<?php
declare(strict_types=1);

class CycleCalculatorService
{
    public function resolveCurrentCycle(array $task, DateTimeImmutable $now): array
    {
        $startDate = $this->parseDate((string) ($task['start_date'] ?? ''));
        if ($startDate === null) {
            return [];
        }

        $startDate = $startDate->setTime(0, 0, 0);
        if ($now < $startDate) {
            return [];
        }

        $frequencyType = (string) ($task['frequency_type'] ?? 'once');
        if ($frequencyType !== 'recurring') {
            return [
                'cycle_key' => 'once',
                'cycle_start_at' => $startDate,
                'cycle_end_at' => $startDate->setTime(23, 59, 59),
                'cycle_boundary_start_at' => $startDate,
                'cycle_boundary_end_at' => $startDate->setTime(23, 59, 59),
            ];
        }

        $unit = (string) ($task['recurrence_unit'] ?? '');
        $interval = max(1, (int) ($task['recurrence_interval'] ?? 1));

        if (!in_array($unit, ['day', 'week', 'month', 'year'], true)) {
            return [];
        }

        if ($unit === 'day') {
            return $this->resolveDayCycle($startDate, $now, $interval);
        }

        if ($unit === 'week') {
            return $this->resolveWeekCycle($startDate, $now, $interval);
        }

        if ($unit === 'month') {
            return $this->resolveMonthCycle($startDate, $now, $interval);
        }

        return $this->resolveYearCycle($startDate, $now, $interval);
    }

    public function resolveInitialCompletionCycle(array $task, DateTimeImmutable $assignedAt): array
    {
        $startDate = $this->parseDate((string) ($task['start_date'] ?? ''));
        if ($startDate === null) {
            return [];
        }

        $startDay = $startDate->setTime(0, 0, 0);
        $assignedDay = $assignedAt->setTime(0, 0, 0);
        $cycleStart = $assignedDay > $startDay ? $assignedDay : $startDay;

        return $this->resolveCompletionCycleFromStart($task, $cycleStart);
    }

    public function resolveNextCompletionCycle(array $task, array $lastAssignment): array
    {
        $lastCycleStart = $this->extractDateTime($lastAssignment['cycle_start_at'] ?? null);
        if ($lastCycleStart === null) {
            return [];
        }

        $completedAt = $this->extractDateTime($lastAssignment['completed_at'] ?? null);
        if ($completedAt === null) {
            return [];
        }

        $unit = (string) ($task['recurrence_unit'] ?? '');
        $interval = max(1, (int) ($task['recurrence_interval'] ?? 1));
        $plannedNextStart = $this->addInterval($lastCycleStart->setTime(0, 0, 0), $unit, $interval);
        if (!($plannedNextStart instanceof DateTimeImmutable)) {
            return [];
        }

        $completionAnchor = $completedAt->setTime(0, 0, 0);
        $cycleStart = $plannedNextStart > $completionAnchor ? $plannedNextStart : $completionAnchor;

        return $this->resolveCompletionCycleFromStart($task, $cycleStart);
    }

    public function resolveDueAt(array $task, array $cycle): ?string
    {
        $cycleStart = $this->extractDateTime($cycle['cycle_start_at'] ?? null);
        $cycleEnd = $this->extractDateTime($cycle['cycle_end_at'] ?? null);
        if ($cycleStart === null || $cycleEnd === null) {
            return null;
        }

        $ruleType = (string) ($task['deadline_rule_type'] ?? 'cycle_end');
        if (!in_array($ruleType, ['cycle_end', 'offset_days', 'weekday', 'monthday'], true)) {
            $ruleType = 'cycle_end';
        }

        $dueAt = null;
        if ($ruleType === 'cycle_end') {
            $dueAt = $cycleEnd;
        } elseif ($ruleType === 'offset_days') {
            $offsetDays = (int) ($task['deadline_offset_days'] ?? 0);
            if ($offsetDays <= 0) {
                return null;
            }

            $dueAt = $cycleStart
                ->modify('+' . $offsetDays . ' days')
                ->setTime(23, 59, 59);
        } elseif ($ruleType === 'weekday') {
            $weekday = (int) ($task['deadline_weekday'] ?? 0);
            if ($weekday < 1 || $weekday > 7) {
                return null;
            }

