【保存版】GASでGoogleカレンダーの空き時間を自動抽出する方法｜初心者でもできるステップ解説！

function extractAvailableTimes() {
  const calendarId = 'primary'; // 'primary' は自分のカレンダー。共有カレンダーIDでも可。
  const calendar = CalendarApp.getCalendarById(calendarId);
  
  const now = new Date();
  const oneWeekLater = new Date();
  oneWeekLater.setDate(now.getDate() + 7);

  const events = calendar.getEvents(now, oneWeekLater);
  
  // 稼働時間設定（9時〜18時）
  const workingHoursStart = 9;
  const workingHoursEnd = 18;
  
  let slots = [];
  let currentTime = new Date(now);

  // 1日単位でループ
  while (currentTime < oneWeekLater) {
    let dayStart = new Date(currentTime);
    dayStart.setHours(workingHoursStart, 0, 0, 0);
    
    let dayEnd = new Date(currentTime);
    dayEnd.setHours(workingHoursEnd, 0, 0, 0);

    let dayEvents = events.filter(event => 
      event.getStartTime().getDate() === currentTime.getDate()
    );
    
    if (dayEvents.length === 0) {
      slots.push([dayStart, dayEnd]);
    } else {
      let pointer = dayStart;
      
      dayEvents.sort((a, b) => a.getStartTime() - b.getStartTime());
      
      dayEvents.forEach(event => {
        const eventStart = event.getStartTime();
        const eventEnd = event.getEndTime();
        
        if (pointer < eventStart) {
          slots.push([pointer, eventStart]);
        }
        
        pointer = eventEnd > pointer ? eventEnd : pointer;
      });
      
      if (pointer < dayEnd) {
        slots.push([pointer, dayEnd]);
      }
    }

    currentTime.setDate(currentTime.getDate() + 1);
    currentTime.setHours(0, 0, 0, 0);
  }

  // スプレッドシート出力
  const sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  sheet.clear();
  sheet.appendRow(['開始時刻', '終了時刻']);
  
  slots.forEach(slot => {
    sheet.appendRow([
      Utilities.formatDate(slot[0], Session.getScriptTimeZone(), 'yyyy/MM/dd HH:mm'),
      Utilities.formatDate(slot[1], Session.getScriptTimeZone(), 'yyyy/MM/dd HH:mm')
    ]);
  });
}