use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Weak};
use std::thread::{spawn, JoinHandle as ThreadJoinHandle};

use crossbeam_channel::{
    bounded as bounded_channel,
    Receiver as ChannelReceiver,
    Sender as ChannelSender,
    TrySendError,
};
use ecs::actions::Actions;
use ecs::component::Component;
use ecs::entity::obtainer::Obtainer as EntityObtainer;
use ecs::event::component::{Added, Changed, Removed};
use ecs::pair::{ChildOf, Pair};
use ecs::phase::{Phase, UPDATE as UPDATE_PHASE};
use ecs::sole::Single;
use ecs::system::observer::Observe;
use ecs::uid::Uid;
use ecs::{declare_entity, Query, Sole};
use raw_window_handle::{DisplayHandle, HandleError, HasDisplayHandle, WindowHandle};
use winit::application::ApplicationHandler;
use winit::dpi::PhysicalPosition;
use winit::error::EventLoopError;
use winit::event::{DeviceEvent, DeviceId, StartCause, WindowEvent};
use winit::event_loop::{
    ActiveEventLoop,
    ControlFlow as EventLoopControlFlow,
    EventLoop,
    OwnedDisplayHandle,
};
use winit::keyboard::PhysicalKey;
use winit::window::{Window as WinitWindow, WindowId as WinitWindowId};

use crate::data_types::dimens::Dimens;
use crate::util::MapVec;
use crate::vector::Vec2;
use crate::windowing::keyboard::{Key, KeyState, Keyboard, UnknownKeyCodeError};
use crate::windowing::mouse::{
    Button as MouseButton,
    ButtonState as MouseButtonState,
    Buttons as MouseButtons,
    Motion as MouseMotion,
};
use crate::windowing::window::{
    Closed as WindowClosed,
    CreationAttributes as WindowCreationAttributes,
    CreationReady as WindowCreationReady,
    CursorGrabMode,
    Id as WindowId,
    Window,
};

pub mod keyboard;
pub mod mouse;
pub mod window;

const MESSAGE_FROM_APP_CHANNEL_CAP: usize = 128;

const MESSAGE_TO_APP_CHANNEL_CAP: usize = 16; // Increase if more messages are added

declare_entity!(
    pub PHASE,
    (
        Phase,
        Pair::builder()
            .relation::<ChildOf>()
            .target_id(*UPDATE_PHASE)
            .build()
    )
);

#[derive(Debug, Default)]
#[non_exhaustive]
pub struct Extension {}

impl ecs::extension::Extension for Extension
{
    fn collect(self, mut collector: ecs::extension::Collector<'_>)
    {
        collector.add_sole(Context::default()).ok();
        collector.add_sole(Keyboard::default()).ok();
        collector.add_sole(MouseMotion::default()).ok();
        collector.add_sole(MouseButtons::default()).ok();

        collector.add_declared_entity(&PHASE);

        collector.add_system(*PHASE, update_stuff);

        collector.add_observer(handle_window_changed);
        collector.add_observer(handle_window_removed);
        collector.add_observer(handle_window_creation_ready);
    }
}

fn handle_window_creation_ready(
    observe: Observe<Pair<Added, WindowCreationReady>>,
    context: Single<Context>,
)
{
    for evt_match in &observe {
        let Some(ent) = evt_match.get_entity() else {
            unreachable!();
        };

        if ent.has_component(Window::id()) || ent.has_component(WindowClosed::id()) {
            continue;
        }

        let Some(window_creation_attrs) = ent.get::<WindowCreationAttributes>() else {
            unreachable!();
        };

        context.try_send_message_to_app(MessageToApp::CreateWindow(
            ent.uid(),
            window_creation_attrs.clone(),
        ));
    }
}

#[tracing::instrument(skip_all)]
fn update_stuff(
    mut context: Single<Context>,
    mut keyboard: Single<Keyboard>,
    mut mouse_motion: Single<MouseMotion>,
    mut mouse_buttons: Single<MouseButtons>,
    mut actions: Actions,
    entity_obtainer: EntityObtainer,
)
{
    keyboard.make_key_states_previous();
    mouse_buttons.make_states_previous();
    mouse_motion.position_delta = Vec2::default();

    let Context {
        ref message_from_app_receiver,
        ref mut display_handle,
        ref mut windows,
        ..
    } = *context;

    for message in message_from_app_receiver.try_iter() {
        match message {
            MessageFromApp::Init(new_display_handle) => {
                *display_handle = Some(new_display_handle);
            }
            MessageFromApp::WindowCreated(
                window_ent_id,
                winit_window,
                window_creation_attrs,
            ) => {
                actions.add_components(
                    window_ent_id,
                    (Window::new(&winit_window, &window_creation_attrs),),
                );

