named-binary-tag/Nbt/NbtPath.cs

using System.Collections;

namespace Nbt;

public static class NbtPath
{
    public static readonly INbtPath Empty = new EmptyNbtPathImpl();

    public static INbtPath CreatePath(INbtPathElement pathElement) => new NbtPathImpl([pathElement]);

    public static INbtPath CreatePath(params INbtPathElement[] pathElements) => CreatePath(pathElements.AsEnumerable());

    public static INbtPath CreatePath(IEnumerable<INbtPathElement> pathElements) => new NbtPathImpl(pathElements);

    public static INbtPath CreatePath(params object[] pathElements) => CreatePath(pathElements.AsEnumerable());

    public static INbtPath CreatePath(IEnumerable<object> pathElements) => CreatePath(pathElements.Select(WrapPathElement));

    private static INbtPathElement WrapPathElement(object pathElement) => pathElement switch
    {
        null => throw new ArgumentNullException(nameof(pathElement)),
        string name => new NbtName(name),
        int index => new NbtIndex(index),
        _ => throw new ArgumentException($"Invalid path element type: {pathElement.GetType().Name}", nameof(pathElement))
    };
}

public interface INbtPath : IEnumerable<INbtPathElement>
{
    int Count { get; }

    bool IsEmpty { get; }

    INbtPathElement PopFirst(out INbtPath rest);

    INbtPathElement this[int index] { get; }

    INbtPath Combine(INbtPath other);

    INbtPath Append(INbtPathElement pathElement);

    INbtPath Insert(int index, INbtPathElement pathElement);

    INbtPath Replace(int index, INbtPathElement pathElement);
}

file class NbtPathImpl(IEnumerable<INbtPathElement> pathElements) : INbtPath
{
    private readonly IList<INbtPathElement> _pathElements = pathElements.AsIList();

    public int Count => _pathElements.Count;

    public bool IsEmpty => Count == 0;

    public INbtPathElement PopFirst(out INbtPath rest)
    {
        var count = Count;

        if (count < 1)
        {
            throw new IndexOutOfRangeException();
        }

        rest = count > 1 ? new NbtPathImpl(_pathElements.Skip(1)) : NbtPath.Empty;
        return _pathElements[0];
    }

    public INbtPathElement this[int index] => _pathElements[index];

    public INbtPath Append(INbtPathElement pathElement) => new NbtPathImpl(_pathElements.Append(pathElement));

    public INbtPath Insert(int index, INbtPathElement pathElement) => new NbtPathImpl(Utils.Insert(_pathElements, index, pathElement));

    public INbtPath Replace(int index, INbtPathElement pathElement) => new NbtPathImpl(Utils.Replace(_pathElements, index, pathElement));

    public INbtPath Combine(INbtPath other) => new NbtPathImpl(_pathElements.Concat(other));

    public IEnumerator<INbtPathElement> GetEnumerator() => _pathElements.GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

file class EmptyNbtPathImpl : INbtPath
{
    public int Count => 0;

    public bool IsEmpty => true;

    public INbtPathElement PopFirst(out INbtPath rest) => throw new IndexOutOfRangeException();

    public INbtPathElement this[int index] => throw new IndexOutOfRangeException();

    public INbtPath Append(INbtPathElement pathElement) => new NbtPathImpl(pathElement.Yield());

    public INbtPath Insert(int index, INbtPathElement pathElement)
    {
        ArgumentOutOfRangeException.ThrowIfNotEqual(index, 0);

        return new NbtPathImpl(pathElement.Yield());
    }

    public INbtPath Replace(int index, INbtPathElement pathElement)
    {
        throw new ArgumentOutOfRangeException(nameof(index));
    }

    public INbtPath Combine(INbtPath other) => other;

    public IEnumerator<INbtPathElement> GetEnumerator() => Enumerable.Empty<INbtPathElement>().GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

public interface INbtPathElement
{
    object Key { get; }
}

public readonly struct NbtName(string name) : INbtPathElement
{
    public string Name { get; } = name;

    object INbtPathElement.Key => Name;

    public static implicit operator NbtName(string tagName) => new(tagName);

    public static implicit operator string(NbtName nbtName) => nbtName.Name;
}

public readonly struct NbtIndex(int index) : INbtPathElement
{
    public int Index { get; } = index;

    object INbtPathElement.Key => Index;

    public static implicit operator NbtIndex(int tagIndex) => new(tagIndex);

    public static implicit operator int(NbtIndex nbtIndex) => nbtIndex.Index;
}