/// <reference lib="webworker" />

import {
	block_light_emission,
	block_light_opacity,
	type BlockRegistry,
	type RenderLayer,
} from "$/common/everything_registry.ts";
import { AIR, CHUNK_HEIGHT, CHUNK_SIZE, ID_MASK, type SpriteRegion, TEXTURE_SIZE } from "$/common/constants.ts";
import type { Texture } from "../renderer/types.ts";
import { type FromChunkWorker, TERRAIN_VERTEX_FLOATS, type ToChunkWorker } from "./chunk_messages.ts";
import { generate_raw_chunk, WorldgenSetup } from "$/common/generation.ts";
import { load_worldgen } from "$/common/worldgen_loader.ts";
import { default_block_value } from "$/common/utils.ts";
import {
	choose_sort_type,
	FACE_NORMALS,
	quad_indices,
	quad_planes,
	sort_by_distance,
	sort_quads,
} from "./translucent_sort.ts";
import {
	LightRegion,
	type LightTables,
	region_block,
	region_block_light,
	REGION_LAYER,
	REGION_SIZE,
	region_sky,
	REGION_VOID,
} from "./lighting.ts";

type TexturesInfo = Record<string, SpriteRegion>;

const FLOATS_PER_QUAD = 4 * TERRAIN_VERTEX_FLOATS;
// keeps texture lookups off the sprite's edge
const UV_PAD = 0.5;

// same order as FACE_NORMALS in translucent_sort.ts
const FACES = ["top", "bottom", "front", "back", "left", "right"] as const;
// each face's corners in drawing order (counter clockwise from outside), as offsets from the block's corner
const FACE_CORNERS = [
	[[0, 1, 1], [1, 1, 1], [1, 1, 0], [0, 1, 0]],
	[[0, 0, 0], [1, 0, 0], [1, 0, 1], [0, 0, 1]],
	[[0, 0, 1], [1, 0, 1], [1, 1, 1], [0, 1, 1]],
	[[1, 0, 0], [0, 0, 0], [0, 1, 0], [1, 1, 0]],
	[[0, 0, 0], [0, 0, 1], [0, 1, 1], [0, 1, 0]],
	[[1, 0, 1], [1, 0, 0], [1, 1, 0], [1, 1, 1]],
] as const;
// which end of the sprite each corner gets, u then v (0 = start, 1 = end)
const CORNER_UVS = [[0, 1], [1, 1], [1, 0], [0, 0]] as const;
// minecraft's shading by direction, so faces stay apart even in flat light
const FACE_SHADE = [1.0, 0.5, 0.8, 0.8, 0.6, 0.6];

// for each face corner, the two cells beside the cell in front of the face that touch that corner,
// as [index offset, y offset] for each. the cell touching both is at the sum of them
const CORNER_SIDES = FACE_CORNERS.map((corners, face) =>
	corners.map((corner) => {
		const sides: number[] = [];
		for (let axis = 0; axis < 3; axis++) {
			if (FACE_NORMALS[face][axis] !== 0) continue;
			const d = corner[axis] * 2 - 1;
			sides.push(axis === 0 ? d : axis === 1 ? d * REGION_LAYER : d * REGION_SIZE, axis === 1 ? d : 0);
		}
		return sides;
	})
);

const SOLID = 0;
const CUTOUT = 1;
const TRANSLUCENT = 2;
const LAYER_IDS: Record<RenderLayer, number> = { solid: SOLID, cutout: CUTOUT, translucent: TRANSLUCENT };

let blocks_registry: BlockRegistry[] = [];
let block_ids: Record<string, number> = {};
// by numeric id, looked up for every face. like sodium's light data cache, everything the mesher asks about a
// block is worked out once instead of per face
const TABLE_SIZE = ID_MASK + 1;
const block_layers = new Uint8Array(TABLE_SIZE);
const block_cull_same = new Uint8Array(TABLE_SIZE);
// darkens the corners it touches (minecraft's ambient occlusion), blocks with a full collision box do
const block_occludes = new Uint8Array(TABLE_SIZE);
// light can come around a corner past it
const block_lets_light_by = new Uint8Array(TABLE_SIZE);
const light_tables: LightTables = { opacity: new Uint8Array(TABLE_SIZE), emission: new Uint8Array(TABLE_SIZE) };
const region = new LightRegion();

