SkateSpots/src/lib/capacitorAmberSigner.ts

/**
 * CapacitorAmberSigner
 *
 * Talks to Amber (NIP-55) using the AMETHYST FOREGROUND-INTENT pattern via our
 * own native `AmberIntent` Capacitor plugin (android-templates/AmberIntentPlugin.java).
 *
 * WHY WE REPLACED THE OLD `NostrSignerPlugin` PATH
 * ------------------------------------------------
 * The stock `nostr-signer-capacitor-plugin` (0.0.5) tries Amber's background
 * ContentProvider FIRST. On GrapheneOS (and other hardened ROMs) that silent
 * cross-app ContentResolver query is blocked and never returns, and the plugin
 * does not fall back cleanly to a foreground intent — so signing hung for 90s
 * and Amber never even appeared. That is the delete/zap/crew hang.
 *
 * Amethyst (the reference NIP-55 client) never hits this: it goes STRAIGHT to a
 * foreground Intent through a properly-registered ActivityResultLauncher, tracks
 * each request by id, and awaits the Activity result with a timeout. Our
 * `AmberIntent` plugin does exactly that — the reliable path that OPENS Amber's
 * Approve/Reject screen and returns the signature, on stock Android AND on
 * GrapheneOS. Every request is a user-visible Amber popup (the intuitive UX).
 *
 * NATIVE API (AmberIntent):
 *   getPublicKey({ permissions? })              → { result: <pubkey>, package }
 *   signEvent({ eventJson, npub })              → { result: <sig>, event }
 *   nipXXEncrypt/Decrypt({ payload, pubKey, npub }) → { result }
 * A user rejection rejects the promise with message "rejected".
 */

import type { NostrEvent, NostrSigner } from '@nostrify/nostrify';
import { Capacitor, registerPlugin } from '@capacitor/core';
import { nip19 } from 'nostr-tools';
import { reconstructSignedEvent } from '@/lib/amber';

/** Raw native bridge interface for our AmberIntent plugin (Android). */
interface AmberIntentNative {
  getPublicKey(options?: { permissions?: string }): Promise<{ result?: string; package?: string; id?: string }>;
  signEvent(options: { eventJson: string; npub: string }): Promise<{ result?: string; event?: string; id?: string }>;
  nip04Encrypt(options: { payload: string; pubKey: string; npub: string }): Promise<{ result: string }>;
  nip04Decrypt(options: { payload: string; pubKey: string; npub: string }): Promise<{ result: string }>;
  nip44Encrypt(options: { payload: string; pubKey: string; npub: string }): Promise<{ result: string }>;
  nip44Decrypt(options: { payload: string; pubKey: string; npub: string }): Promise<{ result: string }>;
}

// Lazily build the native bridge proxy once. `registerPlugin` is a pure factory
// (builds a proxy, touches no native APIs at call time), so it's safe on web too
// — the proxy simply has no implementation there and calls reject.
let nativePlugin: AmberIntentNative | null = null;
function getNativeSigner(): AmberIntentNative | null {
  try {
    if (!Capacitor?.isNativePlatform?.()) return null;
  } catch {
    return null;
  }
  if (!nativePlugin) {
    nativePlugin = registerPlugin<AmberIntentNative>('AmberIntent');
  }
  return nativePlugin;
}

/**
 * Amber is a single foreground Activity. Two concurrent intents can race: one
 * is answered, the others sit until the 60s native timeout, and the user sees
 * Amber apparently open twice / behave unpredictably. Every native call goes
 * through this one-at-a-time queue. The same request is also coalesced below,
 * so duplicate hook work never asks Amber twice for the same thing.
 */
let amberTail: Promise<void> = Promise.resolve();
function runAmber<T>(operation: () => Promise<T>): Promise<T> {
  const run = amberTail.then(operation, operation);
  amberTail = run.then(() => undefined, () => undefined);
  return run;
}

/** Turn Amber's "rejected" rejection into a friendly, catchable message. */
function normalizeAmberError(e: unknown): Error {
  const msg = (e as Error)?.message ?? String(e);
  if (/rejected/i.test(msg)) {
    return new Error('You rejected the request in Amber.');
  }
  return e instanceof Error ? e : new Error(msg);
}

