<?php
	/**
	 * CC-BY 3.0 Alfonso J. Ramos (theraot)
	 * UTF8
	 */
	final class UTF8
	{
		//------------------------------------------------------------
		// Private (Class)
		//------------------------------------------------------------

		private static function CodePointLength($ord)
		{
			if (($ord >> 7) === 0)
			{
				return 1;
			}
			if (($ord >> 5) === 6)
			{
				return 2;
			}
			if (($ord >> 4) === 14)
			{
				return 3;
			}
			if (($ord >> 3) === 30)
			{
				return 4;
			}
			return false;
		}

		private static function CharacterIndex($string, $position, $after)
		{
			$strlen = strlen($string);
			if ($position < 0)
			{
				for ($index = $strlen - 1; $index >= 0; $index--)
				{
					$ord = ord($string{$index});
					if (($ord >> 6) !== 2)
					{
						$position++;
					}
					if ($position === 0)
					{
						return $index;
					}
				}
				return null;
			}
			$count = 0;
			for ($index = $after; $index < $strlen; $count++)
			{
				if ($count === $position)
				{
					return $index;
				}
				$ord = ord($string{$index});
				$add = UTF8::CodePointLength($ord);
				if ($add === false)
				{
					return false;
				}
				/*for ($check = $index + 1; $check < $index + $add; $check++)
				{
					$ord = ord($string{$check});
					if ($ord < 0x80 || $ord > 0xbf)
					{
						return false;
					}
				}*/
				$index += $add;
			}
			if ($count < $position)
			{
				return false;
			}
			return $strlen;
		}

		//------------------------------------------------------------
		// Public (Class)
		//------------------------------------------------------------
		
		/**
		* UTF-8 aware replacement of char
		*/
		public static function Character(/*int*/ $codepoint)
		{
			$codepoint = intval($codepoint);
			if ($codepoint < 127)
			{
				return chr($codepoint);
			}
			if ($codepoint < 2047)
			{
				return chr(192 | (($codepoint >> 6) & 31)).chr(128 | ($codepoint & 63));
			}
			if ($codepoint < 65535)
			{
				return chr(224 | (($codepoint >> 12) & 31)).chr(128 | (($codepoint >> 6) & 63)).chr(128 | ($codepoint & 63));
			}
			if ($codepoint < 1114111)
			{
				return chr(240 | (($codepoint >> 18) & 31)).chr(128 | (($codepoint >> 12) & 63)).chr(128 | (($codepoint >> 6) & 63)).chr(128 | ($codepoint & 63));
			}
		}

		public static function CharacterAt($string, $index)
		{
			$nextIndex = UTF8::CharacterIndex($string, 1, $index);
			if ($nextIndex === false)
			{
				return '';
			}
			return substr($string, $index, $nextIndex - $index);
		}

		public static function CharactersAt($string, $index, $length)
		{
			$nextIndex = UTF8::CharacterIndex($string, $length, $index);
			if ($nextIndex === false)
			{
				return substr($string, $index);
			}
			return substr($string, $index, $nextIndex - $index);
		}

		/**
		* UTF-8 aware replacement of ord
		*/
		public static function CodePoint(/*string*/ $character)
		{
			$ord0 = ord($character{0});
			switch(UTF8::CodePointLength($ord0))
			{
				case 1:
					return $ord0;
				case 2:
					return ($ord0 - 192) * 64 + (ord($character{1}) - 128);
				case 3:
					return ($ord0 - 224) * 4096 + (ord($character{1}) - 128) * 64 + (ord($character{2}) - 128);
				case 4:
					return ($ord0 - 240) * 262144 + (ord($character{1}) - 128) * 4096 + (ord($character{2}) - 128) * 64 + (ord($character{3}) - 128);
				default:
					return false;
			}
		}

		public static function Enumerate($string)
		{
			$strlen = strlen($string);
			for ($index = 0; $index < $strlen; )
			{
				$chr = UTF8::CharacterAt($string, $index);
				if ($chr === '')
				{
					return;
				}
				$index += strlen($chr);
				yield $chr;
			}
		}

		public static function IsASCII($string)
		{
			$strlen = strlen($string);
			$count = 0;
			for ($index = 0; $index < $strlen; $count++)
			{
				$ord = ord($string{$index});
				$add = UTF8::CodePointLength($ord);
				if ($add === false || $add !== 1)
				{
					return false;
				}
				$index += $add;
			}
			return $count;
		}

		public static function IsUTF8($string)
		{
			return UTF8::Length($string) !== false;
		}

		public static function Length($string)
		{
			$strlen = strlen($string);
			$count = 0;
			for ($index = 0; $index < $strlen; $count++)
			{
				$ord = ord($string{$index});
				$add = UTF8::CodePointLength($ord);
				if ($add === false)
				{
					return false;
				}
				for ($check = $index + 1; $check < $index + $add; $check++)
				{
					$ord = ord($string{$check});
					if ($ord < 0x80 || $ord > 0xbf)
					{
						return false;
					}
				}
				$index += $add;
			}
			return $count;
		}

		public static function Split(/*string*/ $string, /*int*/ $length = 1)
		{
			if (intval($length) !== $length || $length < 1)
			{
				trigger_error('The length of each segment must be greater than zero', E_USER_WARNING);
				return false;
			}
			else
			{
				$strlen = strlen($string);
				$result = [];
				$index = 0;
				while($index < $strlen)
				{
					$block = UTF8::CharactersAt($string, $index, $length);
					$result[] = $block;
					$index += strlen($block);
				}
				return $result;
			}
		}
		
		public static function Substr($string, $start, $length = null)
		{
			$startIndex = UTF8::CharacterIndex($string, $start, 0);
			if ($startIndex === null)
			{
				$startIndex = 0;
			}
			if ($startIndex === false)
			{
				return false;
			}
			if ($length === null)
			{
				return substr($string, $startIndex);
			}
			else
			{
				$endIndex = UTF8::CharacterIndex($string, $length, $startIndex);
				if ($endIndex === null)
				{
					return false;
				}
				if ($endIndex === false)
				{
					return substr($string, $startIndex);
				}
				if ($endIndex < $startIndex)
				{
					return $start < 0 ? '' : false;
				}
				return substr($string, $startIndex, $endIndex - $startIndex);
			}
		}

		//------------------------------------------------------------
		// Public (Constructor)
		//------------------------------------------------------------

		/**
		 * Creating instances of this class is not allowed.
		 */
		public function __construct()
		{
			trigger_error('Creating instances of '.__CLASS__.' is forbidden');
		}
	}