key6),
        0x37 => Some(VirtualKeyCode::Key7),
        0x38 => Some(VirtualKeyCode::Key8),
        0x39 => Some(VirtualKeyCode::Key9),
        0x41 => Some(VirtualKeyCode::A),
        0x42 => Some(VirtualKeyCode::B),
        0x43 => Some(VirtualKeyCode::C),
        0x44 => Some(VirtualKeyCode::D),
        0x45 => Some(VirtualKeyCode::E),
        0x46 => Some(VirtualKeyCode::F),
        0x47 => Some(VirtualKeyCode::G),
        0x48 => Some(VirtualKeyCode::H),
        0x49 => Some(VirtualKeyCode::I),
        0x4A => Some(VirtualKeyCode::J),
        0x4B => Some(VirtualKeyCode::K),
        0x4C => Some(VirtualKeyCode::L),
        0x4D => Some(VirtualKeyCode::M),
        0x4E => Some(VirtualKeyCode::N),
        0x4F => Some(VirtualKeyCode::O),
        0x50 => Some(VirtualKeyCode::P),
        0x51 => Some(VirtualKeyCode::Q),
        0x52 => Some(VirtualKeyCode::R),
        0x53 => Some(VirtualKeyCode::S),
        0x54 => Some(VirtualKeyCode::T),
        0x55 => Some(VirtualKeyCode::U),
        0x56 => Some(VirtualKeyCode::V),
        0x57 => Some(VirtualKeyCode::W),
        0x58 => Some(VirtualKeyCode::X),
        0x59 => Some(VirtualKeyCode::Y),
        0x5A => Some(VirtualKeyCode::Z),
        //winuser::VK_LWIN => Some(VirtualKeyCode::Lwin),
        //winuser::VK_RWIN => Some(VirtualKeyCode::Rwin),
        winuser::VK_APPS => Some(VirtualKeyCode::Apps),
        winuser::VK_SLEEP => Some(VirtualKeyCode::Sleep),
        winuser::VK_NUMPAD0 => Some(VirtualKeyCode::Numpad0),
        winuser::VK_NUMPAD1 => Some(VirtualKeyCode::Numpad1),
        winuser::VK_NUMPAD2 => Some(VirtualKeyCode::Numpad2),
        winuser::VK_NUMPAD3 => Some(VirtualKeyCode::Numpad3),
        winuser::VK_NUMPAD4 => Some(VirtualKeyCode::Numpad4),
        winuser::VK_NUMPAD5 => Some(VirtualKeyCode::Numpad5),
        winuser::VK_NUMPAD6 => Some(VirtualKeyCode::Numpad6),
        winuser::VK_NUMPAD7 => Some(VirtualKeyCode::Numpad7),
        winuser::VK_NUMPAD8 => Some(VirtualKeyCode::Numpad8),
        winuser::VK_NUMPAD9 => Some(VirtualKeyCode::Numpad9),
        winuser::VK_MULTIPLY => Some(VirtualKeyCode::Multiply),
        winuser::VK_ADD => Some(VirtualKeyCode::Add),
        //winuser::VK_SEPARATOR => Some(VirtualKeyCode::Separator),
        winuser::VK_SUBTRACT => Some(VirtualKeyCode::Subtract),
        winuser::VK_DECIMAL => Some(VirtualKeyCode::Decimal),
        winuser::VK_DIVIDE => Some(VirtualKeyCode::Divide),
        winuser::VK_F1 => Some(VirtualKeyCode::F1),
        winuser::VK_F2 => Some(VirtualKeyCode::F2),
        winuser::VK_F3 => Some(VirtualKeyCode::F3),
        winuser::VK_F4 => Some(VirtualKeyCode::F4),
        winuser::VK_F5 => Some(VirtualKeyCode::F5),
        winuser::VK_F6 => Some(VirtualKeyCode::F6),
        winuser::VK_F7 => Some(VirtualKeyCode::F7),
        winuser::VK_F8 => Some(VirtualKeyCode::F8),
        winuser::VK_F9 => Some(VirtualKeyCode::F9),
        winuser::VK_F10 => Some(VirtualKeyCode::F10),
        winuser::VK_F11 => Some(VirtualKeyCode::F11),
        winuser::VK_F12 => Some(VirtualKeyCode::F12),
