use std::f32::consts::PI;
use std::process::{Child, Command};
use std::{collections::VecDeque, time::Instant};

use glam::{Affine3A, Vec2, Vec3, Vec3A, Vec3Swizzles};

use smallvec::{SmallVec, smallvec};

use crate::backend::common::OverlaySelector;
use crate::backend::overlay::Positioning;
use crate::config::AStrMapExt;
use crate::overlays::anchor::ANCHOR_NAME;
use crate::state::{AppSession, AppState};
use crate::subsystem::input::KeyboardFocus;

use super::overlay::{OverlayID, OverlayState};
use super::task::{TaskContainer, TaskType};
use super::{common::OverlayContainer, overlay::OverlayData};

pub struct TrackedDevice {
    pub soc: Option<f32>,
    pub charging: bool,
    pub role: TrackedDeviceRole,
}

#[repr(u8)]
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TrackedDeviceRole {
    None,
    Hmd,
    LeftHand,
    RightHand,
    Tracker,
}

pub struct InputState {
    pub hmd: Affine3A,
    pub ipd: f32,
    pub pointers: [Pointer; 2],
    pub devices: Vec<TrackedDevice>,
    processes: Vec<Child>,
}

impl InputState {
    pub fn new() -> Self {
        Self {
            hmd: Affine3A::IDENTITY,
            ipd: 0.0,
            pointers: [Pointer::new(0), Pointer::new(1)],
            devices: Vec::new(),
            processes: Vec::new(),
        }
    }

    pub const fn pre_update(&mut self) {
        self.pointers[0].before = self.pointers[0].now;
        self.pointers[1].before = self.pointers[1].now;
    }

    pub fn post_update(&mut self, session: &AppSession) {
        for hand in &mut self.pointers {
            #[cfg(debug_assertions)]
            debug_print_hand(hand);

            if hand.now.click {
                hand.last_click = Instant::now();
            }

            if hand.now.click_modifier_right {
                hand.interaction.mode = PointerMode::Right;
                continue;
            }

            if hand.now.click_modifier_middle {
                hand.interaction.mode = PointerMode::Middle;
                continue;
            }

            let hmd_up = self.hmd.transform_vector3a(Vec3A::Y);
            let dot = hmd_up.dot(hand.pose.transform_vector3a(Vec3A::X))
                * 2.0f32.mul_add(-(hand.idx as f32), 1.0);

            hand.interaction.mode = if dot < -0.85 {
                PointerMode::Right
            } else if dot > 0.7 {
                PointerMode::Middle
            } else {
                PointerMode::Left
            };

            let middle_click_orientation = false;
            let right_click_orientation = false;
            match hand.interaction.mode {
                PointerMode::Middle => {
                    if !middle_click_orientation {
                        hand.interaction.mode = PointerMode::Left;
                    }
                }
                PointerMode::Right => {
                    if !right_click_orientation {
                        hand.interaction.mode = PointerMode::Left;
                    }
                }
                _ => {}
            }

            if hand.now.alt_click != hand.before.alt_click {
                // Reap previous processes
                self.processes
                    .retain_mut(|child| !matches!(child.try_wait(), Ok(Some(_))));

                let mut args = if hand.now.alt_click {
                    session.config.alt_click_down.iter()
                } else {
                    session.config.alt_click_up.iter()
                };

                if let Some(program) = args.next() {
                    if let Ok(child) = Command::new(program).args(args).spawn() {
                        self.processes.push(child);
                    }
                }
            }
        }
    }
}

