// JSONL framing for the engine pipe and the control socket (#1507, CHAT-03 §1).
//
// Records are split on LF (0x0A) only, and a trailing CR is stripped (rpc.md
// lines 30–38). Node's readline is not used, because it also splits on U+2028
// and U+2029, which JSON strings may carry raw (E2). Splitting happens on
// bytes, before UTF-8 decoding, so a multibyte character split across two
// chunks is never damaged.

export const MAX_LINE_BYTES = 64 * 1024 * 1024;

export class LineSplitter {
  constructor(onLine, { maxBytes = MAX_LINE_BYTES, onOverflow = null } = {}) {
    this.onLine = onLine;
    this.maxBytes = maxBytes;
    this.onOverflow = onOverflow;
    this.parts = [];
    this.size = 0;
    this.overflowed = false;
  }

  push(chunk) {
    if (this.overflowed) return;
    let start = 0;
    for (;;) {
      const lf = chunk.indexOf(0x0a, start);
      if (lf === -1) break;
      this.parts.push(chunk.subarray(start, lf));
      const line = Buffer.concat(this.parts);
      this.parts = [];
      this.size = 0;
      const end = line.length > 0 && line[line.length - 1] === 0x0d ? line.length - 1 : line.length;
      this.onLine(line.subarray(0, end).toString("utf8"));
      start = lf + 1;
    }
    if (start < chunk.length) {
      const rest = chunk.subarray(start);
      this.size += rest.length;
      if (this.size > this.maxBytes) {
        this.overflowed = true;
        this.parts = [];
        this.onOverflow?.();
        return;
      }
      this.parts.push(Buffer.from(rest));
    }
  }

  // Bytes left without a terminating LF when the stream ends. They are never
  // parsed as a record: a partial line is a transport gap, not data.
  pending() {
    return this.size;
  }
}

export function encodeLine(value) {
  return JSON.stringify(value) + "\n";
}

// Parses one line. Returns {value} or {error}; never throws.
export function parseLine(line) {
  try {
    const value = JSON.parse(line);
    if (value === null || typeof value !== "object" || Array.isArray(value)) return { error: "not-an-object" };
    return { value };
  } catch {
    return { error: "unparseable" };
  }
}