import { closeSync, openSync, readSync } from "node:fs";
import { StringDecoder } from "node:string_decoder";

export function forEachSessionJsonlLine(sessionPath: string, onLine: (line: string) => void, chunkSize = 64 * 1024): void {
	const fd = openSync(sessionPath, "r");
	const buffer = Buffer.allocUnsafe(Math.max(1, Math.floor(chunkSize)));
	const decoder = new StringDecoder("utf8");
	let pending = "";
	try {
		for (;;) {
			const bytesRead = readSync(fd, buffer, 0, buffer.length, null);
			if (bytesRead === 0) break;
			pending += decoder.write(buffer.subarray(0, bytesRead));
			let start = 0;
			for (;;) {
				const newline = pending.indexOf("\n", start);
				if (newline < 0) {
					pending = pending.slice(start);
					break;
				}
				const line = pending.slice(start, newline);
				onLine(line.endsWith("\r") ? line.slice(0, -1) : line);
				start = newline + 1;
			}
		}
		pending += decoder.end();
		if (pending.length > 0) onLine(pending.endsWith("\r") ? pending.slice(0, -1) : pending);
	} finally {
		closeSync(fd);
	}
}