#[cfg(debug_assertions)]
fn debug_print_hand(hand: &Pointer) {
    {
        if hand.now.click != hand.before.click {
            log::debug!("Hand {}: click {}", hand.idx, hand.now.click);
        }
        if hand.now.grab != hand.before.grab {
            log::debug!("Hand {}: grab {}", hand.idx, hand.now.grab);
        }
        if hand.now.alt_click != hand.before.alt_click {
            log::debug!("Hand {}: alt_click {}", hand.idx, hand.now.alt_click);
        }
        if hand.now.show_hide != hand.before.show_hide {
            log::debug!("Hand {}: show_hide {}", hand.idx, hand.now.show_hide);
        }
        if hand.now.toggle_dashboard != hand.before.toggle_dashboard {
            log::debug!(
                "Hand {}: toggle_dashboard {}",
                hand.idx,
                hand.now.toggle_dashboard
            );
        }
        if hand.now.space_drag != hand.before.space_drag {
            log::debug!("Hand {}: space_drag {}", hand.idx, hand.now.space_drag);
        }
        if hand.now.space_rotate != hand.before.space_rotate {
            log::debug!("Hand {}: space_rotate {}", hand.idx, hand.now.space_rotate);
        }
        if hand.now.space_reset != hand.before.space_reset {
            log::debug!("Hand {}: space_reset {}", hand.idx, hand.now.space_reset);
        }
        if hand.now.click_modifier_right != hand.before.click_modifier_right {
            log::debug!(
                "Hand {}: click_modifier_right {}",
                hand.idx,
                hand.now.click_modifier_right
            );
        }
        if hand.now.click_modifier_middle != hand.before.click_modifier_middle {
            log::debug!(
                "Hand {}: click_modifier_middle {}",
                hand.idx,
                hand.now.click_modifier_middle
            );
        }
    }
}

pub struct InteractionState {
    pub mode: PointerMode,
    pub grabbed: Option<GrabData>,
    pub clicked_id: Option<OverlayID>,
    pub hovered_id: Option<OverlayID>,
    pub release_actions: VecDeque<Box<dyn Fn()>>,
    pub next_push: Instant,
    pub haptics: Option<f32>,
}

impl Default for InteractionState {
    fn default() -> Self {
        Self {
            mode: PointerMode::Left,
            grabbed: None,
            clicked_id: None,
            hovered_id: None,
            release_actions: VecDeque::new(),
            next_push: Instant::now(),
            haptics: None,
        }
    }
}

pub struct Pointer {
    pub idx: usize,
    pub pose: Affine3A,
    pub raw_pose: Affine3A,
    pub now: PointerState,
    pub before: PointerState,
    pub last_click: Instant,
    pub(super) interaction: InteractionState,
}

impl Pointer {
    pub fn new(idx: usize) -> Self {
        debug_assert!(idx == 0 || idx == 1);
        Self {
            idx,
            pose: Affine3A::IDENTITY,
            raw_pose: Affine3A::IDENTITY,
            now: PointerState::default(),
            before: PointerState::default(),
            last_click: Instant::now(),
            interaction: InteractionState::default(),
        }
    }
}

#[derive(Clone, Copy, Default)]
pub struct PointerState {
    pub scroll_x: f32,
    pub scroll_y: f32,
    pub click: bool,
    pub grab: bool,
    pub alt_click: bool,
    pub show_hide: bool,
    pub toggle_dashboard: bool,
    pub space_drag: bool,
    pub space_rotate: bool,
    pub space_reset: bool,
    pub click_modifier_right: bool,
    pub click_modifier_middle: bool,
    pub move_mouse: bool,
}

#[derive(Debug, Clone, Copy, Default)]
pub struct PointerHit {
    pub pointer: usize,
    pub overlay: OverlayID,
    pub mode: PointerMode,
    pub primary: bool,
    pub uv: Vec2,
    pub dist: f32,
}

