impl/typescript.ts

Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.

import { addDays } from "./dates_add_days.ts";  ← from dates.add-days ^1.0.0 · built alongside by fune
import { BANK_RATE, BANK_RATE_HISTORY } from "./finance_uk_bank_rate_data.ts";  ← this capability’s own data, compiled from data/bank-rate.json into the same file by fune build
import { type BankRate } from "./finance_uk_bank_rate_types.ts";

/** Bank Rate in force on a date: the latest change on or before it. */
export function ukBankRate(onDate: string): BankRate {
  addDays(onDate, 0); // validates the date; ISO dates then compare as strings
  for (const row of BANK_RATE) {
    if (onDate >= row.validFrom && (row.validTo === null || onDate <= row.validTo)) {
      return { basisPoints: row.basisPoints, validFrom: row.validFrom, validTo: row.validTo };
    }
  }
  // A history=current build keeps only the rate in force; answering an older
  // date with it would be exactly the wrong answer this data exists to prevent.
  if (BANK_RATE_HISTORY !== "full" && BANK_RATE.length > 0) {
    const earliest = BANK_RATE.map((r) => r.validFrom).reduce((a, b) => (b < a ? b : a));
    if (onDate < earliest) {
      throw new RangeError(
        `no Bank Rate on ${onDate}: this build was installed with history=${BANK_RATE_HISTORY}, so it only carries rates from ${earliest}. Reinstall with history=full for older dates.`,
      );
    }
  }
  throw new RangeError(`no Bank Rate on ${onDate}`);
}