import { MatrixClient, MatrixError } from 'matrix-js-sdk';

/**
 * Synapse rate-limits `PUT /presence/{user}/status` to ONE request per 10 s per
 * user by default (`rc_presence.per_user`: 0.1/s, burst 1) — and the limit is
 * shared across all of a user's devices. Our presence heartbeat (online/away on
 * visibility and activity changes) can therefore make a manual status save 429.
 *
 * `setPresenceWithRetry` waits out `Retry-After` (bounded) instead of failing,
 * and `PresenceDeduper` lets the heartbeat skip writes that would not change
 * anything, so it stops spending the budget in the first place.
 */
export type PresenceWrite = { presence: 'online' | 'offline' | 'unavailable'; status_msg?: string };

const sleep = (ms: number) =>
  new Promise<void>((r) => {
    setTimeout(r, ms);
  });

export async function setPresenceWithRetry(
  mx: Pick<MatrixClient, 'setPresence'>,
  write: PresenceWrite,
  opts: { maxWaitMs?: number; sleepFn?: (ms: number) => Promise<void> } = {},
): Promise<void> {
  const maxWaitMs = opts.maxWaitMs ?? 25_000;
  const sleepFn = opts.sleepFn ?? sleep;
  let waited = 0;
  for (;;) {
    try {
      // eslint-disable-next-line no-await-in-loop
      await mx.setPresence(write);
      return;
    } catch (e) {
      if (!(e instanceof MatrixError) || e.httpStatus !== 429) throw e;
      const wait = Math.min(e.getRetryAfterMs() ?? 10_500, 15_000);
      if (waited + wait > maxWaitMs) throw e;
      waited += wait;
      // eslint-disable-next-line no-await-in-loop
      await sleepFn(wait);
    }
  }
}

const presenceKey = (write: PresenceWrite): string => `${write.presence}|${write.status_msg ?? ''}`;

/** Remembers the last write that succeeded so identical heartbeats are skipped. */
export class PresenceDeduper {
  private last: string | null = null;

  shouldSend(write: PresenceWrite): boolean {
    return presenceKey(write) !== this.last;
  }

  sent(write: PresenceWrite): void {
    this.last = presenceKey(write);
  }

  reset(): void {
    this.last = null;
  }
}

/** A user-facing sentence for a failed status save. */
export const describePresenceError = (e: unknown): string => {
  if (e instanceof MatrixError) {
    if (e.httpStatus === 429) {
      return 'The server limits how often presence can change (once every 10 seconds, shared by all your devices). Please wait a moment and try again.';
    }
    const serverText = (e.data as { error?: string } | undefined)?.error;
    if (serverText) return `Failed to save status: ${serverText}`;
  }
  return "Failed to save status — couldn't reach the server. Try again.";
};