namespace Firebase.Database.Offline
{
    using System;
    using System.Collections;
    using System.Collections.Concurrent;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;

    using LiteDB;

    /// <summary>
    /// The offline database.
    /// </summary>
    public class ConcurrentOfflineDatabase : IDictionary<string, OfflineEntry>
    {
        private readonly LiteRepository db;
        private readonly ConcurrentDictionary<string, OfflineEntry> ccache;

        /// <summary>
        /// Initializes a new instance of the <see cref="OfflineDatabase"/> class.
        /// </summary>
        /// <param name="itemType"> The item type which is used to determine the database file name.  </param>
        /// <param name="filenameModifier"> Custom string which will get appended to the file name. </param>
        public ConcurrentOfflineDatabase(Type itemType, string filenameModifier)
        {
            var fullName = this.GetFileName(itemType.ToString());
            if(fullName.Length > 100)
            {
                fullName = fullName.Substring(0, 100);
            }

            BsonMapper mapper = BsonMapper.Global;
            mapper.Entity<OfflineEntry>().Id(o => o.Key);

            string root = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
            string filename = fullName + filenameModifier + ".db";
            var path = Path.Combine(root, filename);
            this.db = new LiteRepository(new LiteDatabase(path, mapper));

            var cache = db.Database
                .GetCollection<OfflineEntry>()
                .FindAll()
                .ToDictionary(o => o.Key, o => o);

            this.ccache = new ConcurrentDictionary<string, OfflineEntry>(cache);
            
        }

        /// <summary>
        /// Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary>
        /// <returns> The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>. </returns>
        public int Count => this.ccache.Count;

        /// <summary>
        /// Gets a value indicating whether this is a read-only collection.
        /// </summary>
        public bool IsReadOnly => false;

        /// <summary>
        /// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
        /// </summary>
        /// <returns> An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>. </returns>
        public ICollection<string> Keys => this.ccache.Keys;

        /// <summary>
        /// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
        /// </summary>
        /// <returns> An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>. </returns>
        public ICollection<OfflineEntry> Values => this.ccache.Values;

        /// <summary>
        /// Gets or sets the element with the specified key.
        /// </summary>
        /// <param name="key">The key of the element to get or set.</param>
        /// <returns> The element with the specified key. </returns>   
        public OfflineEntry this[string key]
        {
            get
            {
                return this.ccache[key];
            }

            set
            {
                this.ccache.AddOrUpdate(key, value, (k, existing) => value);
                this.db.Upsert(value);
            }
        }

        /// <summary>
        /// Returns an enumerator that iterates through the collection.
        /// </summary>
        /// <returns> An enumerator that can be used to iterate through the collection. </returns>
        public IEnumerator<KeyValuePair<string, OfflineEntry>> GetEnumerator()
        {
            return this.ccache.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.GetEnumerator();
        }

        /// <summary>
        /// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary>
        /// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
        public void Add(KeyValuePair<string, OfflineEntry> item)
        {
            this.Add(item.Key, item.Value);
        }

        /// <summary>
        /// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary> 
        public void Clear()
        {
            this.ccache.Clear();
            this.db.Delete<OfflineEntry>(Query.All());
        }

        /// <summary>
        /// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"/> contains a specific value.
        /// </summary>
        /// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param> 
        /// <returns> True if <paramref name="item"/> is found in the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. </returns>
        public bool Contains(KeyValuePair<string, OfflineEntry> item)
        {
            return this.ContainsKey(item.Key);
        }

        /// <summary>
        /// Copies the elements of the <see cref="T:System.Collections.Generic.ICollection`1"/> to an <see cref="T:System.Array"/>, starting at a particular <see cref="T:System.Array"/> index.
        /// </summary>
        /// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from <see cref="T:System.Collections.Generic.ICollection`1"/>. The <see cref="T:System.Array"/> must have zero-based indexing.</param>
        /// <param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param>
        public void CopyTo(KeyValuePair<string, OfflineEntry>[] array, int arrayIndex)
        {
            this.ccache.ToList().CopyTo(array, arrayIndex);
        }

        /// <summary>
        /// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary>
        /// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
        /// <returns> True if <paramref name="item"/> was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. This method also returns false if <paramref name="item"/> is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"/>. </returns>
        public bool Remove(KeyValuePair<string, OfflineEntry> item)
        {
            return this.Remove(item.Key);
        }

        /// <summary>
        /// Determines whether the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key.
        /// </summary>
        /// <param name="key">The key to locate in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.</param>
        /// <returns> True if the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the key; otherwise, false. </returns>
        public bool ContainsKey(string key)
        {
            return this.ccache.ContainsKey(key);
        }

        /// <summary>
        /// Adds an element with the provided key and value to the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
        /// </summary>
        /// <param name="key">The object to use as the key of the element to add.</param>
        /// <param name="value">The object to use as the value of the element to add.</param>
        public void Add(string key, OfflineEntry value)
        {
            this.ccache.AddOrUpdate(key, value, (k, existing) => value);
            this.db.Upsert(value);
        }

        /// <summary>
        /// Removes the element with the specified key from the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
        /// </summary>
        /// <param name="key">The key of the element to remove.</param>
        /// <returns> True if the element is successfully removed; otherwise, false.  This method also returns false if <paramref name="key"/> was not found in the original <see cref="T:System.Collections.Generic.IDictionary`2"/>. </returns>
        public bool Remove(string key)
        {
            this.ccache.TryRemove(key, out OfflineEntry _);
            return this.db.Delete<OfflineEntry>(key);
        }

        /// <summary>
        /// Gets the value associated with the specified key.
        /// </summary> 
        /// <param name="key">The key whose value to get.</param><param name="value">When this method returns, the value associated with the specified key, if the key is found; otherwise, the default value for the type of the <paramref name="value"/> parameter. This parameter is passed uninitialized.</param>
        /// <returns> True if the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key; otherwise, false. </returns>
        public bool TryGetValue(string key, out OfflineEntry value)
        {
            return this.ccache.TryGetValue(key, out value);
        }

        private string GetFileName(string fileName)
        {
            var invalidChars = new[] { '`', '[', ',', '=' };
            foreach(char c in invalidChars.Concat(System.IO.Path.GetInvalidFileNameChars()).Distinct())
            {
                fileName = fileName.Replace(c, '_');
            }

            return fileName;
        }
    }
}