/**
 * Bridge Days Calculator
 * Calculates optimal vacation days based on public holidays
 */

/**
 * Calculate bridge days and optimal vacation periods for a month
 * @param {number} year - The year to calculate for
 * @param {number} month - The month (0-11)
 * @param {string} bundesland - The German state code
 * @returns {Array} Array of bridge day recommendations
 */
function calculateBridgeDays(year, month, bundesland) {
  const recommendations = [];
  
  // Get all holidays for the year
  const holidays = getPublicHolidays(year, bundesland);
  
  // Create a calendar map for the entire year
  const calendar = createYearCalendar(year, holidays);
  
  // Find all work day blocks (consecutive work days between weekends/holidays)
  const workBlocks = findWorkDayBlocks(calendar);
  
  // Evaluate each block and calculate benefit
  workBlocks.forEach(block => {
    const benefit = evaluateBlock(block, calendar);
    if (benefit.ratio >= 2.0) { // Only show if at least 2x benefit
      recommendations.push(benefit);
    }
  });
  
  // Sort by benefit ratio (best deals first)
  recommendations.sort((a, b) => b.ratio - a.ratio);
  
  // Filter for the specific month
  const monthRecommendations = recommendations.filter(rec => {
    const startDate = new Date(rec.startDate);
    return startDate.getMonth() === month && startDate.getFullYear() === year;
  });
  
  return monthRecommendations;
}

/**
 * Create a calendar map for the entire year
 * @param {number} year - The year
 * @param {Array} holidays - Array of holiday objects
 * @returns {Map} Map of date strings to day types
 */
function createYearCalendar(year, holidays) {
  const calendar = new Map();
  
  // Create holiday map for fast lookup
  const holidayMap = new Map();
  holidays.forEach(h => {
    const dateStr = formatDateKey(h.date);
    holidayMap.set(dateStr, h.name);
  });
  
  // Process each day of the year
  for (let month = 0; month < 12; month++) {
    const daysInMonth = new Date(year, month + 1, 0).getDate();
    
    for (let day = 1; day <= daysInMonth; day++) {
      const date = new Date(year, month, day);
      const dateStr = formatDateKey(date);
      const dayOfWeek = date.getDay();
      
      let type;
      if (holidayMap.has(dateStr)) {
        type = { status: 'HOLIDAY', name: holidayMap.get(dateStr) };
      } else if (dayOfWeek === 0 || dayOfWeek === 6) {
        type = { status: 'WEEKEND' };
      } else {
        type = { status: 'WORKDAY' };
      }
      
      calendar.set(dateStr, type);
    }
  }
  
  return calendar;
}

/**
 * Format date as YYYY-MM-DD
 */
function formatDateKey(date) {
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, '0');
  const day = String(date.getDate()).padStart(2, '0');
  return `${year}-${month}-${day}`;
}

/**
 * Find all work day blocks in the calendar
 * @param {Map} calendar - The calendar map
 * @returns {Array} Array of work day blocks
 */
function findWorkDayBlocks(calendar) {
  const blocks = [];
  let currentBlock = null;
  
  // Sort dates for sequential processing
  const sortedDates = Array.from(calendar.keys()).sort();
  
  sortedDates.forEach(dateStr => {
    const dayType = calendar.get(dateStr);
    
    if (dayType.status === 'WORKDAY') {
      if (!currentBlock) {
        currentBlock = {
          startDate: dateStr,
          endDate: dateStr,
          days: [dateStr]
        };
      } else {
        currentBlock.endDate = dateStr;
        currentBlock.days.push(dateStr);
      }
    } else {
      if (currentBlock) {
        blocks.push(currentBlock);
        currentBlock = null;
      }
    }
  });
  
  // Don't forget the last block
  if (currentBlock) {
    blocks.push(currentBlock);
  }
  
  return blocks;
}

/**
 * Evaluate a work day block and calculate benefit
 * @param {Object} block - The work day block
 * @param {Map} calendar - The calendar map
 * @returns {Object} Benefit information
 */
function evaluateBlock(block, calendar) {
  const vacationDaysNeeded = block.days.length;
  
  // Find the extended free period (including surrounding weekends/holidays)
  let startDate = new Date(block.startDate);
  let endDate = new Date(block.endDate);
  
  // Extend backwards to include preceding weekends/holidays
  let currentDate = new Date(startDate);
  currentDate.setDate(currentDate.getDate() - 1);
  while (true) {
    const dateStr = formatDateKey(currentDate);
    const dayType = calendar.get(dateStr);
    if (!dayType || dayType.status === 'WORKDAY') break;
    startDate = new Date(currentDate);
    currentDate.setDate(currentDate.getDate() - 1);
  }
  
  // Extend forwards to include following weekends/holidays
  currentDate = new Date(endDate);
  currentDate.setDate(currentDate.getDate() + 1);
  while (true) {
    const dateStr = formatDateKey(currentDate);
    const dayType = calendar.get(dateStr);
    if (!dayType || dayType.status === 'WORKDAY') break;
    endDate = new Date(currentDate);
    currentDate.setDate(currentDate.getDate() + 1);
  }
  
  // Calculate total free days
  const totalFreeDays = Math.floor((endDate - startDate) / (1000 * 60 * 60 * 24)) + 1;
  
  // Calculate benefit ratio
  const ratio = totalFreeDays / vacationDaysNeeded;
  
  // Find holidays in the period for description
  const holidaysInPeriod = [];
  currentDate = new Date(startDate);
  while (currentDate <= endDate) {
    const dateStr = formatDateKey(currentDate);
    const dayType = calendar.get(dateStr);
    if (dayType && dayType.status === 'HOLIDAY') {
      holidaysInPeriod.push(dayType.name);
    }
    currentDate.setDate(currentDate.getDate() + 1);
  }
  
  return {
    startDate: formatDateKey(startDate),
    endDate: formatDateKey(endDate),
    vacationDays: block.days,
    vacationDaysNeeded: vacationDaysNeeded,
    totalFreeDays: totalFreeDays,
    ratio: ratio,
    holidays: holidaysInPeriod
  };
}

/**
 * Get a human-readable description for a bridge day recommendation
 * @param {Object} recommendation - The recommendation object
 * @returns {string} Description text
 */
function getBridgeDayDescription(recommendation) {
  const { vacationDaysNeeded, totalFreeDays, ratio, holidays } = recommendation;
  
  let description = `${vacationDaysNeeded} Urlaubstag${vacationDaysNeeded > 1 ? 'e' : ''} für ${totalFreeDays} freie Tage`;
  
  if (holidays.length > 0) {
    description += ` (inkl. ${holidays.join(', ')})`;
  }
  
  description += ` - ${ratio.toFixed(1)}x Ertrag`;
  
  return description;
}