Eve-Relay/eventEncryptionDecryption.ts

import type { Database } from '@db/sqlite';
import * as nostrTools from '@nostr/tools';
import { nip44 } from '@nostr/tools';
import { MAX_CHUNK_SIZE, MIN_POW, POW_TO_MINE } from './consts.ts';
import {
  getActiveCCN,
  getAllCCNs,
  getCCNPrivateKeyByPubkey,
  randomTimeUpTo2DaysInThePast,
} from './utils.ts';
import { None, type Option, Some, flatMap, map } from './utils/option.ts';
import { sql } from './utils/queries.ts';

export class EventAlreadyExistsException extends Error {}
export class ChunkedEventReceived extends Error {}

export function createEncryptedEventForPubkey(
  pubkey: string,
  event: nostrTools.VerifiedEvent,
) {
  const randomPrivateKey = nostrTools.generateSecretKey();
  const randomPrivateKeyPubKey = nostrTools.getPublicKey(randomPrivateKey);
  const conversationKey = nip44.getConversationKey(randomPrivateKey, pubkey);

  const eventJson = JSON.stringify(event);
  const encryptedEvent = nip44.encrypt(eventJson, conversationKey);

  const sealTemplate = {
    kind: 13,
    created_at: randomTimeUpTo2DaysInThePast(),
    content: encryptedEvent,
    tags: [],
  };

  const seal = nostrTools.finalizeEvent(sealTemplate, randomPrivateKey);
  const giftWrapTemplate = {
    kind: 1059,
    created_at: randomTimeUpTo2DaysInThePast(),
    content: nip44.encrypt(JSON.stringify(seal), conversationKey),
    tags: [['p', pubkey]],
    pubkey: randomPrivateKeyPubKey,
  };
  const minedGiftWrap = nostrTools.nip13.minePow(giftWrapTemplate, POW_TO_MINE);

  const giftWrap = nostrTools.finalizeEvent(minedGiftWrap, randomPrivateKey);
  return giftWrap;
}

export function createEncryptedChunkForPubkey(
  pubkey: string,
  chunk: string,
  chunkIndex: number,
  totalChunks: number,
  messageId: string,
  privateKey: Uint8Array,
) {
  const randomPrivateKey = nostrTools.generateSecretKey();
  const randomPrivateKeyPubKey = nostrTools.getPublicKey(randomPrivateKey);
  const conversationKey = nip44.getConversationKey(randomPrivateKey, pubkey);

  const sealTemplate = {
    kind: 13,
    created_at: randomTimeUpTo2DaysInThePast(),
    content: nip44.encrypt(chunk, conversationKey),
    tags: [['chunk', String(chunkIndex), String(totalChunks), messageId]],
  };

  const seal = nostrTools.finalizeEvent(sealTemplate, privateKey);
  const giftWrapTemplate = {
    kind: 1059,
    created_at: randomTimeUpTo2DaysInThePast(),
    content: nip44.encrypt(JSON.stringify(seal), conversationKey),
    tags: [['p', pubkey]],
    pubkey: randomPrivateKeyPubKey,
  };

  const minedGiftWrap = nostrTools.nip13.minePow(giftWrapTemplate, POW_TO_MINE);
  const giftWrap = nostrTools.finalizeEvent(minedGiftWrap, randomPrivateKey);
  return giftWrap;
}

export async function createEncryptedEvent(
  event: nostrTools.VerifiedEvent,
  db: Database,
): Promise<nostrTools.VerifiedEvent | nostrTools.VerifiedEvent[]> {
  if (!event.id) throw new Error('Event must have an ID');
  if (!event.sig) throw new Error('Event must be signed');

  const activeCCN = getActiveCCN(db);
  if (!activeCCN) throw new Error('No active CCN found');

  const ccnPubKey = activeCCN.pubkey;
  const ccnPrivateKey = await getCCNPrivateKeyByPubkey(ccnPubKey);

  const eventJson = JSON.stringify(event);
  if (eventJson.length <= MAX_CHUNK_SIZE) {
    return createEncryptedEventForPubkey(ccnPubKey, event);
  }

  const chunks: string[] = [];
  for (let i = 0; i < eventJson.length; i += MAX_CHUNK_SIZE)
    chunks.push(eventJson.slice(i, i + MAX_CHUNK_SIZE));

  const messageId = crypto.randomUUID();
  const totalChunks = chunks.length;

  const encryptedChunks = [];
  for (let i = 0; i < chunks.length; i++) {
    const chunk = chunks[i];
    encryptedChunks.push(
      createEncryptedChunkForPubkey(
        ccnPubKey,
        chunk,
        i,
        totalChunks,
        messageId,
        ccnPrivateKey,
      ),
    );
  }

  return encryptedChunks;
}

/**
 * Attempts to decrypt an event using a specific CCN private key
 * @returns The decrypted event with CCN pubkey if successful, None otherwise
 */
function attemptDecryptWithKey(
  event: nostrTools.Event,
  ccnPrivkey: Uint8Array,
  ccnPubkey: string,
): Option<nostrTools.VerifiedEvent> {
  try {
    const conversationKey = nip44.getConversationKey(ccnPrivkey, event.pubkey);
    const sealResult = map(
      Some(nip44.decrypt(event.content, conversationKey)),
      JSON.parse,
    );