                actions.remove_comps::<(WindowCreationReady,)>(window_ent_id);

                tracing::debug!("Added window component to window entity");

                windows.insert(
                    WindowId::from_inner(winit_window.id()),
                    (winit_window, window_ent_id),
                );
            }
            MessageFromApp::WindowResized(window_id, new_window_size) => {
                let Some(window_ent_id) =
                    windows.get(&window_id).map(|(_, ent_id)| ent_id)
                else {
                    continue;
                };

                let Some(window_ent) = entity_obtainer.get_entity(*window_ent_id) else {
                    continue;
                };

                let Some(mut window) = window_ent.get_mut::<Window>() else {
                    continue;
                };

                window.set_inner_size(new_window_size);

                window.set_changed();
            }
            MessageFromApp::WindowCloseRequested(window_id) => {
                let Some(window_ent_id) =
                    windows.get(&window_id).map(|(_, ent_id)| ent_id)
                else {
                    tracing::error!(
                        wid = ?window_id,
                        "Window does not exist in windowing context"
                    );
                    continue;
                };

                actions.remove_comps::<(Window,)>(*window_ent_id);
            }
            MessageFromApp::KeyboardKeyStateChanged(key, key_state) => {
                keyboard.set_key_state(key, key_state);
            }
            MessageFromApp::MouseMoved { position_delta } => {
                mouse_motion.position_delta += position_delta;
            }
            MessageFromApp::MouseButtonStateChanged(mouse_button, mouse_button_state) => {
                mouse_buttons.set(mouse_button, mouse_button_state);
            }
        }
    }
}

fn handle_window_changed(
    observe: Observe<'_, Pair<Changed, Window>>,
    context: Single<Context>,
)
{
    for evt_match in &observe {
        let window_ent_id = evt_match.id();

        let window = evt_match.get_changed_comp();

        let Some((winit_window, _)) = context.windows.get(&window.wid()) else {
            tracing::error!(
                wid = ?window.wid(),
                entity_id = %window_ent_id,
                "Window does not exist in windowing context",
            );
            continue;
        };

        window.apply(winit_window);

        context.try_send_message_to_app(MessageToApp::SetWindowCursorGrabMode(
            window.wid(),
            window.cursor_grab_mode,
        ));
    }
}

fn handle_window_removed(
    observe: Observe<Pair<Removed, Window>>,
    window_query: Query<(&Window,)>,
    mut context: Single<Context>,
    mut actions: Actions,
)
{
    for evt_match in &observe {
        let window = evt_match.get_removed_comp();

        context.windows.remove(window.wid());

        actions.add_components(evt_match.id(), (WindowClosed,));
    }

    if window_query.iter().count() == 1 {
        actions.stop();
    }
}

#[derive(Debug, Sole)]
pub struct Context
{
    _thread: ThreadJoinHandle<()>,
    is_dropped: Arc<AtomicBool>,
    message_from_app_receiver: ChannelReceiver<MessageFromApp>,
    message_to_app_sender: ChannelSender<MessageToApp>,
    display_handle: Option<OwnedDisplayHandle>,
    windows: MapVec<WindowId, (Arc<winit::window::Window>, Uid)>,
}

impl Context
{
    pub fn display_handle(&self) -> Option<DisplayHandle<'_>>
    {
        let display_handle = self.display_handle.as_ref()?;

        display_handle.display_handle().ok()
    }

    /// Returns the specified window as a window handle, if it exists.
    ///
    /// # Safety
    /// The Window handle must only be used with thread safe APIs.
    pub unsafe fn get_window_as_handle(
        &self,
        window_id: &WindowId,
    ) -> Option<Result<WindowHandle<'_>, HandleError>>
    {
        self.windows.get(window_id).map(|(winit_window, _)| {
            #[cfg(windows)]
            {
                use winit::platform::windows::WindowExtWindows;

                // SAFETY: I don't care
                unsafe { winit_window.window_handle_any_thread() }
            }

            #[cfg(not(windows))]
            {
                use raw_window_handle::HasWindowHandle;

                winit_window.window_handle()
            }
        })
    }

    fn try_send_message_to_app(&self, message: MessageToApp)
    {
        if let Err(err) = self.message_to_app_sender.try_send(message) {
            let error = match &err {
                TrySendError::Full(_) => TrySendError::Full(()),
                TrySendError::Disconnected(_) => TrySendError::Disconnected(()),
            };

            let message = err.into_inner();

            tracing::error!("Failed to send message {error}: {message:?}");
        }
    }
}

impl Default for Context
{
    fn default() -> Self
    {
        let is_dropped = Arc::new(AtomicBool::new(false));

        let is_dropped_b = is_dropped.clone();

        let (message_from_app_sender, message_from_app_receiver) =
            bounded_channel::<MessageFromApp>(MESSAGE_FROM_APP_CHANNEL_CAP);

        let message_from_app_receiver_b = message_from_app_receiver.clone();

        let (message_to_app_sender, message_to_app_receiver) =
            bounded_channel::<MessageToApp>(MESSAGE_TO_APP_CHANNEL_CAP);

