router.ts

import { z } from "zod";
import { OutputParserException } from "@langchain/core/output_parsers";
import { JsonMarkdownStructuredOutputParser } from "./structured.js";

/**
 * Defines the input parameters for the RouterOutputParser class. It can
 * include a default destination and an interpolation depth.
 */
export type RouterOutputParserInput = {
  defaultDestination?: string;
  interpolationDepth?: number;
};

/**
 * A type of output parser that extends the
 * JsonMarkdownStructuredOutputParser. It is used to parse the output of a
 * router in LangChain. The class takes a schema and an optional
 * RouterOutputParserInput object as parameters.
 */
export class RouterOutputParser<
  Y extends z.ZodTypeAny
> extends JsonMarkdownStructuredOutputParser<Y> {
  defaultDestination = "DEFAULT";

  constructor(schema: Y, options?: RouterOutputParserInput) {
    super(schema);
    this.defaultDestination =
      options?.defaultDestination ?? this.defaultDestination;
  }

  /**
   * Overrides the parse method from JsonMarkdownStructuredOutputParser.
   * This method takes a string as input, attempts to parse it, and returns
   * the parsed text. If the destination of the parsed text matches the
   * defaultDestination, the destination is set to null. If the parsing
   * fails, an OutputParserException is thrown.
   * @param text The text to be parsed.
   * @returns The parsed text as a Promise.
   */
  async parse(text: string): Promise<z.infer<Y>> {
    try {
      const parsedText = await super.parse(text);
      if (
        parsedText.destination?.toLowerCase() ===
        this.defaultDestination.toLowerCase()
      ) {
        parsedText.destination = null;
      }

      return parsedText;
    } catch (e) {
      throw new OutputParserException(
        `Failed to parse. Text: "${text}". Error: ${e}`,
        text
      );
    }
  }
}