        winuser::VK_F13 => Some(VirtualKeyCode::F13),
        winuser::VK_F14 => Some(VirtualKeyCode::F14),
        winuser::VK_F15 => Some(VirtualKeyCode::F15),
        winuser::VK_F16 => Some(VirtualKeyCode::F16),
        winuser::VK_F17 => Some(VirtualKeyCode::F17),
        winuser::VK_F18 => Some(VirtualKeyCode::F18),
        winuser::VK_F19 => Some(VirtualKeyCode::F19),
        winuser::VK_F20 => Some(VirtualKeyCode::F20),
        winuser::VK_F21 => Some(VirtualKeyCode::F21),
        winuser::VK_F22 => Some(VirtualKeyCode::F22),
        winuser::VK_F23 => Some(VirtualKeyCode::F23),
        winuser::VK_F24 => Some(VirtualKeyCode::F24),
        winuser::VK_NUMLOCK => Some(VirtualKeyCode::Numlock),
        winuser::VK_SCROLL => Some(VirtualKeyCode::Scroll),
        winuser::VK_BROWSER_BACK => Some(VirtualKeyCode::NavigateBackward),
        winuser::VK_BROWSER_FORWARD => Some(VirtualKeyCode::NavigateForward),
        winuser::VK_BROWSER_REFRESH => Some(VirtualKeyCode::WebRefresh),
        winuser::VK_BROWSER_STOP => Some(VirtualKeyCode::WebStop),
        winuser::VK_BROWSER_SEARCH => Some(VirtualKeyCode::WebSearch),
        winuser::VK_BROWSER_FAVORITES => Some(VirtualKeyCode::WebFavorites),
        winuser::VK_BROWSER_HOME => Some(VirtualKeyCode::WebHome),
        winuser::VK_VOLUME_MUTE => Some(VirtualKeyCode::Mute),
        winuser::VK_VOLUME_DOWN => Some(VirtualKeyCode::VolumeDown),
        winuser::VK_VOLUME_UP => Some(VirtualKeyCode::VolumeUp),
        winuser::VK_MEDIA_NEXT_TRACK => Some(VirtualKeyCode::NextTrack),
        winuser::VK_MEDIA_PREV_TRACK => Some(VirtualKeyCode::PrevTrack),
        winuser::VK_MEDIA_STOP => Some(VirtualKeyCode::MediaStop),
        winuser::VK_MEDIA_PLAY_PAUSE => Some(VirtualKeyCode::PlayPause),
        winuser::VK_LAUNCH_MAIL => Some(VirtualKeyCode::Mail),
        winuser::VK_LAUNCH_MEDIA_SELECT => Some(VirtualKeyCode::MediaSelect),
        /*winuser::VK_LAUNCH_APP1 => Some(VirtualKeyCode::Launch_app1),
        winuser::VK_LAUNCH_APP2 => Some(VirtualKeyCode::Launch_app2),*/
        winuser::VK_OEM_PLUS => Some(VirtualKeyCode::Equals),
        winuser::VK_OEM_COMMA => Some(VirtualKeyCode::Comma),
        winuser::VK_OEM_MINUS => Some(VirtualKeyCode::Minus),
        winuser::VK_OEM_PERIOD => Some(VirtualKeyCode::Period),
        winuser::VK_OEM_1 => map_text_keys(vkey),
        winuser::VK_OEM_2 => map_text_keys(vkey),
        winuser::VK_OEM_3 => map_text_keys(vkey),
        winuser::VK_OEM_4 => map_text_keys(vkey),
        winuser::VK_OEM_5 => map_text_keys(vkey),
        winuser::VK_OEM_6 => map_text_keys(vkey),
        winuser::VK_OEM_7 => map_text_keys(vkey),
        /* winuser::VK_OEM_8 => Some(VirtualKeyCode::Oem_8), */
        winuser::VK_OEM_102 => Some(VirtualKeyCode::OEM102),
        /*winuser::VK_PROCESSKEY => Some(VirtualKeyCode::Processkey),
        winuser::VK_PACKET => Some(VirtualKeyCode::Packet),
        winuser::VK_ATTN => Some(VirtualKeyCode::Attn),
        winuser::VK_CRSEL => Some(VirtualKeyCode::Crsel),
        winuser::VK_EXSEL => Some(VirtualKeyCode::Exsel),
