<?php

namespace Kanboard\Plugin\RecoReco\Model;

/**
 * Pure calendar math for RecoReco.
 *
 * Given an anchor due date (the drift-free pattern: it carries the day-of-month, the weekday, and
 * the time), a frequency, and the "last day" flag, it computes occurrence datetimes. It has NO
 * container dependencies, so it is unit-testable in isolation (Test/OccurrenceCalculatorTest.php).
 *
 * Occurrences are always computed from the anchor, never by marching a clamped date forward, so a
 * "30th" schedule goes 30, 28/29, 30, 30... and never drifts.
 */
class OccurrenceCalculator
{
    const MAX_MONTHS = 120;
    const MAX_YEARS = 20;

    /**
     * The earliest occurrence at/after $reference (when $inclusive) or strictly after it.
     *
     * @param  int    $anchor     Unix timestamp: the pattern.
     * @param  string $frequency  daily | weekly | monthly_day | monthly_dow | yearly
     * @param  bool   $lastDay
     * @param  int    $reference  Unix timestamp.
     * @param  bool   $inclusive
     * @return int|null           Occurrence timestamp, or null for an unknown frequency.
     */
    public function occurrenceFrom($anchor, $frequency, $lastDay, $reference, $inclusive = false)
    {
        $anchor = (int) $anchor;
        $reference = (int) $reference;
        $lastDay = (bool) $lastDay;
        $inclusive = (bool) $inclusive;

        switch ($frequency) {
            case 'daily':
                return $this->daily($anchor, $reference, $inclusive);
            case 'weekly':
                return $this->weekly($anchor, $reference, $inclusive);
            case 'monthly_day':
                return $this->monthlyByDay($anchor, $lastDay, $reference, $inclusive);
            case 'monthly_dow':
                return $this->monthlyByWeekday($anchor, $lastDay, $reference, $inclusive);
            case 'yearly':
                return $this->yearly($anchor, $lastDay, $reference, $inclusive);
            default:
                return null;
        }
    }

    private function daily($anchor, $reference, $inclusive)
    {
        $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);
        $d = (int) date('j', $reference);

        for ($k = 0; $k < 3; $k++) {
            $o = mktime($h, $i, $s, $m, $d + $k, $y);

            if ($this->matches($o, $reference, $inclusive)) {
                return $o;
            }
        }

        return null;
    }

    private function weekly($anchor, $reference, $inclusive)
    {
        $h = (int) date('G', $anchor);
        $i = (int) date('i', $anchor);
        $s = (int) date('s', $anchor);
        $w = (int) date('w', $anchor);
        $y = (int) date('Y', $reference);
        $m = (int) date('n', $reference);
        $d = (int) date('j', $reference);

        for ($k = 0; $k < 8; $k++) {
            $o = mktime($h, $i, $s, $m, $d + $k, $y);

            if ((int) date('w', $o) === $w && $this->matches($o, $reference, $inclusive)) {
                return $o;
            }
        }

        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);
            $o = mktime($h, $i, $s, $m, $day, $y);

            if ($this->matches($o, $reference, $inclusive)) {
                return $o;
            }

            $this->nextMonth($m, $y);
        }

        return null;
    }

    private function monthlyByWeekday($anchor, $lastDay, $reference, $inclusive)
    {
        $h = (int) date('G', $anchor);
        $i = (int) date('i', $anchor);
        $s = (int) date('s', $anchor);
        $w = (int) date('w', $anchor);
        $k = intdiv((int) date('j', $anchor) - 1, 7) + 1; // 1..5: which occurrence of $w in the month

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

        for ($j = 0; $j < self::MAX_MONTHS; $j++) {
            $day = $lastDay ? $this->lastWeekdayOfMonth($y, $m, $w) : $this->nthWeekdayOfMonth($y, $m, $w, $k);

            if ($day !== null) {
                $o = mktime($h, $i, $s, $m, $day, $y);

                if ($this->matches($o, $reference, $inclusive)) {
                    return $o;
                }
            }

            $this->nextMonth($m, $y);
        }

        return null;
    }

    private function yearly($anchor, $lastDay, $reference, $inclusive)
    {
        $month = (int) date('n', $anchor);
        $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);

        for ($j = 0; $j < self::MAX_YEARS; $j++) {
            $lastDom = (int) date('t', mktime(0, 0, 0, $month, 1, $y));
            $day = $lastDay ? $lastDom : min($anchorDay, $lastDom);
            $o = mktime($h, $i, $s, $month, $day, $y);

            if ($this->matches($o, $reference, $inclusive)) {
                return $o;
            }

            $y++;
        }

        return null;
    }

    // The day-of-month of the k-th weekday $w in month $m/$y, or null if that month has no k-th one.
    private function nthWeekdayOfMonth($y, $m, $w, $k)
    {
        $firstDow = (int) date('w', mktime(0, 0, 0, $m, 1, $y));
        $firstW = 1 + (($w - $firstDow + 7) % 7);
        $day = $firstW + ($k - 1) * 7;
        $lastDom = (int) date('t', mktime(0, 0, 0, $m, 1, $y));

        return $day <= $lastDom ? $day : null;
    }

    // The day-of-month of the last weekday $w in month $m/$y.
    private function lastWeekdayOfMonth($y, $m, $w)
    {
        $lastDom = (int) date('t', mktime(0, 0, 0, $m, 1, $y));
        $lastDow = (int) date('w', mktime(0, 0, 0, $m, $lastDom, $y));

        return $lastDom - (($lastDow - $w + 7) % 7);
    }

    private function matches($occurrence, $reference, $inclusive)
    {
        return $inclusive ? $occurrence >= $reference : $occurrence > $reference;
    }

    private function nextMonth(&$m, &$y)
    {
        $m++;

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