/**
 * A QR code as terminal lines or an inline SVG.
 *
 * Uses the `qrcode` package only for the module matrix, then draws Unicode
 * half-blocks for a terminal and hands the package's SVG to a page. The package
 * loads on the first QR, not when an extension registers: a session that never
 * shows one pays nothing for it. No ANSI is emitted; the caller decides colours,
 * and the width is the matrix width plus a quiet zone.
 *
 * Two surfaces share this: `wechat` shows a login QR, and `plan` shows a review
 * link a teammate can scan.
 */

interface QrModules {
	size: number;
	get(row: number, col: number): boolean;
}

/** QR error-correction level, one setting for both surfaces. */
const ERROR_CORRECTION = "M" as const;

/** Build the module matrix for `text`, loading `qrcode` on first use. */
export async function qrMatrix(text: string): Promise<QrModules> {
	const { default: QRCode } = await import("qrcode");
	const qr = QRCode.create(text, { errorCorrectionLevel: ERROR_CORRECTION });
	return qr.modules as unknown as QrModules;
}

/**
 * The QR as terminal lines. Each string is exactly `matrix.size + 2 * quiet`
 * columns wide (half-block characters are single width), so a caller can test
 * `qrLines(text)[0].length` against the terminal width.
 */
export async function qrLines(text: string, options: { quiet?: number } = {}): Promise<string[]> {
	const quiet = Math.max(0, options.quiet ?? 2);
	const matrix = await qrMatrix(text);
	const size = matrix.size;
	const isDark = (row: number, col: number): boolean =>
		row >= 0 && col >= 0 && row < size && col < size && matrix.get(row, col);

	const lines: string[] = [];
	for (let y = -quiet; y < size + quiet; y += 2) {
		let line = "";
		for (let x = -quiet; x < size + quiet; x += 1) {
			const top = isDark(y, x);
			const bottom = isDark(y + 1, x);
			line += top && bottom ? "█" : top ? "▀" : bottom ? "▄" : " ";
		}
		lines.push(line);
	}
	return lines;
}

/**
 * The QR as an inline SVG, for a page that can paste markup instead of pixels.
 *
 * The markup is generated by the package from a URL this process built, so it
 * carries no caller-supplied text; a page still serves it under its own CSP,
 * which allows no external image.
 */
export async function qrSvg(text: string): Promise<string> {
	const { default: QRCode } = await import("qrcode");
	return QRCode.toString(text, { type: "svg", errorCorrectionLevel: ERROR_CORRECTION, margin: 1 });
}