class DateTimePlus

class DateTimePlus {
    use ToStringTrait;
    const FORMAT = 'Y-m-d H:i:s';
    
    /**
     * A RFC7231 Compliant date.
     *
     * @see http://tools.ietf.org/html/rfc7231#section-7.1.1.1
     *
     * Example: Sun, 06 Nov 1994 08:49:37 GMT
     */
    const RFC7231 = 'D, d M Y H:i:s \\G\\M\\T';
    
    /**
     * An array of possible date parts.
     */
    protected static $dateParts = [
        'year',
        'month',
        'day',
        'hour',
        'minute',
        'second',
    ];
    
    /**
     * The value of the time value passed to the constructor.
     *
     * @var string
     */
    protected $inputTimeRaw = '';
    
    /**
     * The prepared time, without timezone, for this date.
     *
     * @var string
     */
    protected $inputTimeAdjusted = '';
    
    /**
     * The value of the timezone passed to the constructor.
     *
     * @var string
     */
    protected $inputTimeZoneRaw = '';
    
    /**
     * The prepared timezone object used to construct this date.
     *
     * @var string
     */
    protected $inputTimeZoneAdjusted = '';
    
    /**
     * The value of the format passed to the constructor.
     *
     * @var string
     */
    protected $inputFormatRaw = '';
    
    /**
     * The prepared format, if provided.
     *
     * @var string
     */
    protected $inputFormatAdjusted = '';
    
    /**
     * The value of the language code passed to the constructor.
     */
    protected $langcode = NULL;
    
    /**
     * An array of errors encountered when creating this date.
     */
    protected $errors = [];
    
    /**
     * The DateTime object.
     *
     * @var \DateTime
     */
    protected $dateTimeObject = NULL;
    
    /**
     * Creates a date object from an input date object.
     *
     * @param \DateTime $datetime
     *   A DateTime object.
     * @param array $settings
     *   (optional) A keyed array for settings, suitable for passing on to
     *   __construct().
     *
     * @return static
     *   A new DateTimePlus object.
     */
    public static function createFromDateTime(\DateTime $datetime, $settings = []) {
        return new static($datetime->format(static::FORMAT), $datetime->getTimezone(), $settings);
    }
    
    /**
     * Creates a date object from an array of date parts.
     *
     * Converts the input value into an ISO date, forcing a full ISO
     * date even if some values are missing.
     *
     * @param array $date_parts
     *   An array of date parts, like ('year' => 2014, 'month' => 4).
     * @param mixed $timezone
     *   (optional) \DateTimeZone object, time zone string or NULL. NULL uses the
     *   default system time zone. Defaults to NULL.
     * @param array $settings
     *   (optional) A keyed array for settings, suitable for passing on to
     *   __construct().
     *
     * @return static
     *   A new DateTimePlus object.
     *
     * @throws \InvalidArgumentException
     *   If the array date values or value combination is not correct.
     */
    public static function createFromArray(array $date_parts, $timezone = NULL, $settings = []) {
        $date_parts = static::prepareArray($date_parts, TRUE);
        if (static::checkArray($date_parts)) {
            // Even with validation, we can end up with a value that the
            // DateTime class won't handle, like a year outside the range
            // of -9999 to 9999, which will pass checkdate() but
            // fail to construct a date object.
            $iso_date = static::arrayToISO($date_parts);
            return new static($iso_date, $timezone, $settings);
        }
        else {
            throw new \InvalidArgumentException('The array contains invalid values.');
        }
    }
    
    /**
     * Creates a date object from timestamp input.
     *
     * The timezone of a timestamp is always UTC. The timezone for a
     * timestamp indicates the timezone used by the format() method.
     *
     * @param int $timestamp
     *   A UNIX timestamp.
     * @param mixed $timezone
     *   (optional) \DateTimeZone object, time zone string or NULL. See
     *   __construct() for more details.
     * @param array $settings
     *   (optional) A keyed array for settings, suitable for passing on to
     *   __construct().
     *
     * @return static
     *   A new DateTimePlus object.
     *
     * @throws \InvalidArgumentException
     *   If the timestamp is not numeric.
     */
    public static function createFromTimestamp($timestamp, $timezone = NULL, $settings = []) {
        if (!is_numeric($timestamp)) {
            throw new \InvalidArgumentException('The timestamp must be numeric.');
        }
        $datetime = new static('', $timezone, $settings);
        $datetime->setTimestamp($timestamp);
        return $datetime;
    }
    
