using System;
using System.Diagnostics;
using System.IO;
using System.IO.Compression;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;
using StardewValley;

namespace StardewModdingAPI.Mods.SaveBackup
{
    /// <summary>The main entry point for the mod.</summary>
    public class ModEntry : Mod
    {
        /*********
        ** Fields
        *********/
        /// <summary>The number of backups to keep.</summary>
        private readonly int BackupsToKeep = 10;

        /// <summary>The absolute path to the folder in which to store save backups.</summary>
        private readonly string BackupFolder = Path.Combine(Constants.ExecutionPath, "save-backups");

        /// <summary>A unique label for the save backup to create.</summary>
        private readonly string BackupLabel = $"{DateTime.UtcNow:yyyy-MM-dd} - SMAPI {Constants.ApiVersion} with Stardew Valley {Game1.version}";

        /// <summary>The name of the save archive to create.</summary>
        private string FileName => $"{this.BackupLabel}.zip";


        /*********
        ** Public methods
        *********/
        /// <summary>The mod entry point, called after the mod is first loaded.</summary>
        /// <param name="helper">Provides simplified APIs for writing mods.</param>
        public override void Entry(IModHelper helper)
        {
            try
            {
                // init backup folder
                DirectoryInfo backupFolder = new DirectoryInfo(this.BackupFolder);
                backupFolder.Create();

                // back up & prune saves
                Task
                    .Run(() => this.CreateBackup(backupFolder))
                    .ContinueWith(backupTask => this.PruneBackups(backupFolder, this.BackupsToKeep));
            }
            catch (Exception ex)
            {
                this.Monitor.Log($"Error backing up saves: {ex}", LogLevel.Error);
            }
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Back up the current saves.</summary>
        /// <param name="backupFolder">The folder containing save backups.</param>
        private void CreateBackup(DirectoryInfo backupFolder)
        {
            try
            {
                // get target path
                FileInfo targetFile = new FileInfo(Path.Combine(backupFolder.FullName, this.FileName));
                DirectoryInfo fallbackDir = new DirectoryInfo(Path.Combine(backupFolder.FullName, this.BackupLabel));
                if (targetFile.Exists || fallbackDir.Exists)
                    return;

                // back up saves
                this.Monitor.Log($"Backing up saves to {targetFile.FullName}...", LogLevel.Trace);
                if (!this.TryCompress(Constants.SavesPath, targetFile, out Exception compressError))
                {
                    // log error (expected on Android due to missing compression DLLs)
                    if (Constants.TargetPlatform == GamePlatform.Android)
                        this.Monitor.VerboseLog($"Compression isn't supported on Android:\n{compressError}");
                    else
                    {
                        this.Monitor.Log("Couldn't zip the save backup, creating uncompressed backup instead.", LogLevel.Debug);
                        this.Monitor.Log(compressError.ToString(), LogLevel.Trace);
                    }

                    // fallback to uncompressed
                    this.RecursiveCopy(new DirectoryInfo(Constants.SavesPath), fallbackDir, copyRoot: false);
                }
                this.Monitor.Log("Backup done!", LogLevel.Trace);
            }
            catch (Exception ex)
            {
                this.Monitor.Log("Couldn't back up save files (see log file for details).", LogLevel.Warn);
                this.Monitor.Log(ex.ToString(), LogLevel.Trace);
            }
        }

        /// <summary>Remove old backups if we've exceeded the limit.</summary>
        /// <param name="backupFolder">The folder containing save backups.</param>
        /// <param name="backupsToKeep">The number of backups to keep.</param>
        private void PruneBackups(DirectoryInfo backupFolder, int backupsToKeep)
        {
            try
            {
                var oldBackups = backupFolder
                    .GetFileSystemInfos()
                    .OrderByDescending(p => p.CreationTimeUtc)
                    .Skip(backupsToKeep);

                foreach (FileSystemInfo entry in oldBackups)
                {
                    try
                    {
                        this.Monitor.Log($"Deleting {entry.Name}...", LogLevel.Trace);
                        if (entry is DirectoryInfo folder)
                            folder.Delete(recursive: true);
                        else
                            entry.Delete();
                    }
                    catch (Exception ex)
                    {
                        this.Monitor.Log($"Error deleting old save backup '{entry.Name}': {ex}", LogLevel.Error);
                    }
                }
            }
            catch (Exception ex)
            {
                this.Monitor.Log("Couldn't remove old backups (see log file for details).", LogLevel.Warn);
                this.Monitor.Log(ex.ToString(), LogLevel.Trace);
            }
        }

