const DEFAULT_MAX_RETRIES = 3;
const MAX_BACKOFF_MS = 8000;

function sleep(ms: number) {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

function parseRetryAfterMs(value: string | null): number | null {
  if (!value) return null;
  const seconds = Number(value);
  if (Number.isFinite(seconds) && seconds > 0) {
    return Math.round(seconds * 1000);
  }
  return null;
}

function computeBackoffMs(attempt: number, retryAfterMs: number | null) {
  if (retryAfterMs && retryAfterMs > 0) {
    return Math.min(retryAfterMs, MAX_BACKOFF_MS);
  }
  const exp = Math.min(MAX_BACKOFF_MS, 500 * 2 ** attempt);
  const jitter = Math.floor(Math.random() * 300);
  return exp + jitter;
}

export async function fetchUploadWithRetry(
  formData: FormData,
  options?: {
    maxRetries?: number;
    signal?: AbortSignal;
  }
) {
  const maxRetries = options?.maxRetries ?? DEFAULT_MAX_RETRIES;

  for (let attempt = 0; ; attempt++) {
    const response = await fetch("/api/files/upload", {
      method: "POST",
      body: formData,
      signal: options?.signal,
    });

    if (response.status !== 429 || attempt >= maxRetries) {
      return response;
    }

    let retryAfterMs = parseRetryAfterMs(response.headers.get("Retry-After"));
    if (!retryAfterMs) {
      try {
        const payload = await response.clone().json();
        const retryAfterSec = Number(payload?.retryAfter || 0);
        if (Number.isFinite(retryAfterSec) && retryAfterSec > 0) {
          retryAfterMs = Math.round(retryAfterSec * 1000);
        }
      } catch {}
    }

    const delayMs = computeBackoffMs(attempt, retryAfterMs);
    await sleep(delayMs);
  }
}