// server/utils/gameDay.ts

// Helper to get the start of a given date for daily EXP checks
const getStartOfDay = (date: Date) => {
  const d = new Date(date);
  d.setUTCHours(0, 0, 0, 0); // Use UTC for calendar day consistency
  return d;
};

export function getTodayDay(): string {
  const today = getStartOfDay(new Date());
  return today.toISOString().split('T')[0]; // Returns "YYYY-MM-DD"
}

export function isBeforeDay(day1: string | null | undefined, day2: string): boolean {
  if (!day1) return true; // A null/undefined day is always before any valid day for our logic (e.g., first time processing)
  return day1 < day2; // Lexicographical comparison works for "YYYY-MM-DD"
}

export function getPreviousDay(): string {
  const yesterday = getStartOfDay(new Date());
  yesterday.setUTCDate(yesterday.getUTCDate() - 1);
  return yesterday.toISOString().split('T')[0];
}

export function daysSince(pastDay: string, futureDay: string): number {
  // We work with UTC dates to avoid timezone issues.
  const pastDate = new Date(`${pastDay}T00:00:00Z`);
  const futureDate = new Date(`${futureDay}T00:00:00Z`);

  // getTime() returns milliseconds since epoch
  const diffTime = futureDate.getTime() - pastDate.getTime();
  
  // 1000 ms/s * 60 s/min * 60 min/hr * 24 hr/day
  const diffDays = Math.round(diffTime / (1000 * 60 * 60 * 24));
  
  return diffDays > 0 ? diffDays : 0;
}

/**
 * Converts a "YYYY-MM-DD" string into the application's day-of-week convention.
 * @param gameDay A string in "YYYY-MM-DD" format.
 * @returns A number where Monday is 0 and Sunday is 6.
 */
export function getDayOfWeekFromGameDay(gameDay: string): number {
  // Create a date object from the string. Appending 'T00:00:00Z' ensures it's parsed as UTC,
  // preventing the user's server timezone from shifting the date.
  const date = new Date(`${gameDay}T00:00:00Z`);
  const jsDayOfWeek = date.getUTCDay(); // 0 (Sunday) to 6 (Saturday)
  
  // Convert JS day (Sun=0) to the application's convention (Mon=0, Sun=6)
  return (jsDayOfWeek === 0) ? 6 : jsDayOfWeek - 1;
}

/**
 * Calculates the previous day from a given "YYYY-MM-DD" string.
 * @param gameDay A string in "YYYY-MM-DD" format.
 * @returns The previous day as a "YYYY-MM-DD" string.
 */
export function getPreviousGameDay(gameDay: string): string {
  const date = new Date(`${gameDay}T00:00:00Z`);
  date.setUTCDate(date.getUTCDate() - 1);
  return date.toISOString().split('T')[0];
}