// Minimal, dependency-free SSE frame parser for the companion SDK. The browser's
// EventSource can't set an Authorization header, so the SDK consumes the stream
// over fetch() instead and parses frames itself — this is that parser, kept pure
// so it unit-tests in isolation.
//
// An SSE frame is a block of `field: value` lines terminated by a blank line.
// Comment lines (starting ":") are keep-alives and ignored. A chunk off the wire
// may end mid-frame, so the parser returns the leftover for the next call.

export interface SseEvent {
	/** The `event:` field; defaults to "message" per the SSE spec. */
	event: string;
	/** The joined `data:` field(s). */
	data: string;
}

/** Parse all COMPLETE frames out of an accumulated buffer. Returns the parsed
 *  events plus the unparsed remainder (an incomplete trailing frame). */
export function parseSse(buffer: string): { events: SseEvent[]; rest: string } {
	const events: SseEvent[] = [];
	let working = buffer.replace(/\r\n/g, '\n');
	let sep = working.indexOf('\n\n');
	while (sep !== -1) {
		const block = working.slice(0, sep);
		working = working.slice(sep + 2);
		let event = 'message';
		const dataLines: string[] = [];
		for (const line of block.split('\n')) {
			if (!line || line.startsWith(':')) continue; // blank or comment (keep-alive)
			const ci = line.indexOf(':');
			const field = ci === -1 ? line : line.slice(0, ci);
			let value = ci === -1 ? '' : line.slice(ci + 1);
			if (value.startsWith(' ')) value = value.slice(1); // single leading space stripped
			if (field === 'event') event = value;
			else if (field === 'data') dataLines.push(value);
		}
		if (dataLines.length) events.push({ event, data: dataLines.join('\n') });
		sep = working.indexOf('\n\n');
	}
	return { events, rest: working };
}