<?php

namespace Kanboard\Plugin\RecoReco\Model;

/**
 * Pure calendar math for RecoReco.
 *
 * Given an anchor due date (the drift-free pattern: day-of-month + time), a frequency, and the
 * "last day" flag, it computes occurrence datetimes. It has NO container dependencies, so it is
 * unit-testable in isolation (see Test/OccurrenceCalculatorTest.php).
 *
 * Occurrences are always computed from the anchor's day, never by marching a clamped date forward,
 * so a "30th" schedule goes 30, 28/29, 30, 30... and never drifts to the 28th.
 *
 * v0.3 implements monthly-by-day; the other frequencies arrive in v1.1 (occurrenceFrom returns null
 * for them until then).
 */
class OccurrenceCalculator
{
    const MAX_MONTHS = 120;

    /**
     * The earliest occurrence at/after $reference (when $inclusive) or strictly after it.
     *
     * @param  int    $anchor     Unix timestamp: the pattern (day-of-month + time).
     * @param  string $frequency
     * @param  bool   $lastDay
     * @param  int    $reference  Unix timestamp.
     * @param  bool   $inclusive
     * @return int|null           Occurrence timestamp, or null if the frequency is not yet supported.
     */
    public function occurrenceFrom($anchor, $frequency, $lastDay, $reference, $inclusive = false)
    {
        switch ($frequency) {
            case 'monthly_day':
                return $this->monthlyByDay((int) $anchor, (bool) $lastDay, (int) $reference, (bool) $inclusive);
            default:
                return null;
        }
    }

    private function monthlyByDay($anchor, $lastDay, $reference, $inclusive)
    {
        $anchorDay = (int) date('j', $anchor);
        $h = (int) date('G', $anchor);
        $i = (int) date('i', $anchor);
        $s = (int) date('s', $anchor);

        $y = (int) date('Y', $reference);
        $m = (int) date('n', $reference);

        for ($k = 0; $k < self::MAX_MONTHS; $k++) {
            $lastDom = (int) date('t', mktime(0, 0, 0, $m, 1, $y));
            $day = $lastDay ? $lastDom : min($anchorDay, $lastDom);
            $occurrence = mktime($h, $i, $s, $m, $day, $y);

            if ($inclusive ? $occurrence >= $reference : $occurrence > $reference) {
                return $occurrence;
            }

            $m++;
            if ($m > 12) {
                $m = 1;
                $y++;
            }
        }

        return null;
    }
}