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

// matrix-js-sdk keeps its IMessagesResponse private to client.ts.
type MessagesResponse = Awaited<ReturnType<MatrixClient['createMessagesRequest']>>;

/**
 * [Gitea #169] "Delete all my messages in this room": self-service redaction of
 * every non-state event you sent. Two phases — collect (server-side
 * sender-filtered /messages pagination) and redact (sequential, honours 429).
 * Progress is persisted so a reload can resume; the mxc media behind
 * attachments is NOT purged by a redaction (that is the server admin's job).
 */

export type RedactJobPhase = 'collecting' | 'redacting' | 'done' | 'cancelled' | 'error';

export type RedactJobState = {
  roomId: string;
  phase: RedactJobPhase;
  /** Event ids still to redact (persisted so a reload can resume). */
  pending: string[];
  found: number;
  redacted: number;
  skipped: number;
  error?: string;
  leaveAfter: boolean;
};

const STORAGE_PREFIX = 'lotus-redact-job-';

export const loadRedactJob = (roomId: string): RedactJobState | null => {
  try {
    const raw = localStorage.getItem(STORAGE_PREFIX + roomId);
    if (!raw) return null;
    const parsed = JSON.parse(raw) as RedactJobState;
    return Array.isArray(parsed.pending) ? parsed : null;
  } catch {
    return null;
  }
};

export const saveRedactJob = (state: RedactJobState): void => {
  try {
    // Only a finished (or discarded) job is forgotten; a cancelled/failed one
    // keeps its pending list so it can be resumed after a reload.
    if (state.phase === 'done' || state.pending.length === 0) {
      localStorage.removeItem(STORAGE_PREFIX + state.roomId);
    } else {
      localStorage.setItem(STORAGE_PREFIX + state.roomId, JSON.stringify(state));
    }
  } catch {
    // storage unavailable — the job still runs, it just can't resume
  }
};

/** Event types that are "yours to delete"; state events never qualify. */
export const isRedactableOwnEvent = (ev: {
  type: string;
  state_key?: string;
  unsigned?: { redacted_because?: unknown };
  content?: Record<string, unknown>;
}): boolean => {
  if (typeof ev.state_key === 'string') return false;
  if (ev.unsigned?.redacted_because) return false;
  if (ev.type === 'm.room.redaction') return false;
  // Already-redacted events come back with empty content.
  if (ev.content && Object.keys(ev.content).length === 0) return false;
  return true;
};

export const ownMessagesFilter = (userId: string): Filter => {
  const filter = new Filter(userId);
  filter.setDefinition({
    room: {
      timeline: { senders: [userId], limit: 100 },
    },
  });
  return filter;
};

/**
 * Walk the room history backwards with a server-side sender filter and return
 * the ids of every event we can redact. Calls `onProgress(found)` per page.
 */
export async function collectOwnEventIds(
  mx: MatrixClient,
  roomId: string,
  userId: string,
  onProgress: (found: number) => void,
  signal?: AbortSignal,
): Promise<string[]> {
  const ids: string[] = [];
  const filter = ownMessagesFilter(userId);
  let from: string | null = null;
  for (;;) {
    if (signal?.aborted) throw new DOMException('cancelled', 'AbortError');
    const token: string | null = from;
    // eslint-disable-next-line no-await-in-loop
    const res: MessagesResponse = await withRateLimit(() =>
      mx.createMessagesRequest(roomId, token, 100, Direction.Backward, filter),
    );
    res.chunk.forEach((ev) => {
      if (ev.sender === userId && ev.event_id && isRedactableOwnEvent(ev)) ids.push(ev.event_id);
    });
    onProgress(ids.length);
    if (!res.end || res.end === from || res.chunk.length === 0) break;
    from = res.end;
  }
  return ids;
}

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

async function withRateLimit<T>(op: () => Promise<T>, attempts = 6): Promise<T> {
  let n = 0;
  for (;;) {
    try {
      // eslint-disable-next-line no-await-in-loop
      return await op();
    } catch (e) {
      if (e instanceof MatrixError && e.httpStatus === 429 && n < attempts) {
        n += 1;
        // eslint-disable-next-line no-await-in-loop
        await sleep(e.getRetryAfterMs() ?? Math.min(1000 * 2 ** n, 30_000));
      } else {
        throw e;
      }
    }
  }
}

/**
 * Redact `state.pending` one by one, mutating and persisting `state` as it
 * goes so a reload resumes where it stopped. Missing / already-redacted
 * events are skipped, not fatal.
 */
export async function redactPending(
  mx: MatrixClient,
  state: RedactJobState,
  onProgress: (state: RedactJobState) => void,
  signal?: AbortSignal,
): Promise<void> {
  while (state.pending.length > 0) {
    if (signal?.aborted) throw new DOMException('cancelled', 'AbortError');
    const id = state.pending[0];
    try {
      // eslint-disable-next-line no-await-in-loop
      await withRateLimit(() => mx.redactEvent(state.roomId, id));
      state.redacted += 1;
    } catch (e) {
      if (e instanceof MatrixError && (e.errcode === 'M_NOT_FOUND' || e.httpStatus === 404)) {
        state.skipped += 1;
      } else {
        throw e;
      }
    }
    state.pending.shift();
    saveRedactJob(state);
    onProgress(state);
  }
}