//! Brush element edit modes and viewport element picking.

use bevy::prelude::*;
use bevy_egui::{egui, EguiContexts};
use shared::{BrushDesc, BrushFaceDesc, BrushPlaneDesc, ComponentInstanceId};

use crate::camera::EditorCamera;
use crate::history::{push_command, EditorCommand};
use crate::operators::{ActiveOperator, OperatorPhase, OperatorStatus};
use crate::scene_io::SceneIo;
use crate::selection::ViewportClick;
use crate::state::scene_tools_active;
use crate::ui::{viewport_keyboard_shortcuts_active, UiState};
use crate::viewport::{scene_view_ray, ViewportDisplayMode};

#[derive(Resource, Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum BrushEditMode {
    #[default]
    Object,
    Vertex,
    Edge,
    Face,
    Clip,
}

impl BrushEditMode {
    pub fn label(self) -> &'static str {
        match self {
            Self::Object => "Object",
            Self::Vertex => "Vertex",
            Self::Edge => "Edge",
            Self::Face => "Face",
            Self::Clip => "Clip",
        }
    }

    pub fn is_element_mode(self) -> bool {
        self != Self::Object
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum BrushElementKey {
    Vertex {
        face: ComponentInstanceId,
        index: usize,
    },
    Edge {
        face: ComponentInstanceId,
        index: usize,
    },
    Face {
        face: ComponentInstanceId,
    },
}

#[derive(Resource, Default, Debug, Clone)]
pub struct BrushElementSelection {
    pub brush: Option<Entity>,
    pub elements: Vec<BrushElementKey>,
}

impl BrushElementSelection {
    fn replace(&mut self, brush: Entity, element: BrushElementKey) {
        self.brush = Some(brush);
        self.elements.clear();
        self.elements.push(element);
    }

    fn toggle(&mut self, brush: Entity, element: BrushElementKey) {
        if self.brush != Some(brush) {
            self.replace(brush, element);
            return;
        }
        if let Some(index) = self
            .elements
            .iter()
            .position(|existing| existing == &element)
        {
            self.elements.remove(index);
        } else {
            self.elements.push(element);
        }
    }

    pub fn clear(&mut self) {
        self.brush = None;
        self.elements.clear();
    }
}

pub struct BrushEditPlugin;

impl Plugin for BrushEditPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<BrushEditMode>()
            .init_resource::<BrushElementSelection>()
            .init_resource::<BrushElementDrag>()
            .add_systems(
                Update,
                (
                    brush_edit_hotkeys,
                    brush_element_pick,
                    brush_element_drag,
                    draw_brush_edit_overlays,
                )
                    .chain()
                    .run_if(scene_tools_active),
            );
    }
}

#[derive(Resource, Default, Debug, Clone)]
struct BrushElementDrag {
    brush: Option<Entity>,
    old: Option<BrushDesc>,
    last_floor: Option<Vec3>,
    changed: bool,
}

#[allow(clippy::too_many_arguments)]
fn brush_edit_hotkeys(
    mut mode: ResMut<BrushEditMode>,
    mut element_selection: ResMut<BrushElementSelection>,
    mut active_operator: ResMut<ActiveOperator>,
    mut scene_io: ResMut<SceneIo>,
    keys: Res<ButtonInput<KeyCode>>,
    buttons: Res<ButtonInput<MouseButton>>,
    mut contexts: EguiContexts,
    ui_state: Res<UiState>,
    display: Res<ViewportDisplayMode>,
    brushes: Query<(), With<BrushDesc>>,
) -> Result {
    if display.clean_game_view {
        return Ok(());
    }
    let ctx = contexts.ctx_mut()?;
    if !viewport_keyboard_shortcuts_active(&ui_state, ctx, &buttons) || ctx.wants_keyboard_input() {
        return Ok(());
    }
    if keys.just_pressed(KeyCode::Escape) && mode.is_element_mode() {
        *mode = BrushEditMode::Object;
        element_selection.clear();
        set_brush_edit_status(&mut active_operator, OperatorPhase::Canceled, "Object mode");
        scene_io.status = "Brush edit: Object mode".to_string();
        return Ok(());
    }

