class DoubleQuoteUsageSniff

class DoubleQuoteUsageSniff implements Sniff {
    
    /**
     * Returns an array of tokens this test wants to listen for.
     *
     * @return array<int|string>
     */
    public function register() {
        return [
            T_CONSTANT_ENCAPSED_STRING,
            T_DOUBLE_QUOTED_STRING,
        ];
    }
    
    //end register()
    
    /**
     * Processes this test, when one of its tokens is encountered.
     *
     * @param \PHP_CodeSniffer\Files\File $phpcsFile The file being scanned.
     * @param int                         $stackPtr  The position of the current token
     *                                               in the stack passed in $tokens.
     *
     * @return int
     */
    public function process(File $phpcsFile, $stackPtr) {
        $tokens = $phpcsFile->getTokens();
        // If tabs are being converted to spaces by the tokeniser, the
        // original content should be used instead of the converted content.
        if (isset($tokens[$stackPtr]['orig_content']) === true) {
            $workingString = $tokens[$stackPtr]['orig_content'];
        }
        else {
            $workingString = $tokens[$stackPtr]['content'];
        }
        $lastStringToken = $stackPtr;
        $i = $stackPtr + 1;
        if (isset($tokens[$i]) === true) {
            while ($i < $phpcsFile->numTokens && $tokens[$i]['code'] === $tokens[$stackPtr]['code']) {
                if (isset($tokens[$i]['orig_content']) === true) {
                    $workingString .= $tokens[$i]['orig_content'];
                }
                else {
                    $workingString .= $tokens[$i]['content'];
                }
                $lastStringToken = $i;
                $i++;
            }
        }
        $skipTo = $lastStringToken + 1;
        // Check if it's a double quoted string.
        if ($workingString[0] !== '"' || substr($workingString, -1) !== '"') {
            return $skipTo;
        }
        // The use of variables in double quoted strings is not allowed.
        if ($tokens[$stackPtr]['code'] === T_DOUBLE_QUOTED_STRING) {
            $stringTokens = token_get_all('<?php ' . $workingString);
            foreach ($stringTokens as $token) {
                if (is_array($token) === true && $token[0] === T_VARIABLE) {
                    $error = 'Variable "%s" not allowed in double quoted string; use concatenation instead';
                    $data = [
                        $token[1],
                    ];
                    $phpcsFile->addError($error, $stackPtr, 'ContainsVar', $data);
                }
            }
            return $skipTo;
        }
        
        //end if
        $allowedChars = [
            '\\0',
            '\\1',
            '\\2',
            '\\3',
            '\\4',
            '\\5',
            '\\6',
            '\\7',
            '\\n',
            '\\r',
            '\\f',
            '\\t',
            '\\v',
            '\\x',
            '\\b',
            '\\e',
            '\\u',
            '\'',
        ];
        foreach ($allowedChars as $testChar) {
            if (strpos($workingString, $testChar) !== false) {
                return $skipTo;
            }
        }
        $error = 'String %s does not require double quotes; use single quotes instead';
        $data = [
            str_replace([
                "\r",
                "\n",
            ], [
                '\\r',
                '\\n',
            ], $workingString),
        ];
        $fix = $phpcsFile->addFixableError($error, $stackPtr, 'NotRequired', $data);
        if ($fix === true) {
            $phpcsFile->fixer
                ->beginChangeset();
            $innerContent = substr($workingString, 1, -1);
            $innerContent = str_replace('\\"', '"', $innerContent);
            $innerContent = str_replace('\\$', '$', $innerContent);
            $phpcsFile->fixer
                ->replaceToken($stackPtr, "'{$innerContent}'");
            while ($lastStringToken !== $stackPtr) {
                $phpcsFile->fixer
                    ->replaceToken($lastStringToken, '');
                $lastStringToken--;
            }
            $phpcsFile->fixer
                ->endChangeset();
        }
        return $skipTo;
    }
    
    //end process()

}