SkateSpots/src/components/auth/AmberCallbackHandler.tsx

/**
 * AmberCallbackHandler
 * 
 * This component handles Amber (NIP-55) callbacks at the app level.
 * It processes results from Amber after signing operations and login.
 * 
 * For web apps, Amber communication works via URL redirects:
 * 1. App opens nostrsigner: URL to request signing
 * 2. Amber opens and user approves/rejects
 * 3. Amber redirects back to callbackUrl with result in query params
 * 4. This component processes the result
 * 
 * PWA NOTE: PWAs can lose localStorage when redirecting to external apps.
 * This handler uses multiple fallback strategies:
 * 1. Check localStorage, sessionStorage, and IndexedDB for pending operation
 * 2. If all storage is lost but result looks like a pubkey, assume it's a login
 */

import { useEffect, useRef, useState } from 'react';
import { useLoginActions } from '@/hooks/useLoginActions';
import { useToast } from '@/hooks/useToast';
import { useTranslation } from '@/contexts/language';
import {
  isAmberCallback,
  getAmberCallbackResult,
  getAmberPendingOperationAsync,
  clearAmberPendingOperation,
  cleanAmberCallbackUrl,
  getAmberLogin,
  reconstructSignedEvent,
} from '@/lib/amber';

export function AmberCallbackHandler() {
  const login = useLoginActions();
  const { toast } = useToast();
  const { t } = useTranslation();
  const hasProcessed = useRef(false);
  const [debugInfo, setDebugInfo] = useState<string | null>(null);

  useEffect(() => {
    // If we're already on the /amber-callback route, AmberCallbackPage handles
    // the processing — this global handler must stay silent to avoid a race.
    const hashPath = window.location.hash.replace(/^#/, '').split('?')[0];
    if (hashPath === '/amber-callback') {
      return;
    }

    // Check if this is an Amber callback
    const isCallback = isAmberCallback();

    if (!isCallback) {
      return;
    }

    // Only process once per page load
    if (hasProcessed.current) {
      return;
    }
    hasProcessed.current = true;

    // Show debug info temporarily
    setDebugInfo(t('settingsUi.amberCallback.processing'));

    // Process async to allow IndexedDB lookup
    processAmberCallback();

    async function processAmberCallback() {
      const result = getAmberCallbackResult();

      setDebugInfo(t('settingsUi.amberCallback.gotResult', { result: result ? result.substring(0, 16) + '...' : 'null' }));

      // Clean up URL immediately to prevent re-processing on refresh
      cleanAmberCallbackUrl();

      if (!result) {
        // User cancelled or Amber failed
        clearAmberPendingOperation();
        setDebugInfo(t('settingsUi.amberCallback.noResultDebug'));
        toast({
          title: 'Amber',
          description: t('settingsUi.amberCallback.noResultToast'),
          variant: 'destructive',
        });
        return;
      }

      // Try to get pending operation from any storage
      const pendingOp = await getAmberPendingOperationAsync();
      // Log only the operation TYPE — never the payload (encrypt/decrypt ops can
      // carry plaintext).
      console.log('[AmberCallback] Pending operation type:', pendingOp?.type ?? 'none');

      const pubkeyRegex = /^[0-9a-fA-F]{64}$/;

      // SECURITY: a callback is only valid when it matches an operation this app
      // actually started. Never infer a login from a bare `?event=<pubkey>` URL —
      // that would let any link switch the user into an arbitrary account.
      if (!pendingOp) {
        console.warn('[AmberCallback] No pending operation found — ignoring callback');
        setDebugInfo(t('settingsUi.amberCallback.sessionLostToast'));
        toast({
          title: 'Amber',
          description: t('settingsUi.amberCallback.sessionLostToast'),
          variant: 'destructive',
        });
        return;
      }

      // Process based on operation type
      switch (pendingOp.type) {
        case 'get_public_key': {
          console.log('[AmberCallback] Processing get_public_key...');
          
          if (pubkeyRegex.test(result)) {
            try {
              login.amber(result.toLowerCase());
              clearAmberPendingOperation();
              console.log('[AmberCallback] Login successful!');
              toast({
                title: t('settingsUi.amberCallback.loggedInTitle'),
                description: t('settingsUi.amberCallback.amberLoginDesc'),
              });
            } catch (error) {
              console.error('[AmberCallback] Amber login failed:', error);
              clearAmberPendingOperation();
              toast({
                title: t('settingsUi.amberCallback.loginFailedTitle'),
                description: t('settingsUi.amberCallback.loginFailedDesc'),
                variant: 'destructive',
              });
            }
          } else {
            console.warn('[AmberCallback] Invalid pubkey format:', result);
            clearAmberPendingOperation();
            toast({
              title: t('settingsUi.amberCallback.loginFailedTitle'),
              description: t('settingsUi.amberCallback.invalidPubkeyDesc'),
              variant: 'destructive',
            });
          }
          break;
        }

        case 'sign_event': {
          // Store the signed event result for the caller to retrieve.
          // Amber returns a BARE signature (returnType='signature'), so we
          // reconstruct the full event from the original template + signature
          // and compute its id locally — a raw JSON.parse(result) would throw on
          // a bare signature or produce an event with an empty id that stalls
          // the relay. See reconstructSignedEvent() for details.
          const signedEvent = reconstructSignedEvent(
            result,
            pendingOp.eventJson,
            getAmberLogin() ?? '',
          );
          if (signedEvent) {
            sessionStorage.setItem('amber_signed_event', JSON.stringify(signedEvent));
            clearAmberPendingOperation();
            toast({
              title: t('settingsUi.amberCallback.eventSignedTitle'),
              description: t('settingsUi.amberCallback.eventSignedDesc'),
            });
            // Reload the page to re-submit the event
            // This is a workaround since we can't resolve the original promise
            window.location.reload();
          } else {
            console.error('Failed to reconstruct signed event from Amber result');
            clearAmberPendingOperation();
            toast({
              title: t('settingsUi.amberCallback.signingFailedTitle'),
              description: t('settingsUi.amberCallback.signingFailedDesc'),
              variant: 'destructive',
            });
          }
          break;
        }

        case 'nip04_encrypt':
        case 'nip44_encrypt':
        case 'nip04_decrypt':
        case 'nip44_decrypt': {
          // Store encryption/decryption results
          sessionStorage.setItem('amber_crypto_result', result);
          clearAmberPendingOperation();
          toast({
            title: t('settingsUi.amberCallback.operationCompleteTitle'),
            description: t('settingsUi.amberCallback.operationCompleteDesc', { op: pendingOp.type.replace('_', ' ') }),
          });
          break;
        }

        default: {
          console.warn('Unknown Amber operation type:', pendingOp.type);
          clearAmberPendingOperation();
        }
      }
    }
  }, [login, toast, t]);

  // Show debug overlay when processing Amber callback
  if (debugInfo) {
    return (
      <div className="fixed top-0 left-0 right-0 z-[9999] bg-yellow-500 text-black px-4 py-2 text-center text-sm font-mono">
        🔐 Amber: {debugInfo}
      </div>
    );
  }

  return null;
}