            $cycleEndDay = $cycleEnd->setTime(0, 0, 0);
            $endWeekday = (int) $cycleEndDay->format('N');
            $diff = $endWeekday - $weekday;
            if ($diff < 0) {
                $diff += 7;
            }

            $dueAt = $cycleEndDay
                ->modify('-' . $diff . ' days')
                ->setTime(23, 59, 59);
        } elseif ($ruleType === 'monthday') {
            $monthDay = (int) ($task['deadline_monthday'] ?? 0);
            if ($monthDay < 1 || $monthDay > 31) {
                return null;
            }

            $year = (int) $cycleEnd->format('Y');
            $month = (int) $cycleEnd->format('n');
            $lastDay = (int) $cycleEnd->format('t');
            $resolvedDay = min($monthDay, $lastDay);

            $dueAt = DateTimeImmutable::createFromFormat(
                'Y-m-d H:i:s',
                sprintf('%04d-%02d-%02d 23:59:59', $year, $month, $resolvedDay)
            );

            if ($dueAt === false) {
                return null;
            }
        }

        if (!$dueAt instanceof DateTimeImmutable) {
            return null;
        }

        if ($dueAt < $cycleStart) {
            $dueAt = $cycleStart->setTime(23, 59, 59);
        }

        return $dueAt->format('Y-m-d H:i:s');
    }

    private function resolveCompletionCycleFromStart(array $task, DateTimeImmutable $cycleStart): array
    {
        $frequencyType = (string) ($task['frequency_type'] ?? 'once');
        if ($frequencyType !== 'recurring') {
            return [];
        }

        $unit = (string) ($task['recurrence_unit'] ?? '');
        $interval = max(1, (int) ($task['recurrence_interval'] ?? 1));
        if (!in_array($unit, ['day', 'week', 'month', 'year'], true)) {
            return [];
        }

        $normalizedStart = $cycleStart->setTime(0, 0, 0);
        $cycleEnd = $this->addInterval($normalizedStart, $unit, $interval);
        if (!($cycleEnd instanceof DateTimeImmutable)) {
            return [];
        }
        $cycleEnd = $cycleEnd->modify('-1 second');

        return [
            'cycle_key' => 'roll-' . $normalizedStart->format('Ymd'),
            'cycle_start_at' => $normalizedStart,
            'cycle_end_at' => $cycleEnd,
            'cycle_boundary_start_at' => $normalizedStart,
            'cycle_boundary_end_at' => $cycleEnd,
        ];
    }

    private function addInterval(DateTimeImmutable $start, string $unit, int $interval): ?DateTimeImmutable
    {
        if (!in_array($unit, ['day', 'week', 'month', 'year'], true)) {
            return null;
        }

        if ($interval < 1) {
            $interval = 1;
        }

        if ($unit === 'week') {
            return $start->modify('+' . ($interval * 7) . ' days');
        }

        return $start->modify('+' . $interval . ' ' . $unit . ($interval === 1 ? '' : 's'));
    }

    private function resolveDayCycle(DateTimeImmutable $startDate, DateTimeImmutable $now, int $interval): array
    {
        $currentDay = $now->setTime(0, 0, 0);
        $daysDiff = max(0, (int) $startDate->diff($currentDay)->format('%a'));
        $cycleIndex = (int) floor($daysDiff / $interval);

        $boundaryStart = $startDate->modify('+' . ($cycleIndex * $interval) . ' days');
        $boundaryEnd = $boundaryStart->modify('+' . $interval . ' days')->modify('-1 second');

        return $this->buildCycle(
            'day-' . $boundaryStart->format('Ymd'),
            $startDate,
            $boundaryStart,
            $boundaryEnd
        );
    }

    private function resolveWeekCycle(DateTimeImmutable $startDate, DateTimeImmutable $now, int $interval): array
    {
        $anchorWeekStart = $this->weekStart($startDate);
        $currentWeekStart = $this->weekStart($now);
        $weeksDiff = max(0, intdiv((int) $anchorWeekStart->diff($currentWeekStart)->format('%a'), 7));
        $cycleIndex = (int) floor($weeksDiff / $interval);

