//! MVP brush CSG operations for convex cuboid/prism blockout brushes.

use bevy::math::Affine3A;
use bevy::prelude::*;
use shared::{BrushDesc, LevelObject};

use crate::history::{
    delete_entities_with_history, set_brush_with_history, set_transform_with_history,
};
use crate::scene_io::SceneIo;
use crate::ui::UiState;

#[derive(Debug, Clone, Copy, PartialEq)]
struct BrushBounds {
    min: Vec3,
    max: Vec3,
}

impl BrushBounds {
    fn union(self, other: Self) -> Self {
        Self {
            min: self.min.min(other.min),
            max: self.max.max(other.max),
        }
    }

    fn intersection(self, other: Self) -> Option<Self> {
        let min = self.min.max(other.min);
        let max = self.max.min(other.max);
        ((max.x - min.x) > 0.001 && (max.y - min.y) > 0.001 && (max.z - min.z) > 0.001)
            .then_some(Self { min, max })
    }

    fn center(self) -> Vec3 {
        (self.min + self.max) * 0.5
    }

    fn size(self) -> Vec3 {
        self.max - self.min
    }

    fn volume(self) -> f32 {
        let size = self.size();
        size.x.max(0.0) * size.y.max(0.0) * size.z.max(0.0)
    }
}

pub fn selected_brush_count(world: &World) -> usize {
    world
        .resource::<UiState>()
        .selected_entities
        .iter()
        .filter(|entity| world.get::<BrushDesc>(*entity).is_some())
        .count()
}

pub fn intersect_selected_brushes(world: &mut World) {
    run_bounds_csg(world, BrushCsgOp::Intersect);
}

pub fn merge_selected_brushes(world: &mut World) {
    run_bounds_csg(world, BrushCsgOp::Merge);
}

pub fn subtract_selected_brushes(world: &mut World) {
    run_bounds_csg(world, BrushCsgOp::Subtract);
}

#[derive(Debug, Clone, Copy)]
enum BrushCsgOp {
    Intersect,
    Merge,
    Subtract,
}

fn run_bounds_csg(world: &mut World, op: BrushCsgOp) {
    let selected: Vec<Entity> = world
        .resource::<UiState>()
        .selected_entities
        .iter()
        .filter(|entity| {
            world.get::<LevelObject>(*entity).is_some() && world.get::<BrushDesc>(*entity).is_some()
        })
        .collect();
    if selected.len() < 2 {
        set_status(world, "Select at least two brushes for CSG");
        return;
    }

    let Some(primary_bounds) = brush_world_bounds(world, selected[0]) else {
        set_status(world, "Primary brush has no valid bounds");
        return;
    };

    let result = match op {
        BrushCsgOp::Merge => selected
            .iter()
            .skip(1)
            .filter_map(|entity| brush_world_bounds(world, *entity))
            .fold(primary_bounds, BrushBounds::union),
        BrushCsgOp::Intersect => {
            let mut result = primary_bounds;
            for entity in selected.iter().skip(1) {
                let Some(bounds) = brush_world_bounds(world, *entity) else {
                    continue;
                };
                let Some(intersection) = result.intersection(bounds) else {
                    set_status(world, "Brush intersect failed: no overlap");
                    return;
                };
                result = intersection;
            }
            result
        }
        BrushCsgOp::Subtract => {
            let Some(cutter_bounds) = brush_world_bounds(world, selected[1]) else {
                set_status(world, "Subtract failed: cutter brush has no valid bounds");
                return;
            };
            let Some(overlap) = primary_bounds.intersection(cutter_bounds) else {
                set_status(world, "Subtract failed: brushes do not overlap");
                return;
            };
            let Some(result) = largest_remaining_slab(primary_bounds, overlap) else {
                set_status(world, "Subtract failed: result would be empty");
                return;
            };
            result
        }
    };

