(php) change a duration to something useable by my calendar

I have a series of event dates (variable durations) in the following formats:

• 28 April 2020
• 3 – 5 May 2020
• 3 May – 5 June 2020
• 20 Dec 2020 – 15 Jan 2021

I want to keep these this way, for readability.

But my calendar needs a standard way of reading these so it can output these events:

• 28 April 2020 should become 28 April 2020 – 28 April 2020
• 3 – 5 May 2020 should become 3 May 2020 – 5 May 2020
• 3 May – 5 June 2020 should become 3 May 2020 – 5 June 2020
• 20 Dec 2020 – 15 Jan 2021 ==> this the calendar can handle.

Any thoughts on how to do this in php?

Answer

I would really recommend storing your dates as two separate values (start/end) and then formatting on output rather than trying to decode the formatted output.

If you are stuck with this approach, you can use preg_match to match your different formats and then extract the start and end dates from the matched values:

$dates = array(
    '28 April 2020',
    '3 - 5 May 2020',
    '3 May - 5 June 2020',
    '20 Dec 2020 - 15 Jan 2021'
    );

foreach ($dates as $date) {
    preg_match('/^(d+)s(w+)s(d+)(?:s-s(d+)s(w+)s(d+))?|(d+)s(w+)s-s(d+)s(w+)s(d+)|(d+)s-s(d+)s(w+)s(d+)$/', $date, $matches);
    if (isset($matches[12])) {
        // dd - dd mmm yyyy format
        $start_date = "${matches[12]} ${matches[14]} ${matches[15]}";
        $end_date   = "${matches[13]} ${matches[14]} ${matches[15]}";
    }
    elseif (isset($matches[7])) {
        // dd mmm - dd mmm yyyy format
        $start_date = "${matches[7]} ${matches[8]} ${matches[11]}";
        $end_date   = "${matches[9]} ${matches[10]} ${matches[11]}";
    }
    elseif (isset($matches[4])) {
        // dd mmm yyyy - dd mmm yyyy format
        $start_date = "${matches[1]} ${matches[2]} ${matches[3]}";
        $end_date   = "${matches[4]} ${matches[5]} ${matches[6]}";
    }
    elseif (isset($matches[1])) {
        // dd mmm yyyy format
        $start_date = "${matches[1]} ${matches[2]} ${matches[3]}";
        $end_date   = "${matches[1]} ${matches[2]} ${matches[3]}";
    }
    else {
        // no match
        $start_date = '???';
        $end_date = '???';
    }
    echo "$start_date - $end_daten";
}

Output:

28 April 2020 - 28 April 2020
3 May 2020 - 5 May 2020
3 May 2020 - 5 June 2020
20 Dec 2020 - 15 Jan 2021

Demo on 3v4l.org