9.4 Displaying a Calendar

This section puts the date and time functions to work in displaying a calendar. The show_form( ) function in Example 9-17 displays a form that asks for a month and year. The process_form( ) function hands those values off to the show_calendar( ) function, which does the real work of printing a calendar grid for a particular month.

The structure of the if( ) statement that controls show_form( ), validate_form( ), and process_form( ) is different in Example 9-17 than in previous form examples. That's because we want to display the form above the calendar. Usually, if the form data is valid, show_form( ) is not called—only process_form( ) is. But here, show_form( ) is called before process_form( ) so that the form is displayed above the calendar and the user can pick another month and year to view.

Similarly, the call to show_form( ) that happens when the form has not been submitted (when there is no $_POST['_submit_check'] parameter) is followed by a call to show_calendar( ) to display the calendar for the current month the first time the page is loaded.

Example 9-17. Printing a calendar

<?php

// Use the form helper functions defined in Chapter 6

require 'formhelpers.php';



$months = array(1 => 'January', 2 => 'February', 3 => 'March', 4 => 'April', 

                5 => 'May', 6 => 'June', 7 => 'July', 8 => 'August',

                9 => 'September', 10 => 'October', 11 => 'November', 

                12 => 'December');



$years = array( );

for ($year = date('Y') - 1, $max_year = date('Y') + 5; $year < $max_year; $year++) {

    $years[$year] = $year;

}



if ($_POST['_submit_check']) {

    if ($errors = validate_form( )) {

        show_form($errors);

    } else {

        show_form( );

        process_form( );

    }

} else {

    // When nothing is submitted, show the form and then

    // a calendar for the current month

    show_form( );

    show_calendar(date('n'), date('Y'));

}



function validate_form( ) {

    global $months, $years;

    $errors = array( );



    if (! array_key_exists($_POST['month'], $months)) {

        $errors[  ] = 'Select a valid month.';

    }



    if (! array_key_exists($_POST['year'], $years)) {

        $errors[  ] = 'Select a valid year.';

    }



    return $errors;

}



function show_form($errors = '') {

    global $months, $years, $this_year;



    // If the form is submitted, get defaults from submitted variables

    if ($_POST['_submit_check']) {

        $defaults = $_POST;

    } else {

        // Otherwise, set our own defaults: the current month and year

        $defaults = array('year' => date('Y'),

                          'month' => date('n'));

    }





    if ($errors) {

        print 'You need to correct the following errors: <ul><li>';

        print implode('</li><li>',$errors);

        print '</li></ul>';

    }



    print '<form method="POST" action="'.$_SERVER['PHP_SELF'].'">';

    input_select('month', $defaults, $months);

    input_select('year',  $defaults, $years);

    input_submit('submit','Show Calendar');

    print '<input type="hidden" name="_submit_check" value="1"/>';

    print '</form>';

}



function process_form( ) {

    show_calendar($_POST['month'], $_POST['year']);

}



function show_calendar($month, $year) {

    global $months;

    $weekdays = array('Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa');



    // Find the epoch timestamp for midnight on the first day of the month

    $first_day = mktime(0,0,0,$month, 1, $year);

    // How many days are in the month?

    $days_in_month = date('t', $first_day);

    // What day of the week (numerically) is the first day of the month?

    // You need this to put the first table cell in the right place

    $day_offset = date('w', $first_day);





    // Print the table header and the row of weekday names

    print<<<_HTML_

<table border="0" cellspacing="0" cellpadding="2">

<tr><th colspan="7">$months[$month] $year</th></tr>

<tr><td align="center">

_HTML_;

    print implode('</td><td align="center">', $weekdays);

    print '</td></tr>';





    // If the first day of the month is, say, a Tuesday, then you

    // need to put blank table cells under "Su" and "Mo" in the first

    // row so that the day 1 table cell goes under "Tu"

    if ($day_offset > 0) {

        for ($i = 0; $i < $day_offset; $i++) { print '<td>&nbsp;</td>'; }

    }



    // Print a table cell for each day of the month

    for ($day = 1; $day <= $days_in_month; $day++ ) {

        print '<td align="center">' . $day . '</td>';

        $day_offset++;

        // If this cell was the seventh in the row, then

        // end the table row and reset $day_offset

        if ($day_offset =  = 7) {

            $day_offset = 0;

            print "</tr>\n";

            // If there are more days to come, then

            // start a new table row

            if ($day < $days_in_month) {

                print '<tr>';

            }

        }

    }



    // At this point, one table cell has been printed for each day

    // of the month. If the last day of the month isn't a Saturday

    // then the last row of the table needs to be padded with

    // some blank cells out to the end of the row

    if ($day_offset > 0) {

        for ($i = $day_offset; $i < 7; $i++) {

            print '<td>&nbsp;</td>';

        }

        print '</tr>';

    }

    print '</table>';

}

?>

In October 2004, Example 9-17 produces a page that looks like Figure 9-2.

Figure 9-2. Calendar form and display