PacketStation/frontend/src/components/useGuard.tsx

import { useCallback, useMemo, useState, type ReactNode } from "react";
import { ApiError, errorCode } from "../api/client";
import type { Guarded, SignBody } from "../api/types";
import { ReasonSheet, type ReasonOptions } from "./ReasonSheet";
import { SignatureSheet } from "./SignatureSheet";

type Ask =
  | { kind: "reason"; opts: ReasonOptions; resolve: (r: string | null) => void }
  | {
      kind: "sign";
      meaning: string;
      sub: string | undefined;
      attempt: (sign: SignBody) => Promise<unknown>;
      resolve: (r: { ok: true; value: unknown } | { ok: false }) => void;
      reject: (err: unknown) => void;
    };

export interface RunOptions {
  /** The signature meaning when the step is known to need one. Otherwise the sheet opens on 400 signature_required. */
  sign?: string | undefined;
  /** Shown next to the sheet titles, like the job name. */
  sub?: string | undefined;
}

export interface Guard {
  /**
   * Runs a call. On 400 it_reason_required it asks for the IT reason and retries with `it_reason`.
   * On 400 signature_required it opens the signature sheet and retries with `sign`.
   * Resolves undefined when the user cancels. Other errors are thrown.
   */
  run: <T>(fn: (g: Guarded) => Promise<T>, opts?: RunOptions) => Promise<T | undefined>;
  /** Asks for a reason. Null when cancelled. */
  askReason: (opts: ReasonOptions) => Promise<string | null>;
  /** The open sheet, if any. Render it once in the screen. */
  sheet: ReactNode;
}

export const IT_REASON: ReasonOptions = {
  title: "IT reason",
  label: "Why IT is making this change",
  note: "You are changing this as IT. The reason is recorded with the change.",
  min: 8,
  submitLabel: "Continue",
};

function meaningOf(err: unknown): string {
  if (err instanceof ApiError && err.body && typeof err.body === "object" && "meaning" in err.body) {
    const m = (err.body as { meaning: unknown }).meaning;
    if (typeof m === "string" && m) return m;
  }
  return "Sign this step";
}

/** The IT reason and signature retries, as sheets. */
export function useGuard(): Guard {
  const [ask, setAsk] = useState<Ask | null>(null);

  const askReason = useCallback(
    (opts: ReasonOptions) =>
      new Promise<string | null>((resolve) => {
        setAsk({ kind: "reason", opts, resolve });
      }),
    [],
  );

  const askSign = useCallback(
    <T,>(meaning: string, sub: string | undefined, attempt: (sign: SignBody) => Promise<T>) =>
      new Promise<{ ok: true; value: T } | { ok: false }>((resolve, reject) => {
        setAsk({
          kind: "sign",
          meaning,
          sub,
          attempt,
          resolve: resolve as (r: { ok: true; value: unknown } | { ok: false }) => void,
          reject,
        });
      }),
    [],
  );

  const run = useCallback(
    async <T,>(fn: (g: Guarded) => Promise<T>, opts: RunOptions = {}): Promise<T | undefined> => {
      let itReason: string | undefined;
      let meaning = opts.sign;
      for (let round = 0; round < 4; round++) {
        const call = (sign?: SignBody) => {
          const g: Guarded = {};
          if (itReason) g.it_reason = itReason;
          if (sign) g.sign = sign;
          return fn(g);
        };
        try {
          if (meaning) {
            const r = await askSign(meaning, opts.sub, call);
            return r.ok ? r.value : undefined;
          }
          return await call();
        } catch (err) {
          const code = errorCode(err);
          if (code === "it_reason_required" && !itReason) {
            const r = await askReason({ ...IT_REASON, sub: opts.sub });
            if (r === null) return undefined;
            itReason = r;
            continue;
          }
          if (code === "signature_required" && !meaning) {
            meaning = meaningOf(err);
            continue;
          }
          throw err;
        }
      }
      return undefined;
    },
    [askReason, askSign],
  );

  let sheet: ReactNode = null;
  if (ask?.kind === "reason") {
    sheet = (
      <ReasonSheet
        {...ask.opts}
        onSubmit={(r) => {
          setAsk(null);
          ask.resolve(r);
        }}
        onCancel={() => {
          setAsk(null);
          ask.resolve(null);
        }}
      />
    );
  } else if (ask?.kind === "sign") {
    sheet = (
      <SignatureSheet
        meaning={ask.meaning}
        sub={ask.sub}
        onSign={async (sign) => {
          const value = await ask.attempt(sign);
          setAsk(null);
          ask.resolve({ ok: true, value });
        }}
        onFail={(err) => {
          setAsk(null);
          ask.reject(err);
        }}
        onCancel={() => {
          setAsk(null);
          ask.resolve({ ok: false });
        }}
      />
    );
  }

  return useMemo(() => ({ run, askReason, sheet }), [run, askReason, sheet]);
}