        $boundaryStart = $anchorWeekStart->modify('+' . ($cycleIndex * $interval * 7) . ' days');
        $boundaryEnd = $boundaryStart->modify('+' . ($interval * 7) . ' days')->modify('-1 second');

        return $this->buildCycle(
            'week-' . $boundaryStart->format('Ymd'),
            $startDate,
            $boundaryStart,
            $boundaryEnd
        );
    }

    private function resolveMonthCycle(DateTimeImmutable $startDate, DateTimeImmutable $now, int $interval): array
    {
        $anchorMonthIndex = ((int) $startDate->format('Y') * 12) + ((int) $startDate->format('n') - 1);
        $currentMonthIndex = ((int) $now->format('Y') * 12) + ((int) $now->format('n') - 1);
        $monthDiff = max(0, $currentMonthIndex - $anchorMonthIndex);
        $cycleIndex = (int) floor($monthDiff / $interval);
        $cycleStartIndex = $anchorMonthIndex + ($cycleIndex * $interval);

        $year = (int) floor($cycleStartIndex / 12);
        $month = ($cycleStartIndex % 12) + 1;

        $boundaryStart = DateTimeImmutable::createFromFormat(
            'Y-m-d H:i:s',
            sprintf('%04d-%02d-01 00:00:00', $year, $month)
        );
        if ($boundaryStart === false) {
            return [];
        }

        $boundaryEnd = $boundaryStart->modify('+' . $interval . ' months')->modify('-1 second');

        return $this->buildCycle(
            'month-' . $boundaryStart->format('Y-m'),
            $startDate,
            $boundaryStart,
            $boundaryEnd
        );
    }

    private function resolveYearCycle(DateTimeImmutable $startDate, DateTimeImmutable $now, int $interval): array
    {
        $anchorYear = (int) $startDate->format('Y');
        $currentYear = (int) $now->format('Y');
        $yearDiff = max(0, $currentYear - $anchorYear);
        $cycleIndex = (int) floor($yearDiff / $interval);
        $cycleYear = $anchorYear + ($cycleIndex * $interval);

        $boundaryStart = DateTimeImmutable::createFromFormat(
            'Y-m-d H:i:s',
            sprintf('%04d-01-01 00:00:00', $cycleYear)
        );
        if ($boundaryStart === false) {
            return [];
        }

        $boundaryEnd = $boundaryStart->modify('+' . $interval . ' years')->modify('-1 second');

        return $this->buildCycle(
            'year-' . $boundaryStart->format('Y'),
            $startDate,
            $boundaryStart,
            $boundaryEnd
        );
    }

    private function buildCycle(
        string $cycleKey,
        DateTimeImmutable $startDate,
        DateTimeImmutable $boundaryStart,
        DateTimeImmutable $boundaryEnd
    ): array {
        $effectiveStart = $boundaryStart < $startDate ? $startDate : $boundaryStart;

        return [
            'cycle_key' => $cycleKey,
            'cycle_start_at' => $effectiveStart,
            'cycle_end_at' => $boundaryEnd,
            'cycle_boundary_start_at' => $boundaryStart,
            'cycle_boundary_end_at' => $boundaryEnd,
        ];
    }

    private function weekStart(DateTimeImmutable $date): DateTimeImmutable
    {
        $normalized = $date->setTime(0, 0, 0);
        $weekday = (int) $normalized->format('N');
        $offset = $weekday - 1;

        if ($offset <= 0) {
            return $normalized;
        }

        return $normalized->modify('-' . $offset . ' days');
    }

    private function parseDate(string $value): ?DateTimeImmutable
    {
        if ($value === '') {
            return null;
        }

        try {
            return new DateTimeImmutable($value);
        } catch (Throwable $throwable) {
            return null;
        }
    }

    private function extractDateTime($value): ?DateTimeImmutable
    {
        if ($value instanceof DateTimeImmutable) {
            return $value;
        }

        if (!is_string($value) || trim($value) === '') {
            return null;
        }

        try {
            return new DateTimeImmutable($value);
        } catch (Throwable $throwable) {
            return null;
        }
    }
}