// Renderer-side client for the offline mail replica.
//
// The replica is EVENT-DRIVEN, exactly like the search index next to it: the
// renderer already holds the live JMAP push connection, so a `StateChange` is what
// triggers a sync cycle. There is no polling loop and no background worker.
//
// One cycle is BOUNDED (see lib/offline-replica/sync.ts's BUDGET), so a first
// sync of a large mailbox needs several. `unfinishedWork` is the server saying
// "call again", and `chainSync` below does that with a hard cap - the cap matters,
// because an "unfinished work" signal that is true for a condition the cycle
// cannot change is how the mobile client ended up chaining a new cycle every five
// seconds forever.
//
// Every function here is best-effort and never throws: offline storage failing to
// update must never break the mail UI.

import { apiFetch } from '@/lib/browser-navigation';
import { debug } from '@/lib/debug';
import type { Email, Mailbox } from '@/lib/jmap/types';
import type { StateChange } from '@/lib/jmap/types';

export interface RetentionPolicy {
  envelopeDays: number;
  bodyDays: number;
  maxBodyMB: number;
}

export interface CycleReport {
  ok: boolean;
  unfinishedWork: boolean;
  bootstrapped: boolean;
  reconciled: boolean;
  mailboxesWritten: number;
  envelopesWritten: number;
  envelopesDeleted: number;
  bodiesWritten: number;
  bodiesEvicted: number;
  coveragePhase: string;
  resyncRequired: boolean;
  warnings: string[];
  errorClass?: string;
  error?: string;
  durationMs: number;
}

export interface ReplicaStats {
  mailboxes: number;
  envelopes: number;
  bodies: number;
  bodyBytes: number;
  wantedBodies: number;
  giveUps: number;
  newest: string | null;
  oldest: string | null;
  fileBytes: number;
}

export interface ReplicaStatus {
  ok: boolean;
  policy: RetentionPolicy;
  limits: Record<keyof RetentionPolicy, { min: number; max: number }>;
  synced: boolean;
  stats: ReplicaStats | null;
  coveragePhase: string;
  coveredFrom?: string | null;
  resyncRequired: boolean;
  lastCycleAt: number | null;
  lastCycleOk: boolean | null;
  lastCycleError?: string | null;
}

/** Set once the server says the feature isn't there, so we stop asking. */
let knownUnavailable = false;
let inFlight: Promise<CycleReport | null> | null = null;

function slotQuery(slot?: number, extra?: string): string {
  const params = new URLSearchParams();
  if (typeof slot === 'number') params.set('slot', String(slot));
  const base = params.toString();
  if (extra && base) return `?${base}&${extra}`;
  if (extra) return `?${extra}`;
  return base ? `?${base}` : '';
}

/** True when the replica is known to be absent (not the desktop shell, or gated off). */
export function isReplicaUnavailable(): boolean {
  return knownUnavailable;
}

export function resetReplicaAvailability(): void {
  knownUnavailable = false;
}

/**
 * Runs ONE cycle. Single-flighted on the renderer as well as the server, so a
 * burst of deliveries coalesces instead of queueing N overlapping requests that
 * the server would then serialise anyway.
 */
export async function syncOnce(
  opts: { slot?: number; policy?: RetentionPolicy; forceResync?: boolean } = {},
): Promise<CycleReport | null> {
  if (knownUnavailable) return null;
  if (inFlight) return inFlight;

  const run = (async (): Promise<CycleReport | null> => {
    try {
      const response = await apiFetch(`/api/offline/sync${slotQuery(opts.slot)}`, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ policy: opts.policy, forceResync: opts.forceResync === true }),
      });
      // 404 = not the desktop shell. Permanent for this page load; stop asking so
      // a busy mailbox doesn't post per delivery.
      if (response.status === 404) { knownUnavailable = true; return null; }
      if (response.status === 503) {
        const body = await response.json().catch(() => ({}));
        // A transport-class 503 means the BACKEND is unreachable, which is normal
        // and temporary - it must not latch the feature off for the session. Only
        // a missing binding / key channel does that.
        const code = typeof body?.code === 'string' ? body.code : '';
        if (code === 'no-binding' || code === 'no-key-channel' || code === 'unavailable') {
          knownUnavailable = true;
          return null;
        }
        return null;
      }
      if (!response.ok) return null;
      const body = await response.json();
      debug.log('push', '[replica] cycle', body?.report);
      return (body?.report ?? null) as CycleReport | null;
    } catch {
      return null;
    } finally {
      inFlight = null;
    }
  })();

  inFlight = run;
  return run;
}

/** Hard cap on chained cycles per trigger. */
export const MAX_CHAINED_CYCLES = 12;

