优化PHP动态日历：解决当前日期高亮不更新问题

// ... (部分代码省略)
$datetoday = date('Y-m-d'); // 获取当前日期
// ...
$today = $date==date('Y-m-d')? "today" : ""; // 检查当前循环的日期是否为今天
if($date<date('Y-m-d')){ // 检查日期是否在今天之前
    $calendar.="<td><h4>$currentDay</h4> <button class='btn btn-danger btn-xs'>N/A</button>";
}else{
    $calendar.="<td class='$today'><h4>$currentDay</h4> <a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
}
// ...

// 在函数开始时，获取一次当前日期
$currentDateTime = new DateTime();
$todayDateString = $currentDateTime->format('Y-m-d'); // 获取当前日期的字符串形式，作为比较基准

// 在循环内部，将当前处理的日历日期转换为DateTime对象
$calendarDate = new DateTime($date);

// 比较逻辑
if ($calendarDate < $currentDateTime) { // 如果是过去日期
    $calendar .= "<td><h4>$currentDay</h4> <button class='btn btn-danger btn-xs'>N/A</button>";
} elseif ($calendarDate == $currentDateTime) { // 如果是当前日期
    $calendar .= "<td class='today'><h4>$currentDay</h4> <a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
} else { // 如果是未来日期
    $calendar .= "<td><h4>$currentDay</h4> <a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
}

<?php
function build_calendar($month, $year){

    // 创建一个DateTime对象作为当前日期的基准
    $currentDateTime = new DateTime();
    $todayDateString = $currentDateTime->format('Y-m-d');

    # Creating an array containing names of all days in the week
    $daysOfWeek = array('Sunday', 'Monday','Tuesday','Wednesday','Thursday','Friday','Saturday');

    # What is the first day of the month in question?
    $firstDayOfMonth = mktime(0,0,0,$month,1,$year);

    # How many days does this month contain?
    $numberDays = date('t',$firstDayOfMonth);

    # Retrieve some information about the first day of the month in question.
    $dateComponents = getdate($firstDayOfMonth);

    # What is the name of the month in question?
    $monthName = $dateComponents['month'];

    # What is the index value (0-6) of the first day of the month in question.
    $dayOfWeek = $dateComponents['wday'];

    # Create the table tag opener and day headers
    $calendar = "<table class='table table-bordered'>";
    $calendar .= "<center><h2>$monthName $year</h2>";
    $calendar.= "<a class='btn btn-xs btn-primary' href='?month=".date('m', mktime(0, 0, 0, $month-1, 1, $year))."&year=".date('Y', mktime(0, 0, 0, $month-1, 1, $year))."'>Previous Month</a> ";

    // 链接到当前月份的按钮，确保点击后显示的是当前实际月份
    $calendar.= " <a class='btn btn-xs btn-primary' href='?month=".$currentDateTime->format('m')."&year=".$currentDateTime->format('Y')."'>Current Month</a> ";

    $calendar.= "<a href='?month=".date('m', mktime(0, 0, 0, $month+1, 1, $year))."&year=".date('Y', mktime(0, 0, 0, $month+1, 1, $year))."' class='btn btn-xs btn-primary'>Next Month</a></center><br>";

    $calendar .= "<tr>";

    # Create the calendar headers
    foreach($daysOfWeek as $day) {
        $calendar .= "<th  class='header'>$day</th>";
    } 

    # Create the rest of the calendar
    # Initiate the day counter, starting with the 1st.
    $currentDay = 1;
    $calendar .= "</tr><tr>";

    # The variable $dayOfWeek is used to ensure that the calendar display consists of exactly 7 columns.
    if($dayOfWeek > 0) { 
        for($k=0;$k<$dayOfWeek;$k++){
            $calendar .= "<td  class='empty'></td>"; 
        }
    }

    $month = str_pad($month, 2, "0", STR_PAD_LEFT);

    while ($currentDay <= $numberDays) {

         #Seventh column (Saturday) reached. Start a new row.
         if ($dayOfWeek == 7) {
             $dayOfWeek = 0;
             $calendar .= "</tr><tr>";
         }

         $currentDayRel = str_pad($currentDay, 2, "0", STR_PAD_LEFT);
         $date = "$year-$month-$currentDayRel";

         // 将当前循环的日期转换为DateTime对象或字符串用于比较
         $calendarDateString = $date; // 已经格式化为 Y-m-d

         // 优化日期比较逻辑
         if($calendarDateString < $todayDateString){ // 如果是过去日期
             $calendar.="<td><h4>$currentDay</h4> <button class='btn btn-danger btn-xs'>N/A</button>";
         }elseif($calendarDateString == $todayDateString){ // 如果是当前日期
             $calendar.="<td class='today'><h4>$currentDay</h4> <a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
         }else{ // 如果是未来日期
             $calendar.="<td><h4>$currentDay</h4> <a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
         }

         $calendar .="</td>";

         #Increment counters
         $currentDay++;
         $dayOfWeek++;
     }

     # Complete the row of the last week in month, if necessary
     if ($dayOfWeek != 7) { 
        $remainingDays = 7 - $dayOfWeek;
        for($l=0;$l<$remainingDays;$l++){
            $calendar .= "<td class='empty'></td>"; 
        }
     }

    $calendar .= "</tr>";
    $calendar .= "</table>";
    return $calendar;
}
?>