<?php
declare(strict_types=1);

namespace App;

use DateInterval;
use DateTimeImmutable;
use DateTimeZone;

final class CronExpression
{
    /** @var array<int, true> */
    private array $minutes;
    /** @var array<int, true> */
    private array $hours;
    /** @var array<int, true> */
    private array $daysOfMonth;
    /** @var array<int, true> */
    private array $months;
    /** @var array<int, true> */
    private array $daysOfWeek;

    private function __construct(
        private string $expression,
        array $minutes,
        array $hours,
        array $daysOfMonth,
        array $months,
        array $daysOfWeek,
        private bool $daysOfMonthWildcard,
        private bool $daysOfWeekWildcard
    ) {
        $this->minutes = $minutes;
        $this->hours = $hours;
        $this->daysOfMonth = $daysOfMonth;
        $this->months = $months;
        $this->daysOfWeek = $daysOfWeek;
    }

    public static function parse(string $expression): self
    {
        $normalized = preg_replace('/\s+/', ' ', trim($expression)) ?? '';
        if ($normalized === '') {
            throw new \InvalidArgumentException('Cron-Ausdruck fehlt.');
        }

        $parts = explode(' ', $normalized);
        if (count($parts) !== 5) {
            throw new \InvalidArgumentException('Cron-Ausdruck muss aus 5 Feldern bestehen.');
        }

        return new self(
            $normalized,
            self::parseField($parts[0], 0, 59),
            self::parseField($parts[1], 0, 23),
            self::parseField($parts[2], 1, 31),
            self::parseField($parts[3], 1, 12, [
                'JAN' => 1, 'FEB' => 2, 'MAR' => 3, 'APR' => 4,
                'MAY' => 5, 'JUN' => 6, 'JUL' => 7, 'AUG' => 8,
                'SEP' => 9, 'OCT' => 10, 'NOV' => 11, 'DEC' => 12,
            ]),
            self::parseField($parts[4], 0, 6, [
                'SUN' => 0, 'MON' => 1, 'TUE' => 2, 'WED' => 3,
                'THU' => 4, 'FRI' => 5, 'SAT' => 6,
                '7' => 0,
            ]),
            trim($parts[2]) === '*',
            trim($parts[4]) === '*'
        );
    }

    public function expression(): string
    {
        return $this->expression;
    }

    public function matches(DateTimeImmutable $utcDateTime, DateTimeZone $timezone): bool
    {
        $local = $utcDateTime->setTimezone($timezone);
        $minute = (int) $local->format('i');
        $hour = (int) $local->format('G');
        $dayOfMonth = (int) $local->format('j');
        $month = (int) $local->format('n');
        $dayOfWeek = (int) $local->format('w');

        if (!isset($this->minutes[$minute]) || !isset($this->hours[$hour]) || !isset($this->months[$month])) {
            return false;
        }

        $dayOfMonthMatch = isset($this->daysOfMonth[$dayOfMonth]);
        $dayOfWeekMatch = isset($this->daysOfWeek[$dayOfWeek]);
        if ($this->daysOfMonthWildcard && $this->daysOfWeekWildcard) {
            $dayMatches = true;
        } elseif ($this->daysOfMonthWildcard) {
            $dayMatches = $dayOfWeekMatch;
        } elseif ($this->daysOfWeekWildcard) {
            $dayMatches = $dayOfMonthMatch;
        } else {
            $dayMatches = $dayOfMonthMatch || $dayOfWeekMatch;
        }

        return $dayMatches;
    }

    public function previousRun(DateTimeImmutable $utcDateTime, DateTimeZone $timezone, int $lookbackMinutes = 527040): ?DateTimeImmutable
    {
        $cursor = $this->floorToMinute($utcDateTime);
        for ($i = 0; $i <= $lookbackMinutes; $i++) {
            if ($this->matches($cursor, $timezone)) {
                return $cursor;
            }
            $cursor = $cursor->sub(new DateInterval('PT1M'));
        }

        return null;
    }

    public function nextRun(DateTimeImmutable $utcDateTime, DateTimeZone $timezone, int $lookaheadMinutes = 527040): ?DateTimeImmutable
    {
        $cursor = $this->floorToMinute($utcDateTime)->add(new DateInterval('PT1M'));
        for ($i = 0; $i <= $lookaheadMinutes; $i++) {
            if ($this->matches($cursor, $timezone)) {
                return $cursor;
            }
            $cursor = $cursor->add(new DateInterval('PT1M'));
        }

        return null;
    }

    /** @return array<int, true> */
    private static function parseField(string $field, int $min, int $max, array $aliases = []): array
    {
        $field = strtoupper(trim($field));
        if ($field === '*') {
            $all = [];
            for ($value = $min; $value <= $max; $value++) {
                $all[$value] = true;
            }
            return $all;
        }

        $values = [];
        foreach (explode(',', $field) as $segment) {
            $segment = strtoupper(trim($segment));
            if ($segment === '') {
                continue;
            }

            $step = 1;
            if (str_contains($segment, '/')) {
                [$segment, $stepPart] = explode('/', $segment, 2);
                if (!is_numeric($stepPart) || (int) $stepPart <= 0) {
                    throw new \InvalidArgumentException('Ungueltiger Cron-Step in Feld "' . $field . '".');
                }
                $step = (int) $stepPart;
            }

            if ($segment === '*') {
                $start = $min;
                $end = $max;
            } elseif (str_contains($segment, '-')) {
                [$startPart, $endPart] = explode('-', $segment, 2);
                $start = self::normalizePart($startPart, $aliases);
                $end = self::normalizePart($endPart, $aliases);
            } else {
                $start = self::normalizePart($segment, $aliases);
                $end = $start;
            }

            if ($start < $min || $start > $max || $end < $min || $end > $max || $end < $start) {
                throw new \InvalidArgumentException('Cron-Feld "' . $field . '" liegt ausserhalb des erlaubten Bereichs.');
            }

            for ($value = $start; $value <= $end; $value += $step) {
                $values[$value] = true;
            }
        }

        if ($values === []) {
            throw new \InvalidArgumentException('Cron-Feld "' . $field . '" ist leer.');
        }

        ksort($values);
        return $values;
    }

    private static function normalizePart(string $part, array $aliases): int
    {
        $part = strtoupper(trim($part));
        if ($part === '') {
            throw new \InvalidArgumentException('Leerer Cron-Wert.');
        }

        if (array_key_exists($part, $aliases)) {
            return (int) $aliases[$part];
        }

        if (!is_numeric($part)) {
            throw new \InvalidArgumentException('Ungueltiger Cron-Wert "' . $part . '".');
        }

        return (int) $part;
    }

    private function floorToMinute(DateTimeImmutable $utcDateTime): DateTimeImmutable
    {
        return $utcDateTime->setTime(
            (int) $utcDateTime->format('H'),
            (int) $utcDateTime->format('i'),
            0
        );
    }
}