const fs = require('fs');
const path = require('path');
const os = require('os');
const http = require('http');
const crypto = require('crypto');
const zlib = require('zlib');
const utils = require('./../js/spine-utils.js');
const render = require('./../js/spine-render.js');

/** 简易日志（写入插件目录 thumbnails.log，便于诊断 Eagle 中的间歇失败） */
function log(msg) {
	try {
		const logPath = path.join(__dirname, '..', 'thumbnails.log');
		fs.appendFileSync(logPath, '[' + new Date().toISOString() + '] ' + msg + '\n');
	} catch (e) { /* ignore */ }
}

const sleep = (ms) => new Promise((r) => setTimeout(r, ms));
const discoveryJobs = new Map();
const renderJobs = new Map();
const refreshJobs = new Map();

/** 插件代码版本：每次改动递增，用于确认 Eagle 是否加载到最新代码 */
const VERSION = 'v14';

function coordinationKey(src) {
	const root = utils.findLibraryRoot(src) || path.dirname(path.dirname(src));
	const folders = utils.foldersOfItem(src).slice().sort().join(',') || 'unfiled';
	return root + '|' + folders + '|' + utils.normalizeStem(path.basename(src));
}

/** 返回资源当前的尺寸/修改时间签名，同时确认 atlas 引用的全部贴图均已落盘。 */
function assetSignature(assets) {
	if (!assets || !assets.skeletonPath || !assets.atlasPath) return null;
	let atlasText = '';
	try { atlasText = fs.readFileSync(assets.atlasPath, 'utf8'); } catch (e) { return null; }
	const pages = utils.parseAtlasPages(atlasText);
	if (pages.length === 0 || pages.some((name) => !assets.texturePaths[name])) return null;
	const paths = [assets.skeletonPath, assets.atlasPath].concat(pages.map((name) => assets.texturePaths[name]));
	const stats = [];
	for (const file of paths) {
		try {
			const stat = fs.statSync(file);
			if (!stat.isFile() || stat.size === 0) return null;
			stats.push(file + ':' + stat.size + ':' + Math.round(stat.mtimeMs));
		} catch (e) {
			return null;
		}
	}
	return stats.join('|');
}

/**
 * Eagle 拖入一组文件时会并发触发 atlas/json/skel 的缩略图回调，而文件内容和
 * folders 元数据仍可能继续写入。等同批资源连续三次保持不变后再渲染，避免把
 * 半截 atlas 或旧库中的同名骨骼渲染成占位图。
 */
async function runDiscovery(src, retries, delay) {
	let assets = null;
	let previousSignature = null;
	let stableCount = 0;
	for (let i = 0; i < retries; i++) {
		// 前台缩略图回调只接受同批资源，绝不借用库里旧的同名 atlas/贴图。
		// 分批拖入的跨批次补齐统一交给后台任务处理。
		assets = utils.discoverAssets(src, {
			strictStem: true,
			allowCrossBatch: false,
			refreshIndex: i > 0,
		});
		const signature = assetSignature(assets);
		if (signature && signature === previousSignature) stableCount += 1;
		else stableCount = signature ? 1 : 0;
		previousSignature = signature;
		if (stableCount >= 3) return assets;
		if (i < retries - 1) await sleep(delay);
	}
	return assets;
}

/** 同一资源组的 atlas/json/skel 回调共享发现任务，避免大批量导入时重复全库扫描。 */
async function discoverWithRetry(src, retries = 5, delay = 120) {
	const key = coordinationKey(src);
	if (discoveryJobs.has(key)) return discoveryJobs.get(key);
	const job = runDiscovery(src, retries, delay);
	discoveryJobs.set(key, job);
	try {
		return await job;
	} finally {
		if (discoveryJobs.get(key) === job) discoveryJobs.delete(key);
	}
}

/** JSON 仍在落盘时只做极短等待；普通 JSON 一经确认便立即退出 Spine 流程。 */
async function classifyJsonBriefly(src) {
	let kind = 'pending';
	for (let i = 0; i < 3; i++) {
		kind = utils.classifySkeletonJson(src);
		if (kind !== 'pending') return kind;
		if (i < 2) await sleep(80);
	}
	return kind;
}

