Function transformX

lib/client/doc.js:536–578

(client, server)

// Transform server op data by a client op, and vice versa. Ops are edited in place.
function transformX(client, server) {
  // Order of statements in this function matters. Be especially careful if
  // refactoring this function

  // A client delete op should dominate if both the server and the client
  // delete the document. Thus, any ops following the client delete (such as a
  // subsequent create) will be maintained, since the server op is transformed
  // to a no-op
  if (client.del) return setNoOp(server);

  if (server.del) {
    return new ShareDBError(ERROR_CODE.ERR_DOC_WAS_DELETED, 'Document was deleted');
  }
  if (server.create) {
    return new ShareDBError(ERROR_CODE.ERR_DOC_ALREADY_CREATED, 'Document already created');
  }

  // Ignore no-op coming from server
  if (!('op' in server)) return;

  // I believe that this should not occur, but check just in case
  if (client.create) {
    return new ShareDBError(ERROR_CODE.ERR_DOC_ALREADY_CREATED, 'Document already created');
  }

  // They both edited the document. This is the normal case for this function -
  // as in, most of the time we'll end up down here.
  //
  // You should be wondering why I'm using client.type instead of this.type.
  // The reason is, if we get ops at an old version of the document, this.type
  // might be undefined or a totally different type. By pinning the type to the
  // op data, we make sure the right type has its transform function called.
  if (client.type.transformX) {
    var result = client.type.transformX(client.op, server.op);
    client.op = result[0];
    server.op = result[1];
  } else {
    var clientOp = client.type.transform(client.op, server.op, 'left');
    var serverOp = client.type.transform(server.op, client.op, 'right');
    client.op = clientOp;
    server.op = serverOp;
  }
};

/**
 * Applies the operation to the snapshot