use std::slice::IterMut;

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

use crate::global_state::GlobalState;

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

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

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(Debug, PartialEq)]
enum PolygonView {
    TwoDimensional(PolygonState),
    ThreeDimensional(Option<Entity>),
}

impl PolygonView {
    fn is_2d(&self) -> bool {
        match self {
            PolygonView::TwoDimensional(_) => true,
            PolygonView::ThreeDimensional(_) => false,
        }
    }

    fn is_3d(&self) -> bool {
        !self.is_2d()
    }

    fn two_dimensional_mut(&mut self) -> &mut PolygonState {
        match self {
            PolygonView::TwoDimensional(t) => t,
            PolygonView::ThreeDimensional(_) => panic!("called 2d on 3d!"),
        }
    }

    fn three_dimensional_mut(&mut self) -> &mut Option<Entity> {
        match self {
            PolygonView::TwoDimensional(_) => panic!("called 3d on 2d!"),
            PolygonView::ThreeDimensional(t) => t,
        }
    }
}

impl Default for PolygonView {
    fn default() -> Self {
        Self::TwoDimensional(PolygonState::default())
    }
}

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

impl Polygon {
    const PROXIMITY_THRESHOLD: f32 = 10.0;

    pub fn swap_to_3d(
        &mut self,
        global_state: &GlobalState,
        commands: &mut Commands,
        meshes: &mut ResMut<Assets<Mesh>>,
        materials: &mut ResMut<Assets<StandardMaterial>>,
    ) {
        debug_assert!(self.state.is_2d());

        // clear all 2d entities
        let finished = match self.state.two_dimensional_mut() {
            PolygonState::Collection(collection_ids) => {
                for point in collection_ids.points.iter() {
                    commands.entity(*point).despawn();
                }

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

                false
            }
            PolygonState::Finished(mesh) => {
                commands.entity(*mesh).despawn();

                true
            }
        };

        self.state = PolygonView::ThreeDimensional(if finished {
            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: materials.add(StandardMaterial::from(Color::BLACK)),
                    ..default()
                })
                .id();

            Some(mesh_id)
        } else {
            None
        });
    }

    pub fn swap_to_2d(
        &mut self,
        global_state: &GlobalState,
        commands: &mut Commands,
        meshes: &mut ResMut<Assets<Mesh>>,
        materials: &mut ResMut<Assets<ColorMaterial>>,
    ) {
        debug_assert!(self.state.is_3d());

        // clear 3d entity

        let finished = match self.state.three_dimensional_mut() {
            Some(mesh_id) => {
                commands.entity(*mesh_id).despawn();

                true
            }
            None => false,
        };

        self.state = PolygonView::TwoDimensional(if finished {
            // 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: materials.add(ColorMaterial::from(Color::BLACK)),
                    ..default()
                })
                .id();

            // store triangle entity id in state
            PolygonState::Finished(triangle_id)
        } else {
            // create point meshes for every point
            let point_ids = self
                .points
                .iter()
                .map(|&point| {
                    commands
                        .spawn(MaterialMesh2dBundle {
                            mesh: meshes.add(Mesh::from(shape::Quad::default())).into(),
                            transform: Transform::default()
                                .with_scale(Vec3::splat(4.0))
                                .with_translation(
                                    (point - (global_state.window_extent * 0.5)).extend(0.0),
                                ),
                            material: materials.add(ColorMaterial::from(Color::BLACK)),
                            ..default()
                        })
                        .id()
                })
                .collect();

            // draw lines between the points
            let line_ids = (1..self.points.len())
                .map(|i| {
                    let previous_point = self.points[i - 1];
                    let point = self.points[i];

                    let a = Vec2::X.angle_between((point - previous_point).normalize());

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

            PolygonState::Collection(CollectionIDs {
                points: point_ids,
                lines: line_ids,
            })
        });
    }

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

    pub fn add_point(
        &mut self,
        global_state: &GlobalState,
        commands: &mut Commands,
        meshes: &mut ResMut<Assets<Mesh>>,
        materials: &mut ResMut<Assets<ColorMaterial>>,
    ) -> 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.two_dimensional_mut().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();
                }
            }

            // 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: materials.add(ColorMaterial::from(Color::BLACK)),
                    ..default()
                })
                .id();

            // store triangle entity id in state
            *self.state.two_dimensional_mut() = PolygonState::Finished(triangle_id);

            return true;
        }

        // deny too close points
        if !self.check_all_for_proximity(point) {
            let collection_ids = self.state.two_dimensional_mut().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: 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: 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 {
            PolygonView::TwoDimensional(t) => match t {
                PolygonState::Collection(_) => false,
                PolygonState::Finished(_) => true,
            },
            PolygonView::ThreeDimensional(_) => false,
        }
    }

    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()
    }
}