    let requested = if keys.just_pressed(KeyCode::Digit1) {
        Some(BrushEditMode::Vertex)
    } else if keys.just_pressed(KeyCode::Digit2) {
        Some(BrushEditMode::Edge)
    } else if keys.just_pressed(KeyCode::Digit3) {
        Some(BrushEditMode::Face)
    } else if keys.just_pressed(KeyCode::Digit4) {
        Some(BrushEditMode::Clip)
    } else {
        None
    };
    let Some(requested) = requested else {
        return Ok(());
    };
    let Some(selected_brush) = selected_brush_entity(&ui_state, &brushes) else {
        scene_io.status = "Select a brush before entering brush edit mode".to_string();
        set_brush_edit_status(
            &mut active_operator,
            OperatorPhase::Blocked,
            "Select a brush before editing elements",
        );
        return Ok(());
    };

    *mode = requested;
    element_selection.brush = Some(selected_brush);
    element_selection.elements.clear();
    scene_io.status = format!("Brush edit: {} mode", mode.label());
    set_brush_edit_status(
        &mut active_operator,
        OperatorPhase::Preview,
        format!("{} mode", mode.label()),
    );
    Ok(())
}

#[allow(clippy::too_many_arguments)]
fn brush_element_pick(
    mode: Res<BrushEditMode>,
    mut viewport_click: ResMut<ViewportClick>,
    mut element_selection: ResMut<BrushElementSelection>,
    keys: Res<ButtonInput<KeyCode>>,
    ui_state: Res<UiState>,
    cameras: Query<(&Camera, &GlobalTransform), With<EditorCamera>>,
    brushes: Query<(Entity, &BrushDesc, &GlobalTransform)>,
) {
    if !mode.is_element_mode() {
        return;
    }
    let Some(pointer_pos) = viewport_click.0.take() else {
        return;
    };
    let Some(ray) = viewport_ray(&cameras, pointer_pos, ui_state.viewport_rect) else {
        return;
    };
    let brush_filter = element_selection.brush;
    let mut best: Option<(Entity, BrushElementKey, f32)> = None;
    for (entity, brush, transform) in &brushes {
        if brush_filter.is_some_and(|selected| selected != entity) {
            continue;
        }
        if let Some((element, distance)) = pick_element(*mode, brush, transform, ray) {
            if best
                .as_ref()
                .is_none_or(|(_, _, best_distance)| distance < *best_distance)
            {
                best = Some((entity, element, distance));
            }
        }
    }
    let Some((brush, element, _)) = best else {
        if !keys.any_pressed([KeyCode::ShiftLeft, KeyCode::ShiftRight]) {
            element_selection.clear();
        }
        return;
    };
    if keys.any_pressed([KeyCode::ShiftLeft, KeyCode::ShiftRight]) {
        element_selection.toggle(brush, element);
    } else {
        element_selection.replace(brush, element);
    }
}

#[allow(clippy::too_many_arguments)]
fn brush_element_drag(
    mut commands: Commands,
    mode: Res<BrushEditMode>,
    selection: Res<BrushElementSelection>,
    mut drag: ResMut<BrushElementDrag>,
    mut active_operator: ResMut<ActiveOperator>,
    buttons: Res<ButtonInput<MouseButton>>,
    ui_state: Res<UiState>,
    cameras: Query<(&Camera, &GlobalTransform), With<EditorCamera>>,
    mut brushes: Query<(&mut BrushDesc, &GlobalTransform)>,
) {
    if !mode.is_element_mode() || matches!(*mode, BrushEditMode::Clip) {
        clear_drag(&mut drag);
        return;
    }
    let Some(brush_entity) = selection.brush else {
        clear_drag(&mut drag);
        return;
    };
    if selection.elements.is_empty() {
        clear_drag(&mut drag);
        return;
    }
    let Some(pointer_pos) = ui_state.viewport_pointer_pos else {
        return;
    };
    let Some(current_floor) = pointer_floor_position(&cameras, pointer_pos, ui_state.viewport_rect)
    else {
        return;
    };

