using System;
using System.Collections.Generic;
using System.IO;

namespace IPA.Patcher
{
    /// <summary>
    /// A unit for backup. WIP.
    /// </summary>
    public class BackupUnit
    {
        private string Name { get; }
        
        private readonly DirectoryInfo _backupPath;
        private readonly PatchContext _context;
        private readonly List<string> _files = new List<string>();
        private readonly FileInfo _manifestFile;
        private static string _ManifestFileName = "$manifest$.txt";
        
        public BackupUnit(PatchContext context) : this(context, DateTime.Now.ToString("yyyy-MM-dd_h-mm-ss"))
        {
        }

        private BackupUnit(PatchContext context, string name)
        {
            Name = name;
            _context = context;
            _backupPath = new DirectoryInfo(Path.Combine(_context.BackupPath, Name));
            _manifestFile = new FileInfo(Path.Combine(_backupPath.FullName, _ManifestFileName));
        }
        
        public static BackupUnit FromDirectory(DirectoryInfo directory, PatchContext context)
        {
            var unit = new BackupUnit(context, directory.Name);

            // Read Manifest
            if (unit._manifestFile.Exists)
            {
                var manifest = File.ReadAllText(unit._manifestFile.FullName);
                foreach (var line in manifest.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries))
                    unit._files.Add(line);
            }
            else
            {
                foreach (var file in directory.GetFiles("*", SearchOption.AllDirectories))
                {
                    if (file.Name == _ManifestFileName) continue;
                    var relativePath = file.FullName.Substring(directory.FullName.Length + 1);
                    unit._files.Add(relativePath);
                }
            }

            return unit;
        }

        public void Add(string file)
        {
            Add(new FileInfo(file));
        }

        internal void Delete()
        {
            _backupPath.Delete(true);
        }

        /// <summary>
        /// Adds a file to the list of changed files and backups it.
        /// </summary>
        /// <param name="file">the file to add</param>
        public void Add(FileInfo file)
        {
            if(!file.FullName.StartsWith(_context.ProjectRoot))
            {
                Console.Error.WriteLine("Invalid file path for backup! {0}", file);
                return;
            }

            var relativePath = file.FullName.Substring(_context.ProjectRoot.Length + 1);
            var backupPath = new FileInfo(Path.Combine(_backupPath.FullName, relativePath));
            
            if(_files.Contains(relativePath))
            {
                Console.WriteLine("Skipping backup of {0}", relativePath);
                return;
            }
            
            // Copy over
            backupPath.Directory?.Create();
            if (file.Exists)
            {
                file.CopyTo(backupPath.FullName);
            }
            else
            {
                // Make empty file
                backupPath.Create().Close();
            }

            if (!File.Exists(_manifestFile.FullName))
                _manifestFile.Create().Close();
            var stream = _manifestFile.AppendText();
            stream.WriteLine(relativePath);
            stream.Close();

            // Add to list
            _files.Add(relativePath);
        }

        /// <summary>
        /// Reverts the changes made in this unit.
        /// </summary>
        public void Restore()
        {
            foreach(var relativePath in _files)
            {
                Console.WriteLine("Restoring {0}", relativePath);
                // Original version
                var backupFile = new FileInfo(Path.Combine(_backupPath.FullName, relativePath));
                var target = new FileInfo(Path.Combine(_context.ProjectRoot, relativePath));

                if (backupFile.Exists)
                {
                    if (backupFile.Length > 0)
                    {
                        Console.WriteLine("  {0} => {1}", backupFile.FullName, target.FullName);
                        target.Directory?.Create();
                        backupFile.CopyTo(target.FullName, true);
                    }
                    else
                    {
                        Console.WriteLine("  x {0}", target.FullName);
                        if(target.Exists)
                        {
                            target.Delete();
                        }
                    }
                } else
                {
                    Console.Error.WriteLine("Backup not found!");
                }
            }
        }

    }
}