/** 同一份稳定资源只渲染一次，atlas/json/skel 并发回调共享输出 Buffer。 */
async function renderThumbnailShared(assets, options) {
	const key = assetSignature(assets) + '|' + options.version + '|' + options.runtimeDir + '|' + options.size;
	if (renderJobs.has(key)) {
		log('复用同组渲染结果: ' + (assets.base || path.basename(options.skeletonPath)));
		return renderJobs.get(key);
	}
	log('开始同组统一渲染: ' + (assets.base || path.basename(options.skeletonPath)));
	const job = render.renderThumbnail(options);
	renderJobs.set(key, job);
	try {
		return await job;
	} finally {
		setTimeout(() => { if (renderJobs.get(key) === job) renderJobs.delete(key); }, 2000);
	}
}

/**
 * Eagle 格式扩展缩略图处理函数。
 * 参数：{ src, dest, item }
 *  - src  : 原始文件路径（skel/skel.bytes/json/atlas/atlas.txt）
 *  - dest : 需要生成的缩略图 PNG 路径
 *  - item : 当前 item 对象（可更新宽高）
 */
module.exports = async (options) => {
	const { src, dest, item } = options;
	const changed = require('../js/eagle-compound.js').normalizeItem(src, item);
	// Eagle originally chooses the cache name before invoking the plugin.
	// Supply that requested output as well as the corrected compound-name cache.
	const canonical = changed && path.basename(dest).endsWith('_thumbnail.png')
		? path.join(path.dirname(dest), item.name + '_thumbnail.png') : dest;
	const result = await generate({ ...options, deferRefresh: changed });
	if (canonical !== dest && fs.existsSync(dest)) {
		if (render.canvasLib) {
			const image = await render.canvasLib.loadImage(dest);
			const canvas = render.canvasLib.createCanvas(image.width, image.height);
			canvas.getContext('2d').drawImage(image, 0, 0);
			fs.writeFileSync(canonical, await canvas.encode('webp', 90));
		} else fs.copyFileSync(dest, canonical);
	}
	if (changed && item.id) {
		log('复合后缀元数据已规范化: name=' + item.name + ' ext=' + item.ext);
	}
	const ext = utils.extOf(path.basename(src));
	if (!item.isDeleted && (utils.isAtlasFile(src) || (utils.isSkeletonFile(src) && (ext !== '.json' || utils.classifySkeletonJson(src) === 'spine')))) scheduleBackgroundReconcile(src);
	return result;
};

async function generate({ src, dest, item, deferRefresh }) {
	try {
		// 记录 Eagle 传入的关键信息，便于诊断 src/item 的实际形态
		log('HIT ' + VERSION + ' src=' + src + ' (isTexture=' + utils.isTextureFile(src) + ')');
		try {
			log('  item keys=' + Object.keys(item || {}).join(',') + ' | name=' + (item && item.name) + ' | id=' + (item && item.id) + ' | ext=' + (item && item.ext) + ' | isDeleted=' + (item && item.isDeleted));
		} catch (e) { /* ignore */ }

		// —— 守护：若 src 文件在库中不存在（可能是回收站 isDeleted 残留 / 临时 id），
		// 且 item 标记为已删除，则跳过，避免生成破碎/占位缩略图，交由 Eagle 自身处理。
		if (item && item.isDeleted) {
			log('  skip: item.isDeleted=true');
			return resolve(item);
		}

		// —— 防御：若 src 是图片（png/jpg/jpeg/webp），不生成占位图，
		// 而是把原始图片复制/转换为缩略图，交由系统展示真实内容。
		const srcExt = utils.extOf(path.basename(src));
		// Eagle dispatches compound suffixes as txt/bytes. Only the complete
		// .atlas.txt/.skel.bytes names enter Spine discovery; ordinary files exit.
		if (!srcExt) {
			if (/\.txt$/i.test(src)) {
				// Eagle's native text card requires item.text, even for an empty file.
				item.text = '';
				const fd = fs.openSync(src, 'r');
				try { const buffer = Buffer.alloc(32768); item.text = buffer.subarray(0, fs.readSync(fd, buffer, 0, buffer.length, 0)).toString('utf8'); }
				finally { fs.closeSync(fd); }
			}
			await writeNeutralJsonPlaceholder(dest);
			item.width = 400; item.height = 400;
			return resolve(item);
		}
		if (utils.isTextureFile(src) || srcExt === '.png' || srcExt === '.jpg' || srcExt === '.jpeg' || srcExt === '.webp') {
			await copyImageAsThumb(src, dest);
			try { const s = imageSizeOf(dest); item.width = s.width || item.width; item.height = s.height || item.height; } catch (e) {}
			return resolve(item);
		}

