export function parseSseChunk(buffer) {
  // SSE allows CRLF, LF, or CR line endings; sse-starlette emits CRLF.
  const parts = buffer.split(/\r?\n\r?\n/);
  const rest = parts.pop();
  const events = [];
  for (const part of parts) {
    let event = 'message', data = '';
    for (const line of part.split(/\r?\n/)) {
      if (line.startsWith('event:')) event = line.slice(6).trim();
      else if (line.startsWith('data:')) data += line.slice(5).trim();
    }
    if (data) events.push({ event, data: JSON.parse(data) });
  }
  return { events, rest };
}

async function* sseFetch(url, options) {
  const res = await fetch(url, options);
  if (!res.ok) throw new Error(`${res.status}: ${(await res.text()).slice(0, 300)}`);
  const reader = res.body.getReader();
  const decoder = new TextDecoder();
  let buf = '';
  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    buf += decoder.decode(value, { stream: true });
    const { events, rest } = parseSseChunk(buf);
    buf = rest;
    yield* events;
  }
}

export async function startParse(file) {
  const form = new FormData();
  form.append('file', file);
  const res = await fetch('/api/parse', { method: 'POST', body: form });
  if (!res.ok) throw new Error(`parse failed: ${res.status}`);
  return (await res.json()).jobId;
}

export function jobEvents(jobId) {
  return sseFetch(`/api/jobs/${jobId}/events`);
}

export function annotateStream(body) {
  return sseFetch('/api/annotate', {
    method: 'POST',
    headers: { 'content-type': 'application/json' },
    body: JSON.stringify(body),
  });
}