using System.Runtime.CompilerServices;

namespace FurinaImpact.Kcp
{
    internal sealed class KcpAcknowledgeList
    {
        private readonly KcpSendQueue _sendQueue;
        private (uint SerialNumber, uint Timestamp)[] _array;
        private int _count;
        private SpinLock _lock;

        public KcpAcknowledgeList(KcpSendQueue sendQueue, int windowSize)
        {
            _array = new (uint SerialNumber, uint Timestamp)[windowSize];
            _count = 0;
            _lock = new SpinLock();
            _sendQueue = sendQueue;
        }

        public bool TryGetAt(int index, out uint serialNumber, out uint timestamp)
        {
            bool lockTaken = false;
            try
            {
                _lock.Enter(ref lockTaken);

                if ((uint)index >= (uint)_count)
                {
                    serialNumber = default;
                    timestamp = default;
                    return false;
                }

                (serialNumber, timestamp) = _array[index];
                return true;
            }
            finally
            {
                if (lockTaken)
                {
                    _lock.Exit();
                }
            }
        }

        public void Clear()
        {
            bool lockTaken = false;
            try
            {
                _lock.Enter(ref lockTaken);

                _count = 0;
            }
            finally
            {
                if (lockTaken)
                {
                    _lock.Exit();
                }
            }
            _sendQueue.NotifyAckListChanged(false);
        }

        public void Add(uint serialNumber, uint timestamp)
        {
            bool lockTaken = false;
            try
            {
                _lock.Enter(ref lockTaken);

                EnsureCapacity();
                _array[_count++] = (serialNumber, timestamp);
            }
            finally
            {
                if (lockTaken)
                {
                    _lock.Exit();
                }
            }
            _sendQueue.NotifyAckListChanged(true);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void EnsureCapacity()
        {
            if (_count == _array.Length)
            {
                Expand();
            }
        }

        [MethodImpl(MethodImplOptions.NoInlining)]
        private void Expand()
        {
            int capacity = _count + 1;
            capacity = Math.Max(capacity + capacity / 2, 16);
            var newArray = new (uint SerialNumber, uint Timestamp)[capacity];
            _array.AsSpan(0, _count).CopyTo(newArray);
            _array = newArray;
        }
    }
}