langchain/src/chains/router/multi_route.ts

import { ChainValues } from "@langchain/core/utils/types";
import {
  CallbackManagerForChainRun,
  Callbacks,
} from "@langchain/core/callbacks/manager";
import { BaseChain, ChainInputs } from "../../chains/base.js";

/**
 * A type that represents the inputs for the MultiRouteChain. It is a
 * recursive type that can contain nested objects, arrays, strings, and
 * numbers.
 */
type Inputs = {
  [key: string]: Inputs | Inputs[] | string | string[] | number | number[];
};

/**
 * An interface that represents the route returned by the RouterChain. It
 * includes optional fields for the destination and nextInputs.
 */
export interface Route {
  destination?: string;
  nextInputs: { [key: string]: Inputs };
}

/**
 * An interface that extends the ChainInputs interface and adds additional
 * properties for the routerChain, destinationChains, defaultChain, and
 * silentErrors. It represents the input expected by the MultiRouteChain
 * class.
 */
export interface MultiRouteChainInput extends ChainInputs {
  routerChain: RouterChain;
  destinationChains: { [name: string]: BaseChain };
  defaultChain: BaseChain;
  silentErrors?: boolean;
}

/**
 * A class that represents a router chain. It
 * extends the BaseChain class and provides functionality for routing
 * inputs to different chains.
 */
export abstract class RouterChain extends BaseChain {
  get outputKeys(): string[] {
    return ["destination", "next_inputs"];
  }

  async route(inputs: ChainValues, callbacks?: Callbacks): Promise<Route> {
    const result = await this.call(inputs, callbacks);
    return {
      destination: result.destination,
      nextInputs: result.next_inputs,
    };
  }
}

/**
 * A class that represents a multi-route chain.
 * It extends the BaseChain class and provides functionality for routing
 * inputs to different chains based on a router chain.
 */
export class MultiRouteChain extends BaseChain {
  static lc_name() {
    return "MultiRouteChain";
  }

  routerChain: RouterChain;

  destinationChains: { [name: string]: BaseChain };

  defaultChain: BaseChain;

  silentErrors = false;

  constructor(fields: MultiRouteChainInput) {
    super(fields);
    this.routerChain = fields.routerChain;
    this.destinationChains = fields.destinationChains;
    this.defaultChain = fields.defaultChain;
    this.silentErrors = fields.silentErrors ?? this.silentErrors;
  }

  get inputKeys(): string[] {
    return this.routerChain.inputKeys;
  }

  get outputKeys(): string[] {
    return [];
  }

  async _call(
    values: ChainValues,
    runManager?: CallbackManagerForChainRun
  ): Promise<ChainValues> {
    const { destination, nextInputs } = await this.routerChain.route(
      values,
      runManager?.getChild()
    );
    await runManager?.handleText(
      `${destination}: ${JSON.stringify(nextInputs)}`
    );
    if (!destination) {
      return this.defaultChain
        .call(nextInputs, runManager?.getChild())
        .catch((err) => {
          throw new Error(`Error in default chain: ${err}`);
        });
    }
    if (destination in this.destinationChains) {
      return this.destinationChains[destination]
        .call(nextInputs, runManager?.getChild())
        .catch((err) => {
          throw new Error(`Error in ${destination} chain: ${err}`);
        });
    }
    if (this.silentErrors) {
      return this.defaultChain
        .call(nextInputs, runManager?.getChild())
        .catch((err) => {
          throw new Error(`Error in default chain: ${err}`);
        });
    }
    throw new Error(
      `Destination ${destination} not found in destination chains with keys ${Object.keys(
        this.destinationChains
      )}`
    );
  }

  _chainType(): string {
    return "multi_route_chain";
  }
}