<?php
/**
 * Date helper.
 *
 * @package HostKhata
 */

namespace HostKhata\Support;

defined( 'ABSPATH' ) || exit;

use DateTimeImmutable;
use DateTimeZone;

/**
 * UTC date helpers. Everything is stored in UTC and converted to the site
 * timezone only for display.
 *
 * @since 0.1.0
 */
final class Date {

	const DATETIME = 'Y-m-d H:i:s';
	const DATE     = 'Y-m-d';

	/**
	 * Current UTC date and time in MySQL format.
	 *
	 * @since 0.1.0
	 *
	 * @return string
	 */
	public static function now_gmt(): string {
		return gmdate( self::DATETIME );
	}

	/**
	 * Current UTC date.
	 *
	 * @since 0.1.0
	 *
	 * @return string
	 */
	public static function today_gmt(): string {
		return gmdate( self::DATE );
	}

	/**
	 * Tells whether a string is a real calendar date in Y-m-d format.
	 *
	 * @since 0.1.0
	 *
	 * @param string $date Date string.
	 * @return bool
	 */
	public static function is_valid_date( string $date ): bool {
		$parsed = DateTimeImmutable::createFromFormat( '!' . self::DATE, $date, new DateTimeZone( 'UTC' ) );

		return false !== $parsed && $parsed->format( self::DATE ) === $date;
	}

	/**
	 * Adds days to a Y-m-d date.
	 *
	 * @since 0.1.0
	 *
	 * @param string $date Y-m-d date.
	 * @param int    $days Days to add, may be negative.
	 * @return string
	 */
	public static function add_days( string $date, int $days ): string {
		return self::parse( $date )->modify( sprintf( '%+d days', $days ) )->format( self::DATE );
	}

	/**
	 * Whole days from one Y-m-d date to another (negative when the second is earlier).
	 *
	 * @since 0.1.0
	 *
	 * @param string $from Y-m-d date.
	 * @param string $to   Y-m-d date.
	 * @return int
	 */
	public static function days_between( string $from, string $to ): int {
		$diff = self::parse( $from )->diff( self::parse( $to ) );

		return $diff->invert ? - (int) $diff->days : (int) $diff->days;
	}

	/**
	 * Adds months to a Y-m-d date. When the target month is shorter, the result
	 * is clamped to its last day, so 31 January plus one month is 28 February.
	 *
	 * @since 0.1.0
	 *
	 * @param string $date   Y-m-d date.
	 * @param int    $months Months to add, may be negative.
	 * @return string
	 */
	public static function add_months( string $date, int $months ): string {
		$start = self::parse( $date );
		$day   = (int) $start->format( 'j' );
		$first = $start->modify( 'first day of this month' )->modify( sprintf( '%+d months', $months ) );
		$last  = (int) $first->format( 't' );

		return $first->setDate( (int) $first->format( 'Y' ), (int) $first->format( 'n' ), min( $day, $last ) )->format( self::DATE );
	}

	/**
	 * Converts a UTC MySQL datetime to the site timezone for display.
	 *
	 * @since 0.1.0
	 *
	 * @param string $gmt    UTC datetime.
	 * @param string $format PHP date format. Empty uses the site date and time format.
	 * @return string
	 */
	public static function to_site( string $gmt, string $format = '' ): string {
		if ( '' === $gmt || '0000-00-00 00:00:00' === $gmt ) {
			return '';
		}

		if ( '' === $format ) {
			$format = get_option( 'date_format' ) . ' ' . get_option( 'time_format' );
		}

		return wp_date( $format, strtotime( $gmt . ' UTC' ) );
	}

	/**
	 * Parses a Y-m-d date as midnight UTC.
	 *
	 * @param string $date Y-m-d date.
	 * @return DateTimeImmutable
	 */
	private static function parse( string $date ): DateTimeImmutable {
		return new DateTimeImmutable( $date . ' 00:00:00', new DateTimeZone( 'UTC' ) );
	}
}