/*
    Copyright (C) 2014-2019 de4dot@gmail.com

    This file is part of dnSpy

    dnSpy is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    dnSpy is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with dnSpy.  If not, see <http://www.gnu.org/licenses/>.
*/

using System;
using System.ComponentModel;
using System.Reflection;

namespace dnSpy.Contracts.Images {
	/// <summary>
	/// Image reference
	/// </summary>
	[TypeConverter(typeof(ImageReferenceConverter))]
	public readonly struct ImageReference {
		/// <summary>
		/// Gets an <see cref="ImageReference"/> which isn't referencing any image
		/// </summary>
		public static readonly ImageReference None = default;

		/// <summary>
		/// true if it's the default instance
		/// </summary>
		public bool IsDefault => Assembly is null && Name is null;

		/// <summary>
		/// Assembly of image or null if <see cref="Name"/> is a URI
		/// </summary>
		public Assembly? Assembly { get; }

		/// <summary>
		/// Name of image
		/// </summary>
		public string Name { get; }

		/// <summary>
		/// Constructor
		/// </summary>
		/// <param name="assembly">Assembly of image or null if <paramref name="name"/> is a pack: URI</param>
		/// <param name="name">Name of image</param>
		public ImageReference(Assembly? assembly, string name) {
			Assembly = assembly;
			Name = name ?? throw new ArgumentNullException(nameof(name));
		}

		/// <summary>
		/// Parses a string and tries to create an <see cref="ImageReference"/>
		/// </summary>
		/// <param name="value">String to parse</param>
		/// <param name="result">Result</param>
		/// <returns></returns>
		public static bool TryParse(string? value, out ImageReference result) {
			result = default;
			if (value is null)
				return false;
			if (value == string.Empty)
				return true;

			if (value.StartsWith("/", StringComparison.OrdinalIgnoreCase) ||
				value.StartsWith("pack:", StringComparison.OrdinalIgnoreCase) ||
				value.StartsWith("file:", StringComparison.OrdinalIgnoreCase)) {
				result = new ImageReference(null, value);
				return true;
			}

			int index = value.IndexOf(',');
			if (index < 0) {
				result = new ImageReference(null, value);
				return true;
			}
			var asmName = value.Substring(0, index).Trim();
			var name = value.Substring(index + 1).Trim();
			Assembly asm;
			try {
				asm = Assembly.Load(asmName);
			}
			catch {
				return false;
			}
			result = new ImageReference(asm, name);
			return true;
		}

		/// <summary>
		/// Converts this instance to a string that can be passed to <see cref="TryParse(string, out ImageReference)"/>
		/// </summary>
		/// <returns></returns>
		public override string ToString() {
			if (IsDefault)
				return string.Empty;
			if (Assembly is null)
				return Name;
			return Assembly.GetName().Name + "," + Name;
		}
	}
}