    apply_bounds_result(world, selected[0], result);
    if matches!(op, BrushCsgOp::Merge | BrushCsgOp::Intersect) {
        delete_entities_with_history(world, &selected[1..]);
    }
    set_status(
        world,
        match op {
            BrushCsgOp::Intersect => "Brush intersect committed",
            BrushCsgOp::Merge => "Brush convex merge committed",
            BrushCsgOp::Subtract => "Brush subtract committed",
        },
    );
}

fn apply_bounds_result(world: &mut World, entity: Entity, bounds: BrushBounds) {
    let center = bounds.center();
    let size = bounds.size();
    let new_brush = BrushDesc::cuboid(size);
    let old_transform = world.get::<Transform>(entity).copied().unwrap_or_default();
    let mut new_transform = old_transform;
    new_transform.translation = center;
    new_transform.rotation = Quat::IDENTITY;
    new_transform.scale = Vec3::ONE;
    set_transform_with_history(world, entity, old_transform, new_transform);
    set_brush_with_history(world, entity, new_brush);
}

fn brush_world_bounds(world: &World, entity: Entity) -> Option<BrushBounds> {
    let brush = world.get::<BrushDesc>(entity)?;
    let transform = world
        .get::<GlobalTransform>(entity)
        .map(|global| global.affine())
        .or_else(|| {
            world
                .get::<Transform>(entity)
                .map(|transform| transform.compute_affine())
        })
        .unwrap_or(Affine3A::IDENTITY);
    let mut min = Vec3::splat(f32::INFINITY);
    let mut max = Vec3::splat(f32::NEG_INFINITY);
    let mut found = false;
    for vertex in brush
        .faces
        .iter()
        .flat_map(|face| face.vertices.iter().copied())
    {
        let world_vertex = transform.transform_point3(vertex);
        min = min.min(world_vertex);
        max = max.max(world_vertex);
        found = true;
    }
    found.then_some(BrushBounds { min, max })
}

fn largest_remaining_slab(source: BrushBounds, overlap: BrushBounds) -> Option<BrushBounds> {
    let candidates = [
        BrushBounds {
            min: source.min,
            max: Vec3::new(overlap.min.x, source.max.y, source.max.z),
        },
        BrushBounds {
            min: Vec3::new(overlap.max.x, source.min.y, source.min.z),
            max: source.max,
        },
        BrushBounds {
            min: source.min,
            max: Vec3::new(source.max.x, overlap.min.y, source.max.z),
        },
        BrushBounds {
            min: Vec3::new(source.min.x, overlap.max.y, source.min.z),
            max: source.max,
        },
        BrushBounds {
            min: source.min,
            max: Vec3::new(source.max.x, source.max.y, overlap.min.z),
        },
        BrushBounds {
            min: Vec3::new(source.min.x, source.min.y, overlap.max.z),
            max: source.max,
        },
    ];
    candidates
        .into_iter()
        .filter(|bounds| bounds.size().cmpgt(Vec3::splat(0.001)).all())
        .max_by(|a, b| a.volume().total_cmp(&b.volume()))
}

fn set_status(world: &mut World, status: impl Into<String>) {
    if let Some(mut scene_io) = world.get_resource_mut::<SceneIo>() {
        scene_io.status = status.into();
    }
}

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

    fn bounds(min: Vec3, max: Vec3) -> BrushBounds {
        BrushBounds { min, max }
    }

    #[test]
    fn intersects_overlapping_bounds() {
        let a = bounds(Vec3::ZERO, Vec3::splat(2.0));
        let b = bounds(Vec3::ONE, Vec3::splat(3.0));
        assert_eq!(a.intersection(b), Some(bounds(Vec3::ONE, Vec3::splat(2.0))));
    }

    #[test]
    fn subtract_picks_largest_remaining_slab() {
        let source = bounds(Vec3::ZERO, Vec3::new(4.0, 2.0, 2.0));
        let overlap = bounds(Vec3::ZERO, Vec3::new(1.0, 2.0, 2.0));
        let result = largest_remaining_slab(source, overlap).expect("remaining slab");
        assert_eq!(result.min, Vec3::new(1.0, 0.0, 0.0));
        assert_eq!(result.max, source.max);
    }
}