<?php
/**
 * Copyright (C) 2021-2022 Graham Breach
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
/**
 * For more information, please contact <graham@goat1000.com>
 */

namespace Goat1000\SVGGraph;

/**
 * Class for formatting date/time values
 */
class DateTimeFormatter {

  protected $timezone = null;
  protected $localize = false;
  protected $idf = null;

  public function __construct()
  {
    $this->timezone = new \DateTimeZone(date_default_timezone_get());

    // see if output needs localization
    if(extension_loaded('intl')) {
      $locale = setlocale(LC_TIME, 0);
      if($locale && $locale !== 'C' && $locale !== 'POSIX' &&
        strpos($locale, 'en_') === false) {
        $this->localize = true;
        $this->idf = new \IntlDateFormatter($locale,
          \IntlDateFormatter::FULL, \IntlDateFormatter::FULL);
      }
    }
  }

  /**
   * Returns the formatted, localized date/time
   */
  public function format($dt, $fmt, $strip_offset = false)
  {
    $datetime = clone $dt;
    $datetime->setTimezone($this->timezone);

    if($strip_offset) {
      $offset = $this->timezone->getOffset($datetime);
      if($offset < 0)
        $datetime->modify($offset . ' second');
      else
        $datetime->modify('+' . $offset . ' second');
    }

    if(!$this->localize)
      return $datetime->format($fmt);

    // DateTime class doesn't do localization, so these fields are passed to
    // IntlDateFormatter instead
    $map = [
      'D' => 'E',
      'l' => 'EEEE',
      'M' => 'MMM',
      'F' => 'MMMM',
    ];

    $result = '';
    $unixtime = $datetime->format('U');
    for($i = 0; $i < strlen($fmt); ++$i) {
      $char = $fmt[$i];
      if(isset($map[$char])) {
        $this->idf->setPattern($map[$char]);
        $result .= $this->idf->format($unixtime);
      } else {
        $result .= $datetime->format($fmt[$i]);
      }
    }
    return $result;
  }

  /**
   * Returns the list of day names
   */
  public function getLongDays()
  {
    return $this->getDateStrings('l', 'd');
  }

  /**
   * Returns the list of abbreviated day names
   */
  public function getShortDays()
  {
    return $this->getDateStrings('D', 'd');
  }

  /**
   * Returns the list of month names
   */
  public function getLongMonths()
  {
    return $this->getDateStrings('F', 'm');
  }

  /**
   * Returns the list of abbreviated month names
   */
  public function getShortMonths()
  {
    return $this->getDateStrings('M', 'm');
  }

  /**
   * Returns a list of day or month strings using IntlDateFormatter to localize
   */
  private function getDateStrings($fmt, $inc)
  {
    // 1978 started on a Sunday
    $dt = new \DateTime('1978-01-01T12:00:00Z');
    if($inc == 'm') {
      $count = 12;
      $offset = 'month';
    } else {
      $count = 7;
      $offset = 'day';
    }

    $strings = [];
    for($i = 0; $i < $count; ++$i) {
      if($i)
        $dt->modify('+1 ' . $offset);
      $strings[] = $this->format($dt, $fmt);
    }
    return $strings;
  }
}