using ARMeilleure.Memory;
using Ryujinx.Memory;
using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Threading;

namespace Ryujinx.Cpu
{
    /// <summary>
    /// Represents a CPU memory manager.
    /// </summary>
    public sealed class MemoryManager : IMemoryManager, IDisposable
    {
        public const int PageBits = 12;
        public const int PageSize = 1 << PageBits;
        public const int PageMask = PageSize - 1;

        private const int PteSize = 8;

        public int AddressSpaceBits { get; }

        private readonly ulong _addressSpaceSize;

        private readonly MemoryBlock _backingMemory;
        private readonly MemoryBlock _pageTable;

        public IntPtr PageTablePointer => _pageTable.Pointer;

        /// <summary>
        /// Creates a new instance of the memory manager.
        /// </summary>
        /// <param name="backingMemory">Physical backing memory where virtual memory will be mapped to</param>
        /// <param name="addressSpaceSize">Size of the address space</param>
        public MemoryManager(MemoryBlock backingMemory, ulong addressSpaceSize)
        {
            ulong asSize = PageSize;
            int asBits = PageBits;

            while (asSize < addressSpaceSize)
            {
                asSize <<= 1;
                asBits++;
            }

            AddressSpaceBits = asBits;
            _addressSpaceSize = asSize;
            _backingMemory = backingMemory;
            _pageTable = new MemoryBlock((asSize / PageSize) * PteSize);
        }

        /// <summary>
        /// Maps a virtual memory range into a physical memory range.
        /// </summary>
        /// <remarks>
        /// Addresses and size must be page aligned.
        /// </remarks>
        /// <param name="va">Virtual memory address</param>
        /// <param name="pa">Physical memory address</param>
        /// <param name="size">Size to be mapped</param>
        public void Map(ulong va, ulong pa, ulong size)
        {
            while (size != 0)
            {
                _pageTable.Write((va / PageSize) * PteSize, PaToPte(pa));

                va += PageSize;
                pa += PageSize;
                size -= PageSize;
            }
        }

        /// <summary>
        /// Unmaps a previously mapped range of virtual memory.
        /// </summary>
        /// <param name="va">Virtual address of the range to be unmapped</param>
        /// <param name="size">Size of the range to be unmapped</param>
        public void Unmap(ulong va, ulong size)
        {
            while (size != 0)
            {
                _pageTable.Write((va / PageSize) * PteSize, 0UL);

                va += PageSize;
                size -= PageSize;
            }
        }

        /// <summary>
        /// Reads data from CPU mapped memory.
        /// </summary>
        /// <typeparam name="T">Type of the data being read</typeparam>
        /// <param name="va">Virtual address of the data in memory</param>
        /// <returns>The data</returns>
        public T Read<T>(ulong va) where T : unmanaged
        {
            return MemoryMarshal.Cast<byte, T>(GetSpan(va, Unsafe.SizeOf<T>()))[0];
        }

        /// <summary>
        /// Reads data from CPU mapped memory.
        /// </summary>
        /// <param name="va">Virtual address of the data in memory</param>
        /// <param name="data">Span to store the data being read into</param>
        public void Read(ulong va, Span<byte> data)
        {
            ReadImpl(va, data);
        }

        /// <summary>
        /// Writes data to CPU mapped memory.
        /// </summary>
        /// <typeparam name="T">Type of the data being written</typeparam>
        /// <param name="va">Virtual address to write the data into</param>
        /// <param name="value">Data to be written</param>
        public void Write<T>(ulong va, T value) where T : unmanaged
        {
            Write(va, MemoryMarshal.Cast<T, byte>(MemoryMarshal.CreateSpan(ref value, 1)));
        }

        /// <summary>
        /// Writes data to CPU mapped memory.
        /// </summary>
        /// <param name="va">Virtual address to write the data into</param>
        /// <param name="data">Data to be written</param>
        public void Write(ulong va, ReadOnlySpan<byte> data)
        {
            if (data.Length == 0)
            {
                return;
            }

            MarkRegionAsModified(va, (ulong)data.Length);

            if (IsContiguous(va, data.Length))
            {
                data.CopyTo(_backingMemory.GetSpan(GetPhysicalAddressInternal(va), data.Length));
            }
            else
            {
                int offset = 0, size;

                if ((va & PageMask) != 0)
                {
                    ulong pa = GetPhysicalAddressInternal(va);

                    size = Math.Min(data.Length, PageSize - (int)(va & PageMask));

                    data.Slice(0, size).CopyTo(_backingMemory.GetSpan(pa, size));

                    offset += size;
                }

                for (; offset < data.Length; offset += size)
                {
                    ulong pa = GetPhysicalAddressInternal(va + (ulong)offset);

                    size = Math.Min(data.Length - offset, PageSize);

                    data.Slice(offset, size).CopyTo(_backingMemory.GetSpan(pa, size));
                }
            }
        }

