using System.Collections.Immutable;

namespace HermesSocketServer.Store.Internal
{
    public abstract class GroupSaveStore<K, V> : IStore<K, V> where K : class where V : class
    {
        protected readonly IDictionary<K, V> _store;
        protected readonly IList<K> _added;
        protected readonly IList<K> _modified;
        protected readonly IList<K> _deleted;
        protected readonly ReaderWriterLockSlim _rwls;


        public GroupSaveStore()
        {
            _store = new Dictionary<K, V>();
            _added = new List<K>();
            _modified = new List<K>();
            _deleted = new List<K>();
            _rwls = new ReaderWriterLockSlim();
        }

        public abstract Task Load();
        protected abstract void OnInitialAdd(K key, V value);
        protected abstract void OnInitialModify(K key, V value, V newValue);
        protected abstract void OnPostRemove(K key, V value);
        public abstract Task Save();


        public bool Exists(K key)
        {
            _rwls.EnterReadLock();
            try
            {
                return _store.ContainsKey(key);
            }
            finally
            {
                _rwls.ExitReadLock();
            }
        }

        public V? Get(K key)
        {
            _rwls.EnterReadLock();
            try
            {
                if (_store.TryGetValue(key, out var value))
                    return value;
            }
            finally
            {
                _rwls.ExitReadLock();
            }
            return null;
        }

        public IDictionary<K, V> Get()
        {
            _rwls.EnterReadLock();
            try
            {
                return _store.ToImmutableDictionary();
            }
            finally
            {
                _rwls.ExitReadLock();
            }
        }

        public bool Modify(K? key, V value)
        {
            if (key == null)
                return false;

            _rwls.EnterUpgradeableReadLock();
            try
            {
                if (_store.TryGetValue(key, out V? oldValue))
                {
                    _rwls.EnterWriteLock();
                    try
                    {
                        OnInitialModify(key, oldValue, value);
                        _store[key] = value;
                        if (!_added.Contains(key) && !_modified.Contains(key))
                        {
                            _modified.Add(key);
                        }
                        return true;
                    }
                    finally
                    {
                        _rwls.ExitWriteLock();
                    }
                }
            }
            finally
            {
                _rwls.ExitUpgradeableReadLock();
            }
            return false;
        }

        public bool Modify(K? key, Action<V> modify)
        {
            if (key == null)
                return false;

            _rwls.EnterUpgradeableReadLock();
            try
            {
                if (_store.TryGetValue(key, out V? value))
                {
                    _rwls.EnterWriteLock();
                    try
                    {
                        modify(value);
                        if (!_added.Contains(key) && !_modified.Contains(key))
                        {
                            _modified.Add(key);
                        }
                        return true;
                    }
                    finally
                    {
                        _rwls.ExitWriteLock();
                    }
                }
            }
            finally
            {
                _rwls.ExitUpgradeableReadLock();
            }
            return false;
        }

        public bool Remove(K? key, bool fromCascade = false)
        {
            if (key == null)
                return false;

            _rwls.EnterWriteLock();
            try
            {
                if (_store.TryGetValue(key, out var value))
                {
                    _store.Remove(key);
                    OnPostRemove(key, value);
                    if (!_added.Remove(key))
                    {
                        _modified.Remove(key);
                        if (!fromCascade && !_deleted.Contains(key))
                        {
                            _deleted.Add(key);
                        }
                    }
                    return true;
                }
            }
            finally
            {
                _rwls.ExitWriteLock();
            }
            return false;
        }

        public bool Set(K? key, V value)
        {
            if (key == null)
                return false;

            _rwls.EnterWriteLock();
            try
            {
                if (_store.TryGetValue(key, out V? fetched))
                {
                    OnInitialModify(key, fetched, value);
                    _store[key] = value;
                    if (!_added.Contains(key) && !_modified.Contains(key))
                    {
                        _modified.Add(key);
                    }
                    return true;
                }
                else
                {
                    OnInitialAdd(key, value);
                    _store.Add(key, value);
                    if (!_deleted.Remove(key) && !_added.Contains(key))
                    {
                        _added.Add(key);
                    }
                    return true;
                }
            }
            finally
            {
                _rwls.ExitWriteLock();
            }
        }
    }
}