using System;

namespace Wabbajack.Paths
{
    public struct Extension
    {
        private static readonly Extension None = new("");

        #region ObjectEquality

        private bool Equals(Extension other)
        {
            return string.Equals(_extension, other._extension, StringComparison.InvariantCultureIgnoreCase);
        }

        public override bool Equals(object? obj)
        {
            return obj is Extension other && Equals(other);
        }

        public override string ToString()
        {
            return _extension;
        }

        public override int GetHashCode()
        {
            return _extension.GetHashCode(StringComparison.InvariantCultureIgnoreCase);
        }

        #endregion

        private readonly string _extension;

        public Extension(string extension)
        {
            _extension = extension;
            Validate();
        }

        private void Validate()
        {
            if (!_extension.StartsWith(".") && _extension != "")
                throw new PathException($"Extensions must start with '.' got {_extension}");
        }

        public static explicit operator string(Extension path)
        {
            return path._extension;
        }

        public static explicit operator Extension(string path)
        {
            return new Extension(path);
        }

        public static bool operator ==(Extension a, Extension b)
        {
            return string.Equals(a._extension, b._extension, StringComparison.CurrentCultureIgnoreCase);
        }

        public static bool operator !=(Extension a, Extension b)
        {
            return !(a == b);
        }

        public static Extension FromPath(string path)
        {
            var lastIndex = path.LastIndexOf(".", StringComparison.Ordinal);
            return lastIndex == -1 ? None : new Extension(path[lastIndex..]);
        }
    }
}