#[derive(Clone)]
pub struct Haptics {
    pub intensity: f32,
    pub duration: f32,
    pub frequency: f32,
}

pub trait InteractionHandler {
    fn on_hover(&mut self, app: &mut AppState, hit: &PointerHit) -> Option<Haptics>;
    fn on_left(&mut self, app: &mut AppState, pointer: usize);
    fn on_pointer(&mut self, app: &mut AppState, hit: &PointerHit, pressed: bool);
    fn on_scroll(&mut self, app: &mut AppState, hit: &PointerHit, delta_y: f32, delta_x: f32);
}

pub struct DummyInteractionHandler;

impl InteractionHandler for DummyInteractionHandler {
    fn on_left(&mut self, _app: &mut AppState, _pointer: usize) {}
    fn on_hover(&mut self, _app: &mut AppState, _hit: &PointerHit) -> Option<Haptics> {
        None
    }
    fn on_pointer(&mut self, _app: &mut AppState, _hit: &PointerHit, _pressed: bool) {}
    fn on_scroll(&mut self, _app: &mut AppState, _hit: &PointerHit, _delta_y: f32, _delta_x: f32) {}
}

#[derive(Debug, Clone, Copy, Default)]
struct RayHit {
    overlay: OverlayID,
    global_pos: Vec3A,
    local_pos: Vec2,
    dist: f32,
}

#[derive(Debug, Clone, Copy, Default)]
pub struct GrabData {
    pub offset: Vec3A,
    pub grabbed_id: OverlayID,
    pub old_curvature: Option<f32>,
    pub grab_all: bool,
}

#[repr(u8)]
#[derive(Debug, Clone, Copy, Default)]
pub enum PointerMode {
    #[default]
    Left,
    Right,
    Middle,
    Special,
}

fn update_focus(focus: &mut KeyboardFocus, state: &OverlayState) {
    if let Some(f) = &state.keyboard_focus {
        if *focus != *f {
            log::info!("Setting keyboard focus to {:?}", *f);
            *focus = *f;
        }
    }
}

pub fn interact<O>(
    overlays: &mut OverlayContainer<O>,
    app: &mut AppState,
) -> [(f32, Option<Haptics>); 2]
where
    O: Default,
{
    if app.input_state.pointers[1].last_click > app.input_state.pointers[0].last_click {
        let right = interact_hand(1, overlays, app);
        let left = interact_hand(0, overlays, app);
        [left, right]
    } else {
        let left = interact_hand(0, overlays, app);
        let right = interact_hand(1, overlays, app);
        [left, right]
    }
}

#[allow(clippy::too_many_lines, clippy::cognitive_complexity)]
fn interact_hand<O>(
    idx: usize,
    overlays: &mut OverlayContainer<O>,
    app: &mut AppState,
) -> (f32, Option<Haptics>)
where
    O: Default,
{
    let mut pointer = &mut app.input_state.pointers[idx];
    if let Some(grab_data) = pointer.interaction.grabbed {
        if let Some(grabbed) = overlays.mut_by_id(grab_data.grabbed_id) {
            Pointer::handle_grabbed(idx, grabbed, app);
        } else {
            log::warn!("Grabbed overlay {} does not exist", grab_data.grabbed_id.0);
            pointer.interaction.grabbed = None;
        }
        return (0.1, None);
    }

    let Some(mut hit) = pointer.get_nearest_hit(overlays) else {
        if let Some(hovered_id) = pointer.interaction.hovered_id.take() {
            if let Some(hovered) = overlays.mut_by_id(hovered_id) {
                hovered.backend.on_left(app, idx);
            }
            pointer = &mut app.input_state.pointers[idx];
            pointer.interaction.hovered_id = None;
        }
        if !pointer.now.click && pointer.before.click {
            if let Some(clicked_id) = pointer.interaction.clicked_id.take() {
                if let Some(clicked) = overlays.mut_by_id(clicked_id) {
                    let hit = PointerHit {
                        pointer: pointer.idx,
                        overlay: clicked_id,
                        mode: pointer.interaction.mode,
                        ..Default::default()
                    };
                    clicked.backend.on_pointer(app, &hit, false);
                }
            }
        }
        return (0.0, None); // no hit
    };

    if let Some(hovered_id) = pointer.interaction.hovered_id {
        if hovered_id != hit.overlay {
            if let Some(old_hovered) = overlays.mut_by_id(hovered_id) {
                if Some(pointer.idx) == old_hovered.primary_pointer {
                    old_hovered.primary_pointer = None;
                }
                old_hovered.backend.on_left(app, idx);
                pointer = &mut app.input_state.pointers[idx];
            }
        }
    }
    let Some(hovered) = overlays.mut_by_id(hit.overlay) else {
        log::warn!("Hit overlay {} does not exist", hit.overlay.0);
        return (0.0, None); // no hit
    };

