use std::ops::Deref;

use bevy::prelude::*;

use crate::{
    bloxel::{block::BlockTexture, prelude::*},
    TerrainAtlas, TerrainMaterial,
};

mod mesh_generator;

pub use mesh_generator::*;

/// Generates meshes for chunks that have `ChunkStorage` but no `Mesh3d` yet.
pub fn generate_chunk_mesh(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    terrain_material: Option<Res<TerrainMaterial>>,
    terrain_atlas: Option<Res<TerrainAtlas>>,
    atlas_layouts: Res<Assets<TextureAtlasLayout>>,
    chunks_without_meshes: Query<(Entity, &ChunkData), (With<Chunk>, Without<Mesh3d>)>,
    block_lookup: Query<&BlockTexture, With<Block>>,
) {
    // This system will run before `TerrainMaterial` is available, so to avoid
    // the system failing, we'll make the material and atlas an `Option`.
    // TODO: Should be able to be replaced with `When<>` once available in Bevy.
    let Some(terrain_material) = terrain_material else {
        return;
    };

    // Atlas and layout should exist at this point, if material does.
    let terrain_atlas = terrain_atlas.unwrap();
    let terrain_atlas_layout = atlas_layouts.get(&terrain_atlas.layout).unwrap();

    for (entity, storage) in chunks_without_meshes.iter() {
        let mesh = create_bloxel_mesh(
            storage.deref(),
            terrain_atlas_layout,
            &terrain_atlas.sources,
            &block_lookup,
        );

        commands.entity(entity).insert((
            Mesh3d(meshes.add(mesh)),
            MeshMaterial3d(terrain_material.0.clone()),
        ));
    }
}