packages/petitparser/lib/src/petitparser/context.dart

part of petitparser;

/// An immutable parse context.
class Context {
  const Context(this.buffer, this.position);

  /// The buffer we are working on.
  final buffer;

  /// The current position in the buffer.
  final int position;

  /// Returns a result indicating a parse success.
  Result success(result, [int position]) {
    return new Success(buffer, position == null ? this.position : position, result);
  }

  /// Returns a result indicating a parse failure.
  Result failure(String message, [int position]) {
    return new Failure(buffer, position == null ? this.position : position, message);
  }

  /// Returns a human readable string of the current context.
  String toString() => 'Context[${toPositionString()}]';

  /// Returns the line:column if the input is a string, otherwise the position.
  String toPositionString() => Token.positionString(buffer, position);
}

/// An immutable parse result.
abstract class Result extends Context {
  const Result(buffer, position) : super(buffer, position);

  /// Returns [true] if this result indicates a parse success.
  bool get isSuccess => false;

  /// Returns [true] if this result indicates a parse failure.
  bool get isFailure => false;

  /// Returns the parse result of the current context.
  get value;

  /// Returns the parse message of the current context.
  String get message;
}

/// An immutable parse result in case of a successful parse.
class Success extends Result {
  const Success(buffer, position, this.value) : super(buffer, position);

  @override
  bool get isSuccess => true;

  @override
  final value;

  @override
  String get message => null;

  @override
  String toString() => 'Success[${toPositionString()}]: $value';
}

/// An immutable parse result in case of a failed parse.
class Failure extends Result {
  const Failure(buffer, position, this.message) : super(buffer, position);

  @override
  bool get isFailure => true;

  @override
  get value => throw new ParserError(this);

  @override
  final String message;

  @override
  String toString() => 'Failure[${toPositionString()}]: $message';
}

/// An exception raised in case of a parse error.
class ParserError extends Error {
  final Failure failure;

  ParserError(this.failure);

  @override
  String toString() => '${failure.message} at ${failure.toPositionString()}';
}