    pointer.interaction.hovered_id = Some(hit.overlay);

    if let Some(primary_pointer) = hovered.primary_pointer {
        if hit.pointer <= primary_pointer {
            hovered.primary_pointer = Some(hit.pointer);
            hit.primary = true;
        }
    } else {
        hovered.primary_pointer = Some(hit.pointer);
        hit.primary = true;
    }

    #[cfg(debug_assertions)]
    log::trace!("Hit: {} {:?}", hovered.state.name, hit);

    if pointer.now.grab && !pointer.before.grab && hovered.state.grabbable {
        {
            let mut hid_provider = app.hid_provider.borrow_mut();
            update_focus(&mut hid_provider.keyboard_focus, &hovered.state);
        }
        pointer.start_grab(hovered, &mut app.tasks);
        return (
            hit.dist,
            Some(Haptics {
                intensity: 0.25,
                duration: 0.1,
                frequency: 0.1,
            }),
        );
    }

    // Pass mouse motion events only if not scrolling
    // (allows scrolling on all Chromium-based applications)
    let haptics = hovered.backend.on_hover(app, &hit);

    pointer = &mut app.input_state.pointers[idx];

    if pointer.now.scroll_x.abs() > 0.1 || pointer.now.scroll_y.abs() > 0.1 {
        let scroll_x = pointer.now.scroll_x;
        let scroll_y = pointer.now.scroll_y;
        if app.input_state.pointers[1 - idx]
            .interaction
            .grabbed
            .is_some_and(|x| x.grabbed_id == hit.overlay)
        {
            let can_curve = hovered
                .frame_meta()
                .is_some_and(|e| e.extent[0] >= e.extent[1]);

            if can_curve {
                let cur = hovered.state.curvature.unwrap_or(0.0);
                let new = scroll_y.mul_add(-0.01, cur).min(0.5);
                if new <= f32::EPSILON {
                    hovered.state.curvature = None;
                } else {
                    hovered.state.curvature = Some(new);
                }
            } else {
                hovered.state.curvature = None;
            }
        } else {
            hovered.backend.on_scroll(app, &hit, scroll_y, scroll_x);
        }
        pointer = &mut app.input_state.pointers[idx];
    }

    if pointer.now.click && !pointer.before.click {
        pointer.interaction.clicked_id = Some(hit.overlay);
        {
            let mut hid_provider = app.hid_provider.borrow_mut();
            update_focus(&mut hid_provider.keyboard_focus, &hovered.state);
        }
        hovered.backend.on_pointer(app, &hit, true);
    } else if !pointer.now.click && pointer.before.click {
        if let Some(clicked_id) = pointer.interaction.clicked_id.take() {
            if let Some(clicked) = overlays.mut_by_id(clicked_id) {
                clicked.backend.on_pointer(app, &hit, false);
            }
        } else {
            hovered.backend.on_pointer(app, &hit, false);
        }
    }
    (hit.dist, haptics)
}

impl Pointer {
    fn get_nearest_hit<O>(&mut self, overlays: &mut OverlayContainer<O>) -> Option<PointerHit>
    where
        O: Default,
    {
        let mut hits: SmallVec<[RayHit; 8]> = smallvec!();

        for overlay in overlays.iter() {
            if !overlay.state.want_visible || !overlay.state.interactable {
                continue;
            }

            if let Some(hit) = self.ray_test(
                overlay.state.id,
                &overlay.state.transform,
                overlay.state.curvature.as_ref(),
            ) {
                if hit.dist.is_infinite() || hit.dist.is_nan() {
                    continue;
                }
                hits.push(hit);
            }
        }

        hits.sort_by(|a, b| a.dist.total_cmp(&b.dist));

        for hit in &hits {
            let overlay = overlays.get_by_id(hit.overlay).unwrap(); // safe because we just got the id from the overlay

            let uv = overlay
                .state
                .interaction_transform
                .transform_point2(hit.local_pos);

            if uv.x < 0.0 || uv.x > 1.0 || uv.y < 0.0 || uv.y > 1.0 {
                continue;
            }

            return Some(PointerHit {
                pointer: self.idx,
                overlay: hit.overlay,
                mode: self.interaction.mode,
                primary: false,
                uv,
                dist: hit.dist,
            });
        }

