//! Wayland backend: layer-shell overlay with keyboard and pointer tracking.
//!
//! Creates a full-screen layer-shell surface for the ring light overlay.
//! Tracks pointer position for cursor avoidance and captures keyboard
//! for Escape to exit.

use std::collections::VecDeque;
use std::io::Write;
use std::os::fd::AsFd;
use std::time::Duration;

use wayland_client::{
    delegate_noop,
    protocol::{
        wl_buffer, wl_compositor, wl_keyboard, wl_pointer, wl_region, wl_registry, wl_seat,
        wl_shm, wl_shm_pool, wl_surface,
    },
    Connection, Dispatch, EventQueue, QueueHandle, WEnum,
};
use wayland_protocols_wlr::layer_shell::v1::client::{zwlr_layer_shell_v1, zwlr_layer_surface_v1};

use anyhow::{Context, Result};

// Linux evdev key code for Escape.
const KEY_ESCAPE: u32 = 1;

/// Events emitted by the Wayland backend to the main loop.
pub enum OverlayEvent {
    /// Escape pressed or surface closed by compositor.
    Close,
    /// Pointer moved to (x, y) in surface-local coordinates.
    CursorMoved(f64, f64),
    /// Surface (re-)configured with new dimensions.
    Configure(u32, u32),
}

// ===========================================================================
// WaylandBackend — public API.
// ===========================================================================

pub struct WaylandBackend {
    state: WaylandState,
    event_queue: EventQueue<WaylandState>,
    queue_handle: QueueHandle<WaylandState>,
}

impl WaylandBackend {
    pub fn new() -> Result<Self> {
        let conn = Connection::connect_to_env().context("connect to Wayland display")?;
        let mut event_queue = conn.new_event_queue();
        let queue_handle = event_queue.handle();

        conn.display().get_registry(&queue_handle, ());

        let mut state = WaylandState {
            conn,
            compositor: None,
            shm: None,
            surface: None,
            layer_shell: None,
            layer_surface: None,
            seat: None,
            screen_w: 0,
            screen_h: 0,
            configured: false,
            pending_events: VecDeque::new(),
        };

        event_queue
            .roundtrip(&mut state)
            .context("initial roundtrip")?;

        if state.compositor.is_none() {
            anyhow::bail!("compositor does not advertise wl_compositor");
        }
        if state.shm.is_none() {
            anyhow::bail!("compositor does not advertise wl_shm");
        }
        if state.layer_shell.is_none() {
            anyhow::bail!(
                "compositor does not support wlr-layer-shell-unstable-v1. \
                 Supported compositors: Sway, Hyprland, river, etc."
            );
        }

        state.init_layer_surface(&queue_handle)?;
        event_queue
            .roundtrip(&mut state)
            .context("roundtrip after layer surface")?;

        while !state.configured {
            event_queue
                .blocking_dispatch(&mut state)
                .context("waiting for configure")?;
        }

        Ok(Self {
            state,
            event_queue,
            queue_handle,
        })
    }

    pub fn screen_size(&self) -> (u32, u32) {
        (self.state.screen_w, self.state.screen_h)
    }

    /// Wait up to `timeout` for the next event. Returns `None` on timeout
    /// or if the surface has been torn down.
    pub fn next_event(&mut self, timeout: Duration) -> Result<Option<OverlayEvent>> {
        // First drain any already-buffered events.
        if let Some(ev) = self.state.pending_events.pop_front() {
            return Ok(Some(ev));
        }
        if self.state.surface.is_none() {
            return Ok(None);
        }

        // Flush outgoing requests, then poll the fd with a timeout.
        self.event_queue
            .flush()
            .context("flush before poll")?;

        let read_guard = self.event_queue.prepare_read().unwrap();
        let fd = read_guard.connection_fd();
        let mut pollfd = [nix::poll::PollFd::new(fd, nix::poll::PollFlags::POLLIN)];
        let millis = timeout.as_millis().min(u16::MAX as u128) as u16;
        let n = nix::poll::poll(&mut pollfd, millis).context("poll")?;

        if n > 0 {
            // Data available — read and dispatch.
            let _ = read_guard.read();
        } else {
            // Timeout — drop the read guard (cancels the read).
            drop(read_guard);
            return Ok(None);
        }

        self.event_queue
            .dispatch_pending(&mut self.state)
            .context("dispatch_pending")?;