        Self {
            _thread: spawn(move || {
                let mut app = App {
                    message_from_app_sender,
                    message_from_app_receiver: message_from_app_receiver_b,
                    message_to_app_receiver,
                    is_dropped: is_dropped_b,
                    windows: MapVec::default(),
                    focused_window_id: None,
                };

                let event_loop = match create_event_loop() {
                    Ok(event_loop) => event_loop,
                    Err(err) => {
                        tracing::error!("Failed to create event loop: {err}");
                        return;
                    }
                };

                event_loop.set_control_flow(EventLoopControlFlow::Poll);

                if let Err(err) = event_loop.run_app(&mut app) {
                    tracing::error!("Event loop error occurred: {err}");
                }
            }),
            is_dropped,
            message_from_app_receiver,
            message_to_app_sender,
            display_handle: None,
            windows: MapVec::default(),
        }
    }
}

impl Drop for Context
{
    fn drop(&mut self)
    {
        self.is_dropped.store(true, Ordering::Relaxed);
    }
}

fn create_event_loop() -> Result<EventLoop<()>, EventLoopError>
{
    let mut event_loop_builder = EventLoop::builder();

    #[cfg(any(x11_platform, wayland_platform))]
    winit::platform::x11::EventLoopBuilderExtX11::with_any_thread(
        &mut event_loop_builder,
        true,
    );

    #[cfg(windows)]
    winit::platform::windows::EventLoopBuilderExtWindows::with_any_thread(
        &mut event_loop_builder,
        true,
    );

    #[cfg(not(any(x11_platform, wayland_platform, windows)))]
    compile_error!("Unsupported platform");

    event_loop_builder.build()
}

#[derive(Debug)]
enum MessageFromApp
{
    Init(OwnedDisplayHandle),
    WindowCreated(Uid, Arc<WinitWindow>, WindowCreationAttributes),
    WindowResized(WindowId, Dimens<u32>),
    WindowCloseRequested(WindowId),
    KeyboardKeyStateChanged(Key, KeyState),
    MouseMoved
    {
        position_delta: Vec2<f64>,
    },
    MouseButtonStateChanged(MouseButton, MouseButtonState),
}

#[derive(Debug)]
enum MessageToApp
{
    CreateWindow(Uid, WindowCreationAttributes),
    SetWindowCursorGrabMode(WindowId, CursorGrabMode),
}

#[derive(Debug)]
struct App
{
    message_from_app_sender: ChannelSender<MessageFromApp>,
    message_from_app_receiver: ChannelReceiver<MessageFromApp>,
    message_to_app_receiver: ChannelReceiver<MessageToApp>,
    is_dropped: Arc<AtomicBool>,
    windows: MapVec<WindowId, (Weak<WinitWindow>, WindowSettings)>,
    focused_window_id: Option<WindowId>,
}

impl App
{
    fn handle_received_messages(&mut self, event_loop: &ActiveEventLoop)
    {
        for message in self.message_to_app_receiver.try_iter() {
            match message {
                MessageToApp::CreateWindow(window_ent_id, window_creation_attrs) => {
                    tracing::info!(
                        "Creating window with title {}",
                        window_creation_attrs.title()
                    );

                    let winit_window = Arc::new(
                        match event_loop
                            .create_window(window_creation_attrs.clone().into_inner())
                        {
                            Ok(window) => window,
                            Err(err) => {
                                tracing::error!("Failed to create window: {err}");
                                continue;
                            }
                        },
                    );

                    tracing::info!("Created window has title {}", winit_window.title());

                    self.windows.insert(
                        WindowId::from_inner(winit_window.id()),
                        (Arc::downgrade(&winit_window), WindowSettings::default()),
                    );

                    self.send_message(MessageFromApp::WindowCreated(
                        window_ent_id,
                        winit_window,
                        window_creation_attrs,
                    ));
                }
                MessageToApp::SetWindowCursorGrabMode(window_id, cursor_grab_mode) => {
                    let Some((_, window_settings)) = self.windows.get_mut(&window_id)
                    else {
                        tracing::warn!(
                            window_id=?window_id,
                            "Cannot set window cursor grab mode. Window not found"
                        );