        /// <summary>Create a zip using the best available method.</summary>
        /// <param name="sourcePath">The file or directory path to zip.</param>
        /// <param name="destination">The destination file to create.</param>
        /// <param name="error">The error which occurred trying to compress, if applicable. This is <see cref="NotSupportedException"/> if compression isn't supported on this platform.</param>
        /// <returns>Returns whether compression succeeded.</returns>
        private bool TryCompress(string sourcePath, FileInfo destination, out Exception error)
        {
            try
            {
                if (Constants.TargetPlatform == GamePlatform.Mac)
                    this.CompressUsingMacProcess(sourcePath, destination); // due to limitations with the bundled Mono on Mac, we can't reference System.IO.Compression
                else
                    this.CompressUsingNetFramework(sourcePath, destination);

                error = null;
                return true;
            }
            catch (Exception ex)
            {
                error = ex;
                return false;
            }
        }

        /// <summary>Create a zip using the .NET compression library.</summary>
        /// <param name="sourcePath">The file or directory path to zip.</param>
        /// <param name="destination">The destination file to create.</param>
        /// <exception cref="NotSupportedException">The compression libraries aren't available on this system.</exception>
        private void CompressUsingNetFramework(string sourcePath, FileInfo destination)
        {
            // get compress method
            MethodInfo createFromDirectory;
            try
            {
                // create compressed backup
                Assembly coreAssembly = Assembly.Load("System.IO.Compression, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089") ?? throw new InvalidOperationException("Can't load System.IO.Compression assembly.");
                Assembly fsAssembly = Assembly.Load("System.IO.Compression.FileSystem, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089") ?? throw new InvalidOperationException("Can't load System.IO.Compression assembly.");
                Type compressionLevelType = coreAssembly.GetType("System.IO.Compression.CompressionLevel") ?? throw new InvalidOperationException("Can't load CompressionLevel type.");
                Type zipFileType = fsAssembly.GetType("System.IO.Compression.ZipFile") ?? throw new InvalidOperationException("Can't load ZipFile type.");
                createFromDirectory = zipFileType.GetMethod("CreateFromDirectory", new[] { typeof(string), typeof(string), compressionLevelType, typeof(bool) }) ?? throw new InvalidOperationException("Can't load ZipFile.CreateFromDirectory method.");
            }
            catch (Exception ex)
            {
                throw new NotSupportedException("Couldn't load the .NET compression libraries on this system.", ex);
            }

            // compress file
            createFromDirectory.Invoke(null, new object[] { sourcePath, destination.FullName, CompressionLevel.Fastest, false });
        }

        /// <summary>Create a zip using a process command on MacOS.</summary>
        /// <param name="sourcePath">The file or directory path to zip.</param>
        /// <param name="destination">The destination file to create.</param>
        private void CompressUsingMacProcess(string sourcePath, FileInfo destination)
        {
            DirectoryInfo saveFolder = new DirectoryInfo(sourcePath);
            ProcessStartInfo startInfo = new ProcessStartInfo
            {
                FileName = "zip",
                Arguments = $"-rq \"{destination.FullName}\" \"{saveFolder.Name}\" -x \"*.DS_Store\" -x \"__MACOSX\"",
                WorkingDirectory = $"{saveFolder.FullName}/../",
                CreateNoWindow = true
            };
            new Process { StartInfo = startInfo }.Start();
        }

        /// <summary>Recursively copy a directory or file.</summary>
        /// <param name="source">The file or folder to copy.</param>
        /// <param name="targetFolder">The folder to copy into.</param>
        /// <param name="copyRoot">Whether to copy the root folder itself, or <c>false</c> to only copy its contents.</param>
        /// <remarks>Derived from the SMAPI installer code.</remarks>
        private void RecursiveCopy(FileSystemInfo source, DirectoryInfo targetFolder, bool copyRoot = true)
        {
            if (!targetFolder.Exists)
                targetFolder.Create();

            switch (source)
            {
                case FileInfo sourceFile:
                    sourceFile.CopyTo(Path.Combine(targetFolder.FullName, sourceFile.Name));
                    break;

                case DirectoryInfo sourceDir:
                    DirectoryInfo targetSubfolder = copyRoot ? new DirectoryInfo(Path.Combine(targetFolder.FullName, sourceDir.Name)) : targetFolder;
                    foreach (var entry in sourceDir.EnumerateFileSystemInfos())
                        this.RecursiveCopy(entry, targetSubfolder);
                    break;

                default:
                    throw new NotSupportedException($"Unknown filesystem info type '{source.GetType().FullName}'.");
            }
        }
    }
}