let textures_info: TexturesInfo = {};
let image: Texture;
let worldgen: WorldgenSetup | undefined;
// numeric id to what a generated block stores, with its default states. matches the server
let default_values: number[] = [];
// generating has to wait for mods' worldgen scripts, or this worker's terrain wouldn't match the server's
let worldgen_ready: Promise<void> = Promise.resolve();

self.onmessage = async (event: MessageEvent<ToChunkWorker>) => {
	const message = event.data;
	switch (message.type) {
		case "init":
			blocks_registry = message.blocks_registry;
			block_ids = message.block_ids;
			build_block_tables();
			textures_info = message.textures_info;
			image = message.image as Texture;
			default_values = blocks_registry.map((block, nid) => default_block_value(nid, block));
			worldgen_ready = load_worldgen(message.worldgen_scripts, message.ores).then((setup) => {
				worldgen = setup;
			});
			break;
		case "generate":
			await worldgen_ready;
			generate(message.chunk_x, message.chunk_z, message.seed);
			break;
		case "mesh": {
			region.fill(message.chunks);
			region.compute(light_tables);
			const { solid, cutout, translucent } = make_chunk_mesh(message.chunk_x, message.chunk_z, message.camera);
			post(
				{
					type: "meshed",
					chunk_x: message.chunk_x,
					chunk_z: message.chunk_z,
					version: message.version,
					solid,
					cutout,
					translucent,
					camera: message.camera,
				},
				[
					solid.vertices.buffer,
					cutout.vertices.buffer,
					translucent.vertices.buffer,
					translucent.indices.buffer,
					translucent.centers.buffer,
					...translucent.planes.map((planes) => planes.buffer),
				],
			);
			break;
		}
		case "sort": {
			const [x, y, z] = message.camera;
			const indices = quad_indices(sort_by_distance(message.centers, message.centers.length / 3, x, y, z));
			post({
				type: "sorted",
				chunk_x: message.chunk_x,
				chunk_z: message.chunk_z,
				version: message.version,
				sort_version: message.sort_version,
				indices,
			}, [indices.buffer]);
			break;
		}
	}
};

function post(message: FromChunkWorker, transfer: Transferable[]) {
	self.postMessage(message, transfer);
}

function generate(chunk_x: number, chunk_z: number, seed: string) {
	const { blocks, spills } = generate_raw_chunk(chunk_x, chunk_z, seed, block_ids, worldgen, default_values);
	post({ type: "generated", chunk_x, chunk_z, blocks, spills }, [blocks.buffer, spills.buffer]);
}

function build_block_tables() {
	blocks_registry.forEach((block, nid) => {
		if (!block || nid === AIR) return;
		const layer = LAYER_IDS[block.render_layer ?? "solid"];
		const opacity = block_light_opacity(block);
		block_layers[nid] = layer;
		block_cull_same[nid] = (block.cull_same ?? layer === TRANSLUCENT) ? 1 : 0;
		block_occludes[nid] = block.has_collision && layer !== TRANSLUCENT ? 1 : 0;
		block_lets_light_by[nid] = layer !== SOLID || opacity === 0 ? 1 : 0;
		light_tables.opacity[nid] = opacity;
		light_tables.emission[nid] = block_light_emission(block);
	});
	block_lets_light_by[AIR] = 1;
	block_layers[REGION_VOID] = SOLID;
	block_occludes[REGION_VOID] = 1;
	light_tables.opacity[REGION_VOID] = 15;
}

// the rule vanilla minecraft (and so sodium) uses: solid neighbors hide a face, and some blocks
// hide faces between two of themselves
function show_face(block: number, neighbor: number) {
	if (neighbor === AIR) return true;
	if (block_layers[neighbor] === SOLID) return false;
	return !(neighbor === block && block_cull_same[block]);
}

// per corner of the face being built
const corner_sky = new Float32Array(4);
const corner_block = new Float32Array(4);
const corner_ao = new Float32Array(4);