		// manifest 只能按扩展名接管 JSON，不能按文件内容过滤。因此先做低成本内容判定：
		// 普通 JSON 立即生成中性缩略图，不扫描资源库，也不启动后台补刷。
		if (srcExt === '.json') {
			const jsonKind = await classifyJsonBriefly(src);
			if (jsonKind === 'other') {
				log('普通 JSON，跳过 Spine 资源发现: ' + src);
				await writeNeutralJsonPlaceholder(dest);
				item.width = 400; item.height = 400;
				return resolve(item);
			}
		}

		let assets = await discoverWithRetry(src);

		// 找不到完整 Spine 资源链（骨骼 + atlas + atlas 引用的全部贴图）
		if (!assets.skeletonPath || !assets.atlasPath || !assetSignature(assets)) {
			log('未找到配套资源: ' + src + ' (skeleton=' + !!assets.skeletonPath + ', atlas=' + !!assets.atlasPath + ')');
			if (assets.atlasPath && await writeAtlasFallback(assets, dest)) {
				item.width = 400; item.height = 400;
				return resolve(item);
			}
			await writePlaceholder(dest);
			item.width = 400; item.height = 400;
			return resolve(item);
		}

		let version = utils.detectVersion(assets.skeletonPath);
		let runtimeDir = utils.chooseRuntimeDir(version, assets.isBinary);

		if (!runtimeDir) {
			if (await writeAtlasFallback(assets, dest)) {
				if (!deferRefresh) await refreshRelatedThumbnails(assets, dest, item && item.id);
				item.width = 400; item.height = 400;
				return resolve(item);
			}
			await writePlaceholder(dest);
			item.width = 400; item.height = 400;
			return resolve(item);
		}

		// 渲染首帧到 PNG。若导入过程恰好仍在写大文件，重新发现稳定资源再试，
		// 每次都会重新匹配同批 atlas/json/skel，而不是重复读取原来的错误组合。
		let png = null;
		let lastRenderError = null;
		for (let attempt = 0; attempt < 3; attempt++) {
			try {
				png = await renderThumbnailShared(assets, {
					skeletonPath: assets.skeletonPath,
					atlasPath: assets.atlasPath,
					texturePaths: assets.texturePaths,
					version,
					runtimeDir,
					size: 400,
				});
				break;
			} catch (e) {
				lastRenderError = e;
				log('renderThumbnail 第 ' + (attempt + 1) + ' 次失败: ' + (e && e.message) + '，重新等待同批资源...');
				if (attempt === 2) break;
				await sleep(500);
				assets = await discoverWithRetry(src, 4, 150);
				if (!assets.skeletonPath || !assets.atlasPath || !assetSignature(assets)) continue;
				version = utils.detectVersion(assets.skeletonPath);
				runtimeDir = utils.chooseRuntimeDir(version, assets.isBinary);
			}
		}
		if (!png) {
			if (await writeAtlasFallback(assets, dest)) {
				log('骨骼无法解析，已使用 atlas 贴图缩略图: ' + src);
				if (!deferRefresh) await refreshRelatedThumbnails(assets, dest, item && item.id);
				item.width = 400; item.height = 400;
				return resolve(item);
			}
			throw lastRenderError || new Error('Spine 资源尚未写入完成');
		}

		fs.writeFileSync(dest, png);
		if (!deferRefresh) await refreshRelatedThumbnails(assets, dest, item && item.id);

		try {
			const size = imageSizeOf(dest);
			item.width = size.width || 400;
			item.height = size.height || 400;
		} catch (e) { /* ignore */ }

		return Promise.resolve(item);
	} catch (err) {
		// 兜底：总是生成一张有效 PNG，绝不 reject，避免 Eagle 显示默认图标
		log('缩略图处理异常: ' + (err && err.message) + '\n' + ((err && err.stack) || ''));
		try {
			await writePlaceholder(dest);
			item.width = 400;
			item.height = 400;
			return resolve(item);
		} catch (e2) {
			// 最后兜底：写入一张最小 1x1 PNG
			try { fs.writeFileSync(dest, Buffer.from('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+M8AAAMBAQDJ/pLvAAAAAElFTkSuQmCC', 'base64')); } catch (e3) {}
			item.width = 400; item.height = 400;
			return resolve(item);
		}
	}
};

function resolve(item) {
	return item;
}

function itemIdFromAssetPath(filePath) {
	const match = path.basename(path.dirname(filePath)).match(/^(.+)\.info$/i);
	return match ? match[1] : null;
}