    return flatMap(sealResult, (seal) => {
      if (!seal || seal.kind !== 13) return None();

      const chunkTag = seal.tags.find((tag: string[]) => tag[0] === 'chunk');
      if (!chunkTag) {
        const contentResult = map(
          Some(nip44.decrypt(seal.content, conversationKey)),
          JSON.parse,
        );
        return map(contentResult, (content) => ({ ...content, ccnPubkey }));
      }

      return None();
    });
  } catch {
    return None();
  }
}

/**
 * Handles a chunked message by storing it in the database and checking if all chunks are received
 * @returns The complete decrypted event if all chunks are received, throws ChunkedEventReceived otherwise
 */
function handleChunkedMessage(
  db: Database,
  event: nostrTools.Event,
  ccnPrivkey: Uint8Array,
  ccnPubkey: string,
): nostrTools.VerifiedEvent {
  const conversationKey = nip44.getConversationKey(ccnPrivkey, event.pubkey);
  const sealResult = map(
    Some(nip44.decrypt(event.content, conversationKey)),
    JSON.parse,
  );

  const seal = sealResult.isSome ? sealResult.value : null;
  if (!seal) {
    throw new Error('Invalid chunked message format');
  }

  const chunkTag = seal.tags.find((tag: string[]) => tag[0] === 'chunk');
  if (!chunkTag) {
    throw new Error('Invalid chunked message format');
  }

  const [_, chunkIndex, totalChunks, messageId] = chunkTag;
  const chunk = nip44.decrypt(seal.content, conversationKey);

  const storedChunks = sql`
    SELECT COUNT(*) as count
    FROM event_chunks
    WHERE message_id = ${messageId}
  `(db)[0].count;

  sql`
    INSERT INTO event_chunks (message_id, chunk_index, total_chunks, content, created_at, ccn_pubkey)
    VALUES (${messageId}, ${chunkIndex}, ${totalChunks}, ${chunk}, ${Math.floor(Date.now() / 1000)}, ${ccnPubkey})
  `(db);

  if (storedChunks + 1 === Number(totalChunks)) {
    const allChunks = sql`
      SELECT * FROM event_chunks
      WHERE message_id = ${messageId}
      ORDER BY chunk_index
    `(db);

    let fullContent = '';
    for (const chunk of allChunks) {
      fullContent += chunk.content;
    }

    const content = JSON.parse(fullContent);
    return { ...content, ccnPubkey };
  }

  throw new ChunkedEventReceived();
}

export async function decryptEvent(
  db: Database,
  event: nostrTools.Event,
): Promise<nostrTools.VerifiedEvent & { ccnPubkey: string }> {
  if (event.kind !== 1059) {
    throw new Error('Cannot decrypt event -- not a gift wrap');
  }

  const allCCNs = getAllCCNs(db);
  if (allCCNs.length === 0) {
    throw new Error('No CCNs found');
  }

  const pow = nostrTools.nip13.getPow(event.id);
  const isInvite =
    event.tags.findIndex(
      (tag: string[]) => tag[0] === 'type' && tag[1] === 'invite',
    ) !== -1;
  const eventDestination = event.tags.find(
    (tag: string[]) => tag[0] === 'p',
  )?.[1];

  if (!eventDestination) {
    throw new Error('Cannot decrypt event -- no destination');
  }

  if (isInvite) {
    const ccnPrivkey = await getCCNPrivateKeyByPubkey(eventDestination);
    const decryptedEvent = attemptDecryptWithKey(
      event,
      ccnPrivkey,
      eventDestination,
    );
    if (decryptedEvent.isSome) {
      const recipient = decryptedEvent.value.tags.find(
        (tag: string[]) => tag[0] === 'p',
      )?.[1];
      if (recipient !== eventDestination)
        throw new Error('Cannot decrypt invite');
      return { ...decryptedEvent.value, ccnPubkey: eventDestination };
    }
    throw new Error('Cannot decrypt invite');
  }

  if (pow < MIN_POW) {
    throw new Error('Cannot decrypt event -- PoW too low');
  }

  const ccnPrivkey = await getCCNPrivateKeyByPubkey(eventDestination);
  const decryptedEvent = attemptDecryptWithKey(
    event,
    ccnPrivkey,
    eventDestination,
  );
  if (decryptedEvent.isSome) {
    return { ...decryptedEvent.value, ccnPubkey: eventDestination };
  }

  try {
    const chuncked = handleChunkedMessage(
      db,
      event,
      ccnPrivkey,
      eventDestination,
    );
    return { ...chuncked, ccnPubkey: eventDestination };
  } catch (e) {
    if (e instanceof ChunkedEventReceived) {
      throw e;
    }
  }

  throw new Error('Failed to decrypt event with any CCN key');
}