        /// <summary>
        /// Gets a read-only span of data from CPU mapped memory.
        /// </summary>
        /// <remarks>
        /// This may perform a allocation if the data is not contiguous in memory.
        /// For this reason, the span is read-only, you can't modify the data.
        /// </remarks>
        /// <param name="va">Virtual address of the data</param>
        /// <param name="size">Size of the data</param>
        /// <returns>A read-only span of the data</returns>
        public ReadOnlySpan<byte> GetSpan(ulong va, int size)
        {
            if (size == 0)
            {
                return ReadOnlySpan<byte>.Empty;
            }

            if (IsContiguous(va, size))
            {
                return _backingMemory.GetSpan(GetPhysicalAddressInternal(va), size);
            }
            else
            {
                Span<byte> data = new byte[size];

                ReadImpl(va, data);

                return data;
            }
        }

        /// <summary>
        /// Gets a region of memory that can be written to.
        /// </summary>
        /// <remarks>
        /// If the requested region is not contiguous in physical memory,
        /// this will perform an allocation, and flush the data (writing it
        /// back to guest memory) on disposal.
        /// </remarks>
        /// <param name="va">Virtual address of the data</param>
        /// <param name="size">Size of the data</param>
        /// <returns>A writable region of memory containing the data</returns>
        public WritableRegion GetWritableRegion(ulong va, int size)
        {
            if (size == 0)
            {
                return new WritableRegion(null, va, Memory<byte>.Empty);
            }

            if (IsContiguous(va, size))
            {
                return new WritableRegion(null, va, _backingMemory.GetMemory(GetPhysicalAddressInternal(va), size));
            }
            else
            {
                Memory<byte> memory = new byte[size];

                GetSpan(va, size).CopyTo(memory.Span);

                return new WritableRegion(this, va, memory);
            }
        }

        /// <summary>
        /// Gets a reference for the given type at the specified virtual memory address.
        /// </summary>
        /// <remarks>
        /// The data must be located at a contiguous memory region.
        /// </remarks>
        /// <typeparam name="T">Type of the data to get the reference</typeparam>
        /// <param name="va">Virtual address of the data</param>
        /// <returns>A reference to the data in memory</returns>
        public ref T GetRef<T>(ulong va) where T : unmanaged
        {
            if (!IsContiguous(va, Unsafe.SizeOf<T>()))
            {
                ThrowMemoryNotContiguous();
            }

            MarkRegionAsModified(va, (ulong)Unsafe.SizeOf<T>());

            return ref _backingMemory.GetRef<T>(GetPhysicalAddressInternal(va));
        }

        private void ThrowMemoryNotContiguous() => throw new MemoryNotContiguousException();

        // TODO: Remove that once we have proper 8-bits and 16-bits CAS.
        public ref T GetRefNoChecks<T>(ulong va) where T : unmanaged
        {
            MarkRegionAsModified(va, (ulong)Unsafe.SizeOf<T>());

            return ref _backingMemory.GetRef<T>(GetPhysicalAddressInternal(va));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool IsContiguous(ulong va, int size)
        {
            if (!ValidateAddress(va))
            {
                return false;
            }

            ulong endVa = (va + (ulong)size + PageMask) & ~(ulong)PageMask;

            va &= ~(ulong)PageMask;

            int pages = (int)((endVa - va) / PageSize);

            for (int page = 0; page < pages - 1; page++)
            {
                if (!ValidateAddress(va + PageSize))
                {
                    return false;
                }

                if (GetPhysicalAddressInternal(va) + PageSize != GetPhysicalAddressInternal(va + PageSize))
                {
                    return false;
                }

                va += PageSize;
            }

            return true;
        }

        private void ReadImpl(ulong va, Span<byte> data)
        {
            if (data.Length == 0)
            {
                return;
            }

            int offset = 0, size;

            if ((va & PageMask) != 0)
            {
                ulong pa = GetPhysicalAddressInternal(va);

                size = Math.Min(data.Length, PageSize - (int)(va & PageMask));

                _backingMemory.GetSpan(pa, size).CopyTo(data.Slice(0, size));

                offset += size;
            }

            for (; offset < data.Length; offset += size)
            {
                ulong pa = GetPhysicalAddressInternal(va + (ulong)offset);

                size = Math.Min(data.Length - offset, PageSize);

                _backingMemory.GetSpan(pa, size).CopyTo(data.Slice(offset, size));
            }
        }

