use std::slice::IterMut;

use bevy::{
    prelude::*,
    render::{mesh::Indices, render_resource::PrimitiveTopology, view::RenderLayers},
    sprite::MaterialMesh2dBundle,
};

use crate::global_state::GlobalState;

#[derive(Default, Debug, PartialEq)]
struct CollectionIDs {
    points: Vec<Entity>,
    lines: Vec<Entity>,
}

#[derive(Debug, PartialEq)]
struct FinishedIDs {
    // 2d plane
    plane: Entity,

    // 3d object
    object: Entity,
}

#[derive(Debug, PartialEq)]
enum PolygonState {
    Collection(CollectionIDs),
    Finished(FinishedIDs),
}

impl PolygonState {
    fn collection_mut(&mut self) -> &mut CollectionIDs {
        match self {
            PolygonState::Collection(c) => c,
            PolygonState::Finished(_) => panic!("called collection on finished state!"),
        }
    }
}

impl Default for PolygonState {
    fn default() -> Self {
        Self::Collection(CollectionIDs::default())
    }
}

#[derive(Default, Debug, PartialEq)]
pub struct Polygon {
    points: Vec<Vec2>,
    state: PolygonState,
}

impl Polygon {
    const PROXIMITY_THRESHOLD: f32 = 10.0;

    pub fn swap_to_3d(&mut self, global_state: &GlobalState, commands: &mut Commands) {
        match &self.state {
            PolygonState::Collection(collection_ids) => {
                // add render layer to all points
                for point in collection_ids.points.iter() {
                    let mut handle = commands.entity(*point);

                    handle.insert(global_state.offscreen_render_layer);
                }

                // also add render layer to all lines
                for line in collection_ids.points.iter() {
                    let mut handle = commands.entity(*line);

                    handle.insert(global_state.offscreen_render_layer);
                }
            }
            PolygonState::Finished(finished_ids) => {
                // add render layer to 2d plane
                commands
                    .entity(finished_ids.plane)
                    .insert(global_state.offscreen_render_layer);

                // remove render layer from 3d object
                commands
                    .entity(finished_ids.object)
                    .remove::<RenderLayers>();
            }
        }
    }

    pub fn swap_to_2d(&mut self, global_state: &GlobalState, commands: &mut Commands) {
        match &self.state {
            PolygonState::Collection(collection_ids) => {
                // remove render layer from all points
                for point in collection_ids.points.iter() {
                    let mut handle = commands.entity(*point);

                    handle.remove::<RenderLayers>();
                }

                // remove render layer from all lines
                for line in collection_ids.points.iter() {
                    let mut handle = commands.entity(*line);

                    handle.remove::<RenderLayers>();
                }
            }
            PolygonState::Finished(finished_ids) => {
                // remove render layer from 2d plane
                commands.entity(finished_ids.plane).remove::<RenderLayers>();

                // add render layer to 3d object
                commands
                    .entity(finished_ids.object)
                    .insert(global_state.offscreen_render_layer);
            }
        }
    }

    pub fn points(&self) -> &[Vec2] {
        &self.points
    }

    pub fn add_point(
        &mut self,
        global_state: &GlobalState,
        commands: &mut Commands,
        meshes: &mut ResMut<Assets<Mesh>>,
        color_materials: &mut ResMut<Assets<ColorMaterial>>,
        standard_materials: &mut ResMut<Assets<StandardMaterial>>,
    ) -> bool {
        debug_assert_eq!(self.finished(), false);

        let point = global_state.cursor_position;

        // polygon must be at least an triangle
        // and check if we can close up the polygon
        if self.points.len() >= 3 && self.check_first_for_proximity(point) {
            // remove points and lines from collection state
            {
                let collection_ids = self.state.collection_mut();

                for point_id in collection_ids.points.iter() {
                    commands.entity(*point_id).despawn();
                }

                for line_id in collection_ids.lines.iter() {
                    commands.entity(*line_id).despawn();
                }
            }

            self.order_points();

            // create triangle mesh
            let triangle_mesh = self.create_triangulated_mesh();

            let triangle_id = commands
                .spawn(MaterialMesh2dBundle {
                    mesh: meshes.add(triangle_mesh).into(),
                    transform: Transform::default()
                        .with_translation((-global_state.window_extent * 0.5).extend(0.0)),
                    material: color_materials.add(ColorMaterial::from(Color::BLACK)),
                    ..default()
                })
                .id();

            // create 3d object
            let vertices: Vec<Vec3> = self
                .points
                .iter()
                .map(|p| vec![p.extend(0.0), p.extend(global_state.extrusion_height)])
                .flatten()
                .collect();

            let indices = Indices::U32({
                let mut v = Vec::new();

                for i in 0..self.points.len() {
                    let index = (i as u32) * 2;

                    // create quads from 4 adjacent points
                    v.push(index);
                    v.push((index + 2) % vertices.len() as u32);
                    v.push(index + 1);
                    v.push(index + 1);
                    v.push((index + 2) % vertices.len() as u32);
                    v.push((index + 3) % vertices.len() as u32);
                }