        None
    }

    fn start_grab<O>(&mut self, overlay: &mut OverlayData<O>, tasks: &mut TaskContainer)
    where
        O: Default,
    {
        let offset = self
            .pose
            .inverse()
            .transform_point3a(overlay.state.transform.translation);

        self.interaction.grabbed = Some(GrabData {
            offset,
            grabbed_id: overlay.state.id,
            old_curvature: overlay.state.curvature,
            grab_all: matches!(self.interaction.mode, PointerMode::Right),
        });
        overlay.state.positioning = match overlay.state.positioning {
            Positioning::FollowHand { hand, lerp } => Positioning::FollowHandPaused { hand, lerp },
            Positioning::FollowHead { lerp } => Positioning::FollowHeadPaused { lerp },
            x => x,
        };

        // Show anchor
        tasks.enqueue(TaskType::Overlay(
            OverlaySelector::Name(ANCHOR_NAME.clone()),
            Box::new(|app, o| {
                o.transform = app.anchor
                    * Affine3A::from_scale_rotation_translation(
                        Vec3::ONE * o.spawn_scale,
                        o.spawn_rotation,
                        o.spawn_point.into(),
                    );
                o.dirty = true;
                o.want_visible = true;
            }),
        ));
        log::info!("Hand {}: grabbed {}", self.idx, overlay.state.name);
    }

    fn handle_grabbed<O>(idx: usize, overlay: &mut OverlayData<O>, app: &mut AppState)
    where
        O: Default,
    {
        let mut pointer = &mut app.input_state.pointers[idx];
        if pointer.now.grab {
            if let Some(grab_data) = pointer.interaction.grabbed.as_mut() {
                if pointer.now.click {
                    pointer.interaction.mode = PointerMode::Special;
                    let cur_scale = overlay.state.transform.x_axis.length();
                    if cur_scale < 0.1 && pointer.now.scroll_y > 0.0 {
                        return;
                    }
                    if cur_scale > 20. && pointer.now.scroll_y < 0.0 {
                        return;
                    }

                    overlay.state.transform.matrix3 = overlay
                        .state
                        .transform
                        .matrix3
                        .mul_scalar(0.025f32.mul_add(-pointer.now.scroll_y, 1.0));
                } else if app.session.config.allow_sliding && pointer.now.scroll_y.is_finite() {
                    grab_data.offset.z -= pointer.now.scroll_y * 0.05;
                }
                overlay.state.transform.translation =
                    pointer.pose.transform_point3a(grab_data.offset);
                overlay.state.realign(&app.input_state.hmd);
                overlay.state.dirty = true;
            } else {
                log::error!("Grabbed overlay {} does not exist", overlay.state.id.0);
                pointer.interaction.grabbed = None;
            }
        } else {
            overlay.state.positioning = match overlay.state.positioning {
                Positioning::FollowHandPaused { hand, lerp } => {
                    Positioning::FollowHand { hand, lerp }
                }
                Positioning::FollowHeadPaused { lerp } => Positioning::FollowHead { lerp },
                x => x,
            };

            let save_success = overlay.state.save_transform(app);