async function setEagleCustomThumbnail(itemId, thumbnailPath, expectedFilename) {
	if (expectedFilename) {
		// Eagle's foreground may still hold the old name after a type change.
		// Do not let setCustomThumbnail persist that stale name back to metadata.
		const info = await new Promise((resolveInfo, rejectInfo) => {
			const req = http.get('http://127.0.0.1:41595/api/item/info?id=' + encodeURIComponent(itemId), response => {
				let body = ''; response.on('data', chunk => { body += chunk; });
				response.on('end', () => {
					try { const result = JSON.parse(body); if (result.status !== 'success') throw new Error('Eagle 素材尚未入库'); resolveInfo(result.data); }
					catch (error) { rejectInfo(error); }
				});
			});
			req.setTimeout(3000, () => req.destroy(new Error('Eagle 素材信息请求超时'))); req.on('error', rejectInfo);
		});
		if (!info || info.name + '.' + info.ext !== expectedFilename) throw new Error('Eagle 尚未同步复合后缀名称，请重新打开素材库后刷新缩略图');
	}
	return new Promise((resolveRequest, rejectRequest) => {
		const body = JSON.stringify({ id: itemId, thumbnailPath });
		const request = http.request({
			hostname: '127.0.0.1',
			port: 41595,
			path: '/api/item/setCustomThumbnail',
			method: 'POST',
			headers: { 'Content-Type': 'application/json', 'Content-Length': Buffer.byteLength(body) },
		}, (response) => {
			let data = '';
			response.on('data', (chunk) => { data += chunk; });
			response.on('end', () => {
				if (response.statusCode >= 200 && response.statusCode < 300) resolveRequest(data);
				else rejectRequest(new Error('Eagle API HTTP ' + response.statusCode + ': ' + data));
			});
		});
		request.on('error', rejectRequest);
		request.setTimeout(12000, () => request.destroy(new Error('Eagle 缩略图请求超时')));
		request.end(body);
	});
}

async function createWebpCopy(sourcePath, key) {
	if (!render.canvasLib) return sourcePath;
	const image = await render.canvasLib.loadImage(sourcePath);
	const canvas = render.canvasLib.createCanvas(image.width, image.height);
	canvas.getContext('2d').drawImage(image, 0, 0);
	const unique = crypto.randomBytes(8).toString('hex');
	const output = path.join(os.tmpdir(), 'spineviewer-' + process.pid + '-' + Date.now() + '-' + unique + '-' + key.replace(/[^a-z0-9]/gi, '') + '.webp');
	fs.writeFileSync(output, await canvas.encode('webp', 90));
	return output;
}

/** 将一份已验证的缩略图主动应用到同一资源链的 atlas/json/skel 条目。 */
async function refreshRelatedThumbnails(assets, thumbnailPath, currentItemId) {
	const signature = assetSignature(assets);
	if (!signature) return false;
	const ids = [...new Set((assets.relatedDataPaths || []).map(itemIdFromAssetPath).concat(currentItemId || []).filter(Boolean))];
	if (ids.length === 0) return true;
	const key = signature + '|' + ids.slice().sort().join(',');
	if (refreshJobs.has(key)) return refreshJobs.get(key);
	const job = (async () => {
		let apiPath = thumbnailPath;
		try {
			apiPath = await createWebpCopy(thumbnailPath, utils.normalizeStem(path.basename(assets.skeletonPath || assets.atlasPath)));
			const results = await Promise.allSettled(ids.map((id) => {
				const source = (assets.relatedDataPaths || []).find(file => itemIdFromAssetPath(file) === id);
				return setEagleCustomThumbnail(id, apiPath, source && path.basename(source));
			}));
			const failed = results.filter((result) => result.status === 'rejected');
			if (failed.length) throw failed[0].reason;
			log('统一补刷完成: ' + ids.length + ' 个条目 [' + ids.join(',') + ']');
			return true;
		} catch (e) {
			log('统一补刷失败: ' + ((e && e.message) || String(e)));
			return false;
		} finally {
			if (apiPath !== thumbnailPath) {
				try { fs.unlinkSync(apiPath); } catch (e) { /* ignore */ }
			}
		}
	})();
	refreshJobs.set(key, job);
	try {
		return await job;
	} finally {
		setTimeout(() => { if (refreshJobs.get(key) === job) refreshJobs.delete(key); }, 2000);
	}
}

