<?php

/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @author Derk-Jan Hartman <hartman.wiki@gmail.com>
 */

namespace MediaWiki\User;

use DateInterval;
use DateTime;
use DateTimeZone;
use Exception;

/**
 * Utility class to parse the TimeCorrection string value.
 *
 * These values are used to specify the time offset for a user and are stored in
 * the database as a user preference and returned by the preferences APIs
 *
 * The class will correct invalid input and adjusts timezone offsets to applicable dates,
 * taking into account DST etc.
 *
 * @since 1.37
 */
class UserTimeCorrection {

	/**
	 * @var string (default) Time correction based on the MediaWiki's system offset from UTC.
	 * The System offset can be configured with wgLocalTimezone and/or wgLocalTZoffset
	 */
	public const SYSTEM = 'System';

	/** @var string Time correction based on a user defined offset from UTC */
	public const OFFSET = 'Offset';

	/** @var string Time correction based on a user defined timezone */
	public const ZONEINFO = 'ZoneInfo';

	/* @var DateTime */
	private $date;

	/* @var bool */
	private $valid;

	/* @var string */
	private $correctionType;

	/* @var int Offset in minutes */
	private $offset;

	/* @var DateTimeZone|null */
	private $timeZone;

	/**
	 * @param string $timeCorrection Original time correction string
	 * @param DateTime|null $relativeToDate The date used to calculate the time zone offset of.
	 *            This defaults to the current date and time.
	 * @param int $offset An offset in minutes (default 0)
	 */
	public function __construct(
		string $timeCorrection,
		DateTime $relativeToDate = null,
		int $offset = 0
	) {
		$this->date = $relativeToDate ?? new DateTime();
		$this->offset = $offset;
		$this->valid = false;
		$this->parse( $timeCorrection );
	}

	/**
	 * Get time offset for a user
	 *
	 * @return string Offset that was applied to the user
	 */
	public function getCorrectionType() : string {
		return $this->correctionType;
	}

	/**
	 * Get corresponding time offset for this correction
	 * Note: When correcting dates/times, apply only the offset OR the time zone, not both.
	 * @return int Offset in minutes
	 */
	public function getTimeOffset() : int {
		return $this->offset;
	}

	/**
	 * Get corresponding time offset for this correction
	 * Note: When correcting dates/times, apply only the offset OR the time zone, not both.
	 * @return DateInterval Offset in minutes as a DateInterval
	 */
	public function getTimeOffsetInterval() : DateInterval {
		$offset = abs( $this->offset );
		$interval = new DateInterval( "PT{$offset}M" );
		if ( $this->offset < 1 ) {
			$interval->invert = 1;
		}
		return $interval;
	}

	/**
	 * The time zone if known
	 * Note: When correcting dates/times, apply only the offset OR the time zone, not both.
	 * @return DateTimeZone|null
	 */
	public function getTimeZone() : ?DateTimeZone {
		return $this->timeZone;
	}

	/**
	 * Was the original correction specification valid
	 * @return bool
	 */
	public function isValid() : bool {
		return $this->valid;
	}

	/**
	 * Parse the timecorrection string as stored in the database for a user
	 * or as entered into the Preferences form field
	 *
	 * There can be two forms of these strings:
	 * 1. A pipe separated tuple of a maximum of 3 fields
	 *    - Field 1 is the type of offset definition
	 *    - Field 2 is the offset in minutes from UTC (optional for System type)
	 *    - Field 3 is a timezone identifier from the tz database (only required for ZoneInfo type)
	 *    - The offset for a ZoneInfo type is unreliable because of DST.
	 *      After retrieving it from the database, it should be recalculated based on the TZ identifier.
	 *    Examples:
	 *    - System
	 *    - System|60
	 *    - Offset|60
	 *    - ZoneInfo|60|Europe/Amsterdam
	 *
	 * 2. The following form provides an offset in hours and minutes
	 *    This currently should only be used by the preferences input field,
	 *    but historically they were present in the database.
	 *    TODO: write a maintenance script to migrate these old db values
	 *    Examples:
	 *    - 16:00
	 *    - 10
	 *
	 * @param string $timeCorrection
	 */
	private function parse( string $timeCorrection ) {
		$data = explode( '|', $timeCorrection, 3 );

		// First handle the case of an actual timezone being specified.
		if ( $data[0] === self::ZONEINFO ) {
			try {
				$this->correctionType = self::ZONEINFO;
				$this->timeZone = new DateTimeZone( $data[2] );
				$this->offset = floor( $this->timeZone->getOffset( $this->date ) / 60 );
				$this->valid = true;
				return;
			} catch ( Exception $e ) {
				// Not a valid/known timezone.
				// Fall back to any specified offset
			}
		}

		// If $timeCorrection is in fact a pipe-separated value, check the
		// first value.
		switch ( $data[0] ) {
			case self::OFFSET:
			case self::ZONEINFO:
				$this->correctionType = self::OFFSET;
				// First value is Offset, so use the specified offset
				$this->offset = (int)( $data[1] ?? 0 );
				// If this is ZoneInfo, then we didn't recognize the TimeZone
				$this->valid = isset( $data[1] ) && $data[0] === self::OFFSET;
				return;
			case self::SYSTEM:
				$this->correctionType = self::SYSTEM;
				$this->valid = true;
				return;
		}

		// $timeCorrection actually isn't a pipe separated value, but instead
		// a colon separated value. This is only used by the userinput of the preferences
		// but can also still be present in the Db. (but shouldn't be)
		$diff = 0;
		$data = explode( ':', $timeCorrection, 2 );
		if ( count( $data ) >= 2 ) {
			// Combination hours and minutes.
			$diff = abs( (int)$data[0] ) * 60 + (int)$data[1];
			if ( (int)$data[0] < 0 ) {
				$diff *= -1;
			}
		} elseif ( ctype_digit( $data[0] ) ) {
			// Just hours.
			$diff = (int)$data[0] * 60;
		} else {
			// We really don't know this. Fallback to System
			$this->correctionType = self::SYSTEM;
			return;
		}

		// Max is +14:00 and min is -12:00, see:
		// https://en.wikipedia.org/wiki/Timezone
		if ( $diff >= -12 * 60 && $diff <= 14 * 60 ) {
			$this->valid = true;
		}
		// 14:00
		$diff = min( $diff, 14 * 60 );
		// -12:00
		$diff = max( $diff, -12 * 60 );

		$this->correctionType = self::OFFSET;
		$this->offset = $diff;
	}

	/**
	 * Note: The string value of this object might not be equal to the original value
	 * @return string a timecorrection string representing this value
	 */
	public function toString() : string {
		switch ( $this->correctionType ) {
			case self::ZONEINFO:
				if ( $this->timeZone ) {
					return "ZoneInfo|{$this->offset}|{$this->timeZone->getName()}";
				}
				// If not, fallback:
			case self::SYSTEM:
			case self::OFFSET:
			default:
				return "{$this->correctionType}|{$this->offset}";
		}
	}

	public function __toString() {
		return $this->toString();
	}
}