path: root/src/calls.js

// 1:1 voice and video calls (NIP-AC, the draft Amethyst, nospeak and Noscall
// speak): WebRTC between the two devices, its setup carried over nostr.
//
// Every setup message (offer, answer, ICE candidate, hang-up, reject,
// renegotiate) is an event signed by its sender and wrapped for its one
// recipient in an ephemeral gift wrap (kind 21059: NIP-44 to them, under a
// throwaway key, no seal). Relays see only who it's for. The sound and
// picture go device to device, encrypted by WebRTC itself (DTLS-SRTP); the
// fingerprints that pin that encryption ride in the signed offer and answer,
// so nobody between can stand in for either side. When the two can't reach
// each other directly, TURN relays the (still encrypted) packets.
//
// No DOM here: the app hands in how to sign, send, fetch ICE servers, open
// the camera, and who may ring; it gets back the call's state to draw.
import { finalizeEvent, generateSecretKey, verifyEvent } from 'nostr-tools/pure';
import * as nip44 from 'nostr-tools/nip44';

export const CALL_WRAP = 21059;
export const CALL = { OFFER: 25050, ANSWER: 25051, ICE: 25052, HANGUP: 25053, REJECT: 25054, RENEGOTIATE: 25055 };
const KINDS = new Set(Object.values(CALL));
const ALT = {
  [CALL.OFFER]: 'WebRTC call offer', [CALL.ANSWER]: 'WebRTC call answer', [CALL.ICE]: 'WebRTC ICE candidate',
  [CALL.HANGUP]: 'WebRTC call hangup', [CALL.REJECT]: 'WebRTC call rejection', [CALL.RENEGOTIATE]: 'WebRTC call renegotiation',
};
export const STALE_S = 20; // older setup messages are a relay replaying the past
const RING_MS = 60_000;
const ENDED_MS = 2500; // how long "Call ended" stays up

const now = () => Math.floor(Date.now() / 1000);
const tagOf = (ev, k) => (ev.tags.find((x) => x[0] === k) || [])[1];
export const callIdOf = (ev) => tagOf(ev, 'call-id');
export const uuid = () => (globalThis.crypto && crypto.randomUUID ? crypto.randomUUID()
  : 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => ((Math.random() * 16) | (c === 'x' ? 0 : 8)).toString(16)));

// The unsigned setup message.
export function callEvent(kind, to, callId, content = '', extra = []) {
  return { kind, created_at: now(), content, tags: [['p', to], ['call-id', callId], ['alt', ALT[kind]], ...extra] };
}
// A signed one, wrapped for one recipient.
export function wrapCall(signed, receiverPk) {
  const eph = generateSecretKey();
  return finalizeEvent({
    kind: CALL_WRAP, created_at: now(), tags: [['p', receiverPk]],
    content: nip44.encrypt(JSON.stringify(signed), nip44.getConversationKey(eph, receiverPk)),
  }, eph);
}
// A wrap to us opened: the setup message inside, its signature good, or null
// (not a call — Concord's presence beats ride the same kind — or not ours).
// `decryptFrom(peerPk, ciphertext)`: our key's NIP-44 decryption.
export async function openCall(wrap, decryptFrom) {
  if (!wrap || wrap.kind !== CALL_WRAP) return null;
  let inner;
  try { inner = JSON.parse(await decryptFrom(wrap.pubkey, wrap.content)); } catch { return null; }
  if (!inner || !KINDS.has(inner.kind) || !callIdOf(inner) || !verifyEvent(inner)) return null;
  return inner;
}
// ICE candidates as the spec writes them: JSON of the three fields.
export const candidateJson = (c) => JSON.stringify({ candidate: c.candidate, sdpMid: c.sdpMid, sdpMLineIndex: c.sdpMLineIndex });

// The calls of one identity. env:
//   me()                  our pubkey
//   sign(template)        → signed event (our key or signer)
//   send(peerPk, signed)  wrap and publish to them (the app picks the relays)
//   iceServers()          → RTCIceServer[] (TURN from coinos, STUN at least)
//   media(type, facing)   → MediaStream: microphone, and camera for 'video'
//   mayRing(pk)           whether this person may ring us (followed, or a conversation)
//   changed()             the call's state moved: draw it
//   trickle()             false for a signer that's slow or asks each time (a
//                         bunker, Amber): the candidates go inside the offer or
//                         answer instead of one signed message each
//   RTCPeerConnection     (tests may pass their own)
export function createCalls(env) {
  const PC = env.RTCPeerConnection || globalThis.RTCPeerConnection;
  let call = null; // { id, peer, type, dir, state, reason, pc, local, remote, offer, remoteSet, ice: [], at, connectedAt, muted, camOff, facing }
  const seen = new Set();
  const early = new Map(); // peer -> candidates that came before their call did
  let endTimer = null, ringTimer = null;
  const changed = () => { try { env.changed(); } catch {} };

  async function sendFor(c, kind, to, content = '', extra = []) {
    const signed = await env.sign(callEvent(kind, to, c.id, content, extra));
    await env.send(to, signed);
  }