/**
 * 资源暂不完整时在后台继续观察。贴图最后落盘不会触发格式扩展回调，因此这里负责
 * 在链路补齐后渲染一次，并统一刷新此前已生成占位图的所有数据条目。
 */
function scheduleBackgroundReconcile(src) {
	try { require('../js/spine-reconcile-worker.js').enqueue(src); }
	catch (error) { log('无法启动后台补刷: ' + String(error)); }
}

// Called by a separate Node worker; Eagle closes the thumbnail window when
// its callback resolves, so timers in that window cannot finish this work.
module.exports.reconcileOnce = async (src, previousSignature) => {
	if (!fs.existsSync(src) || utils.isItemDeleted(src)) return { complete: true };
	const assets = utils.discoverAssets(src, { strictStem: true, allowCrossBatch: true, refreshIndex: true });
	const signature = assetSignature(assets);
	if (!signature || signature !== previousSignature) return { signature, complete: false };
	const version = utils.detectVersion(assets.skeletonPath);
	const runtimeDir = utils.chooseRuntimeDir(version, assets.isBinary);
	if (!runtimeDir) return { signature, complete: true };
	const temp = path.join(os.tmpdir(), 'spineviewer-reconcile-' + crypto.randomBytes(12).toString('hex') + '.png');
	try {
		const png = await renderThumbnailShared(assets, { ...assets, version, runtimeDir, size: 400 });
		fs.writeFileSync(temp, png);
		const complete = await refreshRelatedThumbnails(assets, temp);
		return { signature, complete };
	} catch (error) {
		log('后台补刷重试: ' + String(error));
		return { signature, complete: false };
	} finally { try { fs.unlinkSync(temp); } catch (error) { if (error.code !== 'ENOENT') log(String(error)); } }
};

/** 普通 JSON 使用中性文件图形，避免错误显示 Spine badge。 */
async function writeNeutralJsonPlaceholder(dest) {
	const size = 400;
	if (render.canvasLib) {
		try {
			const canvas = render.canvasLib.createCanvas(size, size);
			const ctx = canvas.getContext('2d');
			ctx.fillStyle = '#202126';
			ctx.fillRect(0, 0, size, size);
			ctx.fillStyle = '#555963';
			ctx.beginPath();
			ctx.moveTo(112, 72);
			ctx.lineTo(244, 72);
			ctx.lineTo(288, 116);
			ctx.lineTo(288, 328);
			ctx.lineTo(112, 328);
			ctx.closePath();
			ctx.fill();
			ctx.fillStyle = '#777c87';
			ctx.beginPath();
			ctx.moveTo(244, 72);
			ctx.lineTo(244, 116);
			ctx.lineTo(288, 116);
			ctx.closePath();
			ctx.fill();
			fs.writeFileSync(dest, canvas.toBuffer('image/png'));
			return;
		} catch (e) { /* fall through */ }
	}
	const pixels = Buffer.alloc(size * size * 4);
	for (let i = 0; i < pixels.length; i += 4) {
		pixels[i] = 32; pixels[i + 1] = 33; pixels[i + 2] = 38; pixels[i + 3] = 255;
	}
	fs.writeFileSync(dest, encodePng(size, size, pixels));
}

/** 将任意图片作为缩略图复制/转换为 PNG（PNG 直接拷贝，JPG/WebP 用 @napi-rs/canvas 转换） */
async function copyImageAsThumb(src, dest) {
	const ext = path.extname(src).toLowerCase();
	if (ext === '.png') {
		fs.copyFileSync(src, dest);
		return;
	}
	if (render.canvasLib) {
		try {
			const img = await render.canvasLib.loadImage(src);
			const w = img.width, h = img.height;
			const canvas = render.canvasLib.createCanvas(w, h);
			const ctx = canvas.getContext('2d');
			ctx.drawImage(img, 0, 0, w, h);
			fs.writeFileSync(dest, canvas.toBuffer('image/png'));
			return;
		} catch (e) { /* fall through */ }
	}
	fs.copyFileSync(src, dest);
}