    /**
     * Creates a date object from an input format.
     *
     * @param string $format
     *   PHP date() type format for parsing the input. This is recommended
     *   to use things like negative years, which php's parser fails on, or
     *   any other specialized input with a known format. If provided the
     *   date will be created using the createFromFormat() method.
     *   @see http://php.net/manual/datetime.createfromformat.php
     * @param string $time
     *   String representing the time.
     * @param mixed $timezone
     *   (optional) \DateTimeZone object, time zone string or NULL. See
     *   __construct() for more details.
     * @param array $settings
     *   (optional) A keyed array for settings, suitable for passing on to
     *   __construct(). Supports an additional key:
     *   - validate_format: (optional) Boolean choice to validate the
     *     created date using the input format. The format used in
     *     createFromFormat() allows slightly different values than format().
     *     Using an input format that works in both functions makes it
     *     possible to a validation step to confirm that the date created
     *     from a format string exactly matches the input. This option
     *     indicates the format can be used for validation. Defaults to TRUE.
     *
     * @return static
     *   A new DateTimePlus object.
     *
     * @throws \InvalidArgumentException
     *   If the a date cannot be created from the given format.
     * @throws \UnexpectedValueException
     *   If the created date does not match the input value.
     */
    public static function createFromFormat($format, $time, $timezone = NULL, $settings = []) {
        if (!isset($settings['validate_format'])) {
            $settings['validate_format'] = TRUE;
        }
        // Tries to create a date from the format and use it if possible.
        // A regular try/catch won't work right here, if the value is
        // invalid it doesn't return an exception.
        $datetimeplus = new static('', $timezone, $settings);
        $date = \DateTime::createFromFormat($format, $time, $datetimeplus->getTimezone());
        if (!$date instanceof \DateTime) {
            throw new \InvalidArgumentException('The date cannot be created from a format.');
        }
        else {
            $datetimeplus->setTimestamp($date->getTimestamp());
            $datetimeplus->setTimezone($date->getTimezone());
            // Functions that parse date is forgiving, it might create a date that
            // is not exactly a match for the provided value, so test for that by
            // re-creating the date/time formatted string and comparing it to the input. For
            // instance, an input value of '11' using a format of Y (4 digits) gets
            // created as '0011' instead of '2011'.
            if ($settings['validate_format'] && $date->format($format) != $time) {
                throw new \UnexpectedValueException('The created date does not match the input value.');
            }
        }
        return $datetimeplus;
    }
    
    /**
     * Constructs a date object set to a requested date and timezone.
     *
     * @param string $time
     *   (optional) A date/time string. Defaults to 'now'.
     * @param mixed $timezone
     *   (optional) \DateTimeZone object, time zone string or NULL. NULL uses the
     *   default system time zone. Defaults to NULL. Note that the $timezone
     *   parameter and the current timezone are ignored when the $time parameter
     *   either is a UNIX timestamp (e.g. @946684800) or specifies a timezone
     *   (e.g. 2010-01-28T15:00:00+02:00).
     *   @see http://php.net/manual/datetime.construct.php
     * @param array $settings
     *   (optional) Keyed array of settings. Defaults to empty array.
     *   - langcode: (optional) String two letter language code used to control
     *     the result of the format(). Defaults to NULL.
     *   - debug: (optional) Boolean choice to leave debug values in the
     *     date object for debugging purposes. Defaults to FALSE.
     */
    public function __construct($time = 'now', $timezone = NULL, $settings = []) {
        // Unpack settings.
        $this->langcode = !empty($settings['langcode']) ? $settings['langcode'] : NULL;
        // Massage the input values as necessary.
        $prepared_time = $this->prepareTime($time);
        $prepared_timezone = $this->prepareTimezone($timezone);
        try {
            $this->errors = [];
            if (!empty($prepared_time)) {
                $test = date_parse($prepared_time);
                if (!empty($test['errors'])) {
                    $this->errors = $test['errors'];
                }
            }
            if (empty($this->errors)) {
                $this->dateTimeObject = new \DateTime($prepared_time, $prepared_timezone);
            }
        } catch (\Exception $e) {
            $this->errors[] = $e->getMessage();
        }
        // Clean up the error messages.
        $this->checkErrors();
    }
    
