import { clsx, type ClassValue } from "clsx";
import { twMerge } from "tailwind-merge";

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs));
}

/**
 * Deterministic number formatters.
 *
 * We deliberately avoid `Intl.NumberFormat("en-ZA", …)` because Node and the
 * browser ship different ICU builds — on the server, `en-ZA` falls back to a
 * generic locale and renders "342,707.17", while the browser renders the
 * expected South African "342 707,17". That mismatch blows up SSR hydration
 * (https://react.dev/link/hydration-mismatch). Hard-coding the format keeps
 * server and client byte-identical.
 *
 * Style: space as thousand separator, comma as decimal point, exactly the
 * shape `Intl` produces in a real en-ZA browser. Always positive.
 */
function groupThousands(intPart: string): string {
  // Add a space every 3 digits from the right.
  return intPart.replace(/\B(?=(\d{3})+(?!\d))/g, " ");
}

export function formatNumber(value: number | null | undefined, decimals = 2): string {
  if (value == null || isNaN(value)) return "0";
  // toFixed gives a stable, locale-independent string. Split on the decimal
  // point so we can rejoin with a comma.
  const [intPart, fracPart] = value.toFixed(decimals).split(".");
  const sign = intPart.startsWith("-") ? "-" : "";
  const digits = sign ? intPart.slice(1) : intPart;
  const grouped = groupThousands(digits);
  return fracPart != null ? `${sign}${grouped},${fracPart}` : `${sign}${grouped}`;
}

export function formatCurrency(value: number | null | undefined): string {
  if (value == null || isNaN(value)) return "R0,00";
  return `R ${formatNumber(value, 2)}`;
}

export function formatDate(value: string | Date | null | undefined): string {
  if (!value) return "";
  const d = typeof value === "string" ? new Date(value) : value;
  if (isNaN(d.getTime())) return "";
  // "21 Jul 2026" — stable across server and client.
  const months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
  return `${String(d.getDate()).padStart(2, "0")} ${months[d.getMonth()]} ${d.getFullYear()}`;
}

export function formatDateInput(value: string | Date | null | undefined): string {
  if (!value) return "";
  const d = typeof value === "string" ? new Date(value) : value;
  if (isNaN(d.getTime())) return "";
  // YYYY-MM-DD for <input type="date"> — already locale-neutral.
  const yyyy = d.getFullYear();
  const mm = String(d.getMonth() + 1).padStart(2, "0");
  const dd = String(d.getDate()).padStart(2, "0");
  return `${yyyy}-${mm}-${dd}`;
}