use dejson;
use encoding::json;
use fmt;
use gl::*;
use io;
use math;
use strings;
use trace;

let ATLAS_BLOCKS = ATLAS_EMPTY;

fn load_atlases(assets: *Pack) void = {
	ATLAS_BLOCKS = load_atlas("minecraft:blocks", assets);
};

type Atlas = struct {
	sprites: ObjectRegistry,
	width: u32,
	gl_texture: uint,
};

type Sprite = struct {
	Object,
	texture: *Texture,
	width: u32,
	height: u32,
	x: u32,
	y: u32,
};

def ATLAS_EMPTY = Atlas {
	sprites = OBJREG_EMPTY,
	...
};

fn atlas_findsprite(atlas: *Atlas, ident: str) nullable *Sprite =
	objreg_find(&atlas.sprites, ident): nullable *Sprite;

fn load_atlas(ident: str, assets: *Pack) Atlas = {
	trace::info(&trace::root, "loading atlas {}...", ident);
	const tr = trace::ctx(&trace::root, "load atlas {}", ident);

	const json = match (resource_load_json(
		assets, "atlases", ident, ".json", &tr)) {
	case let json: json::value =>
		yield json;
	case trace::failed =>
		abort("TODO fallback");
	};
	defer json::finish(json);

	const deser = dejson::newdeser(&json);
	const decl = match (deser_atlas_decl(&deser)) {
	case let x: AtlasDecl =>
		yield x;
	case let err: dejson::error =>
		trace::error(&tr, "deser: {}", err): void;
		abort("TODO fallback");
	};
	defer atlas_decl_finish(decl);

	let sprites = newobjreg();
	load_atlas_register_sprite(MISSINGNO,
		textures_find(MISSINGNO) as *Texture, &sprites, &tr);
	for (let i = len(decl.sources); i > 0) {
		i -= 1;
		load_atlas_search_source(&decl.sources[i], &sprites, &tr);
	};

	const max_cells = TEXTURES_MAX_WIDTH: u32 >> 4;
	const max_cells = max_cells * max_cells;

	let ncells = 0u32;
	let sizes: [8][]*Sprite = [[]...];
	defer for (let i = 0z; i < len(sizes); i += 1) {
		free(sizes[i]);
	};
	let fits = true;
	let it = objreg_iter(&sprites);
	for (true) match (objreg_next(&it)) {
	case let spr: *Object =>
		const spr = spr: *Sprite;
		const imgsize = if (spr.width > spr.height)
			spr.width else spr.height;
		const slotsize = math::bit_size_u32(imgsize: u32 - 1) - 4;
		const slotcells = 1 << (slotsize: u32 << 1);
		if (ncells + slotcells > max_cells) {
			fits = false;
			continue;
		};
		ncells += slotcells;
		append(sizes[slotsize], spr);
	case null => break;
	};
	if (!fits) {
		trace::error(&tr,
			"Can't fit all sprites in image (max width {})",
			TEXTURES_MAX_WIDTH): void;
	};

	// Reference: https://lisyarus.github.io/blog/graphics/2022/08/06/texture-packing.html
	// TODO: make extra sure this impl is correct this time...
	const gridsize: u16 = math::bit_size_u32(ncells - 1);
	const gridsize = (gridsize >> 1) + (gridsize & 1); // ceil(gridsize / 2)
	const gridsize = 1 << gridsize;
	const width = gridsize << 4;

	let gl_texture: uint = 0;
	glGenTextures(1, &gl_texture);
	glBindTexture(GL_TEXTURE_2D, gl_texture);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
		GL_NEAREST_MIPMAP_LINEAR: i32);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
		GL_NEAREST: i32);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 4);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_SRGB8_ALPHA8: i32,
		width: i32, width: i32, 0, GL_RGBA, GL_UNSIGNED_BYTE, null);

	let pbo = 0u;
	glGenBuffers(1, &pbo);
	defer glDeleteBuffers(1, &pbo);
	glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);

	let steps: [8][2]u32 = [[0, gridsize]...];
	let steps = steps[..1];
	let pos: [2]u32 = [0...];
	for (let slotsize = len(sizes): u32; slotsize > 0) {
		slotsize -= 1;
		const slots = &sizes[slotsize];
		const slotwidth = 1 << slotsize;
		if (pos[0] > steps[len(steps) - 1][0]) {
			static append(steps, [pos[0], pos[1] + 2 * slotwidth]);
		};
		for (let i = 0z; i < len(slots); i += 1) {
			const spr = slots[i];

			spr.x = pos[0] << 4;
			spr.y = pos[1] << 4;

			load_atlas_upload_sprite(spr, &tr);

			pos[0] += slotwidth;
			if (pos[0] == gridsize) {
				pos[0] = steps[len(steps) - 1][0];
				pos[1] += slotwidth;
				if (len(steps) != 1 && pos[1] + slotwidth
						== steps[len(steps) - 1][1]) {
					static delete(steps[len(steps) - 1]);
				};
			};
		};
	};

	glGenerateMipmap(GL_TEXTURE_2D);

	return Atlas {
		sprites = sprites,
		width = width,
		gl_texture = gl_texture,
	};
};
fn load_atlas_search_source(
	source: *AtlasDeclSource,
	sprites: *ObjectRegistry,
	tr: *trace::tracer,
) void = {
	match (*source) {
	case let source: AtlasDeclSourceDir =>
		const srcpath = strings::trimsuffix(source.source, "/");
		const srcpath = strings::concat(srcpath, "/");
		defer free(srcpath);