    /**
     * Renders the timezone name.
     *
     * @return string
     */
    public function render() {
        return $this->format(static::FORMAT) . ' ' . $this->getTimeZone()
            ->getName();
    }
    
    /**
     * Implements the magic __call method.
     *
     * Passes through all unknown calls onto the DateTime object.
     *
     * @param string $method
     *   The method to call on the decorated object.
     * @param array $args
     *   Call arguments.
     *
     * @return mixed
     *   The return value from the method on the decorated object. If the proxied
     *   method call returns a DateTime object, then return the original
     *   DateTimePlus object, which allows function chaining to work properly.
     *   Otherwise, the value from the proxied method call is returned.
     *
     * @throws \Exception
     *   Thrown when the DateTime object is not set.
     * @throws \BadMethodCallException
     *   Thrown when there is no corresponding method on the DateTime object to
     *   call.
     */
    public function __call($method, array $args) {
        // @todo consider using assert() as per https://www.drupal.org/node/2451793.
        if (!isset($this->dateTimeObject)) {
            throw new \Exception('DateTime object not set.');
        }
        if (!method_exists($this->dateTimeObject, $method)) {
            throw new \BadMethodCallException(sprintf('Call to undefined method %s::%s()', static::class, $method));
        }
        $result = call_user_func_array([
            $this->dateTimeObject,
            $method,
        ], $args);
        return $result === $this->dateTimeObject ? $this : $result;
    }
    
    /**
     * Returns the difference between two DateTimePlus objects.
     *
     * @param \Drupal\Component\Datetime\DateTimePlus|\DateTime $datetime2
     *   The date to compare to.
     * @param bool $absolute
     *   Should the interval be forced to be positive?
     *
     * @return \DateInterval
     *   A DateInterval object representing the difference between the two dates.
     *
     * @throws \BadMethodCallException
     *    If the input isn't a DateTime or DateTimePlus object.
     */
    public function diff($datetime2, $absolute = FALSE) {
        if ($datetime2 instanceof DateTimePlus) {
            $datetime2 = $datetime2->dateTimeObject;
        }
        if (!$datetime2 instanceof \DateTime) {
            throw new \BadMethodCallException(sprintf('Method %s expects parameter 1 to be a \\DateTime or \\Drupal\\Component\\Datetime\\DateTimePlus object', __METHOD__));
        }
        return $this->dateTimeObject
            ->diff($datetime2, $absolute);
    }
    
    /**
     * Implements the magic __callStatic method.
     *
     * Passes through all unknown static calls onto the DateTime object.
     */
    public static function __callStatic($method, $args) {
        if (!method_exists('\\DateTime', $method)) {
            throw new \BadMethodCallException(sprintf('Call to undefined method %s::%s()', static::class, $method));
        }
        return call_user_func_array([
            '\\DateTime',
            $method,
        ], $args);
    }
    
    /**
     * Implements the magic __clone method.
     *
     * Deep-clones the DateTime object we're wrapping.
     */
    public function __clone() {
        $this->dateTimeObject = clone $this->dateTimeObject;
    }
    
    /**
     * Prepares the input time value.
     *
     * Changes the input value before trying to use it, if necessary.
     * Can be overridden to handle special cases.
     *
     * @param mixed $time
     *   An input value, which could be a timestamp, a string,
     *   or an array of date parts.
     *
     * @return mixed
     *   The massaged time.
     */
    protected function prepareTime($time) {
        return $time;
    }
    