    if buttons.just_pressed(MouseButton::Left) && drag.brush.is_none() {
        if let Ok((brush, _)) = brushes.get(brush_entity) {
            drag.brush = Some(brush_entity);
            drag.old = Some(brush.clone());
            drag.last_floor = Some(current_floor);
            drag.changed = false;
        }
        return;
    }

    if buttons.pressed(MouseButton::Left) && drag.brush == Some(brush_entity) {
        let Some(last_floor) = drag.last_floor else {
            drag.last_floor = Some(current_floor);
            return;
        };
        let world_delta = current_floor - last_floor;
        if world_delta.length_squared() <= 0.000001 {
            return;
        }
        if let Ok((mut brush, transform)) = brushes.get_mut(brush_entity) {
            let local_delta = transform.affine().inverse().transform_vector3(world_delta);
            if move_selected_elements(&mut brush, &selection.elements, local_delta) {
                drag.changed = true;
                drag.last_floor = Some(current_floor);
                set_brush_edit_status(
                    &mut active_operator,
                    OperatorPhase::Preview,
                    format!("Dragging {} element(s)", selection.elements.len()),
                );
            }
        }
    }

    if buttons.just_released(MouseButton::Left) {
        if let (Some(brush), Some(old)) = (drag.brush, drag.old.take()) {
            if drag.changed {
                if let Ok((brush_desc, _)) = brushes.get(brush) {
                    let new = brush_desc.clone();
                    commands.queue(move |world: &mut World| {
                        push_command(
                            world,
                            EditorCommand::SetBrush {
                                entity: brush,
                                old: Some(old),
                                new,
                            },
                        );
                    });
                    set_brush_edit_status(
                        &mut active_operator,
                        OperatorPhase::Committed,
                        "Committed brush element edit",
                    );
                }
            }
        }
        clear_drag(&mut drag);
    }
}

fn clear_drag(drag: &mut BrushElementDrag) {
    drag.brush = None;
    drag.old = None;
    drag.last_floor = None;
    drag.changed = false;
}

fn draw_brush_edit_overlays(
    mode: Res<BrushEditMode>,
    selection: Res<BrushElementSelection>,
    ui_state: Res<UiState>,
    brushes: Query<(Entity, &BrushDesc, &GlobalTransform)>,
    mut gizmos: Gizmos,
) {
    if !mode.is_element_mode() {
        return;
    }
    let selected_brushes: Vec<Entity> = ui_state.selected_entities.iter().collect();
    for (entity, brush, transform) in &brushes {
        if !selected_brushes.contains(&entity) {
            continue;
        }
        let active = selection.brush == Some(entity);
        draw_brush_elements(
            *mode,
            brush,
            transform,
            &selection.elements,
            active,
            &mut gizmos,
        );
    }
}

fn draw_brush_elements(
    mode: BrushEditMode,
    brush: &BrushDesc,
    transform: &GlobalTransform,
    selected: &[BrushElementKey],
    active: bool,
    gizmos: &mut Gizmos,
) {
    let base_color = match mode {
        BrushEditMode::Vertex => Color::srgb(0.2, 0.72, 1.0),
        BrushEditMode::Edge => Color::srgb(1.0, 0.68, 0.24),
        BrushEditMode::Face => Color::srgb(0.24, 1.0, 0.56),
        BrushEditMode::Clip => Color::srgb(0.92, 0.36, 1.0),
        BrushEditMode::Object => Color::WHITE,
    };
    let selected_color = Color::srgb(1.0, 0.95, 0.2);
    for face in &brush.faces {
        let vertices = world_vertices(face, transform);
        if vertices.is_empty() {
            continue;
        }
        let face_center = average_point(&vertices);
        let normal = transform
            .affine()
            .transform_vector3(face.plane.normal)
            .normalize_or_zero();
        if matches!(mode, BrushEditMode::Face | BrushEditMode::Clip) {
            let key = BrushElementKey::Face {
                face: face.id.clone(),
            };
            let color = if active && selected.contains(&key) {
                selected_color
            } else {
                base_color
            };
            gizmos.sphere(face_center, 0.08, color);
            gizmos.line(face_center, face_center + normal * 0.55, color);
        }
        for index in 0..vertices.len() {
            let next = (index + 1) % vertices.len();
            if matches!(mode, BrushEditMode::Vertex) {
                let key = BrushElementKey::Vertex {
                    face: face.id.clone(),
                    index,
                };
                let color = if active && selected.contains(&key) {
                    selected_color
                } else {
                    base_color
                };
                gizmos.sphere(vertices[index], 0.06, color);
            }
            if matches!(mode, BrushEditMode::Edge | BrushEditMode::Clip) {
                let key = BrushElementKey::Edge {
                    face: face.id.clone(),
                    index,
                };
                let color = if active && selected.contains(&key) {
                    selected_color
                } else {
                    base_color
                };
                gizmos.line(vertices[index], vertices[next], color);
            }
        }
    }
}

