using System;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using Centron.Tests.EndToEnd.Infrastructure;
using Xunit;
using Xunit.Abstractions;

namespace Centron.Tests.EndToEnd.Tests.FileEncoding
{
    public class FileEncodingTest : CentronTest
    {
        public FileEncodingTest(ITestOutputHelper testOutputHelper) 
            : base(testOutputHelper)
        {
        }

        [Fact]
        public void CSharpFilesHaveCorrectEncoding()
        {
            CheckFileEncoding("*.cs");
        }
        
        [Fact]
        public void XamlFilesHaveCorrectEncoding()
        {
            CheckFileEncoding("*.xaml");
        }

        private void CheckFileEncoding(string fileNamePattern, [CallerFilePath]string path = null)
        {
            var preamble = Encoding.UTF8.GetPreamble(); //UTF8 with BOM is our default encoding for all source-code files
            var slnDirectory = new FileInfo(path).Directory.Parent.Parent.Parent.Parent;
            
            var filesWithIncorrectEncoding = Directory.GetFiles(slnDirectory.FullName, fileNamePattern, SearchOption.AllDirectories)
                .Where(file => IsInBinOrObjDirectory(file) == false)
                .Where(file => FileStartsWith(file, preamble) == false)
                .ToList();

            if (filesWithIncorrectEncoding.Any())
            {
                string message = $"All our source-code files are supposed to have UTF8-BOM encoding, but there are some files that have a different encoding.{Environment.NewLine}" +
                                 $"Change the encoding in these files to UTF8-BOM by saving them again.{Environment.NewLine}{Environment.NewLine}" +
                                 $"The following files have an incorrect encoding:{Environment.NewLine}";
                message += string.Join(Environment.NewLine, filesWithIncorrectEncoding);

                throw new Exception(message);
            }
        }

        private static readonly string BinDirectory = Path.DirectorySeparatorChar + "bin" + Path.DirectorySeparatorChar;
        private static readonly string ObjDirectory = Path.DirectorySeparatorChar + "obj" + Path.DirectorySeparatorChar;
        private bool IsInBinOrObjDirectory(string file)
        {
            return file.IndexOf(BinDirectory, StringComparison.InvariantCultureIgnoreCase) > 0 ||
                   file.IndexOf(ObjDirectory, StringComparison.InvariantCultureIgnoreCase) > 0;
        }

        private bool FileStartsWith(string filePath, byte[] preamble)
        {
            using (var stream = File.OpenRead(filePath))
            {
                var bytesInFile = new byte[preamble.Length];
                stream.ReadExactly(bytesInFile, 0, bytesInFile.Length);

                return preamble.SequenceEqual(bytesInFile);
            }
        }
    }
}