/**
 * Runs cycles while the server reports unfinished work.
 *
 * The cap is the whole point. `unfinishedWork` is a hint, and a hint that stays
 * true for something the cycle cannot resolve turns into an endless chain - which
 * is exactly what happened on the mobile client when a body-queue counter reported
 * attempted rather than inserted rows. The server-side fixes make that
 * self-terminating; this cap means even a future regression costs a bounded number
 * of requests rather than an infinite loop.
 */
export async function chainSync(
  opts: { slot?: number; max?: number; onReport?: (report: CycleReport) => void } = {},
): Promise<CycleReport | null> {
  const max = Math.min(opts.max ?? MAX_CHAINED_CYCLES, MAX_CHAINED_CYCLES);
  let last: CycleReport | null = null;
  for (let i = 0; i < max; i++) {
    const report = await syncOnce({ slot: opts.slot });
    if (!report) return last;
    last = report;
    opts.onReport?.(report);
    if (!report.ok || !report.unfinishedWork) return report;
  }
  return last;
}

/** The push-driven entry point. Fire-and-forget: the mail UI must not wait on it. */
export function syncOnStateChange(change: StateChange, opts: { slot?: number } = {}): void {
  if (knownUnavailable) return;
  // Only mail-shaped changes are worth a cycle. A `Mailbox` state change alone is
  // usually just an unread-count move, but the replica DOES hold those counts, so
  // unlike the search index it is worth reacting to.
  const relevant = Object.values(change.changed ?? {}).some(
    (perAccount) => perAccount && (perAccount.Email || perAccount.Mailbox),
  );
  if (!relevant) return;
  void syncOnce({ slot: opts.slot });
}

export async function fetchReplicaStatus(slot?: number): Promise<ReplicaStatus | null> {
  try {
    const response = await apiFetch(`/api/offline/status${slotQuery(slot)}`);
    if (!response.ok) return null;
    return (await response.json()) as ReplicaStatus;
  } catch {
    return null;
  }
}

export async function updateRetentionPolicy(
  policy: RetentionPolicy,
  slot?: number,
): Promise<boolean> {
  try {
    const response = await apiFetch(`/api/offline/status${slotQuery(slot)}`, {
      method: 'PUT',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify(policy),
    });
    return response.ok;
  } catch {
    return false;
  }
}

export async function purgeReplica(slot?: number): Promise<boolean> {
  try {
    const response = await apiFetch(`/api/offline/status${slotQuery(slot)}`, { method: 'DELETE' });
    return response.ok;
  } catch {
    return false;
  }
}

// ── reads ───────────────────────────────────────────────────────────────────

interface ReadEnvelope<T> {
  ok?: boolean;
  available?: boolean;
  error?: string;
  data?: T;
}

async function read<T>(query: string): Promise<(T & { available: boolean }) | null> {
  if (knownUnavailable) return null;
  try {
    const response = await apiFetch(`/api/offline/mail${query}`);
    if (response.status === 404) { knownUnavailable = true; return null; }
    if (!response.ok) return null;
    const body = (await response.json()) as ReadEnvelope<unknown> & Record<string, unknown>;
    if (body?.available !== true) return null;
    return body as unknown as T & { available: boolean };
  } catch {
    return null;
  }
}

export async function readOfflineMailboxes(slot?: number): Promise<Mailbox[] | null> {
  const body = await read<{ mailboxes: Mailbox[] }>(slotQuery(slot, 'kind=mailboxes'));
  return body?.mailboxes ?? null;
}

export async function readOfflineList(
  mailboxId: string | null,
  opts: { limit?: number; offset?: number; slot?: number } = {},
): Promise<{ emails: Email[]; total: number; hasMore: boolean } | null> {
  const params = new URLSearchParams({ kind: 'list' });
  if (mailboxId !== null) params.set('mailboxId', mailboxId);
  if (opts.limit !== undefined) params.set('limit', String(opts.limit));
  if (opts.offset !== undefined) params.set('offset', String(opts.offset));
  const body = await read<{ emails: Email[]; total: number; hasMore: boolean }>(
    slotQuery(opts.slot, params.toString()),
  );
  if (!body) return null;
  return { emails: body.emails ?? [], total: body.total ?? 0, hasMore: body.hasMore === true };
}

export async function readOfflineMessage(
  id: string,
  slot?: number,
): Promise<{ email: Email | null; hasBody: boolean } | null> {
  const params = new URLSearchParams({ kind: 'message', id });
  const body = await read<{ email: Email | null; hasBody: boolean }>(
    slotQuery(slot, params.toString()),
  );
  if (!body) return null;
  return { email: body.email ?? null, hasBody: body.hasBody === true };
}