                        continue;
                    };

                    window_settings.cursor_grab_mode = cursor_grab_mode;
                }
            }
        }
    }

    fn send_message(&self, message: MessageFromApp)
    {
        if self.message_from_app_sender.is_full() {
            tracing::warn!(
                "Message channel is full! Dropping oldest message from channel"
            );

            self.message_from_app_receiver.try_recv().ok();
        }

        if let Err(err) = self.message_from_app_sender.try_send(message) {
            let error = match &err {
                TrySendError::Full(_) => TrySendError::Full(()),
                TrySendError::Disconnected(_) => TrySendError::Disconnected(()),
            };

            let message = err.into_inner();

            tracing::error!("Failed to send message {error}: {message:?}");
        }
    }
}

impl ApplicationHandler for App
{
    fn new_events(&mut self, event_loop: &ActiveEventLoop, cause: StartCause)
    {
        match cause {
            StartCause::Init => {
                self.send_message(MessageFromApp::Init(
                    event_loop.owned_display_handle(),
                ));
            }
            StartCause::Poll => {
                if self.is_dropped.load(Ordering::Relaxed) {
                    event_loop.exit();
                    return;
                }

                self.handle_received_messages(event_loop);
            }
            _ => {}
        }
    }

    fn about_to_wait(&mut self, _event_loop: &ActiveEventLoop)
    {
        for (window, _) in self.windows.values() {
            let Some(window) = window.upgrade() else {
                continue;
            };

            window.request_redraw();
        }
    }

    fn resumed(&mut self, _event_loop: &ActiveEventLoop) {}

    fn window_event(
        &mut self,
        _event_loop: &ActiveEventLoop,
        window_id: WinitWindowId,
        event: WindowEvent,
    )
    {
        match event {
            WindowEvent::Resized(new_window_size) => {
                self.send_message(MessageFromApp::WindowResized(
                    WindowId::from_inner(window_id),
                    new_window_size.into(),
                ));
            }
            WindowEvent::CloseRequested => {
                self.send_message(MessageFromApp::WindowCloseRequested(
                    WindowId::from_inner(window_id),
                ));
            }
            WindowEvent::KeyboardInput {
                device_id: _,
                event: keyboard_event,
                is_synthetic: _,
            } => {
                if keyboard_event.repeat {
                    return;
                }

                let key_code = match keyboard_event.physical_key {
                    PhysicalKey::Code(key_code) => key_code,
                    PhysicalKey::Unidentified(native_key) => {
                        tracing::warn!("Ignoring unidentified key: {native_key:?}");
                        return;
                    }
                };

                let key: Key = match key_code.try_into() {
                    Ok(key) => key,
                    Err(UnknownKeyCodeError) => {
                        tracing::warn!("Ignoring key with unknown key code {key_code:?}");
                        return;
                    }
                };

                self.send_message(MessageFromApp::KeyboardKeyStateChanged(
                    key,
                    keyboard_event.state.into(),
                ));
            }
            WindowEvent::MouseInput { device_id: _, state, button } => {
                self.send_message(MessageFromApp::MouseButtonStateChanged(
                    button.into(),
                    state.into(),
                ));
            }
            WindowEvent::Focused(is_focused) => {
                if is_focused {
                    self.focused_window_id = Some(WindowId::from_inner(window_id));
                } else {
                    self.focused_window_id = None;
                }
            }
            _ => {}
        }
    }

    fn device_event(
        &mut self,
        _event_loop: &ActiveEventLoop,
        _device_id: DeviceId,
        device_event: DeviceEvent,
    )
    {
        match device_event {
            DeviceEvent::MouseMotion { delta } => {
                self.send_message(MessageFromApp::MouseMoved {
                    position_delta: Vec2 { x: delta.0, y: delta.1 },
                });

                let Some(focused_window_id) = self.focused_window_id else {
                    return;
                };

                let Some((focused_window, focused_window_settings)) =
                    self.windows.get(&focused_window_id)
                else {
                    tracing::error!(
                        window_id=?focused_window_id,
                        "Focused window not found"
                    );
                    return;
                };

                if focused_window_settings.cursor_grab_mode != CursorGrabMode::Locked {
                    return;
                }

                // TODO: This might need to be optimized
                let Some(focused_window) = focused_window.upgrade() else {
                    return;
                };

                let focused_window_size = focused_window.inner_size();

                if let Err(err) = focused_window.set_cursor_position(PhysicalPosition {
                    x: focused_window_size.width / 2,
                    y: focused_window_size.height / 2,
                }) {
                    tracing::error!(
                        window_id=?focused_window_id,
                        "Failed to set cursor position in focused window: {err}"
                    );
                };
            }
            _ => {}
        }
    }
}

#[derive(Debug, Default)]
struct WindowSettings
{
    cursor_grab_mode: CursorGrabMode,
}