class CharacterStream

final class CharacterStream {
    
    /** Pre-computed for optimization */
    private const UTF8_LENGTH_MAP = [
        "\x00" => 1,
        "\x01" => 1,
        "\x02" => 1,
        "\x03" => 1,
        "\x04" => 1,
        "\x05" => 1,
        "\x06" => 1,
        "\x07" => 1,
        "\x08" => 1,
        "\t" => 1,
        "\n" => 1,
        "\v" => 1,
        "\f" => 1,
        "\r" => 1,
        "\x0e" => 1,
        "\x0f" => 1,
        "\x10" => 1,
        "\x11" => 1,
        "\x12" => 1,
        "\x13" => 1,
        "\x14" => 1,
        "\x15" => 1,
        "\x16" => 1,
        "\x17" => 1,
        "\x18" => 1,
        "\x19" => 1,
        "\x1a" => 1,
        "\x1b" => 1,
        "\x1c" => 1,
        "\x1d" => 1,
        "\x1e" => 1,
        "\x1f" => 1,
        " " => 1,
        "!" => 1,
        "\"" => 1,
        "#" => 1,
        "\$" => 1,
        "%" => 1,
        "&" => 1,
        "'" => 1,
        "(" => 1,
        ")" => 1,
        "*" => 1,
        "+" => 1,
        "," => 1,
        "-" => 1,
        "." => 1,
        "/" => 1,
        "0" => 1,
        "1" => 1,
        "2" => 1,
        "3" => 1,
        "4" => 1,
        "5" => 1,
        "6" => 1,
        "7" => 1,
        "8" => 1,
        "9" => 1,
        ":" => 1,
        ";" => 1,
        "<" => 1,
        "=" => 1,
        ">" => 1,
        "?" => 1,
        "@" => 1,
        "A" => 1,
        "B" => 1,
        "C" => 1,
        "D" => 1,
        "E" => 1,
        "F" => 1,
        "G" => 1,
        "H" => 1,
        "I" => 1,
        "J" => 1,
        "K" => 1,
        "L" => 1,
        "M" => 1,
        "N" => 1,
        "O" => 1,
        "P" => 1,
        "Q" => 1,
        "R" => 1,
        "S" => 1,
        "T" => 1,
        "U" => 1,
        "V" => 1,
        "W" => 1,
        "X" => 1,
        "Y" => 1,
        "Z" => 1,
        "[" => 1,
        "\\" => 1,
        "]" => 1,
        "^" => 1,
        "_" => 1,
        "`" => 1,
        "a" => 1,
        "b" => 1,
        "c" => 1,
        "d" => 1,
        "e" => 1,
        "f" => 1,
        "g" => 1,
        "h" => 1,
        "i" => 1,
        "j" => 1,
        "k" => 1,
        "l" => 1,
        "m" => 1,
        "n" => 1,
        "o" => 1,
        "p" => 1,
        "q" => 1,
        "r" => 1,
        "s" => 1,
        "t" => 1,
        "u" => 1,
        "v" => 1,
        "w" => 1,
        "x" => 1,
        "y" => 1,
        "z" => 1,
        "{" => 1,
        "|" => 1,
        "}" => 1,
        "~" => 1,
        "" => 1,
        "\x80" => 0,
        "\x81" => 0,
        "\x82" => 0,
        "\x83" => 0,
        "\x84" => 0,
        "\x85" => 0,
        "\x86" => 0,
        "\x87" => 0,
        "\x88" => 0,
        "\x89" => 0,
        "\x8a" => 0,
        "\x8b" => 0,
        "\x8c" => 0,
        "\x8d" => 0,
        "\x8e" => 0,
        "\x8f" => 0,
        "\x90" => 0,
        "\x91" => 0,
        "\x92" => 0,
        "\x93" => 0,
        "\x94" => 0,
        "\x95" => 0,
        "\x96" => 0,
        "\x97" => 0,
        "\x98" => 0,
        "\x99" => 0,
        "\x9a" => 0,
        "\x9b" => 0,
        "\x9c" => 0,
        "\x9d" => 0,
        "\x9e" => 0,
        "\x9f" => 0,
        "\xa0" => 0,
        "\xa1" => 0,
        "\xa2" => 0,
        "\xa3" => 0,
        "\xa4" => 0,
        "\xa5" => 0,
        "\xa6" => 0,
        "\xa7" => 0,
        "\xa8" => 0,
        "\xa9" => 0,
        "\xaa" => 0,
        "\xab" => 0,
        "\xac" => 0,
        "\xad" => 0,
        "\xae" => 0,
        "\xaf" => 0,
        "\xb0" => 0,
        "\xb1" => 0,
        "\xb2" => 0,
        "\xb3" => 0,
        "\xb4" => 0,
        "\xb5" => 0,
        "\xb6" => 0,
        "\xb7" => 0,
        "\xb8" => 0,
        "\xb9" => 0,
        "\xba" => 0,
        "\xbb" => 0,
        "\xbc" => 0,
        "\xbd" => 0,
        "\xbe" => 0,
        "\xbf" => 0,
        "\xc0" => 2,
        "\xc1" => 2,
        "\xc2" => 2,
        "\xc3" => 2,
        "\xc4" => 2,
        "\xc5" => 2,
        "\xc6" => 2,
        "\xc7" => 2,
        "\xc8" => 2,
        "\xc9" => 2,
        "\xca" => 2,
        "\xcb" => 2,
        "\xcc" => 2,
        "\xcd" => 2,
        "\xce" => 2,
        "\xcf" => 2,
        "\xd0" => 2,
        "\xd1" => 2,
        "\xd2" => 2,
        "\xd3" => 2,
        "\xd4" => 2,
        "\xd5" => 2,
        "\xd6" => 2,
        "\xd7" => 2,
        "\xd8" => 2,
        "\xd9" => 2,
        "\xda" => 2,
        "\xdb" => 2,
        "\xdc" => 2,
        "\xdd" => 2,
        "\xde" => 2,
        "\xdf" => 2,
        "\xe0" => 3,
        "\xe1" => 3,
        "\xe2" => 3,
        "\xe3" => 3,
        "\xe4" => 3,
        "\xe5" => 3,
        "\xe6" => 3,
        "\xe7" => 3,
        "\xe8" => 3,
        "\xe9" => 3,
        "\xea" => 3,
        "\xeb" => 3,
        "\xec" => 3,
        "\xed" => 3,
        "\xee" => 3,
        "\xef" => 3,
        "\xf0" => 4,
        "\xf1" => 4,
        "\xf2" => 4,
        "\xf3" => 4,
        "\xf4" => 4,
        "\xf5" => 4,
        "\xf6" => 4,
        "\xf7" => 4,
        "\xf8" => 5,
        "\xf9" => 5,
        "\xfa" => 5,
        "\xfb" => 5,
        "\xfc" => 6,
        "\xfd" => 6,
        "\xfe" => 0,
        "\xff" => 0,
    ];
    private string $data = '';
    private int $dataSize = 0;
    private array $map = [];
    private int $charCount = 0;
    private int $currentPos = 0;
    private int $fixedWidth = 0;
    