        Ok(self.state.pending_events.pop_front())
    }

    /// Copy an ARGB8888 pixel buffer to the overlay surface via wl_shm.
    pub fn present(&mut self, pixels: &[u8], width: u32, height: u32) -> Result<()> {
        let shm = self.state.shm.as_ref().context("wl_shm not available")?;
        let surface = self
            .state
            .surface
            .as_ref()
            .context("wl_surface not available")?;

        let stride = width * 4;
        let mut file = tempfile::tempfile().context("create shm tempfile")?;
        file.write_all(pixels).context("write pixel buffer")?;

        let pool = shm.create_pool(file.as_fd(), pixels.len() as i32, &self.queue_handle, ());
        let buffer = pool.create_buffer(
            0,
            width as i32,
            height as i32,
            stride as i32,
            wl_shm::Format::Argb8888,
            &self.queue_handle,
            (),
        );

        surface.attach(Some(&buffer), 0, 0);
        surface.damage_buffer(0, 0, width as i32, height as i32);
        surface.commit();
        pool.destroy();
        Ok(())
    }
}

impl Drop for WaylandBackend {
    fn drop(&mut self) {
        if let Some(ls) = self.state.layer_surface.take() {
            ls.destroy();
        }
        if let Some(s) = self.state.surface.take() {
            s.destroy();
        }
        let _ = self.state.conn.flush();
    }
}

// ===========================================================================
// Internal state.
// ===========================================================================

struct WaylandState {
    conn: Connection,

    compositor: Option<wl_compositor::WlCompositor>,
    shm: Option<wl_shm::WlShm>,
    seat: Option<wl_seat::WlSeat>,
    layer_shell: Option<zwlr_layer_shell_v1::ZwlrLayerShellV1>,

    surface: Option<wl_surface::WlSurface>,
    layer_surface: Option<zwlr_layer_surface_v1::ZwlrLayerSurfaceV1>,

    screen_w: u32,
    screen_h: u32,
    configured: bool,

    pending_events: VecDeque<OverlayEvent>,
}

impl WaylandState {
    fn init_layer_surface(&mut self, qh: &QueueHandle<Self>) -> Result<()> {
        let compositor = self
            .compositor
            .as_ref()
            .context("wl_compositor not available")?;
        let layer_shell = self
            .layer_shell
            .as_ref()
            .context("zwlr_layer_shell_v1 not available")?;

        let surface = compositor.create_surface(qh, ());
        let layer_surface = layer_shell.get_layer_surface(
            &surface,
            None,
            zwlr_layer_shell_v1::Layer::Overlay,
            "ringa".to_string(),
            qh,
            (),
        );

        layer_surface.set_size(0, 0);
        layer_surface.set_anchor(
            zwlr_layer_surface_v1::Anchor::Top
                | zwlr_layer_surface_v1::Anchor::Bottom
                | zwlr_layer_surface_v1::Anchor::Left
                | zwlr_layer_surface_v1::Anchor::Right,
        );
        layer_surface.set_exclusive_zone(-1);
        layer_surface
            .set_keyboard_interactivity(zwlr_layer_surface_v1::KeyboardInteractivity::Exclusive);

        surface.commit();

        self.surface = Some(surface);
        self.layer_surface = Some(layer_surface);
        Ok(())
    }
}