  function stopMedia(c) {
    for (const s of [c.local]) if (s) for (const t of s.getTracks()) { try { t.stop(); } catch {} }
    try { c.pc && c.pc.close(); } catch {}
  }
  function end(reason, c = call) {
    if (!c || c !== call || c.state === 'ended') return;
    clearTimeout(ringTimer);
    stopMedia(c);
    c.state = 'ended'; c.reason = reason; c.endedAt = Date.now();
    changed();
    clearTimeout(endTimer);
    endTimer = setTimeout(() => { if (call === c) { call = null; changed(); } }, ENDED_MS);
  }

  async function connection(c) {
    const pc = new PC({ iceServers: await env.iceServers(), bundlePolicy: 'max-bundle' });
    c.pc = pc;
    c.remote = new MediaStream();
    pc.ontrack = (e) => { for (const t of (e.streams[0] || { getTracks: () => [e.track] }).getTracks()) if (!c.remote.getTracks().includes(t)) c.remote.addTrack(t); changed(); };
    c.trickle = env.trickle ? env.trickle() !== false : true;
    pc.onicecandidate = (e) => { if (c.trickle && e.candidate && call === c && c.state !== 'ended') sendFor(c, CALL.ICE, c.peer, candidateJson(e.candidate)).catch(() => {}); };
    pc.onconnectionstatechange = () => {
      if (call !== c) return;
      const s = pc.connectionState;
      if (s === 'connected' && c.state !== 'connected') { c.state = 'connected'; c.connectedAt = Date.now(); clearTimeout(ringTimer); changed(); }
      else if (s === 'failed') end('failed', c);
    };
    for (const t of c.local.getTracks()) pc.addTrack(t, c.local);
    return pc;
  }
  // without trickle: the description once its candidates are gathered (a few seconds at most)
  async function described(c) {
    const pc = c.pc;
    if (!c.trickle && pc.iceGatheringState !== 'complete') {
      await new Promise((resolve) => {
        const done = () => { if (pc.iceGatheringState === 'complete') resolve(); };
        pc.addEventListener('icegatheringstatechange', done);
        setTimeout(resolve, 4000);
      });
    }
    return pc.localDescription.sdp;
  }
  async function addCandidates(c) {
    const list = [...(early.get(c.peer) || []), ...c.ice];
    early.delete(c.peer); c.ice = [];
    for (const cand of list) { try { await c.pc.addIceCandidate(cand); } catch {} }
  }

  // ---- what the person does
  async function start(peer, type = 'voice') {
    if (call && call.state !== 'ended') throw new Error('busy');
    clearTimeout(endTimer);
    const c = call = { id: uuid(), peer, type, dir: 'out', state: 'starting', ice: [], at: Date.now(), muted: false, camOff: false, facing: 'user' };
    changed();
    try {
      c.local = await env.media(type, c.facing);
      if (call !== c) { stopMedia(c); return c; }
      const pc = await connection(c);
      await pc.setLocalDescription(await pc.createOffer());
      c.state = 'offering';
      changed();
      await sendFor(c, CALL.OFFER, peer, await described(c), [['call-type', type]]);
      ringTimer = setTimeout(() => { if (call === c && c.state === 'offering') { sendFor(c, CALL.HANGUP, peer, 'timeout').catch(() => {}); end('no-answer', c); } }, RING_MS);
    } catch (e) {
      end(e && e.name === 'NotAllowedError' ? 'no-permission' : 'error', c);
    }
    return c;
  }
  async function accept() {
    const c = call;
    if (!c || c.state !== 'incoming') return;
    clearTimeout(ringTimer);
    c.state = 'connecting';
    changed();
    try {
      c.local = await env.media(c.type, c.facing);
      if (call !== c) { stopMedia(c); return; }
      const pc = await connection(c);
      await pc.setRemoteDescription({ type: 'offer', sdp: c.offer });
      c.remoteSet = true;
      await addCandidates(c);
      await pc.setLocalDescription(await pc.createAnswer());
      const signed = await env.sign(callEvent(CALL.ANSWER, c.peer, c.id, await described(c)));
      await env.send(c.peer, signed);
      // our other devices stop ringing: answered here
      env.send(env.me(), await env.sign(callEvent(CALL.ANSWER, env.me(), c.id, ''))).catch(() => {});
    } catch (e) {
      sendFor(c, CALL.HANGUP, c.peer, 'error').catch(() => {});
      end(e && e.name === 'NotAllowedError' ? 'no-permission' : 'error', c);
    }
  }
  async function reject() {
    const c = call;
    if (!c || c.state !== 'incoming') return;
    sendFor(c, CALL.REJECT, c.peer).catch(() => {});
    env.sign(callEvent(CALL.REJECT, env.me(), c.id)).then((s) => env.send(env.me(), s)).catch(() => {});
    end('declined', c);
  }
  function hangup() {
    const c = call;
    if (!c || c.state === 'ended') return;
    if (c.state === 'incoming') { reject(); return; }
    sendFor(c, CALL.HANGUP, c.peer).catch(() => {});
    end('hung-up', c);
  }
  function setMuted(on) {
    if (!call || !call.local) return;
    call.muted = on;
    for (const t of call.local.getAudioTracks()) t.enabled = !on;
    changed();
  }
  function setCamOff(on) {
    if (!call || !call.local) return;
    call.camOff = on;
    for (const t of call.local.getVideoTracks()) t.enabled = !on;
    changed();
  }
  // the other camera: the sender's track swapped, no new offer needed
  async function flip() {
    const c = call;
    if (!c || !c.local || !c.local.getVideoTracks().length) return;
    const facing = c.facing === 'user' ? 'environment' : 'user';
    try {
      const fresh = await env.media('video-only', facing);
      const track = fresh.getVideoTracks()[0];
      const sender = c.pc && c.pc.getSenders().find((s) => s.track && s.track.kind === 'video');
      if (sender) await sender.replaceTrack(track);
      for (const old of c.local.getVideoTracks()) { c.local.removeTrack(old); old.stop(); }
      track.enabled = !c.camOff;
      c.local.addTrack(track);
      c.facing = facing;
      changed();
    } catch {}
  }

