dchain/client-app/hooks/useMessages.ts

/**
 * Subscribe to the relay inbox via WebSocket and decrypt incoming envelopes
 * for the active chat. Falls back to 30-second polling whenever the WS is
 * not connected — preserves correctness on older nodes or flaky networks.
 *
 * Flow:
 *   1. On mount: one HTTP fetch so we have whatever is already in the inbox
 *   2. Subscribe to topic `inbox:<my_x25519>` — the node pushes a summary
 *      for each fresh envelope as soon as mailbox.Store() succeeds
 *   3. On each push, pull the full envelope list (cheap — bounded by
 *      MailboxPerRecipientCap) and decrypt anything we haven't seen yet
 *   4. If WS disconnects for > 15 seconds, start a 30 s HTTP poll until it
 *      reconnects
 */

import { useEffect, useCallback, useRef } from 'react';
import { fetchInbox } from '@/lib/api';
import { getWSClient } from '@/lib/ws';
import { decryptMessage } from '@/lib/crypto';
import { appendMessage } from '@/lib/storage';
import { useStore } from '@/lib/store';

const FALLBACK_POLL_INTERVAL  = 30_000;  // HTTP poll when WS is down
const WS_GRACE_BEFORE_POLLING = 15_000;  // don't start polling immediately on disconnect

export function useMessages(contactX25519: string) {
  const keyFile   = useStore(s => s.keyFile);
  const appendMsg = useStore(s => s.appendMessage);

  const pullAndDecrypt = useCallback(async () => {
    if (!keyFile || !contactX25519) return;
    try {
      const envelopes = await fetchInbox(keyFile.x25519_pub);
      for (const env of envelopes) {
        // Only process messages from this contact
        if (env.sender_pub !== contactX25519) continue;

        const text = decryptMessage(
          env.ciphertext,
          env.nonce,
          env.sender_pub,
          keyFile.x25519_priv,
        );
        if (!text) continue;

        const msg = {
          id:        `${env.sender_pub}_${env.timestamp}_${env.nonce.slice(0, 8)}`,
          from:      env.sender_pub,
          text,
          timestamp: env.timestamp,
          mine:      false,
        };
        appendMsg(contactX25519, msg);
        await appendMessage(contactX25519, msg);
      }
    } catch (e) {
      // Don't surface inbox errors aggressively — next event or poll retries
      console.warn('[useMessages] pull error:', e);
    }
  }, [keyFile, contactX25519, appendMsg]);

  // ── Fallback polling state ────────────────────────────────────────────
  const pollTimerRef       = useRef<ReturnType<typeof setInterval> | null>(null);
  const disconnectTORef    = useRef<ReturnType<typeof setTimeout>  | null>(null);

  const startPolling = useCallback(() => {
    if (pollTimerRef.current) return;
    console.log('[useMessages] WS down — starting HTTP poll fallback');
    pullAndDecrypt();
    pollTimerRef.current = setInterval(pullAndDecrypt, FALLBACK_POLL_INTERVAL);
  }, [pullAndDecrypt]);

  const stopPolling = useCallback(() => {
    if (pollTimerRef.current) {
      clearInterval(pollTimerRef.current);
      pollTimerRef.current = null;
    }
    if (disconnectTORef.current) {
      clearTimeout(disconnectTORef.current);
      disconnectTORef.current = null;
    }
  }, []);

  useEffect(() => {
    if (!keyFile || !contactX25519) return;

    const ws = getWSClient();

    // Initial fetch — populate whatever landed before we mounted.
    pullAndDecrypt();

    // Subscribe to our x25519 inbox — the node emits on mailbox.Store.
    // Topic filter: only envelopes for ME; we then filter by sender inside
    // the handler so we only render messages in THIS chat.
    const offInbox = ws.subscribe('inbox:' + keyFile.x25519_pub, (frame) => {
      if (frame.event !== 'inbox') return;
      const d = frame.data as { sender_pub?: string } | undefined;
      // Optimisation: if the envelope is from a different peer, skip the
      // whole refetch — we'd just drop it in the sender filter below anyway.
      if (d?.sender_pub && d.sender_pub !== contactX25519) return;
      pullAndDecrypt();
    });

    // Manage fallback polling based on WS connection state.
    const offConn = ws.onConnectionChange((ok) => {
      if (ok) {
        stopPolling();
        // Catch up anything we missed while disconnected.
        pullAndDecrypt();
      } else if (disconnectTORef.current === null) {
        disconnectTORef.current = setTimeout(startPolling, WS_GRACE_BEFORE_POLLING);
      }
    });

    ws.connect();

    return () => {
      offInbox();
      offConn();
      stopPolling();
    };
  }, [keyFile, contactX25519, pullAndDecrypt, startPolling, stopPolling]);
}