// XAML Map Control - https://github.com/ClemensFischer/XAML-Map-Control
// © 2017 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

using System;
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Storage;
using Windows.Storage.Streams;
using Windows.UI.Xaml;
using FileDbNs;

namespace MapControl.Caching
{
    /// <summary>
    /// IImageCache implementation based on FileDb, a free and simple No-SQL database by EzTools Software.
    /// See http://www.eztools-software.com/tools/filedb/.
    /// </summary>
    public sealed class FileDbCache : IImageCache, IDisposable
    {
        private const string keyField = "Key";
        private const string valueField = "Value";
        private const string expiresField = "Expires";

        private readonly FileDb fileDb = new FileDb();
        private readonly StorageFolder folder;
        private readonly string fileName;

        public FileDbCache(StorageFolder folder, string fileName = "TileCache.fdb", bool autoFlush = true, int autoCleanThreshold = -1)
        {
            if (folder == null)
            {
                throw new ArgumentNullException("The parameter folder must not be null.");
            }

            if (string.IsNullOrEmpty(fileName))
            {
                throw new ArgumentNullException("The parameter fileName must not be null.");
            }

            this.folder = folder;
            this.fileName = fileName;

            fileDb.AutoFlush = autoFlush;
            fileDb.AutoCleanThreshold = autoCleanThreshold;

            Application.Current.Resuming += async (s, e) => await Open();
            Application.Current.Suspending += (s, e) => Close();

            var task = Open();
        }

        public void Dispose()
        {
            Close();
        }

        public void Clean()
        {
            if (fileDb.IsOpen)
            {
                int deleted = fileDb.DeleteRecords(new FilterExpression(expiresField, DateTime.UtcNow, ComparisonOperatorEnum.LessThan));

                if (deleted > 0)
                {
                    Debug.WriteLine("FileDbCache: Deleted {0} expired items", deleted);
                    fileDb.Clean();
                }
            }
        }

        public Task<ImageCacheItem> GetAsync(string key)
        {
            if (key == null)
            {
                throw new ArgumentNullException("The parameter key must not be null.");
            }

            if (!fileDb.IsOpen)
            {
                return null;
            }

            return Task.Run(() => Get(key));
        }

        public Task SetAsync(string key, IBuffer buffer, DateTime expiration)
        {
            if (key == null)
            {
                throw new ArgumentNullException("The parameter key must not be null.");
            }

            if (buffer == null)
            {
                throw new ArgumentNullException("The parameter buffer must not be null.");
            }

            return Task.Run(async () =>
            {
                if (fileDb.IsOpen)
                {
                    var bytes = buffer.ToArray();
                    var ok = AddOrUpdateRecord(key, bytes, expiration);

                    if (!ok && (await RepairDatabase()))
                    {
                        AddOrUpdateRecord(key, bytes, expiration);
                    }
                }
            });
        }

        private async Task Open()
        {
            if (!fileDb.IsOpen)
            {
                try
                {
                    var file = await folder.GetFileAsync(fileName);
                    var stream = await file.OpenAsync(FileAccessMode.ReadWrite);

                    fileDb.Open(stream.AsStream());
                    Debug.WriteLine("FileDbCache: Opened database with {0} cached items in {1}", fileDb.NumRecords, file.Path);

                    Clean();
                }
                catch
                {
                    await CreateDatabase();
                }
            }
        }

        private void Close()
        {
            if (fileDb.IsOpen)
            {
                fileDb.Close();
            }
        }

        private async Task CreateDatabase()
        {
            Close();

            var file = await folder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);
            var stream = await file.OpenAsync(FileAccessMode.ReadWrite);

            fileDb.Create(stream.AsStream(), new Field[]
            {
                new Field(keyField, DataTypeEnum.String) { IsPrimaryKey = true },
                new Field(valueField, DataTypeEnum.Byte) { IsArray = true },
                new Field(expiresField, DataTypeEnum.DateTime)
            });

            Debug.WriteLine("FileDbCache: Created database " + file.Path);
        }

        private async Task<bool> RepairDatabase()
        {
            try
            {
                fileDb.Reindex();
                return true;
            }
            catch (Exception ex)
            {
                Debug.WriteLine("FileDbCache: FileDb.Reindex(): " + ex.Message);
            }

            try
            {
                await CreateDatabase();
                return true;
            }
            catch (Exception ex)
            {
                Debug.WriteLine("FileDbCache: Creating database {0}: {1}", Path.Combine(folder.Path, fileName), ex.Message);
            }

            return false;
        }

        private ImageCacheItem Get(string key)
        {
            var fields = new string[] { valueField, expiresField };

            try
            {
                var record = fileDb.GetRecordByKey(key, fields, false);

                if (record != null)
                {
                    return new ImageCacheItem
                    {
                        Buffer = ((byte[])record[0]).AsBuffer(),
                        Expiration = (DateTime)record[1]
                    };
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine("FileDbCache: FileDb.GetRecordByKey(\"{0}\"): {1}", key, ex.Message);
            }

            return null;
        }

        private bool AddOrUpdateRecord(string key, byte[] value, DateTime expiration)
        {
            var fieldValues = new FieldValues(3);
            fieldValues.Add(valueField, value);
            fieldValues.Add(expiresField, expiration);

            bool recordExists;

            try
            {
                recordExists = fileDb.GetRecordByKey(key, new string[0], false) != null;
            }
            catch (Exception ex)
            {
                Debug.WriteLine("FileDbCache: FileDb.GetRecordByKey(\"{0}\"): {1}", key, ex.Message);
                return false;
            }

            if (recordExists)
            {
                try
                {
                    fileDb.UpdateRecordByKey(key, fieldValues);
                }
                catch (Exception ex)
                {
                    Debug.WriteLine("FileDbCache: FileDb.UpdateRecordByKey(\"{0}\"): {1}", key, ex.Message);
                    return false;
                }
            }
            else
            {
                try
                {
                    fieldValues.Add(keyField, key);
                    fileDb.AddRecord(fieldValues);
                }
                catch (Exception ex)
                {
                    Debug.WriteLine("FileDbCache: FileDb.AddRecord(\"{0}\"): {1}", key, ex.Message);
                    return false;
                }
            }

            //Debug.WriteLine("FileDbCache: Writing \"{0}\", Expires {1}", key, expiration.ToLocalTime());
            return true;
        }
    }
}