using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace AMWD.Common.Test
{
	/// <summary>
	/// Implements a snapshot comparison for content aggregation (e.g. files).
	/// </summary>
	public sealed class SnapshotAssert
	{
		/// <summary>
		/// Tests whether the specified string is equal to the saved snapshot.
		/// </summary>
		/// <param name="actual">The current aggregated content string.</param>
		/// <param name="message">An error message.</param>
		/// <param name="callerFilePath">The absolute file path of the calling file (filled automatically by the compiler service).</param>
		/// <param name="callerMemberName">The name of the calling method (filled automatically by the compiler service).</param>
		public static void AreEqual(string actual, string message = null, [CallerFilePath] string callerFilePath = null, [CallerMemberName] string callerMemberName = null)
		{
			string cleanLineEnding = actual
				.Replace("\r\n", "\n")   // Windows
				.Replace("\r", "\n");    // old MacOS
			AreEqual(Encoding.UTF8.GetBytes(cleanLineEnding), message, callerFilePath, callerMemberName);
		}

		/// <summary>
		/// Tests whether the specified byte array is equal to the saved snapshot.
		/// </summary>
		/// <param name="actual">The current aggregated content bytes.</param>
		/// <param name="message">An error message.</param>
		/// <param name="callerFilePath">The absolute file path of the calling file (filled automatically by the compiler service).</param>
		/// <param name="callerMemberName">The name of the calling method (filled automatically by the compiler service).</param>
		public static void AreEqual(byte[] actual, string message = null, [CallerFilePath] string callerFilePath = null, [CallerMemberName] string callerMemberName = null)
			=> AreEqual(actual, 0, -1, message, callerFilePath, callerMemberName);

		/// <summary>
		/// Tests whether the specified byte array is equal to the saved snapshot.
		/// </summary>
		/// <remarks>
		/// The past has shown, that e.g. wkhtmltopdf prints the current timestamp at the beginning of the PDF file.
		/// Therefore only a specific part of that file can be asserted to be equal.
		/// </remarks>
		/// <param name="actual">The current aggregated content bytes.</param>
		/// <param name="firstByteIndex">The first byte to compare.</param>
		/// <param name="lastByteIndex">The last byte to compare.</param>
		/// <param name="message">An error message.</param>
		/// <param name="callerFilePath">The absolute file path of the calling file (filled automatically by the compiler service).</param>
		/// <param name="callerMemberName">The name of the calling method (filled automatically by the compiler service).</param>
		public static void AreEqual(byte[] actual, int firstByteIndex, int lastByteIndex, string message = null, [CallerFilePath] string callerFilePath = null, [CallerMemberName] string callerMemberName = null)
		{
			string callerDir = Path.GetDirectoryName(callerFilePath);
			string callerFile = Path.GetFileNameWithoutExtension(callerFilePath);

			string snapshotDir = Path.Combine(callerDir, "Snapshots", callerFile);
			string snapshotFile = Path.Combine(snapshotDir, $"{callerMemberName}.snap");

			if (File.Exists(snapshotFile))
			{
				byte[] expected = File.ReadAllBytes(snapshotFile);

				var actualBytes = actual.Skip(firstByteIndex);
				var expectedBytes = expected.Skip(firstByteIndex);

				if (lastByteIndex > firstByteIndex)
				{
					actualBytes = actualBytes.Take(lastByteIndex - firstByteIndex);
					expectedBytes = expectedBytes.Take(lastByteIndex - firstByteIndex);
				}

				if (message == null)
					CollectionAssert.AreEqual(expectedBytes.ToArray(), actualBytes.ToArray());
				else
					CollectionAssert.AreEqual(expectedBytes.ToArray(), actualBytes.ToArray(), message);
			}
			else
			{
				if (!Directory.Exists(snapshotDir))
					Directory.CreateDirectory(snapshotDir);

				File.WriteAllBytes(snapshotFile, actual);
			}
		}
	}
}