/** 骨骼二进制无法解析时，用真实 atlas 贴图生成可辨认的回退缩略图。 */
async function writeAtlasFallback(assets, dest) {
	if (!render.canvasLib || !assets || !assets.texturePaths) return false;
	const texturePath = Object.values(assets.texturePaths).find((file) => {
		try { return fs.statSync(file).size > 0; } catch (e) { return false; }
	});
	if (!texturePath) return false;
	try {
		const img = await render.canvasLib.loadImage(texturePath);
		const size = 400;
		const canvas = render.canvasLib.createCanvas(size, size);
		const ctx = canvas.getContext('2d');
		ctx.fillStyle = '#1e1e22';
		ctx.fillRect(0, 0, size, size);
		const scale = Math.min((size - 24) / img.width, (size - 24) / img.height);
		const w = Math.max(1, Math.round(img.width * scale));
		const h = Math.max(1, Math.round(img.height * scale));
		ctx.drawImage(img, Math.round((size - w) / 2), Math.round((size - h) / 2), w, h);
		await render.drawSpineBadge(ctx, size, size);
		if (assets.skeletonPath) require('../js/spine-badge.js').drawVersion(ctx, size, size, utils.detectVersion(assets.skeletonPath));
		fs.writeFileSync(dest, canvas.toBuffer('image/png'));
		return true;
	} catch (e) {
		log('atlas 贴图回退失败: ' + (e && e.message));
		return false;
	}
}

/** 读取 PNG 宽高（仅支持 PNG 头部） */
function imageSizeOf(file) {
	const buf = fs.readFileSync(file);
	if (buf.slice(0, 8).toString('hex') === '89504e470d0a1a0a') {
		return { width: buf.readUInt32BE(16), height: buf.readUInt32BE(20) };
	}
	return { width: 0, height: 0 };
}

/** 生成一个纯 JS 占位 PNG（无需外部依赖），作为兜底 */
async function writePlaceholder(dest) {
	const w = 400, h = 400;
	if (render.canvasLib) {
		try {
			const canvas = render.canvasLib.createCanvas(w, h);
			const ctx = canvas.getContext('2d');
			ctx.fillStyle = '#1e1e22';
			ctx.fillRect(0, 0, w, h);
			await render.drawSpineBadge(ctx, w, h);
			fs.writeFileSync(dest, canvas.toBuffer('image/png'));
			return;
		} catch (e) { /* fall through to pure JS encoder */ }
	}
	// 深色底
	const pixels = Buffer.alloc(w * h * 4);
	for (let y = 0; y < h; y++) {
		for (let x = 0; x < w; x++) {
			const i = (y * w + x) * 4;
			pixels[i] = 30; pixels[i + 1] = 30; pixels[i + 2] = 34; pixels[i + 3] = 255;
		}
	}
	// 简单的斜线纹理，让占位图不单调
	for (let i = 0; i < w + h; i += 8) {
		for (let k = 0; k < 3; k++) {
			const x = Math.min(w - 1, i - k);
			const y = Math.min(h - 1, k);
			const idx = (y * w + x) * 4;
			pixels[idx] = 60; pixels[idx + 1] = 62; pixels[idx + 2] = 68;
		}
	}
	fs.writeFileSync(dest, encodePng(w, h, pixels));
}

/** 最小 PNG 编码器（纯 JS，使用 zlib deflate） */
function encodePng(width, height, rgba) {
	const sig = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
	const ihdr = Buffer.alloc(13);
	ihdr.writeUInt32BE(width, 0);
	ihdr.writeUInt32BE(height, 4);
	ihdr[8] = 8; // bit depth
	ihdr[9] = 6; // color type RGBA
	ihdr[10] = 0; ihdr[11] = 0; ihdr[12] = 0;
	const ihdrChunk = chunk('IHDR', ihdr);

	const raw = Buffer.alloc((width * 4 + 1) * height);
	for (let y = 0; y < height; y++) {
		raw[y * (width * 4 + 1)] = 0; // filter type 0
		rgba.copy(raw, y * (width * 4 + 1) + 1, y * width * 4, (y + 1) * width * 4);
	}
	const idat = zlib.deflateSync(raw);
	const idatChunk = chunk('IDAT', idat);
	const iend = chunk('IEND', Buffer.alloc(0));
	return Buffer.concat([sig, ihdrChunk, idatChunk, iend]);
}

function chunk(type, data) {
	const len = Buffer.alloc(4);
	len.writeUInt32BE(data.length, 0);
	const typeBuf = Buffer.from(type, 'ascii');
	const crcBuf = Buffer.alloc(4);
	crcBuf.writeUInt32BE(crc32(Buffer.concat([typeBuf, data])), 0);
	return Buffer.concat([len, typeBuf, data, crcBuf]);
}

function crc32(buf) {
	let c, crc = 0xFFFFFFFF;
	for (let i = 0; i < buf.length; i++) {
		c = (crc ^ buf[i]) & 0xFF;
		for (let k = 0; k < 8; k++) c = c & 1 ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1);
		crc = (crc >>> 8) ^ c;
	}
	return (crc ^ 0xFFFFFFFF) >>> 0;
}