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

namespace Ryujinx.Graphics.Device
{
    /// <summary>
    /// Device memory manager.
    /// </summary>
    public class DeviceMemoryManager : IWritableBlock
    {
        private const int PtLvl0Bits = 10;
        private const int PtLvl1Bits = 10;
        public const int PtPageBits = 12;

        private const ulong PtLvl0Size = 1UL << PtLvl0Bits;
        private const ulong PtLvl1Size = 1UL << PtLvl1Bits;
        public const ulong PageSize = 1UL << PtPageBits;

        private const ulong PtLvl0Mask = PtLvl0Size - 1;
        private const ulong PtLvl1Mask = PtLvl1Size - 1;
        public const ulong PageMask = PageSize - 1;

        private const int PtLvl0Bit = PtPageBits + PtLvl1Bits;
        private const int PtLvl1Bit = PtPageBits;
        private const int AddressSpaceBits = PtPageBits + PtLvl1Bits + PtLvl0Bits;

        public const ulong PteUnmapped = ulong.MaxValue;

        private readonly ulong[][] _pageTable;

        private readonly IVirtualMemoryManager _physical;

        /// <summary>
        /// Creates a new instance of the GPU memory manager.
        /// </summary>
        /// <param name="physicalMemory">Physical memory that this memory manager will map into</param>
        public DeviceMemoryManager(IVirtualMemoryManager physicalMemory)
        {
            _physical = physicalMemory;
            _pageTable = new ulong[PtLvl0Size][];
        }

        /// <summary>
        /// Reads data from GPU mapped memory.
        /// </summary>
        /// <typeparam name="T">Type of the data</typeparam>
        /// <param name="va">GPU virtual address where the data is located</param>
        /// <returns>The data at the specified memory location</returns>
        public T Read<T>(ulong va) where T : unmanaged
        {
            int size = Unsafe.SizeOf<T>();

            if (IsContiguous(va, size))
            {
                return _physical.Read<T>(Translate(va));
            }
            else
            {
                Span<byte> data = new byte[size];

                ReadImpl(va, data);

                return MemoryMarshal.Cast<byte, T>(data)[0];
            }
        }

        /// <summary>
        /// Gets a read-only span of data from GPU mapped memory.
        /// </summary>
        /// <param name="va">GPU virtual address where the data is located</param>
        /// <param name="size">Size of the data</param>
        /// <returns>The span of the data at the specified memory location</returns>
        public ReadOnlySpan<byte> GetSpan(ulong va, int size)
        {
            if (IsContiguous(va, size))
            {
                return _physical.GetSpan(Translate(va), size);
            }
            else
            {
                Span<byte> data = new byte[size];

                ReadImpl(va, data);

                return data;
            }
        }

        /// <summary>
        /// Reads data from a possibly non-contiguous region of GPU mapped memory.
        /// </summary>
        /// <param name="va">GPU virtual address of the data</param>
        /// <param name="data">Span to write the read data into</param>
        private void ReadImpl(ulong va, Span<byte> data)
        {
            if (data.Length == 0)
            {
                return;
            }

            int offset = 0, size;

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

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

                if (pa != PteUnmapped && _physical.IsMapped(pa))
                {
                    _physical.GetSpan(pa, size).CopyTo(data[..size]);
                }

                offset += size;
            }

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

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

                if (pa != PteUnmapped && _physical.IsMapped(pa))
                {
                    _physical.GetSpan(pa, size).CopyTo(data.Slice(offset, size));
                }
            }
        }

        /// <summary>
        /// Gets a writable region from GPU mapped memory.
        /// </summary>
        /// <param name="va">Start address of the range</param>
        /// <param name="size">Size in bytes to be range</param>
        /// <returns>A writable region with the data at the specified memory location</returns>
        public WritableRegion GetWritableRegion(ulong va, int size)
        {
            if (IsContiguous(va, size))
            {
                return _physical.GetWritableRegion(Translate(va), size, tracked: true);
            }
            else
            {
                Memory<byte> memory = new byte[size];

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

                return new WritableRegion(this, va, memory, tracked: true);
            }
        }

        /// <summary>
        /// Writes data to GPU mapped memory.
        /// </summary>
        /// <typeparam name="T">Type of the data</typeparam>
        /// <param name="va">GPU virtual address to write the value into</param>
        /// <param name="value">The value 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 GPU mapped memory.
        /// </summary>
        /// <param name="va">GPU virtual address to write the data into</param>
        /// <param name="data">The data to be written</param>
        public void Write(ulong va, ReadOnlySpan<byte> data)
        {
            if (IsContiguous(va, data.Length))
            {
                _physical.Write(Translate(va), data);
            }
            else
            {
                int offset = 0, size;

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

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

                    if (pa != PteUnmapped && _physical.IsMapped(pa))
                    {
                        _physical.Write(pa, data[..size]);
                    }

                    offset += size;
                }

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

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

                    if (pa != PteUnmapped && _physical.IsMapped(pa))
                    {
                        _physical.Write(pa, data.Slice(offset, size));
                    }
                }
            }
        }