fn selected_brush_entity(
    ui_state: &UiState,
    brushes: &Query<(), With<BrushDesc>>,
) -> Option<Entity> {
    ui_state
        .selected_entities
        .iter()
        .find(|entity| brushes.contains(*entity))
}

fn viewport_ray(
    cameras: &Query<(&Camera, &GlobalTransform), With<EditorCamera>>,
    pointer_pos: egui::Pos2,
    scene_rect: egui::Rect,
) -> Option<Ray3d> {
    let (camera, transform) = cameras
        .iter()
        .find(|(camera, _)| camera.is_active)
        .or_else(|| cameras.iter().next())?;
    scene_view_ray(camera, transform, pointer_pos, scene_rect)
}

fn pick_element(
    mode: BrushEditMode,
    brush: &BrushDesc,
    transform: &GlobalTransform,
    ray: Ray3d,
) -> Option<(BrushElementKey, f32)> {
    match mode {
        BrushEditMode::Vertex => pick_vertex(brush, transform, ray),
        BrushEditMode::Edge => pick_edge(brush, transform, ray),
        BrushEditMode::Face | BrushEditMode::Clip => pick_face(brush, transform, ray),
        BrushEditMode::Object => None,
    }
}

fn pointer_floor_position(
    cameras: &Query<(&Camera, &GlobalTransform), With<EditorCamera>>,
    pointer_pos: egui::Pos2,
    scene_rect: egui::Rect,
) -> Option<Vec3> {
    let ray = viewport_ray(cameras, pointer_pos, scene_rect)?;
    let direction = ray.direction.as_vec3();
    if direction.y.abs() < 0.0001 {
        return Some(ray.origin);
    }
    let t = -ray.origin.y / direction.y;
    Some(ray.origin + direction * t.max(0.0))
}

fn move_selected_elements(
    brush: &mut BrushDesc,
    selected: &[BrushElementKey],
    delta: Vec3,
) -> bool {
    if delta.length_squared() <= 0.000001 {
        return false;
    }
    let anchors = selected_anchor_positions(brush, selected);
    if anchors.is_empty() {
        return false;
    }
    let mut changed = false;
    for face in &mut brush.faces {
        for vertex in &mut face.vertices {
            if anchors
                .iter()
                .any(|anchor| vertex.distance_squared(*anchor) <= 0.0001)
            {
                *vertex += delta;
                changed = true;
            }
        }
    }
    if changed {
        recompute_face_planes(brush);
    }
    changed
}

fn selected_anchor_positions(brush: &BrushDesc, selected: &[BrushElementKey]) -> Vec<Vec3> {
    let mut anchors = Vec::new();
    for element in selected {
        match element {
            BrushElementKey::Vertex { face, index } => {
                if let Some(face_desc) = brush.faces.iter().find(|candidate| &candidate.id == face)
                {
                    if let Some(vertex) = face_desc.vertices.get(*index) {
                        push_unique_anchor(&mut anchors, *vertex);
                    }
                }
            }
            BrushElementKey::Edge { face, index } => {
                if let Some(face_desc) = brush.faces.iter().find(|candidate| &candidate.id == face)
                {
                    if !face_desc.vertices.is_empty() {
                        let next = (*index + 1) % face_desc.vertices.len();
                        if let Some(vertex) = face_desc.vertices.get(*index) {
                            push_unique_anchor(&mut anchors, *vertex);
                        }
                        if let Some(vertex) = face_desc.vertices.get(next) {
                            push_unique_anchor(&mut anchors, *vertex);
                        }
                    }
                }
            }
            BrushElementKey::Face { face } => {
                if let Some(face_desc) = brush.faces.iter().find(|candidate| &candidate.id == face)
                {
                    for vertex in &face_desc.vertices {
                        push_unique_anchor(&mut anchors, *vertex);
                    }
                }
            }
        }
    }
    anchors
}