    /**
     * @param resource|string $input
     */
    public function __construct($input, ?string $charset = 'utf-8') {
        $charset = strtolower(trim($charset)) ?: 'utf-8';
        if ('utf-8' === $charset || 'utf8' === $charset) {
            $this->fixedWidth = 0;
            $this->map = [
                'p' => [],
                'i' => [],
            ];
        }
        else {
            $this->fixedWidth = match ($charset) {    'ucs2', 'ucs-2', 'utf16', 'utf-16' => 2,
                'ucs4', 'ucs-4', 'utf32', 'utf-32' => 4,
                default => 1,
            
            };
        }
        if (\is_resource($input)) {
            $blocks = 16372;
            while (false !== ($read = fread($input, $blocks))) {
                $this->write($read);
            }
        }
        else {
            $this->write($input);
        }
    }
    public function read(int $length) : ?string {
        if ($this->currentPos >= $this->charCount) {
            return null;
        }
        $length = $this->currentPos + $length > $this->charCount ? $this->charCount - $this->currentPos : $length;
        if ($this->fixedWidth > 0) {
            $len = $length * $this->fixedWidth;
            $ret = substr($this->data, $this->currentPos * $this->fixedWidth, $len);
            $this->currentPos += $length;
        }
        else {
            $end = $this->currentPos + $length;
            $end = min($end, $this->charCount);
            $ret = '';
            $start = 0;
            if ($this->currentPos > 0) {
                $start = $this->map['p'][$this->currentPos - 1];
            }
            $to = $start;
            for (; $this->currentPos < $end; ++$this->currentPos) {
                if (isset($this->map['i'][$this->currentPos])) {
                    $ret .= substr($this->data, $start, $to - $start) . '?';
                    $start = $this->map['p'][$this->currentPos];
                }
                else {
                    $to = $this->map['p'][$this->currentPos];
                }
            }
            $ret .= substr($this->data, $start, $to - $start);
        }
        return $ret;
    }
    public function readBytes(int $length) : ?array {
        if (null !== ($read = $this->read($length))) {
            return array_map('ord', str_split($read, 1));
        }
        return null;
    }
    public function setPointer(int $charOffset) : void {
        if ($this->charCount < $charOffset) {
            $charOffset = $this->charCount;
        }
        $this->currentPos = $charOffset;
    }
    public function write(string $chars) : void {
        $ignored = '';
        $this->data .= $chars;
        if ($this->fixedWidth > 0) {
            $strlen = \strlen($chars);
            $ignoredL = $strlen % $this->fixedWidth;
            $ignored = $ignoredL ? substr($chars, -$ignoredL) : '';
            $this->charCount += ($strlen - $ignoredL) / $this->fixedWidth;
        }
        else {
            $this->charCount += $this->getUtf8CharPositions($chars, $this->dataSize, $ignored);
        }
        $this->dataSize = \strlen($this->data) - \strlen($ignored);
    }
    private function getUtf8CharPositions(string $string, int $startOffset, string &$ignoredChars) : int {
        $strlen = \strlen($string);
        $charPos = \count($this->map['p']);
        $foundChars = 0;
        $invalid = false;
        for ($i = 0; $i < $strlen; ++$i) {
            $char = $string[$i];
            $size = self::UTF8_LENGTH_MAP[$char];
            if (0 == $size) {
                
                /* char is invalid, we must wait for a resync */
                $invalid = true;
                continue;
            }
            if ($invalid) {
                
                /* We mark the chars as invalid and start a new char */
                $this->map['p'][$charPos + $foundChars] = $startOffset + $i;
                $this->map['i'][$charPos + $foundChars] = true;
                ++$foundChars;
                $invalid = false;
            }
            if ($i + $size > $strlen) {
                $ignoredChars = substr($string, $i);
                break;
            }
            for ($j = 1; $j < $size; ++$j) {
                $char = $string[$i + $j];
                if ($char > "" && $char < "\xc0") {
                    // Valid - continue parsing
                }
                else {
                    
                    /* char is invalid, we must wait for a resync */
                    $invalid = true;
                    continue 2;
                }
            }
            
            /* Ok we got a complete char here */
            $this->map['p'][$charPos + $foundChars] = $startOffset + $i + $size;
            $i += $j - 1;
            ++$foundChars;
        }
        return $foundChars;
    }

}