// minecraft's smooth lighting: each corner averages the light of the cell in front of the face and the three
// cells around it that touch the corner, and gets darker for each of those that's a full block
function light_face_corners(face: number, front: number, front_y: number) {
	const front_id = region_block(region, front, front_y);
	const front_sky = region_sky(region, front, front_y);
	const front_block = region_block_light(region, front, front_y);
	const front_ao = block_occludes[front_id] ? 0.2 : 1;

	for (let corner = 0; corner < 4; corner++) {
		const [a_offset, a_dy, b_offset, b_dy] = CORNER_SIDES[face][corner];
		const a = front + a_offset;
		const a_y = front_y + a_dy;
		const b = front + b_offset;
		const b_y = front_y + b_dy;
		const a_id = region_block(region, a, a_y);
		const b_id = region_block(region, b, b_y);

		let a_sky = region_sky(region, a, a_y);
		let a_block = region_block_light(region, a, a_y);
		let b_sky = region_sky(region, b, b_y);
		let b_block = region_block_light(region, b, b_y);
		const a_ao = block_occludes[a_id] ? 0.2 : 1;
		const b_ao = block_occludes[b_id] ? 0.2 : 1;

		// with both sides closed the corner cell can't be seen, vanilla uses a side's values instead
		let c_sky = a_sky;
		let c_block = a_block;
		let c_ao = a_ao;
		if (block_lets_light_by[a_id] || block_lets_light_by[b_id]) {
			const c = a + b_offset;
			const c_y = a_y + b_dy;
			c_sky = region_sky(region, c, c_y);
			c_block = region_block_light(region, c, c_y);
			c_ao = block_occludes[region_block(region, c, c_y)] ? 0.2 : 1;
		}

		// cells with no light at all are usually inside solid blocks, vanilla counts them as the front cell
		// so corners against walls don't go black
		if (a_sky === 0 && a_block === 0) {
			a_sky = front_sky;
			a_block = front_block;
		}
		if (b_sky === 0 && b_block === 0) {
			b_sky = front_sky;
			b_block = front_block;
		}
		if (c_sky === 0 && c_block === 0) {
			c_sky = front_sky;
			c_block = front_block;
		}

		corner_sky[corner] = (a_sky + b_sky + c_sky + front_sky) / 4;
		corner_block[corner] = (a_block + b_block + c_block + front_block) / 4;
		corner_ao[corner] = (a_ao + b_ao + c_ao + front_ao) / 4;
	}
}

// sodium's rule for which diagonal splits the quad: the brighter one, otherwise the ambient occlusion
// gets smeared across the whole face
function should_flip() {
	const ao_02 = corner_ao[0] + corner_ao[2];
	const ao_13 = corner_ao[1] + corner_ao[3];
	if (ao_02 !== ao_13) {
		return ao_02 < ao_13;
	}
	const light = (corner: number) => corner_sky[corner] * 16 + corner_block[corner];
	return light(0) + light(2) > light(1) + light(3);
}

function push_quad(
	vertices: Float32Array,
	i: number,
	face: number,
	x: number,
	y: number,
	z: number,
	sprite: SpriteRegion,
	alpha: number,
) {
	const u0 = (sprite.x * TEXTURE_SIZE + UV_PAD) / image.width;
	const v0 = (sprite.y * TEXTURE_SIZE + UV_PAD) / image.height;
	const u1 = ((sprite.x + 1) * TEXTURE_SIZE - UV_PAD) / image.width;
	const v1 = ((sprite.y + 1) * TEXTURE_SIZE - UV_PAD) / image.height;
	const shade = FACE_SHADE[face];
	// starting from the second corner moves the diagonal, the winding stays the same
	const first = should_flip() ? 1 : 0;

	for (let k = 0; k < 4; k++) {
		const corner = (first + k) & 3;
		const [cx, cy, cz] = FACE_CORNERS[face][corner];
		const [cu, cv] = CORNER_UVS[corner];
		const brightness = shade * corner_ao[corner];
		vertices[i++] = x + cx;
		vertices[i++] = y + cy;
		vertices[i++] = z + cz;
		vertices[i++] = cu ? u1 : u0;
		vertices[i++] = cv ? v1 : v0;
		vertices[i++] = brightness;
		vertices[i++] = brightness;
		vertices[i++] = brightness;
		vertices[i++] = alpha;
		// where to read the lightmap, block light across and sky light down
		vertices[i++] = (corner_block[corner] + 0.5) / 16;
		vertices[i++] = (corner_sky[corner] + 0.5) / 16;
	}
	return i;
}

// region has to be filled and lit first
function make_chunk_mesh(chunk_x: number, chunk_z: number, camera: number[]) {
	const layers = [SOLID, CUTOUT, TRANSLUCENT].map(() => ({ vertices: new Float32Array(4096), floats: 0 }));
	// for sorting the translucent quads
	let centers = new Float32Array(256);
	let faces = new Uint8Array(256);