/**
 * Amber may compress a large result (gzip, base64, prefixed `Signer1`) — NIP-55
 * lets a client opt out with `compressionType=none`, which the native intents now
 * send, but this is a belt-and-braces decoder for any signer that compresses
 * anyway. Without it a long `nip44_decrypt` payload (e.g. a long DM) arrives as
 * `Signer1…` and is handed to `JSON.parse` as garbage.
 */
async function decodeAmberResult(value: string): Promise<string> {
  if (!value || !value.startsWith('Signer1')) return value;
  try {
    const binary = atob(value.slice('Signer1'.length));
    const bytes = Uint8Array.from(binary, (c) => c.charCodeAt(0));
    const stream = new Blob([bytes]).stream().pipeThrough(new DecompressionStream('gzip'));
    return await new Response(stream).text();
  } catch {
    // DecompressionStream unavailable or bad data — return as-is.
    return value;
  }
}

/**
 * Login: get public key from Amber via the foreground intent.
 *
 * The native plugin OMITS the package on get_public_key (per NIP-55) so Android
 * opens Amber's UI directly — no ContentProvider, no GrapheneOS stall. We
 * pre-authorize all the permissions the app needs so Amber can (optionally)
 * remember the user's choice for a smoother, popup-light experience afterwards.
 */
let publicKeyInFlight: Promise<string> | null = null;

export function getAmberPublicKeyViaPlugin(): Promise<string> {
  if (publicKeyInFlight) return publicKeyInFlight;

  const task = (async (): Promise<string> => {
    const plugin = getNativeSigner();
    if (!plugin) {
      throw new Error('Amber signing is only available in the SkateSpots Android app.');
    }

    const permissions = JSON.stringify([
      { type: 'get_public_key' },
      { type: 'sign_event' },
      { type: 'nip04_encrypt' },
      { type: 'nip04_decrypt' },
      { type: 'nip44_encrypt' },
      { type: 'nip44_decrypt' },
    ]);

    let result: { result?: string; package?: string };
    try {
      result = await runAmber(() => plugin.getPublicKey({ permissions }));
    } catch (e) {
      throw normalizeAmberError(e);
    }

    // JSObject from Capacitor — normalize to a plain object for reliable access.
    const plain = JSON.parse(JSON.stringify(result)) as Record<string, string>;
    const value = await decodeAmberResult(plain.result ?? plain.npub ?? plain.pubkey ?? '');

    if (!value) throw new Error('Amber returned empty key');

    if (/^[0-9a-f]{64}$/i.test(value)) {
      return value.toLowerCase();
    }

    if (value.startsWith('npub1')) {
      const decoded = nip19.decode(value);
      if (decoded.type !== 'npub') throw new Error('Unexpected key format from Amber');
      return decoded.data as string;
    }

    throw new Error(`Unexpected Amber response: "${value.slice(0, 30)}"`);
  })();

  publicKeyInFlight = task;
  void task.finally(() => {
    if (publicKeyInFlight === task) publicKeyInFlight = null;
  }).catch(() => undefined);
  return task;
}

const signInFlight = new Map<string, Promise<{ result?: string; event?: string; id?: string }>>();
const cryptoInFlight = new Map<string, Promise<string>>();
/**
 * Decrypt-only result cache. Decryption is deterministic for a given
 * (identity, sender, ciphertext), so a re-render or a second screen can reuse
 * the plaintext without making Amber ask again. Encrypt results are NOT cached
 * (NIP-44 encryption is randomized). Memory-only and bounded; encrypted/private
 * content is also cached by the feature hooks themselves.
 */
const DECRYPT_CACHE_MAX = 600;
const decryptCache = new Map<string, string>();

function rememberDecrypt(key: string, value: string): void {
  if (decryptCache.size >= DECRYPT_CACHE_MAX) {
    const oldest = decryptCache.keys().next().value;
    if (oldest !== undefined) decryptCache.delete(oldest);
  }
  decryptCache.set(key, value);
}

export class CapacitorAmberSigner implements NostrSigner {
  readonly pubkey: string;
  private readonly npub: string;

  constructor(pubkeyHex: string) {
    this.pubkey = pubkeyHex;
    this.npub = nip19.npubEncode(pubkeyHex);
  }

  async getPublicKey(): Promise<string> {
    return this.pubkey;
  }

  /** Get the native AmberIntent bridge, or throw a friendly error off-native. */
  private plugin(): AmberIntentNative {
    const plugin = getNativeSigner();
    if (!plugin) {
      throw new Error('Amber signing is only available in the SkateSpots Android app.');
    }
    return plugin;
  }

  async signEvent(event: Omit<NostrEvent, 'id' | 'sig'>): Promise<NostrEvent> {
    const plugin = this.plugin();
    const eventJson = JSON.stringify(event);
    const requestKey = `${this.npub}:${eventJson}`;
    let res: { result?: string; event?: string; id?: string };
    try {
      const existing = signInFlight.get(requestKey);
      if (existing) {
        res = await existing;
      } else {
        const task = runAmber(() => plugin.signEvent({
          eventJson,
          npub: this.npub,
        }));
        signInFlight.set(requestKey, task);
        try {
          res = await task;
        } finally {
          signInFlight.delete(requestKey);
        }
      }
    } catch (e) {
      throw normalizeAmberError(e);
    }