fn push_unique_anchor(anchors: &mut Vec<Vec3>, vertex: Vec3) {
    if !anchors
        .iter()
        .any(|existing| existing.distance_squared(vertex) <= 0.0001)
    {
        anchors.push(vertex);
    }
}

fn recompute_face_planes(brush: &mut BrushDesc) {
    for face in &mut brush.faces {
        let Some(plane) = plane_from_vertices(&face.vertices, face.plane.normal) else {
            continue;
        };
        face.plane = plane;
    }
}

fn plane_from_vertices(vertices: &[Vec3], fallback_normal: Vec3) -> Option<BrushPlaneDesc> {
    if vertices.len() < 3 {
        return None;
    }
    let normal = (vertices[1] - vertices[0])
        .cross(vertices[2] - vertices[0])
        .try_normalize()
        .or_else(|| fallback_normal.try_normalize())?;
    Some(BrushPlaneDesc {
        normal,
        distance: normal.dot(vertices[0]),
    })
}

fn pick_vertex(
    brush: &BrushDesc,
    transform: &GlobalTransform,
    ray: Ray3d,
) -> Option<(BrushElementKey, f32)> {
    let mut best = None;
    for face in &brush.faces {
        for (index, vertex) in world_vertices(face, transform).iter().enumerate() {
            let distance = distance_ray_point(ray, *vertex);
            if distance < 0.25 && best.as_ref().is_none_or(|(_, best)| distance < *best) {
                best = Some((
                    BrushElementKey::Vertex {
                        face: face.id.clone(),
                        index,
                    },
                    distance,
                ));
            }
        }
    }
    best
}

fn pick_edge(
    brush: &BrushDesc,
    transform: &GlobalTransform,
    ray: Ray3d,
) -> Option<(BrushElementKey, f32)> {
    let mut best = None;
    for face in &brush.faces {
        let vertices = world_vertices(face, transform);
        for index in 0..vertices.len() {
            let next = (index + 1) % vertices.len();
            let distance = distance_ray_segment(ray, vertices[index], vertices[next]);
            if distance < 0.2 && best.as_ref().is_none_or(|(_, best)| distance < *best) {
                best = Some((
                    BrushElementKey::Edge {
                        face: face.id.clone(),
                        index,
                    },
                    distance,
                ));
            }
        }
    }
    best
}

fn pick_face(
    brush: &BrushDesc,
    transform: &GlobalTransform,
    ray: Ray3d,
) -> Option<(BrushElementKey, f32)> {
    let mut best = None;
    for face in &brush.faces {
        let vertices = world_vertices(face, transform);
        if vertices.len() < 3 {
            continue;
        }
        let normal = transform
            .affine()
            .transform_vector3(face.plane.normal)
            .normalize_or_zero();
        let denom = normal.dot(ray.direction.as_vec3());
        if denom.abs() < 0.0001 {
            continue;
        }
        let distance = normal.dot(vertices[0] - ray.origin) / denom;
        if distance < 0.0 {
            continue;
        }
        let hit = ray.origin + ray.direction.as_vec3() * distance;
        if point_in_convex_polygon(hit, &vertices, normal)
            && best.as_ref().is_none_or(|(_, best)| distance < *best)
        {
            best = Some((
                BrushElementKey::Face {
                    face: face.id.clone(),
                },
                distance,
            ));
        }
    }
    best
}

fn world_vertices(face: &BrushFaceDesc, transform: &GlobalTransform) -> Vec<Vec3> {
    face.vertices
        .iter()
        .map(|vertex| transform.transform_point(*vertex))
        .collect()
}

