GBase/GBase/GBaseTable.cs

// Author: Gockner, Simon
// Created: 2020-01-27
// Copyright(c) 2020 SimonG. All Rights Reserved.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Threading;
using System.Threading.Tasks;
using GBase.Api;
using GBase.Attributes;
using GBase.Factories;
using GBase.FileHandling.Factories;
using GBase.Interfaces;
using GBase.Interfaces.FileHandling;

namespace GBase
{
    /// <summary>
    /// A <see cref="IGBase"/> table
    /// </summary>
    public class GBaseTable<T> : IGBaseTable<T> where T : INotifyGBaseEntryChanged
    {
        private readonly IFileHandler _fileHandler;
        private readonly IGBaseColumnFactory _gBaseColumnFactory;

        /// <summary>
        /// A <see cref="IGBase"/> table
        /// </summary>
        public GBaseTable(IFileHandlerFactory fileHandlerFactory, IGBaseColumnFactory gBaseColumnFactory)
        {
            _fileHandler = fileHandlerFactory.Create();
            _gBaseColumnFactory = gBaseColumnFactory;

            Columns = new List<IGBaseColumn>();
            Entries = new List<T>();
        }


        /// <summary>
        /// The <see cref="System.Type"/> of the class that this <see cref="IGBaseTable"/> represents
        /// </summary>
        public Type Type { get; private set; }

        /// <summary>
        /// The name of this <see cref="IGBaseTable"/>
        /// </summary>
        public string FolderName { get; private set; }

        /// <summary>
        /// The <see cref="IGBaseColumn"/>s of this <see cref="IGBaseTable"/>
        /// </summary>
        public List<IGBaseColumn> Columns { get; }

        /// <summary>
        /// The entries of this <see cref="IGBaseTable"/>
        /// </summary>
        public List<T> Entries { get; }


        /// <summary>
        /// Initialize this <see cref="IGBase"/>
        /// </summary>
        /// <param name="type">The <see cref="System.Type"/> of the class that this <see cref="IGBaseTable"/> represents</param>
        /// <param name="databasePath">The path to the database files</param>
        /// <param name="folderName"></param>
        /// <param name="cancellationToken">A <see cref="CancellationToken"/> to cancel the asynchronous operation</param>
        /// <returns>True if successful, false if not</returns>
        public async Task<bool> Init(Type type, string databasePath, string folderName, CancellationToken cancellationToken)
        {
            Type = type;
            FolderName = folderName;
            await _fileHandler.Init(databasePath, cancellationToken);

            //TODO: Init columns list depending on GBaseColumnAttributes set for this GBaseTable
            foreach (var property in type.GetProperties())
            {
                GBaseColumnAttribute gBaseColumnAttribute = property.GetCustomAttribute<GBaseColumnAttribute>();
                if (gBaseColumnAttribute == null)
                    continue;

                IGBaseColumn gBaseColumn = _gBaseColumnFactory.Create();
                AddColumn(gBaseColumn);
            }

            return true;
        }

        /// <summary>
        /// Add a given <see cref="IGBaseColumn"/> to this <see cref="IGBaseTable"/>
        /// </summary>
        /// <param name="column">The given <see cref="IGBaseColumn"/></param>
        /// <returns>True if successful, false if not</returns>
        public bool AddColumn(IGBaseColumn column) //TODO: if a column is added, it has to be added to every entry file as well
        {
            if (Columns.Contains(column))
                return false;

            Columns.Add(column);
            return true;
        }

        /// <summary>
        /// Remove a given <see cref="IGBaseColumn"/> from this <see cref="IGBaseTable"/>
        /// </summary>
        /// <param name="column">The given <see cref="IGBaseColumn"/></param>
        /// <returns>True if successful, false if not</returns>
        public bool RemoveColumn(IGBaseColumn column) //TODO: if a column is removed, it has to be removed from every entry file as well
        {
            if (!Columns.Contains(column))
                return false;

            return Columns.Remove(column);
        }

        /// <summary>
        /// Add an entry that implements <see cref="INotifyGBaseEntryChanged"/> to this <see cref="IGBaseTable"/>
        /// </summary>
        /// <param name="entry">The entry implementing <see cref="INotifyGBaseEntryChanged"/></param>
        /// <param name="cancellationToken"></param>
        /// <returns>True if successful, false if not</returns>
        public async Task<bool> AddEntry(T entry, CancellationToken cancellationToken)
        {
            Entries.Add(entry);
            entry.GBaseEntryChanged += OnGBaseEntryChanged;

            await _fileHandler.AddEntry(entry, this, cancellationToken);

            return true;
        }

        /// <summary>
        /// Remove an entry that implements <see cref="INotifyGBaseEntryChanged"/> from this <see cref="IGBaseTable"/>
        /// </summary>
        /// <param name="entry">The entry implementing <see cref="INotifyGBaseEntryChanged"/></param>
        /// <returns>True if successful, false if not</returns>
        public async Task<bool> RemoveEntry(T entry)
        {
            if (!Entries.Contains(entry))
                return false;

            entry.GBaseEntryChanged -= OnGBaseEntryChanged;

            await _fileHandler.RemoveEntry(entry);

            return Entries.Remove(entry);
        }

        /// <summary>
        /// Modify the property of a given entry with the given value
        /// </summary>
        /// <param name="entry">The entry</param>
        /// <param name="propertyName">The name of the property</param>
        /// <param name="value">The new value to set</param>
        /// <returns>True if successful, false if not</returns>
        private bool ModifyEntry(object entry, string propertyName, object value) //TODO: Write to file
        {
            //don't need to change value of property in `Entries` list, the instance is saved there, any property change is already changed there as well
            return true;
        }

        /// <summary>
        /// A <see cref="IGBase"/> entry changed
        /// </summary>
        /// <param name="entry">The entry (sender)</param>
        /// <param name="args">The <see cref="GBaseEntryChangedEventArgs"/></param>
        private void OnGBaseEntryChanged(object entry, GBaseEntryChangedEventArgs args)
        {
            //TODO: Might change, depending on #23
            bool success = ModifyEntry(entry, args.ColumnName, args.Value);

            if (!success)
                throw new Exception("Failed to handle EntryChanged"); //TODO: Decide what to do here
        }

        /// <summary>
        /// The <see cref="IAsyncDisposable.DisposeAsync"/> method
        /// </summary>
        /// <returns>A <see cref="ValueTask"/> to await</returns>
        public async ValueTask DisposeAsync()
        {
            await _fileHandler.DisposeAsync();

            foreach (var column in Columns)
            {
                await column.DisposeAsync();
            }

            Columns.Clear();

            foreach (var entry in Entries.ToList())
            {
                await RemoveEntry(entry);
            }

            Entries.Clear();
        }
    }
}