        /// <summary>
        /// Checks if a specified virtual memory region has been modified by the CPU since the last call.
        /// </summary>
        /// <param name="va">Virtual address of the region</param>
        /// <param name="size">Size of the region</param>
        /// <param name="id">Resource identifier number (maximum is 15)</param>
        /// <param name="modifiedRanges">Optional array where the modified ranges should be written</param>
        /// <returns>The number of modified ranges</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public int QueryModified(ulong va, ulong size, int id, (ulong, ulong)[] modifiedRanges = null)
        {
            if (!ValidateAddress(va))
            {
                return 0;
            }

            ulong maxSize = _addressSpaceSize - va;

            if (size > maxSize)
            {
                size = maxSize;
            }

            // We need to ensure that the tagged pointer value is negative,
            // JIT generated code checks that to take the slow paths and call the MemoryManager Read/Write methods.
            long tag = (0x8000L | (1L << id)) << 48;

            ulong endVa = (va + size + PageMask) & ~(ulong)PageMask;

            va &= ~(ulong)PageMask;

            ulong rgStart = va;
            ulong rgSize = 0;

            int rangeIndex = 0;

            for (; va < endVa; va += PageSize)
            {
                while (true)
                {
                    ref long pte = ref _pageTable.GetRef<long>((va >> PageBits) * PteSize);

                    long pteValue = pte;

                    // If the PTE value is 0, that means that the page is unmapped.
                    // We behave as if the page was not modified, since modifying a page
                    // that is not even mapped is impossible.
                    if ((pteValue & tag) == tag || pteValue == 0)
                    {
                        if (rgSize != 0)
                        {
                            if (modifiedRanges != null && rangeIndex < modifiedRanges.Length)
                            {
                                modifiedRanges[rangeIndex] = (rgStart, rgSize);
                            }

                            rangeIndex++;

                            rgSize = 0;
                        }

                        break;
                    }
                    else
                    {
                        if (Interlocked.CompareExchange(ref pte, pteValue | tag, pteValue) == pteValue)
                        {
                            if (rgSize == 0)
                            {
                                rgStart = va;
                            }

                            rgSize += PageSize;

                            break;
                        }
                    }
                }
            }

            if (rgSize != 0)
            {
                if (modifiedRanges != null && rangeIndex < modifiedRanges.Length)
                {
                    modifiedRanges[rangeIndex] = (rgStart, rgSize);
                }

                rangeIndex++;
            }

            return rangeIndex;
        }

        /// <summary>
        /// Checks if the page at a given CPU virtual address.
        /// </summary>
        /// <param name="va">Virtual address to check</param>
        /// <returns>True if the address is mapped, false otherwise</returns>
        public bool IsMapped(ulong va)
        {
            if (!ValidateAddress(va))
            {
                return false;
            }

            return _pageTable.Read<ulong>((va / PageSize) * PteSize) != 0;
        }

        private bool ValidateAddress(ulong va)
        {
            return va < _addressSpaceSize;
        }

        /// <summary>
        /// Performs address translation of the address inside a CPU mapped memory range.
        /// </summary>
        /// <remarks>
        /// If the address is invalid or unmapped, -1 will be returned.
        /// </remarks>
        /// <param name="va">Virtual address to be translated</param>
        /// <returns>The physical address</returns>
        public ulong GetPhysicalAddress(ulong va)
        {
            // We return -1L if the virtual address is invalid or unmapped.
            if (!ValidateAddress(va) || !IsMapped(va))
            {
                return ulong.MaxValue;
            }

            return GetPhysicalAddressInternal(va);
        }

        private ulong GetPhysicalAddressInternal(ulong va)
        {
            return PteToPa(_pageTable.Read<ulong>((va / PageSize) * PteSize) & ~(0xffffUL << 48)) + (va & PageMask);
        }

        private void MarkRegionAsModified(ulong va, ulong size)
        {
            ulong endVa = (va + size + PageMask) & ~(ulong)PageMask;

            while (va < endVa)
            {
                ref long pageRef = ref _pageTable.GetRef<long>((va >> PageBits) * PteSize);

                long pte;

                do
                {
                    pte = Volatile.Read(ref pageRef);

                    if (pte >= 0)
                    {
                        break;
                    }
                }
                while (Interlocked.CompareExchange(ref pageRef, pte & ~(0xffffL << 48), pte) != pte);

                va += PageSize;
            }
        }

        private ulong PaToPte(ulong pa)
        {
            return (ulong)_backingMemory.GetPointer(pa, PageSize).ToInt64();
        }

        private ulong PteToPa(ulong pte)
        {
            return (ulong)((long)pte - _backingMemory.Pointer.ToInt64());
        }

        public void Dispose()
        {
            _pageTable.Dispose();
        }
    }
}