                // TODO: proper ear cutting algo
                for i in 2..self.points.len() as u32 {
                    let index = (i as u32) * 2 + 1;

                    v.push(1);
                    v.push(index - 2);
                    v.push(index);
                }

                v
            });

            let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
            mesh.set_indices(Some(indices));
            mesh.insert_attribute(Mesh::ATTRIBUTE_POSITION, vertices);

            let mesh_id = commands
                .spawn((
                    MaterialMeshBundle {
                        mesh: meshes.add(mesh).into(),
                        transform: Transform::default(),
                        material: standard_materials.add(StandardMaterial::from(Color::BLACK)),
                        ..default()
                    },
                    global_state.offscreen_render_layer,
                ))
                .id();

            // store finished entities in state
            self.state = PolygonState::Finished(FinishedIDs {
                plane: triangle_id,
                object: mesh_id,
            });

            return true;
        }

        // deny too close points
        if !self.check_all_for_proximity(point) {
            let collection_ids = self.state.collection_mut();

            // create point mesh at click position
            let point_id = commands
                .spawn(MaterialMesh2dBundle {
                    mesh: meshes.add(Mesh::from(shape::Quad::default())).into(),
                    transform: Transform::default()
                        .with_scale(Vec3::splat(4.0))
                        .with_translation(
                            (global_state.cursor_position - (global_state.window_extent * 0.5))
                                .extend(0.0),
                        ),
                    material: color_materials.add(ColorMaterial::from(Color::BLACK)),
                    ..default()
                })
                .id();

            collection_ids.points.push(point_id);

            // draw a line between new point and last point
            if let Some(&last_point) = self.points.last() {
                let a = Vec2::X.angle_between((point - last_point).normalize());

                let line_id = commands
                    .spawn(MaterialMesh2dBundle {
                        mesh: meshes.add(Self::create_line_mesh(last_point, point)).into(),
                        transform: Transform::default()
                            .with_translation(
                                (last_point - (global_state.window_extent * 0.5)).extend(0.0),
                            )
                            .with_rotation(Quat::from_rotation_z(a)),
                        material: color_materials.add(ColorMaterial::from(Color::BLACK)),
                        ..default()
                    })
                    .id();

                collection_ids.lines.push(line_id);
            }

            self.points.push(point);
        }

        false
    }

    pub fn finished(&self) -> bool {
        match &self.state {
            PolygonState::Collection(_) => false,
            PolygonState::Finished(_) => true,
        }
    }

    fn order_points(&mut self) {
        let n = Vec3::Z;

        let v1 = (self.points[0] - self.points[1]).normalize().extend(0.0);
        let v2 = (self.points[1] - self.points[2]).normalize().extend(0.0);

        let c1 = v1.cross(n);

        let d = c1.dot(v2);

        // dot product is bigger than 0 if normal and connection line are facing in the same direction
        // reverse the order of points, thus the face of the 3d object is directed to the outside
        if d >= 0.0 {
            self.points = self.points.iter().cloned().rev().collect();
        }
    }

    fn check_all_for_proximity(&self, point: Vec2) -> bool {
        self.points
            .iter()
            .any(|p| p.distance(point) < Self::PROXIMITY_THRESHOLD)
    }

    fn check_first_for_proximity(&self, point: Vec2) -> bool {
        debug_assert!(!self.points.is_empty());

        self.points.first().unwrap().distance(point) < Self::PROXIMITY_THRESHOLD
    }

    fn create_triangulated_mesh(&self) -> Mesh {
        let vertices: Vec<_> = self.points.iter().map(|p| p.extend(0.0)).collect();

        // TODO: proper ear cutting algo
        let indices = Indices::U32({
            let mut v = Vec::new();

            for i in 2..self.points.len() as u32 {
                v.push(0);
                v.push(i - 1);
                v.push(i);
            }

            v
        });

        let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
        mesh.set_indices(Some(indices));
        mesh.insert_attribute(Mesh::ATTRIBUTE_POSITION, vertices);

        mesh
    }

    fn create_line_mesh(start: Vec2, end: Vec2) -> Mesh {
        let d = start.distance(end);

        let vertices = [[0.0, 0.0, 0.0], [d, 0.0, 0.0]];

        let mut mesh = Mesh::new(PrimitiveTopology::LineList);
        mesh.insert_attribute(
            Mesh::ATTRIBUTE_POSITION,
            vertices.into_iter().map(|v| v).collect::<Vec<_>>(),
        );

        mesh
    }
}

#[derive(Resource, Default, Debug, PartialEq)]
pub struct ObjectInfos {
    polygons: Vec<Polygon>,
}

impl ObjectInfos {
    pub fn active_polygon(&mut self) -> Option<&mut Polygon> {
        self.polygons.iter_mut().find(|polygon| !polygon.finished())
    }

    pub fn add_polygon(&mut self) -> &mut Polygon {
        self.polygons.push(Polygon::default());
        self.polygons.last_mut().unwrap()
    }

    pub fn iter_mut(&mut self) -> IterMut<'_, Polygon> {
        self.polygons.iter_mut()
    }
}