fn average_point(points: &[Vec3]) -> Vec3 {
    points.iter().copied().sum::<Vec3>() / points.len() as f32
}

fn point_in_convex_polygon(point: Vec3, vertices: &[Vec3], normal: Vec3) -> bool {
    let mut expected_sign = 0.0f32;
    for index in 0..vertices.len() {
        let next = (index + 1) % vertices.len();
        let edge = vertices[next] - vertices[index];
        let to_point = point - vertices[index];
        let side = edge.cross(to_point).dot(normal);
        if side.abs() <= 0.0001 {
            continue;
        }
        if expected_sign == 0.0 {
            expected_sign = side.signum();
        } else if side.signum() != expected_sign {
            return false;
        }
    }
    true
}

fn distance_ray_point(ray: Ray3d, point: Vec3) -> f32 {
    let to_point = point - ray.origin;
    let t = to_point.dot(ray.direction.as_vec3()).max(0.0);
    (ray.origin + ray.direction.as_vec3() * t - point).length()
}

fn distance_ray_segment(ray: Ray3d, a: Vec3, b: Vec3) -> f32 {
    let ray_dir = ray.direction.as_vec3();
    let segment = b - a;
    let w0 = ray.origin - a;
    let a_dot = ray_dir.dot(ray_dir);
    let b_dot = ray_dir.dot(segment);
    let c_dot = segment.dot(segment);
    let d_dot = ray_dir.dot(w0);
    let e_dot = segment.dot(w0);
    let denom = a_dot * c_dot - b_dot * b_dot;
    let ray_t = if denom.abs() > 0.0001 {
        ((b_dot * e_dot - c_dot * d_dot) / denom).max(0.0)
    } else {
        0.0
    };
    let segment_t = if c_dot > 0.0001 {
        ((a_dot * e_dot - b_dot * d_dot) / denom.max(0.0001)).clamp(0.0, 1.0)
    } else {
        0.0
    };
    let ray_point = ray.origin + ray_dir * ray_t;
    let segment_point = a + segment * segment_t;
    ray_point.distance(segment_point)
}

fn set_brush_edit_status(
    active_operator: &mut ActiveOperator,
    phase: OperatorPhase,
    hint: impl Into<String>,
) {
    active_operator.status = Some(OperatorStatus {
        id: "brush.edit_mode".to_string(),
        label: "Brush Edit".to_string(),
        phase,
        hint: hint.into(),
        warnings: Vec::new(),
    });
}

#[cfg(test)]
mod tests {
    use super::*;
    use shared::BrushDesc;

    #[test]
    fn point_inside_convex_polygon_is_detected() {
        let vertices = vec![
            Vec3::new(-1.0, 0.0, -1.0),
            Vec3::new(1.0, 0.0, -1.0),
            Vec3::new(1.0, 0.0, 1.0),
            Vec3::new(-1.0, 0.0, 1.0),
        ];
        assert!(point_in_convex_polygon(Vec3::ZERO, &vertices, Vec3::Y));
        assert!(!point_in_convex_polygon(
            Vec3::new(2.0, 0.0, 0.0),
            &vertices,
            Vec3::Y
        ));
    }

    #[test]
    fn moving_selected_vertex_moves_matching_welded_corners() {
        let mut brush = BrushDesc::default();
        let selected_vertex = brush.faces[0].vertices[0];
        let before = brush
            .faces
            .iter()
            .flat_map(|face| face.vertices.iter())
            .filter(|vertex| vertex.distance_squared(selected_vertex) <= 0.0001)
            .count();
        let face = brush.faces[0].id.clone();

        let changed = move_selected_elements(
            &mut brush,
            &[BrushElementKey::Vertex { face, index: 0 }],
            Vec3::new(0.5, 0.0, 0.0),
        );

        let after = brush
            .faces
            .iter()
            .flat_map(|face| face.vertices.iter())
            .filter(|vertex| vertex.distance_squared(selected_vertex + Vec3::X * 0.5) <= 0.0001)
            .count();
        assert!(changed);
        assert_eq!(before, after);
    }
}