lib/src/relative_span_scanner.dart

// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:source_span/source_span.dart';

import 'exception.dart';
import 'line_scanner.dart';
import 'span_scanner.dart';
import 'string_scanner.dart';
import 'utils.dart';

/// A [SpanScanner] that scans within an existing [FileSpan].
///
/// This re-implements chunks of [SpanScanner] rather than using a dummy span or
/// inheritance because scanning is often a performance-critical operation, so
/// it's important to avoid adding extra overhead when relative scanning isn't
/// needed.
class RelativeSpanScanner extends StringScanner implements SpanScanner {
  /// The source of the scanner.
  ///
  /// This caches line break information and is used to generate [Span]s.
  final SourceFile _sourceFile;

  /// The start location of the span within which this scanner is scanning.
  ///
  /// This is used to convert between span-relative and file-relative fields.
  final FileLocation _startLocation;

  int get line => _sourceFile.getLine(_startLocation.offset + position) -
      _startLocation.line;

  int get column {
    var line = _sourceFile.getLine(_startLocation.offset + position);
    var column = _sourceFile.getColumn(_startLocation.offset + position,
        line: line);
    return line == _startLocation.line
        ? column - _startLocation.column
        : column;
  }

  LineScannerState get state => new _SpanScannerState(this, position);

  set state(LineScannerState state) {
    if (state is! _SpanScannerState ||
        !identical((state as _SpanScannerState)._scanner, this)) {
      throw new ArgumentError("The given LineScannerState was not returned by "
          "this LineScanner.");
    }

    this.position = state.position;
  }

  FileSpan get lastSpan => _lastSpan;
  FileSpan _lastSpan;

  FileLocation get location =>
      _sourceFile.location(_startLocation.offset + position);

  FileSpan get emptySpan => location.pointSpan();

  RelativeSpanScanner(FileSpan span)
      : _sourceFile = span.file,
        _startLocation = span.start,
        super(span.text, sourceUrl: span.sourceUrl);

  FileSpan spanFrom(LineScannerState startState, [LineScannerState endState]) {
    var endPosition = endState == null ? position : endState.position;
    return _sourceFile.span(
        _startLocation.offset + startState.position,
        _startLocation.offset + endPosition);
  }

  bool matches(Pattern pattern) {
    if (!super.matches(pattern)) {
      _lastSpan = null;
      return false;
    }

    _lastSpan = _sourceFile.span(
        _startLocation.offset + position,
        _startLocation.offset + lastMatch.end);
    return true;
  }

  void error(String message, {Match match, int position, int length}) {
    validateErrorArgs(string, match, position, length);

    if (match == null && position == null && length == null) match = lastMatch;
    if (position == null) {
      position = match == null ? this.position : match.start;
    }
    if (length == null) length = match == null ? 1 : match.end - match.start;

    var span = _sourceFile.span(
        _startLocation.offset + position,
        _startLocation.offset + position + length);
    throw new StringScannerException(message, span, string);
  }
}

/// A class representing the state of a [SpanScanner].
class _SpanScannerState implements LineScannerState {
  /// The [SpanScanner] that created this.
  final RelativeSpanScanner _scanner;

  final int position;
  int get line => _scanner._sourceFile.getLine(position);
  int get column => _scanner._sourceFile.getColumn(position);

  _SpanScannerState(this._scanner, this.position);
}