        /// <summary>
        /// Writes data to GPU mapped memory without write tracking.
        /// </summary>
        /// <param name="va">GPU virtual address to write the data into</param>
        /// <param name="data">The data to be written</param>
        public void WriteUntracked(ulong va, ReadOnlySpan<byte> data)
        {
            throw new NotSupportedException();
        }

        /// <summary>
        /// Maps a given range of pages to the specified CPU virtual address.
        /// </summary>
        /// <remarks>
        /// All addresses and sizes must be page aligned.
        /// </remarks>
        /// <param name="pa">CPU virtual address to map into</param>
        /// <param name="va">GPU virtual address to be mapped</param>
        /// <param name="kind">Kind of the resource located at the mapping</param>
        public void Map(ulong pa, ulong va, ulong size)
        {
            lock (_pageTable)
            {
                for (ulong offset = 0; offset < size; offset += PageSize)
                {
                    SetPte(va + offset, PackPte(pa + offset));
                }
            }
        }

        /// <summary>
        /// Unmaps a given range of pages at the specified GPU virtual memory region.
        /// </summary>
        /// <param name="va">GPU virtual address to unmap</param>
        /// <param name="size">Size in bytes of the region being unmapped</param>
        public void Unmap(ulong va, ulong size)
        {
            lock (_pageTable)
            {
                for (ulong offset = 0; offset < size; offset += PageSize)
                {
                    SetPte(va + offset, PteUnmapped);
                }
            }
        }

        /// <summary>
        /// Checks if a region of GPU mapped memory is contiguous.
        /// </summary>
        /// <param name="va">GPU virtual address of the region</param>
        /// <param name="size">Size of the region</param>
        /// <returns>True if the region is contiguous, false otherwise</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private bool IsContiguous(ulong va, int size)
        {
            if (!ValidateAddress(va) || GetPte(va) == PteUnmapped)
            {
                return false;
            }

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

            va &= ~PageMask;

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

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

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

                va += PageSize;
            }

            return true;
        }

        /// <summary>
        /// Validates a GPU virtual address.
        /// </summary>
        /// <param name="va">Address to validate</param>
        /// <returns>True if the address is valid, false otherwise</returns>
        private static bool ValidateAddress(ulong va)
        {
            return va < (1UL << AddressSpaceBits);
        }

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

        /// <summary>
        /// Translates a GPU virtual address to a CPU virtual address.
        /// </summary>
        /// <param name="va">GPU virtual address to be translated</param>
        /// <returns>CPU virtual address, or <see cref="PteUnmapped"/> if unmapped</returns>
        public ulong Translate(ulong va)
        {
            if (!ValidateAddress(va))
            {
                return PteUnmapped;
            }

            ulong pte = GetPte(va);

            if (pte == PteUnmapped)
            {
                return PteUnmapped;
            }

            return UnpackPaFromPte(pte) + (va & PageMask);
        }

        /// <summary>
        /// Gets the Page Table entry for a given GPU virtual address.
        /// </summary>
        /// <param name="va">GPU virtual address</param>
        /// <returns>Page table entry (CPU virtual address)</returns>
        private ulong GetPte(ulong va)
        {
            ulong l0 = (va >> PtLvl0Bit) & PtLvl0Mask;
            ulong l1 = (va >> PtLvl1Bit) & PtLvl1Mask;

            if (_pageTable[l0] == null)
            {
                return PteUnmapped;
            }

            return _pageTable[l0][l1];
        }

        /// <summary>
        /// Sets a Page Table entry at a given GPU virtual address.
        /// </summary>
        /// <param name="va">GPU virtual address</param>
        /// <param name="pte">Page table entry (CPU virtual address)</param>
        private void SetPte(ulong va, ulong pte)
        {
            ulong l0 = (va >> PtLvl0Bit) & PtLvl0Mask;
            ulong l1 = (va >> PtLvl1Bit) & PtLvl1Mask;

            if (_pageTable[l0] == null)
            {
                _pageTable[l0] = new ulong[PtLvl1Size];

                for (ulong index = 0; index < PtLvl1Size; index++)
                {
                    _pageTable[l0][index] = PteUnmapped;
                }
            }

            _pageTable[l0][l1] = pte;
        }

        /// <summary>
        /// Creates a page table entry from a physical address and kind.
        /// </summary>
        /// <param name="pa">Physical address</param>
        /// <returns>Page table entry</returns>
        private static ulong PackPte(ulong pa)
        {
            return pa;
        }

        /// <summary>
        /// Unpacks physical address from a page table entry.
        /// </summary>
        /// <param name="pte">Page table entry</param>
        /// <returns>Physical address</returns>
        private static ulong UnpackPaFromPte(ulong pte)
        {
            return pte;
        }
    }
}
