CanonSharp/CanonSharp.Pascal/Scanner/StringReadState.cs

using CanonSharp.Combinator.Abstractions;

namespace CanonSharp.Pascal.Scanner;

/// <summary>
/// 字符串输入流状态
/// </summary>
public sealed class StringReadState : IReadState<char, StringReadState>
{
    private readonly string _source;

    private readonly int _index;

    public char Current => _source[_index];

    public bool HasValue => _index < _source.Length;

    public StringReadState Next => new(_source, _index + 1);

    private StringReadState(string source, int index)
    {
        _source = source;
        _index = index;
    }

    public StringReadState(string source) : this(source, 0)
    {
    }

    public bool Equals(StringReadState? other)
    {
        if (other is null)
        {
            return false;
        }

        return _source == other._source && _index == other._index;
    }

    public override bool Equals(object? obj) => obj is StringReadState other && Equals(other);

    public override int GetHashCode() => _source.GetHashCode() ^ _index;

    public override string ToString()
    {
        return HasValue ? $"{ToReadableString(Current)}<0x{(int)Current:X2}>" : "End of string.";
    }

    private static string ToReadableString(char token)
        => token switch
        {
            '\0' => "\\0",
            '\a' => "\\a",
            '\b' => "\\b",
            '\f' => "\\f",
            '\n' => "\\n",
            '\r' => "\\r",
            '\t' => "\\t",
            '\v' => "\\v",
            _ => token.ToString(),
        };
}