learnharness/src/agent/subagents/headless.ts

import * as fs from "node:fs";
import * as os from "node:os";
import * as path from "node:path";
import { pathToFileURL } from "node:url";

/**
 * Shared headless-browser helper for the verifying sub-agents (W6):
 * the demo-builder executes demos and captures errors; the visual-maker
 * rasterizes SVGs so it can look at them. Both use the SAME system Chrome
 * via puppeteer-core — NO bundled chromium is downloaded.
 *
 * Chrome resolution: process.env.CHROME_PATH first, then the common
 * macOS/Linux install paths. If none exists we fall back to puppeteer's
 * `channel: "chrome"` at launch time; `available()` is cheap and only knows
 * about the explicit candidates, so a channel-only setup reports unavailable
 * and the builders refuse to run (the house rule: never skip testing).
 *
 * Test seam: `headlessOverride.current` replaces the whole API (tests inject
 * a fake; nothing here touches a real browser). Builders call `getHeadless()`.
 */

export interface DemoRunResult {
	/** console.error / console messages of type "error". */
	consoleErrors: string[];
	/** Uncaught exceptions (window.onerror / unhandled rejections). */
	pageErrors: string[];
	/** Network requests that failed (CDN scripts that didn't load, …). */
	failedRequests: string[];
	/** Value of the optional probe expression, when requested and successful. */
	probeResult?: unknown;
	/** True when nothing above recorded anything. */
	ok: boolean;
}

export interface RunDemoOptions {
	/** How long to let the page settle (animations, async CDN loads) — default 2s. */
	settleMs?: number;
	/** Optional JS expression evaluated in the page after settling; its value
	 * is returned to the builder so it can assert on internal state. */
	probe?: string;
}

export interface RenderSvgOptions {
	/** Viewport size — defaults to the SVG's width/height attrs, else 900×700. */
	width?: number;
	height?: number;
}

export interface HeadlessApi {
	/** True when a Chrome executable is resolvable (cheap, no launch). */
	available(): boolean;
	/** Why not — for error messages. */
	unavailableReason(): string | null;
	/** Load the HTML in headless Chrome, capture errors, optionally probe. */
	runDemo(html: string, opts?: RunDemoOptions): Promise<DemoRunResult>;
	/** Rasterize an SVG to a PNG buffer (for verify-by-looking). */
	renderSvg(svg: string, opts?: RenderSvgOptions): Promise<Buffer>;
}

/** Test seam — undefined in production. */
export const headlessOverride: { current?: HeadlessApi } = {};

export function getHeadless(): HeadlessApi {
	return headlessOverride.current ?? realHeadless;
}

// ─── Chrome resolution ───────────────────────────────────────────────────────

const CHROME_CANDIDATES = [
	"/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
	"/Applications/Chromium.app/Contents/MacOS/Chromium",
	"/Applications/Microsoft Edge.app/Contents/MacOS/Microsoft Edge",
	"/usr/bin/google-chrome",
	"/usr/bin/google-chrome-stable",
	"/usr/bin/chromium",
	"/usr/bin/chromium-browser",
];

export function resolveChromeExecutablePath(): string | null {
	const candidates = [process.env.CHROME_PATH, ...CHROME_CANDIDATES].filter(
		(p): p is string => typeof p === "string" && p.length > 0,
	);
	for (const candidate of candidates) {
		try {
			if (fs.existsSync(candidate)) return candidate;
		} catch {
			/* not readable — try the next */
		}
	}
	return null;
}

const NO_CHROME_MESSAGE =
	"No Chrome/Chromium found for headless testing. Install Google Chrome or set CHROME_PATH to a Chrome executable. " +
	"(Verification is mandatory — demos and visuals are never delivered untested.)";

async function launchBrowser(): Promise<import("puppeteer-core").Browser> {
	const puppeteer = (await import("puppeteer-core")).default;
	const executablePath = resolveChromeExecutablePath();
	const browser = await puppeteer.launch({
		headless: true,
		// Explicit path when we found one; otherwise let puppeteer resolve the
		// system Chrome install itself via the "chrome" channel.
		...(executablePath ? { executablePath } : { channel: "chrome" as const }),
		args: ["--disable-gpu", "--no-sandbox", "--disable-dev-shm-usage"],
	});
	return browser;
}

