using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using LiteDB;

namespace Net.BITKit.Database
{
    public class LiteDbDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IDisposable where TKey : notnull
    {
        // 内部的 LiteDB 数据库实例
        private readonly LiteDatabase _db;

        // LiteDB 集合名称可以自定义，默认为 "kv"
        private readonly ILiteCollection<KeyValueItem> _collection;

        // 内部使用的键值项（POCO类）
        private class KeyValueItem
        {
            // LiteDB 将此字段作为文档的 _id（主键）
            [BsonId] public TKey Key { get; set; }
            public TValue Value { get; set; }
        }

        public LiteDbDictionary()
        {
            _db = new LiteDatabase(":memory:");
            _collection = _db.GetCollection<KeyValueItem>(typeof(TValue).Name);
            _collection.EnsureIndex(x => x.Key);
        }
        
        /// <summary>
        /// 构造函数
        /// connectionString 可以是磁盘文件（如 "Filename=MyData.db;Mode=Shared"）
        /// 或内存数据库（如 ":memory:"）
        /// </summary>
        /// <param name="connectionString">数据库连接字符串</param>
        /// <param name="collectionName">集合名称，默认 "kv"</param>
        public LiteDbDictionary(string connectionString, string collectionName = "kv")
        {
            _db = new LiteDatabase(connectionString);
            _collection = _db.GetCollection<KeyValueItem>(collectionName);
            // 确保对键生成索引
            _collection.EnsureIndex(x => x.Key);
        }

        #region IDictionary 实现

        public TValue this[TKey key]
        {
            get
            {
                var bsonId = _db.Mapper.Serialize(typeof(TKey), key);
                var item = _collection.FindById(bsonId);
                if (item == null) throw new KeyNotFoundException($"Key '{key}' not found.");
                return item.Value;
            }
            set
            {
                var item = new KeyValueItem { Key = key, Value = value };
                _collection.Upsert(item);
            }
        }

        public ICollection<TKey> Keys => _collection.FindAll().Select(x => x.Key).ToList();
        public ICollection<TValue> Values => _collection.FindAll().Select(x => x.Value).ToList();
        public int Count => _collection.Count();
        public bool IsReadOnly => false;

        public void Add(TKey key, TValue value)
        {
            if (ContainsKey(key))
                throw new ArgumentException($"An element with the key '{key}' already exists.");
            _collection.Insert(new KeyValueItem { Key = key, Value = value });
        }

        public bool ContainsKey(TKey key)
        {
            return _collection.Exists(x => x.Key.Equals(key));
        }

        public bool Remove(TKey key)
        {
            var bsonKey = _db.Mapper.Serialize(typeof(TKey), key);
            return _collection.Delete(bsonKey);
        }


        public bool TryGetValue(TKey key, out TValue value)
        {
            var bsonKey = _db.Mapper.Serialize(typeof(TKey), key);
            var doc = _collection.FindById(bsonKey);
            if (doc == null)
            {
                value = default;
                return false;
            }

            value = doc.Value;
            return true;
        }


        public void Add(KeyValuePair<TKey, TValue> item)
        {
            Add(item.Key, item.Value);
        }

        public void Clear()
        {
            _collection.DeleteAll();
        }

        public bool Contains(KeyValuePair<TKey, TValue> item)
        {
            if (TryGetValue(item.Key, out var val))
                return EqualityComparer<TValue>.Default.Equals(val, item.Value);
            return false;
        }

        public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
        {
            foreach (var kv in this)
            {
                array[arrayIndex++] = kv;
            }
        }

        public bool Remove(KeyValuePair<TKey, TValue> item)
        {
            if (Contains(item))
                return Remove(item.Key);
            return false;
        }

        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
        {
            foreach (var item in _collection.FindAll())
            {
                yield return new KeyValuePair<TKey, TValue>(item.Key, item.Value);
            }
        }

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

        #endregion

        #region IDisposable 实现

        public void Dispose()
        {
            _db?.Dispose();
        }

        #endregion
    }
}