<?php

// Print error message and exit
function printStderr($msg) {
    error_log($msg);
    exit(-1);
}

class ShiftPres {
    // For German date matching
    const  PREG = '/^(0[1-9]|[12][0-9]|3[01])\.(0[1-9]|1[0-2])\.([1-9]\d{3})$/';
    // Read "past.md" and "vor.md" into instance arrays and set up new vor.txt
    public function __construct($vor='vor.md', $past='past.md') {
        $this->CET = new DateTimeZone('Europe/Berlin');
        $this->vor = $vor;
        $this->vorMd = file($vor, FILE_IGNORE_NEW_LINES);
        $vorBase = basename($vor, '.md');
        $this->vorT = $vorBase . '.txt';
        $this->vorTxt = [];
        $this->pastT = $past;
        $this->pastMd = file($this->pastT, FILE_IGNORE_NEW_LINES);
        $this->exit = 0; // Default return value
    }

    // Save "vor.txt" and "past.md"  before leaving
    public function save() {
        // Backup files first
        copy($this->vorT, $this->vorT . '.bak');
        copy($this->pastT, $this->pastT . '.bak');
        file_put_contents($this->vorT, implode(PHP_EOL, $this->vorTxt) . PHP_EOL);
        file_put_contents($this->pastT, implode(PHP_EOL, $this->pastMd) . PHP_EOL);
        // Signal to calling bash script to put files into git
        $this->exit = 1;
    }

    // Shift from "vor.md" to "past.md", creating "vor.txt" along the way
    public function shift() {
        $yester = (new DateTime('now', $this->CET))->modify('- 1 day');
        $yester->setTime(0, 0);
        // For correct insertion into past array
        $past = $this->findPast();
        if ($past < 0) {
            printStderr("Can't locate insert position in $this->pastT, exiting");
        }

        // Loop through "vor.md" and check if yesterday is 4th Tuesday => shift to "past.md"
        // Otherwise copy to "vor.txt", including custom date if found (as in: not 4th Tuesday)
        foreach ($this->vorMd as $line) {
            $fields = array_filter(explode('|', $line));
            $ff = explode(', ', $fields[1]);
            // Does 1st field contain date?
            if (count($ff) > 1) {
                $dat = trim($ff[1]);
                // If so, in valid format
                if (preg_match(self::PREG, $dat)) {
                    $dp = new DateTime($dat, $this->CET);
                    $dp->setTime(0, 0);
                    // if we are not invoked on the morning of the 4th Wednesday, copy to "vor.txt"
                    if ($dp != $yester) {
                        // If manually set date doesn't equal fourth Tuesday, copy
                        if ($dp != $this->get4Tuesday($dat)) {
                            $str0 = '|' . implode($fields, '|') . '|';
                        } else {
                            // Otherwise, only copy text
                            $str0 = '|' . implode(array_slice($fields, 1), '|') . '|';
                        }
                        $this->vorTxt[] = $str0;
                    } else {
                        // Shift to "past.md"
                        array_splice($this->pastMd, $past, 0, $line);
                    }
                }
            }
        }
    }

    // Check if "vor.txt" and "past.md" need to be saved (length of "vor.md" and "vor.txt" differ => line shifted)
    public  function checkSave() {
        // Take header of "vor.md" into account
        return count($this->vorTxt) != count($this->vorMd)-2;
    }

    public function getExit() {
        return $this->exit;
    }

    // Find first entry in PAST
    private function findPast() {
        for ($i = 0; $i < count($this->pastMd); $i++) {
            $fields = array_filter(explode('|', $this->pastMd[$i]));
            $ff = explode(', ', $fields[1]);
            if (count($ff) > 1) {
                $dat = trim($ff[1]);
                if (preg_match(self::PREG, $dat)) {
                    return $i;
                }
            }
        }
        return -1;
    }
    
    private function get4Tuesday($dat) {
        // This is for PHP >= 8.1 as the old strftime will be deprecated by then, so use datefmt_format_object if we are running on PHP beyond version 7
        $date_time = new DateTime($dat, $this->CET);
        $first_day = $date_time->modify('first day of this month');
        $ts = $first_day->getTimeStamp();
        if (intval(explode(".", phpversion())[0]) >= 7) {
            $date_time->setTimestamp(strtotime('fourth tuesday of this month', $ts));
            $tuesday = datefmt_format_object($date_time, 'd.M.yyyy ', 'de_DE.utf8');
        } else {
            $tuesday = strftime('%d.%m.%Y ', strtotime('fourth tuesday of this month', $ts));
        }
        return new DateTime($tuesday);
    }
}

setlocale(LC_TIME, 'de_DE.utf8');
date_default_timezone_set('Europe/Berlin');
$shift = new ShiftPres();
$shift->shift();
if ($shift->checkSave()) {
    $shift->save();
}
// Signal to calling bash script
exit($shift->getExit());
?>