Function mergeInPlace

packages/kosong/src/message.ts:141–172

(target: StreamedMessagePart, source: StreamedMessagePart)

 * Returns `true` if the merge was performed, `false` otherwise.
 */
export function mergeInPlace(target: StreamedMessagePart, source: StreamedMessagePart): boolean {
  // TextPart + TextPart
  if (target.type === 'text' && source.type === 'text') {
    target.text += source.text;
    return true;
  }

  // ThinkPart + ThinkPart
  if (target.type === 'think' && source.type === 'think') {
    if (target.encrypted !== undefined) {
      return false;
    }
    target.think += source.think;
    if (source.encrypted !== undefined) {
      target.encrypted = source.encrypted;
    }
    return true;
  }

  // ToolCall + ToolCallPart
  if (target.type === 'function' && source.type === 'tool_call_part') {
    if (source.argumentsPart !== null) {
      target.arguments =
        target.arguments === null
          ? source.argumentsPart
          : target.arguments + source.argumentsPart;
    }
    return true;
  }

  return false;
}

/**
 * Extract the concatenated text from a message's content parts.