PHP日历功能优化：确保当前日期动态更新的策略

if($date<date('Y-m-d')){
    $calendar.="<td><h4>$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>";
}

function build_calendar($month, $year){
    // ... 其他初始化代码 ...

    // 统一获取当前日期，避免多次调用date()
    $currentDateTime = new DateTime();
    $todayFormatted = $currentDateTime->format('Y-m-d'); // 例如 '2023-10-27'

    // ... 后续代码使用 $todayFormatted 进行比较 ...
}

    // ... (在while循环内部) ...
    while ($currentDay <= $numberDays) {
        // ... (省略部分代码) ...

        $currentDayRel = str_pad($currentDay, 2, "0", STR_PAD_LEFT);
        $date = "$year-$month-$currentDayRel"; // 当前日历单元格的日期

        $cellClass = '';
        $buttonHtml = '';

        if ($date == $todayFormatted) {
            // 当前日期
            $cellClass = 'today'; // 添加 'today' 类以高亮显示
            $buttonHtml = "<a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
        } elseif ($date < $todayFormatted) {
            // 过去日期
            $cellClass = 'past-day'; // 可选：为过去日期添加样式
            $buttonHtml = "<button class='btn btn-danger btn-xs'>N/A</button>";
        } else {
            // 未来日期
            $cellClass = 'future-day'; // 可选：为未来日期添加样式
            $buttonHtml = "<a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
        }

        $calendar .= "<td class='$cellClass'><h4>$currentDay</h4> $buttonHtml</td>";

        // ... (省略部分代码) ...
        $currentDay++;
        $dayOfWeek++;
    }
    // ... (while循环结束) ...

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

    // 统一获取当前日期，避免多次调用date()
    $currentDateTime = new DateTime();
    $todayFormatted = $currentDateTime->format('Y-m-d'); // 例如 '2023-10-27'

    # 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> ";

    // 确保“Current Month”按钮指向当前实际的月份
    $calendar.= " <a class='btn btn-xs btn-primary' href='?month=".$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"; // 当前日历单元格的日期

         $cellClass = '';
         $buttonHtml = '';

         if ($date == $todayFormatted) {
             // 当前日期
             $cellClass = 'today'; // 添加 'today' 类以高亮显示
             $buttonHtml = "<a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
         } elseif ($date < $todayFormatted) {
             // 过去日期
             $cellClass = 'past-day'; // 可选：为过去日期添加样式
             $buttonHtml = "<button class='btn btn-danger btn-xs'>N/A</button>";
         } else {
             // 未来日期
             $cellClass = 'future-day'; // 可选：为未来日期添加样式
             $buttonHtml = "<a href='book.php?date=".$date."' class='btn btn-success btn-xs'>Book</a>";
         }

         $calendar .= "<td class='$cellClass'><h4>$currentDay</h4> $buttonHtml</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;
}
?>

.table-bordered .today {
    background-color: #d4edda; /* 浅绿色背景 */
    border: 2px solid #28a745; /* 绿色边框 */
    font-weight: bold;
}
/* 可选的过去和未来日期样式 */
.table-bordered .past-day {
    background-color: #f8d7da; /* 浅红色背景 */
    color: #6c757d; /* 灰色文字 */
}
.table-bordered .future-day {
    background-color: #e2e6ea; /* 浅灰色背景 */
}