    /**
     * Prepares the input timezone value.
     *
     * Changes the timezone before trying to use it, if necessary.
     * Most importantly, makes sure there is a valid timezone
     * object before moving further.
     *
     * @param mixed $timezone
     *   Either a timezone name or a timezone object or NULL.
     *
     * @return \DateTimeZone
     *   The massaged time zone.
     */
    protected function prepareTimezone($timezone) {
        // If the input timezone is a valid timezone object, use it.
        if ($timezone instanceof \DateTimezone) {
            $timezone_adjusted = $timezone;
        }
        elseif (!empty($timezone) && is_string($timezone)) {
            $timezone_adjusted = new \DateTimeZone($timezone);
        }
        // Default to the system timezone when not explicitly provided.
        // If the system timezone is missing, use 'UTC'.
        if (empty($timezone_adjusted) || !$timezone_adjusted instanceof \DateTimezone) {
            $system_timezone = date_default_timezone_get();
            $timezone_name = !empty($system_timezone) ? $system_timezone : 'UTC';
            $timezone_adjusted = new \DateTimeZone($timezone_name);
        }
        // We are finally certain that we have a usable timezone.
        return $timezone_adjusted;
    }
    
    /**
     * Prepares the input format value.
     *
     * Changes the input format before trying to use it, if necessary.
     * Can be overridden to handle special cases.
     *
     * @param string $format
     *   A PHP format string.
     *
     * @return string
     *   The massaged PHP format string.
     */
    protected function prepareFormat($format) {
        return $format;
    }
    
    /**
     * Examines getLastErrors() to see what errors to report.
     *
     * Two kinds of errors are important: anything that DateTime
     * considers an error, and also a warning that the date was invalid.
     * PHP creates a valid date from invalid data with only a warning,
     * 2011-02-30 becomes 2011-03-03, for instance, but we don't want that.
     *
     * @see http://php.net/manual/time.getlasterrors.php
     */
    public function checkErrors() {
        $errors = \DateTime::getLastErrors();
        if (!empty($errors['errors'])) {
            $this->errors = array_merge($this->errors, $errors['errors']);
        }
        // Most warnings are messages that the date could not be parsed
        // which causes it to be altered. For validation purposes, a warning
        // as bad as an error, because it means the constructed date does
        // not match the input value.
        if (!empty($errors['warnings'])) {
            $this->errors[] = 'The date is invalid.';
        }
        $this->errors = array_values(array_unique($this->errors));
    }
    
    /**
     * Detects if there were errors in the processing of this date.
     *
     * @return bool
     *   TRUE if there were errors in the processing of this date, FALSE
     *   otherwise.
     */
    public function hasErrors() {
        return (bool) count($this->errors);
    }
    
    /**
     * Gets error messages.
     *
     * Public function to return the error messages.
     *
     * @return array
     *   An array of errors encountered when creating this date.
     */
    public function getErrors() {
        return $this->errors;
    }
    
    /**
     * Creates an ISO date from an array of values.
     *
     * @param array $array
     *   An array of date values keyed by date part.
     * @param bool $force_valid_date
     *   (optional) Whether to force a full date by filling in missing
     *   values. Defaults to FALSE.
     *
     * @return string
     *   The date as an ISO string.
     */
    public static function arrayToISO($array, $force_valid_date = FALSE) {
        $array = static::prepareArray($array, $force_valid_date);
        $input_time = '';
        if ($array['year'] !== '') {
            $input_time = static::datePad(intval($array['year']), 4);
            if ($force_valid_date || $array['month'] !== '') {
                $input_time .= '-' . static::datePad(intval($array['month']));
                if ($force_valid_date || $array['day'] !== '') {
                    $input_time .= '-' . static::datePad(intval($array['day']));
                }
            }
        }
        if ($array['hour'] !== '') {
            $input_time .= $input_time ? 'T' : '';
            $input_time .= static::datePad(intval($array['hour']));
            if ($force_valid_date || $array['minute'] !== '') {
                $input_time .= ':' . static::datePad(intval($array['minute']));
                if ($force_valid_date || $array['second'] !== '') {
                    $input_time .= ':' . static::datePad(intval($array['second']));
                }
            }
        }
        return $input_time;
    }
    