	// where the neighbor on each face is, same order as FACES
	const face_offsets = FACE_NORMALS.map(([nx, ny, nz]) => nx + ny * REGION_LAYER + nz * REGION_SIZE);

	for (let y = 0; y < CHUNK_HEIGHT; y++) {
		for (let z = 0; z < CHUNK_SIZE; z++) {
			for (let x = 0; x < CHUNK_SIZE; x++) {
				// the middle chunk of the region
				const index = y * REGION_LAYER + (z + CHUNK_SIZE) * REGION_SIZE + x + CHUNK_SIZE;
				const block_nid = region.blocks[index];
				if (block_nid === AIR) continue;

				const block_info = blocks_registry[block_nid];
				const layer_id = block_layers[block_nid];
				const layer = layers[layer_id];
				const alpha = layer_id === TRANSLUCENT ? block_info.alpha ?? 1 : 1;

				const texture_ids = {
					top: "engine:missing",
					bottom: "engine:missing",
					front: "engine:missing",
					back: "engine:missing",
					left: "engine:missing",
					right: "engine:missing",
				};

				const textures = block_info.textures;
				if (!textures) throw new Error(`no textures for ${block_nid}`);

				if (typeof textures === "string") {
					texture_ids.top = textures;
					texture_ids.bottom = textures;
					texture_ids.front = textures;
					texture_ids.back = textures;
					texture_ids.left = textures;
					texture_ids.right = textures;
				} else if ("top" in textures && "bottom" in textures && "side" in textures) {
					texture_ids.top = textures.top;
					texture_ids.bottom = textures.bottom;
					texture_ids.front = textures.side;
					texture_ids.back = textures.side;
					texture_ids.left = textures.side;
					texture_ids.right = textures.side;
				} else if ("front" in textures && "side" in textures) {
					texture_ids.top = textures.side;
					texture_ids.bottom = textures.side;
					texture_ids.front = textures.front;
					texture_ids.back = textures.side;
					texture_ids.left = textures.side;
					texture_ids.right = textures.side;
				}

				const wx = chunk_x * CHUNK_SIZE + x;
				const wz = chunk_z * CHUNK_SIZE + z;

				for (let face = 0; face < 6; face++) {
					const front = index + face_offsets[face];
					const front_y = y + FACE_NORMALS[face][1];
					if (!show_face(block_nid, region_block(region, front, front_y))) {
						continue;
					}

					light_face_corners(face, front, front_y);
					layer.vertices = ensure_capacity(layer.vertices, layer.floats + FLOATS_PER_QUAD);
					layer.floats = push_quad(
						layer.vertices,
						layer.floats,
						face,
						wx,
						y,
						wz,
						textures_info[texture_ids[FACES[face]]],
						alpha,
					);

					if (layer_id === TRANSLUCENT) {
						const quad = layer.floats / FLOATS_PER_QUAD - 1;
						centers = ensure_capacity(centers, (quad + 1) * 3);
						faces = ensure_capacity(faces, quad + 1);
						const [nx, ny, nz] = FACE_NORMALS[face];
						centers[quad * 3] = wx + 0.5 + nx * 0.5;
						centers[quad * 3 + 1] = y + 0.5 + ny * 0.5;
						centers[quad * 3 + 2] = wz + 0.5 + nz * 0.5;
						faces[quad] = face;
					}
				}
			}
		}
	}

	const [solid, cutout, translucent] = layers.map((layer) => ({
		vertices: layer.vertices,
		quad_count: layer.floats / FLOATS_PER_QUAD,
	}));

	const quads = { centers, faces, count: translucent.quad_count };
	const sort_type = choose_sort_type(quads);
	const [camera_x, camera_y, camera_z] = camera;

	return {
		solid,
		cutout,
		translucent: {
			...translucent,
			indices: sort_quads(quads, sort_type, camera_x, camera_y, camera_z),
			sort_type,
			centers: centers.slice(0, quads.count * 3),
			planes: quad_planes(quads),
		},
	};
}

function ensure_capacity<T extends Float32Array<ArrayBuffer> | Uint8Array<ArrayBuffer>>(
	buffer: T,
	required: number,
): T {
	if (required <= buffer.length) return buffer;

	let new_length = buffer.length;
	while (new_length < required) {
		new_length *= 2;
	}

	const new_buffer = new (buffer.constructor as new (length: number) => T)(new_length);
	new_buffer.set(buffer as ArrayLike<number>);
	return new_buffer;
}