		let it = textures_iter();
		for (true) match (textures_next(&it)) {
		case let tex: *Texture =>
			const (ns, name) = ident_split(tex.name);
			if (strings::hasprefix(name, srcpath)) {
				const name = strings::trimprefix(name, srcpath);
				const ident = strings::concat(
					ns, ":", source.prefix, name);
				defer free(ident);
				load_atlas_register_sprite(
					ident, tex, sprites, tr);
			};
		case null => break;
		};
	case let source: AtlasDeclSourceSingle =>
		match (textures_find(source.resource)) {
		case let tex: *Texture =>
			load_atlas_register_sprite(
				source.sprite, tex, sprites, tr);
		case null =>
			trace::error(tr, "Unknown texture {}",
				source.resource): void;
		};
	};
};

fn load_atlas_register_sprite(
	ident: str,
	tex: *Texture,
	sprites: *ObjectRegistry,
	tr: *trace::tracer,
) void = {
	const tr = trace::ctx(tr, "sprite {}", ident);

	if (!(objreg_find(sprites, ident) is null)) {
		return;
	};

	const spr = alloc(Sprite {
		name = strings::dup(ident),
		texture = tex,
		width = tex.width,
		height = tex.height,
		...
	});
	objreg_register(sprites, spr);

	// TODO: once mipmapping works properly, there's probably no reason to
	// forbid non-16-pixel-aligned textures.
	if (spr.width == 0 || spr.height == 0
			|| spr.width & 7 != 0 || spr.height & 7 != 0
			|| spr.width > 2048 || spr.height > 2048) {
		trace::error(&tr, "Invalid dimensions: {}, {}",
			spr.width, spr.height): void;
		spr.texture = textures_find(MISSINGNO) as *Texture;
		spr.width = spr.texture.width;
		spr.height = spr.texture.height;
	};
};

fn load_atlas_upload_sprite(spr: *Sprite, tr: *trace::tracer) void = {
	const tr = trace::ctx(tr, "sprite {}", spr.name);

	const tex = spr.texture;
	const bufsize = tex.width * tex.height * 4;

	for (true) {
		glBufferData(GL_PIXEL_UNPACK_BUFFER,
			bufsize: uintptr, null, GL_STREAM_DRAW);
		const pixels = glMapBufferRange(GL_PIXEL_UNPACK_BUFFER,
			0, bufsize: uintptr, GL_MAP_WRITE_BIT) as *opaque;
		texture_load(tex, pixels: *[*]u8, tex.width * 4, &tr);
		if (glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER) == GL_TRUE) {
			break;
		};
		trace::warn(&tr,
			"glUnmapBuffer returned false; retrying upload");
	};

	glTexSubImage2D(GL_TEXTURE_2D, 0, spr.x: i32, spr.y: i32,
		spr.width: i32, spr.height: i32,
		GL_RGBA, GL_UNSIGNED_BYTE, null);
};

type AtlasDecl = struct {
	sources: []AtlasDeclSource,
};

type AtlasDeclSource = (AtlasDeclSourceDir | AtlasDeclSourceSingle);
type AtlasDeclSourceDir = struct {
	source: str,
	prefix: str,
};
type AtlasDeclSourceSingle = struct {
	resource: str,
	sprite: str,
};

fn atlas_decl_finish(decl: AtlasDecl) void = {
	for (let i = 0z; i < len(decl.sources); i += 1) {
		atlas_decl_source_finish(decl.sources[i]);
	};
	free(decl.sources);
};

fn atlas_decl_source_finish(source: AtlasDeclSource) void = {
	match (source) {
	case let source: AtlasDeclSourceDir =>
		free(source.source);
		free(source.prefix);
	case let source: AtlasDeclSourceSingle =>
		free(source.resource);
		free(source.sprite);
	};
};

fn deser_atlas_decl(de: *dejson::deser) (AtlasDecl | dejson::error) = {
	let success = false;

	wassert_fields(de, "sources")?;

	const de_sources = dejson::field(de, "sources")?;
	let nsources = dejson::length(&de_sources)?;
	let res = AtlasDecl {
		sources = alloc([], nsources),
	};
	defer if (!success) atlas_decl_finish(res);
	for (let i = 0z; i < nsources; i += 1) {
		const de_source = dejson::index(&de_sources, i)?;

		const srctype = dejson::field(&de_source, "type")?;
		const srctype = dejson::string(&srctype)?;
		switch (srctype) {
		case "directory" =>
			const source = dejson::field(&de_source, "source")?;
			const source = dejson::string(&source)?;
			const prefix = dejson::field(&de_source, "prefix")?;
			const prefix = dejson::string(&prefix)?;
			append(res.sources, AtlasDeclSourceDir {
				source = strings::dup(source),
				prefix = strings::dup(prefix),
			});
		case "single" =>
			const resource = dejson::field(&de_source, "resource")?;
			const resource = dejson::string(&resource)?;
			const sprite = match (
				dejson::optfield(&de_source, "sprite")?) {
			case let de_sprite: dejson::deser =>
				yield dejson::string(&de_sprite)?;
			case void =>
				yield resource;
			};
			append(res.sources, AtlasDeclSourceSingle {
				resource = ident_qual(resource),
				sprite = ident_qual(sprite),
			});
		case =>
			return dejson::fail(&de_source,
				"Unknown source type {}", srctype);
		};
	};

	success = true;
	return res;
};