import type { DateTimeString } from '@/types/Opportunities';

const ZERO_TIME_PREFIX = '0001-01-01';

const dateFormat = new Intl.DateTimeFormat('en-GB', {
  day: 'numeric',
  month: 'short',
  year: 'numeric',
});

const dateTimeFormat = new Intl.DateTimeFormat('en-GB', {
  day: 'numeric',
  month: 'short',
  year: 'numeric',
  hour: '2-digit',
  minute: '2-digit',
});

const moneyFormat = new Intl.NumberFormat('en-GB', {
  style: 'currency',
  currency: 'GBP',
  maximumFractionDigits: 0,
});

// en-GB's compact suffixes are k, m and bn; amounts under £1,000 are left
// whole.
const shortMoneyFormat = new Intl.NumberFormat('en-GB', {
  style: 'currency',
  currency: 'GBP',
  notation: 'compact',
});

const countFormat = new Intl.NumberFormat('en-GB');

/** Treats null and Go's zero time.Time as "no date". */
export function parseDate(value: DateTimeString | null | undefined): Date | null {
  if (!value || value.startsWith(ZERO_TIME_PREFIX)) return null;
  const d = new Date(value);
  return Number.isNaN(d.getTime()) ? null : d;
}

/** A date for display, e.g. "3 Mar 2026", or a dash for no date. */
export function formatDate(value: DateTimeString | null | undefined): string {
  const d = parseDate(value);
  return d ? dateFormat.format(d) : '—';
}

/** A date and time for display, e.g. "3 Mar 2026, 09:30", or a dash for none. */
export function formatDateTime(value: DateTimeString | null | undefined): string {
  const d = parseDate(value);
  return d ? dateTimeFormat.format(d) : '—';
}

/** An amount in pounds for display, e.g. "£125,001", or a dash for none. */
export function formatMoney(value: number): string {
  return value > 0 ? moneyFormat.format(value) : '—';
}

/**
 * An amount in pounds shortened with a suffix, e.g. "£250k", "£1.5m" or
 * "£36bn", or a dash for none. Amounts under £1,000 are shown whole.
 */
export function formatMoneyShort(value: number): string {
  return value > 0 ? shortMoneyFormat.format(value) : '—';
}

/** A count for display, e.g. "4,854". */
export function formatCount(value: number): string {
  return countFormat.format(value);
}

/**
 * An amount in its currency for display, e.g. "€1,201", or a dash for none.
 * A currency code Intl doesn't know is shown after the number.
 */
export function formatValue(amount: number, currency: string): string {
  if (amount <= 0) return '—';
  if (currency === '' || currency === 'GBP') return moneyFormat.format(amount);
  try {
    return new Intl.NumberFormat('en-GB', {
      style: 'currency',
      currency,
      maximumFractionDigits: 0,
    }).format(amount);
  } catch {
    return `${countFormat.format(Math.round(amount))} ${currency}`;
  }
}