    // Amber may return a full event JSON in `event`, or only a bare signature in
    // `result`. Reconstruct defensively so signature-only responses (common for
    // kind:5 deletions and kind:1985 labels) still produce a valid, publishable
    // event.
    const rawCandidate =
      res.event && res.event.trim()
        ? res.event
        : (res.result ?? '');

    const raw = await decodeAmberResult(rawCandidate);

    const signed = reconstructSignedEvent(raw, JSON.stringify(event), this.pubkey);
    if (!signed || !signed.sig) {
      throw new Error(
        'Amber returned an incomplete signature. Open Amber, approve the request, then try again.',
      );
    }
    return signed;
  }

  /**
   * Queue + coalesce one crypto operation. A second identical decrypt/encrypt
   * while the first is open waits on the same native result instead of opening
   * a second Amber screen.
   */
  private async crypto(
    type: 'nip04_encrypt' | 'nip04_decrypt' | 'nip44_encrypt' | 'nip44_decrypt',
    pubkey: string,
    payload: string,
  ): Promise<string> {
    const key = `${type}:${this.npub}:${pubkey}:${payload}`;
    if (type.endsWith('_decrypt')) {
      const cached = decryptCache.get(key);
      if (cached !== undefined) return cached;
    }
    const existing = cryptoInFlight.get(key);
    if (existing) return existing;

    const task = (async (): Promise<string> => {
      try {
        const plugin = this.plugin();
        const { result } = type === 'nip04_encrypt'
          ? await runAmber(() => plugin.nip04Encrypt({ payload, pubKey: pubkey, npub: this.npub }))
          : type === 'nip04_decrypt'
            ? await runAmber(() => plugin.nip04Decrypt({ payload, pubKey: pubkey, npub: this.npub }))
            : type === 'nip44_encrypt'
              ? await runAmber(() => plugin.nip44Encrypt({ payload, pubKey: pubkey, npub: this.npub }))
              : await runAmber(() => plugin.nip44Decrypt({ payload, pubKey: pubkey, npub: this.npub }));
        const decoded = await decodeAmberResult(result);
        if (type.endsWith('_decrypt')) rememberDecrypt(key, decoded);
        return decoded;
      } catch (e) {
        throw normalizeAmberError(e);
      }
    })();
    cryptoInFlight.set(key, task);
    try {
      return await task;
    } finally {
      cryptoInFlight.delete(key);
    }
  }

  readonly nip04 = {
    encrypt: async (pubkey: string, plaintext: string): Promise<string> =>
      this.crypto('nip04_encrypt', pubkey, plaintext),
    decrypt: async (pubkey: string, ciphertext: string): Promise<string> =>
      this.crypto('nip04_decrypt', pubkey, ciphertext),
  };

  readonly nip44 = {
    encrypt: async (pubkey: string, plaintext: string): Promise<string> =>
      this.crypto('nip44_encrypt', pubkey, plaintext),
    decrypt: async (pubkey: string, ciphertext: string): Promise<string> =>
      this.crypto('nip44_decrypt', pubkey, ciphertext),
  };
}

/**
 * True when we're running inside the native Capacitor app AND the native
 * NostrSigner bridge is usable. This is the ONLY reliable native check —
 * reading `window.Capacitor` from a component can be false at mount time or in
 * builds where Capacitor doesn't attach itself to `window`. Always call this at
 * the moment of the action (e.g. inside the login click handler), not at render.
 */
export function isNativeAmberAvailable(): boolean {
  try {
    return !!Capacitor?.isNativePlatform?.() && !!getNativeSigner();
  } catch {
    return false;
  }
}

/**
 * Is an external signer (Amber) usable on this device?
 *
 * We no longer do an explicit package-visibility check: on Android 11+/GrapheneOS
 * that check is unreliable (it can report false even when Amber IS installed),
 * and the login flow already attempts the foreground intent directly and surfaces
 * a clear error if Amber can't be opened. So this simply mirrors native
 * availability of the AmberIntent bridge.
 */
export async function isAmberInstalled(): Promise<boolean> {
  return isNativeAmberAvailable();
}