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

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

// REMOVED: `convertToLocalTime`, `convertToIST` and `getRelativeTime`.
//
// All three were Rudy-era, all three had ZERO call sites, and all three were WRONG for a US product:
// - `convertToIST` - hardcoded India's +5:30 offset.
// - `getRelativeTime` - hardcoded `Asia/Kolkata` twice in its body.
// - `convertToLocalTime` - labelled "FIXED: Proper timezone conversion", but re-shifted a Date that
// `new Date(isoString)` already returns in local time. Double-shifted.
//
// They were deleted rather than corrected because the danger was never the arithmetic - it was that a
// session with a timezone problem greps for a helper, finds one commented "FIXED", and trusts it.
// had just made timezone handling something sessions go looking for, which is what turned dead code into a
// live hazard. The practice's timezone now lives in `src/utils/practiceTimezone.ts`; use that.
export const formatDateForDisplay = (dateString: string): string => {
  if (!dateString) return "";
  
  const [year, month, day] = dateString.split("-").map(Number);
  let date = new Date(year, month - 1, day);

  if(!(date instanceof Date && !isNaN(date.getTime()))) {
    date = new Date(dateString);
  }
      return date.toLocaleDateString("en-US", {
    weekday: "long",
    year: "numeric",
    month: "long",
    day: "numeric",
  });
};

export const formatTimeForDisplay = (dateString: string): string => {
  if (!dateString) return "";

  const date = new Date(dateString);
  const userTimeZone = Intl.DateTimeFormat().resolvedOptions().timeZone;
  return date.toLocaleTimeString("en-US", {
    hour: "2-digit",
    minute: "2-digit",
    hour12: true,
    timeZone: userTimeZone
  });
};

// COMMENT CORRECTED, code untouched. It previously read "FIXED: Use India timezone for
// accurate day difference" - it does NOT use India's timezone; it uses the VIEWER's, resolved below. The
// behaviour was right and the label was wrong, which is the same trap that made the deleted helpers
// dangerous: this file's comments have been trusted over its code before.
// The viewer's timezone is the correct basis for "Today / Tomorrow" on a patient's own screen, but note
// it is the VIEWER's, not the PRACTICE's - see for where that distinction does matter.
export const getDaysDifference = (dateString: string): string => {
  if (!dateString) return "";
  
  const appointmentDate = new Date(dateString);
  const now = new Date();
  
  const timeZone = Intl.DateTimeFormat().resolvedOptions().timeZone;
  const appointmentDateIST = appointmentDate.toLocaleString("en-US", { timeZone });
  const nowLocal = now.toLocaleString("en-US", { timeZone });
  
  // Create new dates from India timezone strings
  const appDate = new Date(appointmentDateIST);
  const currentDate = new Date(nowLocal);
  
  // Set both dates to start of day
  const appDateStart = new Date(
    appDate.getFullYear(),
    appDate.getMonth(),
    appDate.getDate()
  );
  
  const currentDateStart = new Date(
    currentDate.getFullYear(),
    currentDate.getMonth(),
    currentDate.getDate()
  );
  
  const diffTime = appDateStart.getTime() - currentDateStart.getTime();
  const diffDays = Math.round(diffTime / (1000 * 60 * 60 * 24));
  
  if (diffDays === 0) return "Today";
  if (diffDays === 1) return "Tomorrow";
  if (diffDays > 1) return `In ${diffDays} days`;
  if (diffDays === -1) return "Yesterday";
  return `${Math.abs(diffDays)} days ago`;
};