// ===========================================================================
// Wayland dispatch implementations.
// ===========================================================================

impl Dispatch<wl_registry::WlRegistry, ()> for WaylandState {
    fn event(
        state: &mut Self,
        registry: &wl_registry::WlRegistry,
        event: wl_registry::Event,
        _: &(),
        _: &Connection,
        qh: &QueueHandle<Self>,
    ) {
        let wl_registry::Event::Global {
            name,
            interface,
            version,
        } = event
        else {
            return;
        };
        match interface.as_str() {
            "wl_compositor" => {
                state.compositor = Some(registry.bind(name, version.min(4), qh, ()));
            }
            "wl_shm" => {
                state.shm = Some(registry.bind(name, 1, qh, ()));
            }
            "wl_seat" => {
                state.seat = Some(registry.bind(name, version.min(7), qh, ()));
            }
            "zwlr_layer_shell_v1" => {
                state.layer_shell = Some(registry.bind(name, version.min(4), qh, ()));
            }
            _ => {}
        }
    }
}

impl Dispatch<wl_seat::WlSeat, ()> for WaylandState {
    fn event(
        _state: &mut Self,
        seat: &wl_seat::WlSeat,
        event: wl_seat::Event,
        _: &(),
        _: &Connection,
        qh: &QueueHandle<Self>,
    ) {
        if let wl_seat::Event::Capabilities {
            capabilities: WEnum::Value(caps),
        } = event
        {
            if caps.contains(wl_seat::Capability::Keyboard) {
                seat.get_keyboard(qh, ());
            }
            if caps.contains(wl_seat::Capability::Pointer) {
                seat.get_pointer(qh, ());
            }
        }
    }
}

impl Dispatch<wl_keyboard::WlKeyboard, ()> for WaylandState {
    fn event(
        state: &mut Self,
        _: &wl_keyboard::WlKeyboard,
        event: wl_keyboard::Event,
        _: &(),
        _: &Connection,
        _: &QueueHandle<Self>,
    ) {
        if let wl_keyboard::Event::Key {
            key,
            state: WEnum::Value(wl_keyboard::KeyState::Pressed),
            ..
        } = event
        {
            if key == KEY_ESCAPE {
                state.pending_events.push_back(OverlayEvent::Close);
            }
        }
    }
}

impl Dispatch<wl_pointer::WlPointer, ()> for WaylandState {
    fn event(
        state: &mut Self,
        _: &wl_pointer::WlPointer,
        event: wl_pointer::Event,
        _: &(),
        _: &Connection,
        _: &QueueHandle<Self>,
    ) {
        match event {
            wl_pointer::Event::Enter {
                surface_x,
                surface_y,
                ..
            } => {
                state
                    .pending_events
                    .push_back(OverlayEvent::CursorMoved(surface_x, surface_y));
            }
            wl_pointer::Event::Motion {
                surface_x,
                surface_y,
                ..
            } => {
                state
                    .pending_events
                    .push_back(OverlayEvent::CursorMoved(surface_x, surface_y));
            }
            _ => {}
        }
    }
}

impl Dispatch<zwlr_layer_surface_v1::ZwlrLayerSurfaceV1, ()> for WaylandState {
    fn event(
        state: &mut Self,
        layer_surface: &zwlr_layer_surface_v1::ZwlrLayerSurfaceV1,
        event: zwlr_layer_surface_v1::Event,
        _: &(),
        _: &Connection,
        _: &QueueHandle<Self>,
    ) {
        match event {
            zwlr_layer_surface_v1::Event::Configure {
                serial,
                width,
                height,
            } => {
                layer_surface.ack_configure(serial);
                const MAX_SCREEN_DIM: u32 = 16384;
                if width > 0 && height > 0 && width <= MAX_SCREEN_DIM && height <= MAX_SCREEN_DIM {
                    state.screen_w = width;
                    state.screen_h = height;
                    state.configured = true;
                    state
                        .pending_events
                        .push_back(OverlayEvent::Configure(width, height));
                }
            }
            zwlr_layer_surface_v1::Event::Closed => {
                state.pending_events.push_back(OverlayEvent::Close);
            }
            _ => {}
        }
    }
}

delegate_noop!(WaylandState: ignore wl_compositor::WlCompositor);
delegate_noop!(WaylandState: ignore wl_region::WlRegion);
delegate_noop!(WaylandState: ignore wl_surface::WlSurface);
delegate_noop!(WaylandState: ignore wl_shm::WlShm);
delegate_noop!(WaylandState: ignore wl_shm_pool::WlShmPool);
delegate_noop!(WaylandState: ignore wl_buffer::WlBuffer);
delegate_noop!(WaylandState: ignore zwlr_layer_shell_v1::ZwlrLayerShellV1);