frontends/react/src/PyodideBackend.ts

const PYODIDE_URL = "https://cdn.jsdelivr.net/pyodide/v0.26.1/full/pyodide.mjs";

import managerCode from "../../../backend/src/manager.py?raw";
import logicCode from "../../../backend/src/logic.py?raw";
import type { CsvParseResult, CsvSettings, DataPoints, DecisionBoundaryResult, DecisionBoundarySettings, ModelSettings } from "./types";


export class PyodideBackend {
  private initialized: boolean = false;
  private initPromise: Promise<void> | null = null;

  private chain: Promise<void> = Promise.resolve();

  private pyodide: any = null;
  private manager: any = null;
  private errorHandler: ((message: string) => void) | null = null;

  setErrorHandler(handler: (message: string) => void): void {
    this.errorHandler = handler;
  }

  async init(): Promise<void> {
    if (this.initialized) {
      return;
    }
    if (this.initPromise) {
      return this.initPromise;
    }

    this.initPromise = (async () => {
      const { loadPyodide } = await import(/* @vite-ignore */ PYODIDE_URL);

      this.pyodide = await loadPyodide({
        indexURL: "https://cdn.jsdelivr.net/pyodide/v0.26.1/full/"
      });

      await this.pyodide.loadPackage(["numpy", "scikit-learn", "pandas"]);

      this.pyodide.FS.writeFile("logic.py", logicCode);
      this.pyodide.FS.writeFile("manager.py", managerCode);
      this.pyodide.runPython(`from manager import Manager; manager = Manager();`);
      this.manager = this.pyodide.globals.get("manager");

      if (!this.manager) {
        throw new Error("Failed to initialize pyodide manager");
      }

      console.log("Pyodide initialized");
      this.initialized = true;
    })();

    return this.initPromise;
  }

  async setDataset2d(dataset: DataPoints): Promise<void> {
    console.log("setting datset 2d");
    await this.init();

    const inputs = dataset.xPoints.map((x, i) => [x, dataset.yPoints[i]]);
    const outputs = dataset.labels;
    await this.handleCall<void>("handle_set_dataset", { inputs, outputs });
  }

  async setModelConfig(settings: ModelSettings): Promise<void> {
    await this.handleCall<void>(
      "handle_set_model_config", { type: settings.type, arguments: settings.arguments }
    );
  }

  async buildModel(): Promise<void> {
    await this.handleCall<void>("handle_build_model");
  }

  async getDecisionBoundary(settings: DecisionBoundarySettings): Promise<DecisionBoundaryResult> {
    return await this.handleCall<DecisionBoundaryResult>("handle_get_decision_boundary", settings);
  }

  async setDatasetCsv(buffer: ArrayBuffer, settings: CsvSettings): Promise<CsvParseResult> {
    return await this.handleCall<CsvParseResult>(
      "handle_set_dataset_csv", { buffer: buffer, settings }
    );
  }

  async setCsvSettings(settings: CsvSettings): Promise<CsvParseResult> {
    return await this.handleCall<CsvParseResult>("handle_set_csv_settings", settings);
  }

  async getDatasetCsv(): Promise<string> {
    return await this.handleCall<string>("handle_get_dataset_csv");
  }

  private enqueue<T>(fn: () => Promise<T>): Promise<T> {
    const next = this.chain.then(() => fn(), () => fn());
    this.chain = next.then(() => undefined, () => undefined);
    return next;
  }

  private async handleCall<T>(methodName: string, args?: unknown): Promise<T> {
    await this.init();

    return this.enqueue(async () => {
      let pyArgs: any = null;
      let pyResult: any = null;

      try {
        if (args !== undefined) {
          pyArgs = this.pyodide.toPy(args);
        }

        const fn = this.manager[methodName];
        if (!fn) {
          throw new Error(`Manager has no method named ${methodName}`);
        }

        pyResult = args === undefined ? fn.call(this.manager) : fn.call(this.manager, pyArgs);

        const result = pyResult && typeof pyResult.toJs === "function" 
          ? pyResult.toJs({ dict_converter: Object.fromEntries })
          : pyResult;

        if (result?.status === "USER_ERROR") {
          const message = result.message || "An error occurred in the backend";
          throw new Error(message);
        }
        
        return result as T;

      } catch (error) {
        const message = error instanceof Error ? error.message : String(error);
        this.errorHandler?.(message);
        throw error instanceof Error ? error : new Error(message);

      } finally {
        if (pyArgs && typeof pyArgs.destroy === "function") {
          pyArgs.destroy();
        }
        if (pyResult && typeof pyResult.destroy === "function") {
          pyResult.destroy();
        }
      }
    });
  }
};