<?php
namespace DayTidy\DisplayViews;

use DateTime;
use DateTimeZone;
use Exception;

class DateWindow
{
    /**
     * @var mixed[]
     */
    private array $config;

    /**
     * @param mixed[] $config
     */
    public function __construct(array $config)
    {
        $this->config = Config::normalize($config);
    }

    /**
     * @return array{range_start: string, range_end: string, empty_range: bool}
     */
    public function queryArgs(): array
    {
        $bounds = $this->bounds();
        $start = $bounds['start'];
        $end = $bounds['end'];

        return [
            'range_start' => $start instanceof DateTime ? $start->format('Y-m-d H:i:s') : '',
            'range_end' => $end instanceof DateTime ? $end->format('Y-m-d H:i:s') : '',
            'empty_range' => $start instanceof DateTime && $end instanceof DateTime && $start >= $end,
        ];
    }

    public function coverageTarget(): ?DateTime
    {
        $bounds = $this->bounds();

        if ($bounds['end'] instanceof DateTime)
        {
            return clone $bounds['end'];
        }

        if ($bounds['start'] instanceof DateTime)
        {
            $target = clone $bounds['start'];
            $target->modify('+1 year');

            return $target;
        }

        return null;
    }

    /**
     * @return array{start: ?DateTime, end: ?DateTime}
     */
    private function bounds(): array
    {
        $range = isset($this->config['date_range']) && is_array($this->config['date_range'])
            ? $this->config['date_range']
            : [];
        $tz = function_exists('wp_timezone') ? wp_timezone() : new DateTimeZone('UTC');
        $utc = new DateTimeZone('UTC');
        $start = self::resolveBoundary(isset($range['start']) && is_array($range['start']) ? $range['start'] : [], 'start', $tz);
        $end = self::resolveBoundary(isset($range['end']) && is_array($range['end']) ? $range['end'] : [], 'end', $tz);

        if ($start instanceof DateTime) $start->setTimezone($utc);
        if ($end instanceof DateTime) $end->setTimezone($utc);

        return [
            'start' => $start,
            'end' => $end,
        ];
    }

    /**
     * @param mixed[] $boundary
     */
    private static function resolveBoundary(array $boundary, string $side, DateTimeZone $tz): ?DateTime
    {
        $mode = sanitize_key((string) ($boundary['mode'] ?? 'none'));
        if ($mode === 'none') return null;

        try
        {
            $date = self::dateForMode($boundary, $mode, $tz);
        }
        catch (Exception $e)
        {
            return null;
        }

        if (!$date) return null;

        $date->setTime(0, 0, 0);
        if ($side === 'end') $date->modify('+1 day');

        return $date;
    }

    /**
     * @param mixed[] $boundary
     */
    private static function dateForMode(array $boundary, string $mode, DateTimeZone $tz): ?DateTime
    {
        switch ($mode)
        {
            case 'today':
                return new DateTime('today', $tz);

            case 'tomorrow':
                return new DateTime('tomorrow', $tz);

            case 'yesterday':
                return new DateTime('yesterday', $tz);

            case 'start_previous_month':
                return new DateTime('first day of previous month', $tz);

            case 'start_current_month':
                return new DateTime('first day of this month', $tz);

            case 'start_next_month':
                return new DateTime('first day of next month', $tz);

            case 'end_previous_month':
                return new DateTime('last day of previous month', $tz);

            case 'end_current_month':
                return new DateTime('last day of this month', $tz);

            case 'end_next_month':
                return new DateTime('last day of next month', $tz);

            case 'fixed':
                return self::fixedDate((string) ($boundary['date'] ?? ''), $tz);

            case 'relative':
                return self::relativeDate($boundary, $tz);
        }

        return null;
    }

    private static function fixedDate(string $date, DateTimeZone $tz): ?DateTime
    {
        if (!preg_match('/^\d{4}-\d{2}-\d{2}$/', $date)) return null;

        $value = DateTime::createFromFormat('!Y-m-d', $date, $tz);
        $errors = DateTime::getLastErrors();

        if (!$value instanceof DateTime) return null;
        if ($errors !== false && ($errors['warning_count'] || $errors['error_count'])) return null;

        return $value;
    }

    /**
     * @param mixed[] $boundary
     */
    private static function relativeDate(array $boundary, DateTimeZone $tz): DateTime
    {
        $amount = max(0, min(10000, absint($boundary['amount'] ?? 0)));
        $direction = sanitize_key((string) ($boundary['direction'] ?? 'future')) === 'past' ? '-' : '+';
        $unit = sanitize_key((string) ($boundary['unit'] ?? 'days'));
        $unit = array_key_exists($unit, Registry::dateRangeUnits()) ? $unit : 'days';
        $date = new DateTime('today', $tz);

        if ($amount > 0)
        {
            $date->modify($direction . $amount . ' ' . $unit);
        }

        return $date;
    }
}