class UTF8Utils

class UTF8Utils {
    
    /**
     * The Unicode replacement character.
     */
    const FFFD = "�";
    
    /**
     * Count the number of characters in a string.
     * UTF-8 aware. This will try (in order) iconv, MB, and finally a custom counter.
     *
     * @param string $string
     *
     * @return int
     */
    public static function countChars($string) {
        // Get the length for the string we need.
        if (function_exists('mb_strlen')) {
            return mb_strlen($string, 'utf-8');
        }
        if (function_exists('iconv_strlen')) {
            return iconv_strlen($string, 'utf-8');
        }
        $count = count_chars($string);
        // 0x80 = 0x7F - 0 + 1 (one added to get inclusive range)
        // 0x33 = 0xF4 - 0x2C + 1 (one added to get inclusive range)
        return array_sum(array_slice($count, 0, 0x80)) + array_sum(array_slice($count, 0xc2, 0x33));
    }
    
    /**
     * Convert data from the given encoding to UTF-8.
     *
     * This has not yet been tested with charactersets other than UTF-8.
     * It should work with ISO-8859-1/-13 and standard Latin Win charsets.
     *
     * @param string $data     The data to convert
     * @param string $encoding A valid encoding. Examples: http://www.php.net/manual/en/mbstring.supported-encodings.php
     *
     * @return string
     */
    public static function convertToUTF8($data, $encoding = 'UTF-8') {
        
        /*
         * From the HTML5 spec: Given an encoding, the bytes in the input stream must be converted
         * to Unicode characters for the tokeniser, as described by the rules for that encoding,
         * except that the leading U+FEFF BYTE ORDER MARK character, if any, must not be stripped
         * by the encoding layer (it is stripped by the rule below). Bytes or sequences of bytes
         * in the original byte stream that could not be converted to Unicode characters must be
         * converted to U+FFFD REPLACEMENT CHARACTER code points.
         */
        // mb_convert_encoding is chosen over iconv because of a bug. The best
        // details for the bug are on http://us1.php.net/manual/en/function.iconv.php#108643
        // which contains links to the actual but reports as well as work around
        // details.
        if (function_exists('mb_convert_encoding')) {
            // mb library has the following behaviors:
            // - UTF-16 surrogates result in false.
            // - Overlongs and outside Plane 16 result in empty strings.
            // Before we run mb_convert_encoding we need to tell it what to do with
            // characters it does not know. This could be different than the parent
            // application executing this library so we store the value, change it
            // to our needs, and then change it back when we are done. This feels
            // a little excessive and it would be great if there was a better way.
            $save = mb_substitute_character();
            mb_substitute_character('none');
            $data = mb_convert_encoding($data, 'UTF-8', $encoding);
            mb_substitute_character($save);
        }
        elseif (function_exists('iconv') && 'auto' !== $encoding) {
            // fprintf(STDOUT, "iconv found\n");
            // iconv has the following behaviors:
            // - Overlong representations are ignored.
            // - Beyond Plane 16 is replaced with a lower char.
            // - Incomplete sequences generate a warning.
            $data = @iconv($encoding, 'UTF-8//IGNORE', $data);
        }
        else {
            throw new Exception('Not implemented, please install mbstring or iconv');
        }
        
        /*
         * One leading U+FEFF BYTE ORDER MARK character must be ignored if any are present.
         */
        if ("" === substr($data, 0, 3)) {
            $data = substr($data, 3);
        }
        return $data;
    }
    
    /**
     * Checks for Unicode code points that are not valid in a document.
     *
     * @param string $data A string to analyze
     *
     * @return array An array of (string) error messages produced by the scanning
     */
    public static function checkForIllegalCodepoints($data) {
        // Vestigal error handling.
        $errors = array();
        
        /*
         * All U+0000 null characters in the input must be replaced by U+FFFD REPLACEMENT CHARACTERs.
         * Any occurrences of such characters is a parse error.
         */
        for ($i = 0, $count = substr_count($data, "\x00"); $i < $count; ++$i) {
            $errors[] = 'null-character';
        }
        
        /*
         * Any occurrences of any characters in the ranges U+0001 to U+0008, U+000B, U+000E to U+001F, U+007F
         * to U+009F, U+D800 to U+DFFF , U+FDD0 to U+FDEF, and characters U+FFFE, U+FFFF, U+1FFFE, U+1FFFF,
         * U+2FFFE, U+2FFFF, U+3FFFE, U+3FFFF, U+4FFFE, U+4FFFF, U+5FFFE, U+5FFFF, U+6FFFE, U+6FFFF, U+7FFFE,
         * U+7FFFF, U+8FFFE, U+8FFFF, U+9FFFE, U+9FFFF, U+AFFFE, U+AFFFF, U+BFFFE, U+BFFFF, U+CFFFE, U+CFFFF,
         * U+DFFFE, U+DFFFF, U+EFFFE, U+EFFFF, U+FFFFE, U+FFFFF, U+10FFFE, and U+10FFFF are parse errors.
         * (These are all control characters or permanently undefined Unicode characters.)
         */
        // Check PCRE is loaded.
        $count = preg_match_all('/(?:
        [\\x01-\\x08\\x0B\\x0E-\\x1F\\x7F] # U+0001 to U+0008, U+000B,  U+000E to U+001F and U+007F
      |
        \\xC2[\\x80-\\x9F] # U+0080 to U+009F
      |
        \\xED(?:\\xA0[\\x80-\\xFF]|[\\xA1-\\xBE][\\x00-\\xFF]|\\xBF[\\x00-\\xBF]) # U+D800 to U+DFFFF
      |
        \\xEF\\xB7[\\x90-\\xAF] # U+FDD0 to U+FDEF
      |
        \\xEF\\xBF[\\xBE\\xBF] # U+FFFE and U+FFFF
      |
        [\\xF0-\\xF4][\\x8F-\\xBF]\\xBF[\\xBE\\xBF] # U+nFFFE and U+nFFFF (1 <= n <= 10_{16})
      )/x', $data, $matches);
        for ($i = 0; $i < $count; ++$i) {
            $errors[] = 'invalid-codepoint';
        }
        return $errors;
    }

}