  // ---- what arrives
  async function handle(ev) {
    if (!ev || seen.has(ev.id)) return;
    seen.add(ev.id);
    if (seen.size > 5000) seen.clear();
    if (now() - ev.created_at > STALE_S) return;
    const me = env.me();
    const id = callIdOf(ev), from = ev.pubkey, self = from === me;
    const c = call;
    switch (ev.kind) {
      case CALL.OFFER: {
        if (self) return;
        if (c && c.state !== 'ended') {
          if (c.id !== id) { const s = await env.sign(callEvent(CALL.REJECT, from, id, 'busy')); env.send(from, s).catch(() => {}); }
          return;
        }
        if (!(await env.mayRing(from))) return;
        clearTimeout(endTimer);
        const type = tagOf(ev, 'call-type') === 'video' ? 'video' : 'voice';
        const n = call = { id, peer: from, type, dir: 'in', state: 'incoming', offer: ev.content, ice: [], at: Date.now(), muted: false, camOff: false, facing: 'user' };
        ringTimer = setTimeout(() => { if (call === n && n.state === 'incoming') end('missed', n); }, RING_MS);
        changed();
        return;
      }
      case CALL.ANSWER: {
        if (!c || c.id !== id) return;
        if (self) { if (c.state === 'incoming') end('answered-elsewhere', c); return; } // another of our devices took it
        if (from !== c.peer) return;
        if (c.state === 'offering') {
          c.state = 'connecting'; changed();
          try { await c.pc.setRemoteDescription({ type: 'answer', sdp: ev.content }); c.remoteSet = true; await addCandidates(c); }
          catch { end('error', c); }
        } else if (c.renegotiating) { // their answer to our renegotiation
          c.renegotiating = false;
          try { await c.pc.setRemoteDescription({ type: 'answer', sdp: ev.content }); } catch {}
        }
        return;
      }
      case CALL.ICE: {
        if (self) return;
        let cand; try { cand = JSON.parse(ev.content); } catch { return; }
        if (c && c.id === id && from === c.peer) {
          if (c.pc && c.remoteSet) { try { await c.pc.addIceCandidate(cand); } catch {} }
          else c.ice.push(cand);
        } else {
          // before the offer that opens its call: kept for when it does
          const list = early.get(from) || []; list.push(cand); early.set(from, list.slice(-50));
        }
        return;
      }
      case CALL.HANGUP: {
        if (self || !c || c.id !== id || from !== c.peer) return;
        end(c.state === 'incoming' ? 'missed' : 'peer-hung-up', c);
        return;
      }
      case CALL.REJECT: {
        if (!c || c.id !== id) return;
        if (self) { if (c.state === 'incoming') end('declined-elsewhere', c); return; }
        if (from !== c.peer) return;
        end(ev.content === 'busy' ? 'busy' : 'peer-declined', c);
        return;
      }
      case CALL.RENEGOTIATE: {
        if (self || !c || c.id !== id || from !== c.peer || !c.pc) return;
        try {
          if (c.pc.signalingState === 'have-local-offer') {
            if (me > from) return; // ours wins (the higher key), theirs is dropped
            await c.pc.setLocalDescription({ type: 'rollback' });
          }
          await c.pc.setRemoteDescription({ type: 'offer', sdp: ev.content });
          await c.pc.setLocalDescription(await c.pc.createAnswer());
          await sendFor(c, CALL.ANSWER, c.peer, c.pc.localDescription.sdp);
        } catch {}
        return;
      }
    }
  }

  return {
    get call() { return call; },
    start, accept, reject, hangup, setMuted, setCamOff, flip, handle,
    // a sign-out or account switch: whatever was going on ends here
    stop() { if (call && call.state !== 'ended') hangup(); call = null; early.clear(); },
  };
}