ai/src/ui/transform-text-to-ui-message-stream.ts

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import { UIMessageChunk } from '../ui-message-stream/ui-message-chunks';

export function transformTextToUiMessageStream({
  stream,
}: {
  stream: ReadableStream<string>;
}) {
  return stream.pipeThrough(
    new TransformStream<string, UIMessageChunk>({
      start(controller) {
        controller.enqueue({ type: 'start' });
        controller.enqueue({ type: 'start-step' });
        controller.enqueue({ type: 'text-start', id: 'text-1' });
      },

      async transform(part, controller) {
        controller.enqueue({ type: 'text-delta', id: 'text-1', delta: part });
      },

      async flush(controller) {
        controller.enqueue({ type: 'text-end', id: 'text-1' });
        controller.enqueue({ type: 'finish-step' });
        controller.enqueue({ type: 'finish' });
      },
    }),
  );
}