    /**
     * Creates a complete array from a possibly incomplete array of date parts.
     *
     * @param array $array
     *   An array of date values keyed by date part.
     * @param bool $force_valid_date
     *   (optional) Whether to force a valid date by filling in missing
     *   values with valid values or just to use empty values instead.
     *   Defaults to FALSE.
     *
     * @return array
     *   A complete array of date parts.
     */
    public static function prepareArray($array, $force_valid_date = FALSE) {
        if ($force_valid_date) {
            $now = new \DateTime();
            $array += [
                'year' => $now->format('Y'),
                'month' => 1,
                'day' => 1,
                'hour' => 0,
                'minute' => 0,
                'second' => 0,
            ];
        }
        else {
            $array += [
                'year' => '',
                'month' => '',
                'day' => '',
                'hour' => '',
                'minute' => '',
                'second' => '',
            ];
        }
        return $array;
    }
    
    /**
     * Checks that arrays of date parts will create a valid date.
     *
     * Checks that an array of date parts has a year, month, and day,
     * and that those values create a valid date. If time is provided,
     * verifies that the time values are valid. Sort of an
     * equivalent to checkdate().
     *
     * @param array $array
     *   An array of datetime values keyed by date part.
     *
     * @return bool
     *   TRUE if the datetime parts contain valid values, otherwise FALSE.
     */
    public static function checkArray($array) {
        $valid_date = FALSE;
        $valid_time = TRUE;
        // Check for a valid date using checkdate(). Only values that
        // meet that test are valid. An empty value, either a string or a 0, is not
        // a valid value.
        if (!empty($array['year']) && !empty($array['month']) && !empty($array['day'])) {
            $valid_date = checkdate($array['month'], $array['day'], $array['year']);
        }
        // Testing for valid time is reversed. Missing time is OK,
        // but incorrect values are not.
        foreach ([
            'hour',
            'minute',
            'second',
        ] as $key) {
            if (array_key_exists($key, $array)) {
                $value = $array[$key];
                switch ($key) {
                    case 'hour':
                        if (!preg_match('/^([1-2][0-3]|[01]?[0-9])$/', $value)) {
                            $valid_time = FALSE;
                        }
                        break;
                    case 'minute':
                    case 'second':
                    default:
                        if (!preg_match('/^([0-5][0-9]|[0-9])$/', $value)) {
                            $valid_time = FALSE;
                        }
                        break;
                }
            }
        }
        return $valid_date && $valid_time;
    }
    
    /**
     * Pads date parts with zeros.
     *
     * Helper function for a task that is often required when working with dates.
     *
     * @param int $value
     *   The value to pad.
     * @param int $size
     *   (optional) Size expected, usually 2 or 4. Defaults to 2.
     *
     * @return string
     *   The padded value.
     */
    public static function datePad($value, $size = 2) {
        return sprintf("%0" . $size . "d", $value);
    }
    
    /**
     * Formats the date for display.
     *
     * @param string $format
     *   Format accepted by date().
     * @param array $settings
     *   - timezone: (optional) String timezone name. Defaults to the timezone
     *     of the date object.
     *
     * @return string|null
     *   The formatted value of the date or NULL if there were construction
     *   errors.
     */
    public function format($format, $settings = []) {
        // If there were construction errors, we can't format the date.
        if ($this->hasErrors()) {
            return;
        }
        // Format the date and catch errors.
        try {
            // Clone the date/time object so we can change the time zone without
            // disturbing the value stored in the object.
            $dateTimeObject = clone $this->dateTimeObject;
            if (isset($settings['timezone'])) {
                $dateTimeObject->setTimezone(new \DateTimeZone($settings['timezone']));
            }
            $value = $dateTimeObject->format($format);
        } catch (\Exception $e) {
            $this->errors[] = $e->getMessage();
        }
        return $value;
    }
    
    /**
     * Sets the default time for an object built from date-only data.
     *
     * The default time for a date without time can be anything, so long as it is
     * consistently applied. If we use noon, dates in most timezones will have the
     * same value for in both the local timezone and UTC.
     */
    public function setDefaultDateTime() {
        $this->dateTimeObject
            ->setTime(12, 0, 0);
    }
    
    /**
     * Gets a clone of the proxied PHP \DateTime object wrapped by this class.
     *
     * @return \DateTime
     *   A clone of the wrapped PHP \DateTime object.
     */
    public function getPhpDateTime() {
        return clone $this->dateTimeObject;
    }

}