/** A temp dir per invocation; removed in finally. */
function tempDir(prefix: string): string {
	return fs.mkdtempSync(path.join(os.tmpdir(), prefix));
}

// ─── Demo execution ──────────────────────────────────────────────────────────

async function runDemo(html: string, opts: RunDemoOptions = {}): Promise<DemoRunResult> {
	const settleMs = opts.settleMs ?? 2000;
	const dir = tempDir("lh-demo-");
	const file = path.join(dir, "demo.html");
	fs.writeFileSync(file, html, "utf-8");

	const consoleErrors: string[] = [];
	const pageErrors: string[] = [];
	const failedRequests: string[] = [];
	let probeResult: unknown;
	let probed = false;

	const browser = await launchBrowser();
	try {
		const page = await browser.newPage();
		page.on("console", (msg) => {
			if (msg.type() === "error") consoleErrors.push(msg.text());
		});
		page.on("pageerror", (err) => pageErrors.push(err instanceof Error ? err.message : String(err)));
		page.on("requestfailed", (req) => failedRequests.push(`${req.url()} (${req.failure()?.errorText ?? "failed"})`));

		try {
			await page.goto(pathToFileURL(file).href, { waitUntil: "load", timeout: 30_000 });
			await new Promise((resolve) => setTimeout(resolve, settleMs));
			if (opts.probe) {
				try {
					probeResult = await page.evaluate(opts.probe);
				} catch (err) {
					pageErrors.push(`probe failed: ${err instanceof Error ? err.message : String(err)}`);
				}
				probed = true;
			}
		} catch (err) {
			pageErrors.push(err instanceof Error ? err.message : String(err));
		}
	} finally {
		await browser.close().catch(() => {});
		try {
			fs.rmSync(dir, { recursive: true, force: true });
		} catch {
			/* best-effort cleanup */
		}
	}

	return {
		consoleErrors,
		pageErrors,
		failedRequests,
		...(probed ? { probeResult } : {}),
		ok: consoleErrors.length === 0 && pageErrors.length === 0 && failedRequests.length === 0,
	};
}

// ─── SVG rasterization ───────────────────────────────────────────────────────

function svgViewport(svg: string, opts: RenderSvgOptions): { width: number; height: number } {
	if (opts.width && opts.height) return { width: opts.width, height: opts.height };
	const width = Number(svg.match(/\bwidth\s*=\s*"?(\d+(?:\.\d+)?)/)?.[1]);
	const height = Number(svg.match(/\bheight\s*=\s*"?(\d+(?:\.\d+)?)/)?.[1]);
	return {
		width: Math.ceil(Number.isFinite(width) && width > 0 ? width : 900),
		height: Math.ceil(Number.isFinite(height) && height > 0 ? height : 700),
	};
}

async function renderSvg(svg: string, opts: RenderSvgOptions = {}): Promise<Buffer> {
	const dir = tempDir("lh-visual-");
	const file = path.join(dir, "figure.html");
	fs.writeFileSync(
		file,
		`<!doctype html><html><head><meta charset="utf-8"><style>html,body{margin:0;padding:0;background:#fff}svg{display:block}</style></head><body>${svg}</body></html>`,
		"utf-8",
	);

	const browser = await launchBrowser();
	try {
		const page = await browser.newPage();
		const { width, height } = svgViewport(svg, opts);
		await page.setViewport({ width, height });
		await page.goto(pathToFileURL(file).href, { waitUntil: "load", timeout: 30_000 });
		const png = (await page.screenshot({ fullPage: true, type: "png" })) as Buffer;
		return png;
	} finally {
		await browser.close().catch(() => {});
		try {
			fs.rmSync(dir, { recursive: true, force: true });
		} catch {
			/* best-effort cleanup */
		}
	}
}

// ─── the real API ────────────────────────────────────────────────────────────

export const realHeadless: HeadlessApi = {
	available() {
		return resolveChromeExecutablePath() !== null;
	},
	unavailableReason() {
		return resolveChromeExecutablePath() === null ? NO_CHROME_MESSAGE : null;
	},
	runDemo,
	renderSvg,
};