        winuser::VK_EREOF => Some(VirtualKeyCode::Ereof),
        winuser::VK_PLAY => Some(VirtualKeyCode::Play),
        winuser::VK_ZOOM => Some(VirtualKeyCode::Zoom),
        winuser::VK_NONAME => Some(VirtualKeyCode::Noname),
        winuser::VK_PA1 => Some(VirtualKeyCode::Pa1),
        winuser::VK_OEM_CLEAR => Some(VirtualKeyCode::Oem_clear),*/
        _ => None,
    }
}

pub fn handle_extended_keys(
    vkey: c_int,
    mut scancode: UINT,
    extended: bool,
) -> Option<(c_int, UINT)> {
    // Welcome to hell https://blog.molecular-matters.com/2011/09/05/properly-handling-keyboard-input/
    let vkey = match vkey {
        winuser::VK_SHIFT => unsafe {
            winuser::MapVirtualKeyA(scancode, winuser::MAPVK_VSC_TO_VK_EX) as _
        },
        winuser::VK_CONTROL => {
            if extended {
                winuser::VK_RCONTROL
            } else {
                winuser::VK_LCONTROL
            }
        }
        winuser::VK_MENU => {
            if extended {
                winuser::VK_RMENU
            } else {
                winuser::VK_LMENU
            }
        }
        _ => {
            match scancode {
                // This is only triggered when using raw input. Without this check, we get two events whenever VK_PAUSE is
                // pressed, the first one having scancode 0x1D but vkey VK_PAUSE...
                0x1D if vkey == winuser::VK_PAUSE => return None,
                // ...and the second having scancode 0x45 but an unmatched vkey!
                0x45 => winuser::VK_PAUSE,
                // VK_PAUSE and VK_SCROLL have the same scancode when using modifiers, alongside incorrect vkey values.
                0x46 => {
                    if extended {
                        scancode = 0x45;
                        winuser::VK_PAUSE
                    } else {
                        winuser::VK_SCROLL
                    }
                }
                _ => vkey,
            }
        }
    };
    Some((vkey, scancode))
}

pub fn process_key_params(
    wparam: WPARAM,
    lparam: LPARAM,
) -> Option<(ScanCode, Option<VirtualKeyCode>)> {
    let scancode = ((lparam >> 16) & 0xff) as UINT;
    let extended = (lparam & 0x01000000) != 0;
    handle_extended_keys(wparam as _, scancode, extended)
        .map(|(vkey, scancode)| (scancode, vkey_to_winit_vkey(vkey)))
}

// This is needed as windows doesn't properly distinguish
// some virtual key codes for different keyboard layouts
fn map_text_keys(win_virtual_key: i32) -> Option<VirtualKeyCode> {
    let char_key =
        unsafe { winuser::MapVirtualKeyA(win_virtual_key as u32, winuser::MAPVK_VK_TO_CHAR) }
            & 0x7FFF;
    match char::from_u32(char_key) {
        Some(';') => Some(VirtualKeyCode::Semicolon),
        Some('/') => Some(VirtualKeyCode::Slash),
        Some('`') => Some(VirtualKeyCode::Grave),
        Some('[') => Some(VirtualKeyCode::LBracket),
        Some(']') => Some(VirtualKeyCode::RBracket),
        Some('\'') => Some(VirtualKeyCode::Apostrophe),
        Some('\\') => Some(VirtualKeyCode::Backslash),
        _ => None,
    }
}