/**
 * Format a date string (YYYY-MM-DD HH:MM:SS) to a relative time string.
 * Examples: "just now", "5 min ago", "1 hour ago", "2 days ago", "1 week ago", "1 month ago"
 * @param {string|null} dateString - Date string in format "YYYY-MM-DD HH:MM:SS" or ISO
 * @returns {string} Relative time string
 */
export function formatRelative(dateString) {
  if (!dateString) return "";

  const date = parseDate(dateString);
  if (!date) return dateString;

  const now = new Date();
  const diffMs = now - date;
  const diffSecs = Math.floor(diffMs / 1000);
  const diffMins = Math.floor(diffSecs / 60);
  const diffHours = Math.floor(diffMins / 60);
  const diffDays = Math.floor(diffHours / 24);
  const diffWeeks = Math.floor(diffDays / 7);
  const diffMonths = Math.floor(diffDays / 30);

  if (diffSecs < 10) return "just now";
  if (diffSecs < 60) return `${diffSecs} sec ago`;
  if (diffMins < 60) return `${diffMins} min ago`;
  if (diffHours < 24) {
    const remainderMins = diffMins % 60;
    if (remainderMins > 0) {
      return `${diffHours} hour${diffHours > 1 ? "s" : ""} ${remainderMins} min ago`;
    }
    return `${diffHours} hour${diffHours > 1 ? "s" : ""} ago`;
  }
  if (diffDays < 7) return `${diffDays} day${diffDays > 1 ? "s" : ""} ago`;
  if (diffWeeks < 4) return `${diffWeeks} week${diffWeeks > 1 ? "s" : ""} ago`;
  if (diffMonths < 12) return `${diffMonths} month${diffMonths > 1 ? "s" : ""} ago`;

  const diffYears = Math.floor(diffDays / 365);
  return `${diffYears} year${diffYears > 1 ? "s" : ""} ago`;
}

/**
 * Format a date string to a readable format for tooltips.
 * Returns: "Jun 8, 2026 14:30" or "8 Jun 2026 14:30"
 * @param {string|null} dateString - Date string in format "YYYY-MM-DD HH:MM:SS" or ISO
 * @returns {string} Formatted date string
 */
export function formatDateTime(dateString) {
  if (!dateString) return "";

  const date = parseDate(dateString);
  if (!date) return dateString;

  const months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
  const month = months[date.getMonth()];
  const day = date.getDate();
  const year = date.getFullYear();
  const hours = String(date.getHours()).padStart(2, "0");
  const minutes = String(date.getMinutes()).padStart(2, "0");

  return `${month} ${day}, ${year} ${hours}:${minutes}`;
}

/**
 * Format a date string to a short date format.
 * Returns: "Jun 8, 2026"
 * @param {string|null} dateString - Date string in format "YYYY-MM-DD HH:MM:SS" or ISO
 * @returns {string} Short date string
 */
export function formatDate(dateString) {
  if (!dateString) return "";

  const date = parseDate(dateString);
  if (!date) return dateString;

  const months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
  const month = months[date.getMonth()];
  const day = date.getDate();
  const year = date.getFullYear();

  return `${month} ${day}, ${year}`;
}

/**
 * Parse a date string in various formats to a Date object.
 * @param {string} dateString - Date string in format "YYYY-MM-DD HH:MM:SS" or ISO
 * @returns {Date|null} Parsed Date object or null if invalid
 */
function parseDate(dateString) {
  if (!dateString) return null;

  // Handle "YYYY-MM-DD HH:MM:SS" format (MySQL datetime)
  const mysqlDateTimeRegex = /^(\d{4})-(\d{2})-(\d{2})\s+(\d{2}):(\d{2}):(\d{2})$/;
  const match = dateString.match(mysqlDateTimeRegex);

  if (match) {
    const [, year, month, day, hours, mins, secs] = match;
    return new Date(year, parseInt(month) - 1, day, hours, mins, secs);
  }

  // Try ISO format and other standard formats
  const parsed = new Date(dateString);
  if (!isNaN(parsed.getTime())) {
    return parsed;
  }

  return null;
}