StorageService.cs

using System.Text;
using Waher.Events;
using Waher.Events.Persistence;
using Waher.Persistence;
using Waher.Persistence.Files;
using Waher.Persistence.Serialization;
using Waher.Runtime.Inventory;
 
namespace NeuroAccessMaui.Services.Storage
{
    [Singleton]
    internal sealed class StorageService : IStorageService, IDisposable
    {
        private readonly LinkedList<TaskCompletionSource<bool>> tasksWaiting = new();
        private readonly string dataFolder;
        private FilesProvider? databaseProvider;
        private PersistedEventLog? persistedEventLog;
        private bool? initialized = null;
        private bool started = false;
 
        public StorageService()
        {
            string appDataFolder = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
            this.dataFolder = Path.Combine(appDataFolder, "Data");
        }
 
        public string DataFolder => this.dataFolder;
 
        #region LifeCycle management
 
        public async Task Init(CancellationToken? cancellationToken)
        {
            lock (this.tasksWaiting)
            {
                if (this.started)
                    return;
 
                this.started = true;
            }
 
            try
            {
                if (Database.HasProvider)
                    this.databaseProvider = Database.Provider as FilesProvider;
 
                if (this.databaseProvider is null)
                {
                    this.databaseProvider = await this.CreateDatabaseFile();
 
                    await this.databaseProvider.RepairIfInproperShutdown(string.Empty);
                    await this.databaseProvider.Start();
                }
 
                if (this.databaseProvider is not null)
                {
                    Database.Register(this.databaseProvider, false);
                    Log.Register(this.persistedEventLog = new PersistedEventLog(90));
                    this.InitDone(true);
                    return;
                }
            }
            catch (Exception e1)
            {
                e1 = Log.UnnestException(e1);
                ServiceRef.LogService.LogException(e1);
            }
 
            /* On iOS the UI is not initialized at this point, need to find another solution
            if (await ServiceRef.UiSerializer.DisplayAlert(ServiceRef.Localizer[nameof(AppResources.DatabaseIssue"], ServiceRef.Localizer[nameof(AppResources.DatabaseCorruptInfoText"], ServiceRef.Localizer[nameof(AppResources.RepairAndContinue"], ServiceRef.Localizer[nameof(AppResources.ContinueAnyway"]))
            */
            //TODO: when UI is ready, show an alert that the database was reset due to unrecoverable error
            //TODO: say to close the application in a controlled manner
            {
                try
                {
                    Directory.Delete(this.dataFolder, true);
 
                    this.databaseProvider = await this.CreateDatabaseFile();
 
                    await this.databaseProvider.RepairIfInproperShutdown(string.Empty);
 
                    await this.databaseProvider.Start();
 
                    if (!Database.HasProvider)
                    {
                        Database.Register(this.databaseProvider, false);
                        Log.Register(this.persistedEventLog = new PersistedEventLog(90));
                        this.InitDone(true);
                        return;
                    }
                }
                catch (Exception e3)
                {
                    e3 = Log.UnnestException(e3);
                    ServiceRef.LogService.LogException(e3);
 
                    await App.Stop();
                    /*
                    Thread?.NewState("UI");
                    await ServiceRef.UiSerializer.DisplayAlert(ServiceRef.Localizer[nameof(AppResources.DatabaseIssue"], ServiceRef.Localizer[nameof(AppResources.DatabaseRepairFailedInfoText"], ServiceRef.Localizer[nameof(AppResources.Ok"]);
                    */
                }
            }
 
            this.InitDone(false);
        }
 
        private void InitDone(bool Result)
        {
            lock (this.tasksWaiting)
            {
                this.initialized = Result;
 
                foreach (TaskCompletionSource<bool> Wait in this.tasksWaiting)
                    Wait.TrySetResult(Result);
 
                this.tasksWaiting.Clear();
            }
        }
 
        public Task<bool> WaitInitDone()
        {
            lock (this.tasksWaiting)
            {
                if (this.initialized.HasValue)
                    return Task.FromResult<bool>(this.initialized.Value);
 
                TaskCompletionSource<bool> Wait = new();
                this.tasksWaiting.AddLast(Wait);
 
                return Wait.Task;
            }
        }
 
        public async Task Shutdown()
        {
            lock (this.tasksWaiting)
            {
                this.initialized = null;
                this.started = false;
            }
 
            try
            {
                if (this.persistedEventLog is not null)
                {
                    Log.Unregister(this.persistedEventLog);
                    this.persistedEventLog.Dispose();
                    this.persistedEventLog = null;
                }
 
                if (this.databaseProvider is not null)
                {
                    Database.Register(new NullDatabaseProvider(), false);
                    await this.databaseProvider.Flush();
                    await this.databaseProvider.Stop();
                    this.databaseProvider = null;
                }
            }
            catch (Exception ex)
            {
                ServiceRef.LogService.LogException(ex);
            }
        }
 
        private Task<FilesProvider> CreateDatabaseFile()
        {
            FilesProvider.AsyncFileIo = false;  // Asynchronous file I/O induces a long delay during startup on mobile platforms. Why??
 
            return FilesProvider.CreateAsync(this.dataFolder, "Default", 8192, 10000, 8192, Encoding.UTF8,
                (int)Constants.Timeouts.Database.TotalMilliseconds, ServiceRef.CryptoService.GetCustomKey);
        }
 
        public void Dispose()
        {
            this.persistedEventLog?.Dispose();
            this.persistedEventLog = null;
 
            this.databaseProvider?.Dispose();
            this.databaseProvider = null;
        }
 
        #endregion
 
        public async Task Insert(object obj)
        {
            await Database.Insert(obj);
            await Database.Provider.Flush();
        }
 
        public async Task Update(object obj)
        {
            await Database.Update(obj);
            await Database.Provider.Flush();
        }
 
        public Task<T> FindFirstDeleteRest<T>() where T : class
        {
            return Database.FindFirstDeleteRest<T>();
        }
 
        public Task<T> FindFirstIgnoreRest<T>() where T : class
        {
            return Database.FindFirstIgnoreRest<T>();
        }
 
        public Task Export(IDatabaseExport exportOutput)
        {
            return Database.Export(exportOutput);
        }
 
        public void FlagForRepair()
        {
            this.DeleteFile("Start.txt");
            this.DeleteFile("Stop.txt");
        }
 
        private void DeleteFile(string FileName)
        {
            try
            {
                FileName = Path.Combine(this.dataFolder, FileName);
 
                if (File.Exists(FileName))
                    File.Delete(FileName);
            }
            catch (Exception)
            {
                // Ignore, to avoid infinite loops if event log has an inconsistency.
            }
        }
    }
}