            // re-borrow
            pointer = &mut app.input_state.pointers[idx];

            if save_success {
                if let Some(grab_data) = pointer.interaction.grabbed.as_ref() {
                    if overlay.state.curvature != grab_data.old_curvature {
                        if let Some(val) = overlay.state.curvature {
                            app.session
                                .config
                                .curve_values
                                .arc_set(overlay.state.name.clone(), val);
                        } else {
                            let ref_name = overlay.state.name.as_ref();
                            app.session.config.curve_values.arc_rm(ref_name);
                        }
                    }
                }
                app.session.config.transform_values.arc_set(
                    overlay.state.name.clone(),
                    overlay.state.saved_transform.unwrap(), // safe
                );
            }

            pointer.interaction.grabbed = None;

            // Hide anchor
            app.tasks.enqueue(TaskType::Overlay(
                OverlaySelector::Name(ANCHOR_NAME.clone()),
                Box::new(|_app, o| {
                    o.want_visible = false;
                }),
            ));
            log::info!("Hand {}: dropped {}", idx, overlay.state.name);
        }
    }

    fn ray_test(
        &self,
        overlay: OverlayID,
        transform: &Affine3A,
        curvature: Option<&f32>,
    ) -> Option<RayHit> {
        let (dist, local_pos) = curvature.map_or_else(
            || {
                Some(raycast_plane(
                    &self.pose,
                    Vec3A::NEG_Z,
                    transform,
                    Vec3A::NEG_Z,
                ))
            },
            |curvature| raycast_cylinder(&self.pose, Vec3A::NEG_Z, transform, *curvature),
        )?;

        if dist < 0.0 {
            // hit is behind us
            return None;
        }

        Some(RayHit {
            overlay,
            global_pos: self.pose.transform_point3a(Vec3A::NEG_Z * dist),
            local_pos,
            dist,
        })
    }
}

fn raycast_plane(
    source: &Affine3A,
    source_fwd: Vec3A,
    plane: &Affine3A,
    plane_norm: Vec3A,
) -> (f32, Vec2) {
    let plane_normal = plane.transform_vector3a(plane_norm);
    let ray_dir = source.transform_vector3a(source_fwd);

    let d = plane.translation.dot(-plane_normal);
    let dist = -(d + source.translation.dot(plane_normal)) / ray_dir.dot(plane_normal);

    let hit_local = plane
        .inverse()
        .transform_point3a(source.translation + ray_dir * dist)
        .xy();

    (dist, hit_local)
}

fn raycast_cylinder(
    source: &Affine3A,
    source_fwd: Vec3A,
    plane: &Affine3A,
    curvature: f32,
) -> Option<(f32, Vec2)> {
    // this is solved locally; (0,0) is the center of the cylinder, and the cylinder is aligned with the Y axis
    let size = plane.x_axis.length();
    let to_local = Affine3A {
        matrix3: plane.matrix3.mul_scalar(1.0 / size),
        translation: plane.translation,
    }
    .inverse();

    let radius = size / (2.0 * PI * curvature);

    let ray_dir = to_local.transform_vector3a(source.transform_vector3a(source_fwd));
    let ray_origin = to_local.transform_point3a(source.translation) + Vec3A::NEG_Z * radius;

    let v_dir = ray_dir.xz();
    let v_pos = ray_origin.xz();

    let l_dir = v_dir.dot(v_dir);
    let l_pos = v_dir.dot(v_pos);
    let c = radius.mul_add(-radius, v_pos.dot(v_pos));

    let d = l_pos.mul_add(l_pos, -(l_dir * c));
    if d < f32::EPSILON {
        return None;
    }

    let sqrt_d = d.sqrt();

    let t1 = (-l_pos - sqrt_d) / l_dir;
    let t2 = (-l_pos + sqrt_d) / l_dir;

    let t = t1.max(t2);

    if t < f32::EPSILON {
        return None;
    }

    let mut hit_local = ray_origin + ray_dir * t;
    if hit_local.z > 0.0 {
        // hitting the opposite half of the cylinder
        return None;
    }

    let max_angle = 2.0 * (size / (2.0 * radius));
    let x_angle = (hit_local.x / radius).asin();

    hit_local.x = x_angle / max_angle;
    hit_local.y /= size;

    Some((t, hit_local.xy()))
}