/**
 * The test's starting state, as opposed to the app: a balance that is too low to run a test that spends, an account that cannot do what the test needs.
 * A failure of this kind has the reason "pre-state" (docs/design/protocol.md), so a report and a person can tell it from the app being wrong:
 * nobody should file a bug against the app because a test account ran out of testnet money.
 */
export type PreStateVerdict = { ok: true } | { ok: false; reason: "pre-state" | "internal"; message: string; expected?: string; found?: string };

const escape = (s: string): string => s.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
const num = (n: number): string => String(Math.round(n * 1e9) / 1e9);

/** Whether the balance the page shows (a number after the label, such as "Balance: 12.5 MALLBUCKS") is at least what the test needs. */
export function judgeBalance(input: { account: string; needed: number; label: string; pageText: string }): PreStateVerdict {
  if (!Number.isFinite(input.needed) || input.needed < 0) return { ok: false, reason: "internal", message: "balance-at-least needs an amount of zero or more" };
  if (input.label.trim() === "") return { ok: false, reason: "internal", message: "balance-at-least needs the label the page shows next to the balance, for example Balance" };
  const text = input.pageText.replace(/\s+/g, " ");
  const found = new RegExp(`(?<![A-Za-z])${escape(input.label.trim())}(?![A-Za-z])\\s*:?\\s*([0-9]+(?:\\.[0-9]+)?)`, "i").exec(text);
  if (found === null) {
    return { ok: false, reason: "pre-state", message: `Cannot find a "${input.label.trim().slice(0, 40)}" amount on the page for ${input.account.slice(0, 80)}, so the test's starting balance is unknown. This is about the test's starting state, not a failure of the app.` };
  }
  const have = Number(found[1]);
  if (have >= input.needed) return { ok: true };
  const shown = found[1]!.length > 30 ? `${found[1]!.slice(0, 30)}...` : found[1]!;
  return {
    ok: false,
    reason: "pre-state",
    message: `${input.account.slice(0, 80)} has ${shown} but this test needs ${num(input.needed)} (short by ${num(input.needed - have)}). This is about the test's starting state, not a failure of the app: refill the account (see docs/runbook-sessions.md) and run again.`,
    expected: `>= ${num(input.needed)}`,
    found: shown,
  };
}