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

/** Merge conditional class names and de-duplicate Tailwind utilities. */
export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs));
}

/** Format a number of cents (e.g. 900) as a currency string ("$9"). */
export function formatPrice(cents: number, currency = "USD") {
  const dollars = cents / 100;
  return new Intl.NumberFormat("en-US", {
    style: "currency",
    currency,
    maximumFractionDigits: dollars % 1 === 0 ? 0 : 2,
  }).format(dollars);
}

/** The monthly usage bucket key, e.g. "2026-06". Pass a date for testability. */
export function periodKey(date: Date): string {
  const y = date.getUTCFullYear();
  const m = String(date.getUTCMonth() + 1).padStart(2, "0");
  return `${y}-${m}`;
}

/**
 * Returns `path` only if it is a safe same-origin relative path; otherwise
 * falls back to "/dashboard". Guards against open-redirect attacks by rejecting
 * protocol-relative ("//", "/\"), absolute ("https://…"), and backslash URLs.
 */
export function safeRedirect(path: string | null | undefined): string {
  if (!path) return "/dashboard";
  // Must be a single-slash-rooted relative path with no scheme or backslash escapes.
  if (
    !path.startsWith("/") ||
    path.startsWith("//") ||
    path.startsWith("/\\") ||
    path.startsWith("\\") ||
    path.includes("://")
  ) {
    return "/dashboard";
  }
  return path;
}