//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="L4.Prefetch"
// Project: StgSharp
// AuthorGroup: Nitload Space
// Copyright (c) Nitload Space. All rights reserved.
//     
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//     
// -----------------------------------------------------------------------
// -----------------------------------------------------------------------
using System.ComponentModel;

namespace StgSharp.HighPerformance.Memory
{
    public unsafe partial class L4
    {

        public const int MaxActivateCacheLineCount = 1024;

        private partial void Prefetch()
        {
            if (PrefetchPredict is null) {
                return;
            }
            if (_activeCount > MaxActivateCacheLineCount) {
                throw new OverflowException("Too many activated cache line in external reference.");
            }
            Span<CacheLinePrediction> span = new(_prediction, PredictionCount);
            if (!(PrefetchPredict.Predict(span, out int actualCount) && actualCount > 0)) {
                return;
            }
            int missIndex = 0;
            AgeAll();
            for (int i = 0; i < actualCount; i++)
            {
                ref CacheLinePrediction handle = ref span[i];
                nuint address = handle.Address;
                if (!TestHit(address))
                {
                    // miss and record
                    span[missIndex] = handle;
                    missIndex++;
                }
            }

            // now prefetch the misses
            for (int i = 0; i < missIndex; i++)
            {
                ref CacheLinePrediction handle = ref span[i];
                nuint address = handle.Address;
                if (TestHit(address))
                {
                    continue;
                }

                int retryCount = 0, index, remain = missIndex - i;
                const int maxRetry = 1024;
                while (!TryGetEmptyLine(out index))
                {
                    missIndex = Evict(missIndex);
                    retryCount++;
                    if (retryCount > maxRetry) {
                        throw new OverflowException($"Failed to evict cache line after {maxRetry} retries.");
                    }
                }
                CacheLineHead* head = &_head[index];
                head->_id = index;
                head->_origin = address;
                head->_profile = handle.MapPolicy;
                head->_refCount = 0;
                head->_address = (nuint)(&_data[index]);

                // pre fetch them here
                PrefetchPredict.Prefetch(head->_origin, head->_profile, new Span<byte>((byte*)head->_address, Unsafe.SizeOf<CacheLineData>()));
                _ = _map.TryAddOrSet(address, (nuint)head, out _);
            }
            _ = Interlocked.Add(ref _aheadCount, actualCount);
        }

        private partial bool TestHit(nuint origin)
        {
            if (_map.TryGet(origin, out nuint handle))
            {
                CacheLineHead* head = (CacheLineHead*)handle;
                int index = head->_id;
                (*_eviction)[index] = 0; // reset eviction counter
                return true;
            }
            return false;
        }

    }
}