import type { EvalLanguage } from "./types.ts";

const TIMEOUT_STATE_GRACE_MS = 5500;

function fallbackTimeoutMessage(base: string): string {
  return `${base} Kernel state may have been lost; re-establish any variables the next cell needs.`;
}

/**
 * Appends the kernel's actual post-timeout state to a TimeoutError, waiting a
 * bounded window for the interrupt outcome so the model knows whether its
 * variables survived. Falls back to an honest unknown when no outcome arrives.
 */
export async function describeTimeoutState(
  error: Error,
  execution: { readonly interruptStateRetained: Promise<boolean> | undefined }
): Promise<Error> {
  const outcome = execution.interruptStateRetained;
  if (outcome === undefined) {
    error.message = fallbackTimeoutMessage(error.message);
    return error;
  }
  let timer: ReturnType<typeof setTimeout> | undefined;
  const retained = await Promise.race([
    outcome,
    new Promise<boolean | undefined>((resolve) => {
      timer = setTimeout(() => resolve(undefined), TIMEOUT_STATE_GRACE_MS);
    }),
  ]).finally(() => {
    if (timer !== undefined) {
      clearTimeout(timer);
    }
  });
  if (retained === undefined) {
    error.message = fallbackTimeoutMessage(error.message);
  } else if (retained) {
    error.message = `${error.message} The kernel remains running; its existing variables are preserved.`;
  } else {
    error.message = `${error.message} The kernel was unresponsive and restarted; variables from earlier cells are lost.`;
  }
  return error;
}

const LANGUAGE_LABEL: Record<EvalLanguage, string> = {
  py: "Python kernel",
  js: "JavaScript worker",
  rb: "Ruby kernel",
  ts: "TypeScript worker",
};

/**
 * Composes the user-facing note for a cancelled eval cell from the interrupt
 * outcome the kernel actually reported — never a per-language assumption.
 *
 * Returns undefined when there is nothing truthful to add (no interrupt ran).
 */
export function interruptionStateNote(
  language: EvalLanguage,
  stateRetained: boolean | undefined
): string | undefined {
  if (stateRetained === undefined) {
    return;
  }
  const label = LANGUAGE_LABEL[language];
  if (stateRetained) {
    return `${label} was interrupted and remains running; its existing variables are preserved.`;
  }
  return `${label} was unresponsive to interrupt and was restarted; variables from earlier cells are lost.`;
}