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<?php
/**
* SCSSPHP
*
* @copyright 2012-2020 Leaf Corcoran
*
* @license http://opensource.org/licenses/MIT MIT
*
* @link http://scssphp.github.io/scssphp
*/
namespace ScssPhp\ScssPhp\Parser;
use ScssPhp\ScssPhp\SourceSpan\FileSpan;
use ScssPhp\ScssPhp\SourceSpan\SourceFile;
/**
* A port of Dart's string_scanner package to be used by the parser.
*
* The scanner only supports UTF-8 strings.
*
* Differences with Dart:
* - reading a character is reading a byte, not an UTF-16 code unit (as PHP strings are not UTF-16). The
* {@see readUtf8Char} method can be used to consume an UTF-8 char.
* - characters are represented as a single-char string, not as an integer with their UTF-16 char code
* - offsets are based on bytes, not on UTF-16 code units. In practice, parsing Sass generally needs
* to peak following chars only when already knowing that the current char is an ASCII one, which
* makes this safe. When this assumption does not hold anymore, a different logic should be used
* - as strings and regexp cannot be used interchangeably in PHP (in Dart, regexps are a different
* object, and both String and Regexp are implementing a Pattern interface for matching), the scanner
* exposes supports only strings in scan() and expect(). Should we need support for regexps, a
* separate method will be added.
*
* @internal
*/
class StringScanner
{
/**
* @var string
* @readonly
*/
private $string;
/**
* @var int
*/
private $position = 0;
/**
* @var SourceFile
* @readonly
*/
private $sourceFile;
public function __construct(string $content, ?string $sourceUrl = null)
{
$this->string = $content;
$this->sourceFile = new SourceFile($content, $sourceUrl);
}
public function getString(): string
{
return $this->string;
}
public function getPosition(): int
{
return $this->position;
}
public function setPosition(int $position): void
{
$this->position = $position;
}
public function spanFrom(int $start, ?int $end = null): FileSpan
{
$end = $end ?? $this->position;
return $this->sourceFile->span($start, $end);
}
/**
* Returns an empty span at the current location.
*/
public function getEmptySpan(): FileSpan
{
return $this->sourceFile->span($this->position, $this->position);
}
public function isDone(): bool
{
return $this->position === \strlen($this->string);
}
/**
* @throws FormatException if the end of the string is reached
*
* @phpstan-impure
*/
public function readChar(): string
{
if ($this->position === \strlen($this->string)) {
$this->fail('more input');
}
return $this->string[$this->position++];
}
/**
* @throws FormatException if the end of the string is reached
*
* @phpstan-impure
*/
public function readUtf8Char(): string
{
if ($this->position === \strlen($this->string)) {
$this->fail('more input');
}
if (\ord($this->string[$this->position]) < 0x80) {
return $this->string[$this->position++];
}
if (!preg_match('/./usA', $this->string, $m, 0, $this->position)) {
$this->fail('utf-8 char');
}
$this->position += \strlen($m[0]);
return $m[0];
}
/**
* Consumes the next character in the string if it the provided character.
*
* @param string $char
*
* @return bool Whether the character was consumed.
*
* @phpstan-impure
*/
public function scanChar(string $char): bool
{
if ($this->position === \strlen($this->string)) {
return false;
}
if ($this->string[$this->position] !== $char) {
return false;
}
++$this->position;
return true;
}
/**
* Consumes the provided string if it appears at the current position.
*
* @param string $string
*
* @return bool Whether the string was consumed.
*
* @phpstan-impure
*/
public function scan(string $string): bool
{
if (!$this->matches($string)) {
return false;
}
$this->position += \strlen($string);
return true;
}
/**
* Returns whether or not the provided string appears at the current position.
*
* This doesn't move the scan pointer forward.
*/
public function matches(string $string): bool
{
if ($this->position - 1 + \strlen($string) >= \strlen($this->string)) {
return false;
}
return substr($this->string, $this->position, \strlen($string)) === $string;
}
/**
* If the next character in the string is $character, consumes it.
*
* If $character could not be consumed, throws an exception
* describing the position of the failure. $name is used in this error as
* the expected name of the character being matched; if it's `null`, the
* character itself is used instead.
*
* @param string $character
* @param string|null $name
*
* @return void
*
* @throws FormatException
*
* @phpstan-impure
*/
public function expectChar(string $character, ?string $name = null): void
{
if ($this->scanChar($character)) {
return;
}
if ($name === null) {
$name = '"' . $character . '"';
}
$this->fail($name);
}
/**
* @param string $string
*
* @return void
*
* @throws FormatException
*
* @phpstan-impure
*/
public function expect(string $string): void
{
if ($this->scan($string)) {
return;
}
$this->fail('"' . $string . '"');
}
/**
* @throws FormatException
*/
public function expectDone(): void
{
if ($this->isDone()) {
return;
}
$this->fail('no more input');
}
/**
* Returns the character at the given offset of the current position.
*
* The offset can be negative to peek already seen characters.
* Returns null if the offset goes out of range.
* This does not affect the position or the last match.
*
* @param int $offset
*
* @return string|null
*/
public function peekChar(int $offset = 0): ?string
{
$pos = $this->position + $offset;
if ($pos < 0 || $pos >= \strlen($this->string)) {
return null;
}
return $this->string[$pos];
}
/**
* Returns the substring of the string between $start and $end (excluded).
*
* $end defaults to the current position.
*
* @param int $start
* @param int|null $end
*
* @return string
*/
public function substring(int $start, ?int $end = null): string
{
if ($end === null) {
$end = $this->position;
}
if ($end < $start) {
return '';
}
return substr($this->string, $start, $end - $start);
}
/**
* The scanner's current (zero-based) line number.
*
* @return int
*/
public function getLine(): int
{
return $this->sourceFile->getLine($this->position);
}
/**
* The scanner's current (zero-based) column number.
*
* @return int
*/
public function getColumn(): int
{
return $this->sourceFile->getColumn($this->position);
}
/**
* @param string $message
* @param int|null $position
* @param int|null $length
*
* @throws FormatException
*
* @return never-returns
*/
public function error(string $message, ?int $position = null, ?int $length = null)
{
$position = $position ?? $this->position;
$length = $length ?? 0;
$span = $this->sourceFile->span($position, $position + $length);
throw new FormatException($message, $span);
}
/**
* @param string $message
*
* @throws FormatException
*
* @return never-returns
*/
private function fail(string $message)
{
$this->error("expected $message.");
}
}
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