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

namespace Ryujinx.Graphics.Gpu.Memory
{
    /// <summary>
    /// GPU memory manager.
    /// </summary>
    public class MemoryManager
    {
        private const int PtLvl0Bits = 14;
        private const int PtLvl1Bits = 14;
        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;

        public const ulong PteUnmapped = 0xffffffff_ffffffff;

        private readonly ulong[][] _pageTable;

        public event EventHandler<UnmapEventArgs> MemoryUnmapped;

        private GpuContext _context;

        /// <summary>
        /// Creates a new instance of the GPU memory manager.
        /// </summary>
        public MemoryManager(GpuContext context)
        {
            _context = context;
            _pageTable = new ulong[PtLvl0Size][];
        }

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

            return MemoryMarshal.Cast<byte, T>(_context.PhysicalMemory.GetSpan(processVa, Unsafe.SizeOf<T>()))[0];
        }

        /// <summary>
        /// Gets a read-only span of data from GPU mapped memory.
        /// </summary>
        /// <param name="gpuVa">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 gpuVa, int size)
        {
            ulong processVa = Translate(gpuVa);

            return _context.PhysicalMemory.GetSpan(processVa, size);
        }

        /// <summary>
        /// Gets a writable region from GPU mapped memory.
        /// </summary>
        /// <param name="address">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 gpuVa, int size)
        {
            ulong processVa = Translate(gpuVa);

            return _context.PhysicalMemory.GetWritableRegion(processVa, size);
        }

        /// <summary>
        /// Writes data to GPU mapped memory.
        /// </summary>
        /// <typeparam name="T">Type of the data</typeparam>
        /// <param name="gpuVa">GPU virtual address to write the value into</param>
        /// <param name="value">The value to be written</param>
        public void Write<T>(ulong gpuVa, T value) where T : unmanaged
        {
            ulong processVa = Translate(gpuVa);

            _context.PhysicalMemory.Write(processVa, MemoryMarshal.Cast<T, byte>(MemoryMarshal.CreateSpan(ref value, 1)));
        }

        /// <summary>
        /// Writes data to GPU mapped memory.
        /// </summary>
        /// <param name="gpuVa">GPU virtual address to write the data into</param>
        /// <param name="data">The data to be written</param>
        public void Write(ulong gpuVa, ReadOnlySpan<byte> data)
        {
            ulong processVa = Translate(gpuVa);

            _context.PhysicalMemory.Write(processVa, data);
        }

        /// <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="size">Size in bytes of the mapping</param>
        /// <returns>GPU virtual address of the mapping</returns>
        public ulong Map(ulong pa, ulong va, ulong size)
        {
            lock (_pageTable)
            {
                MemoryUnmapped?.Invoke(this, new UnmapEventArgs(va, size));

                for (ulong offset = 0; offset < size; offset += PageSize)
                {
                    SetPte(va + offset, pa + offset);
                }
            }

            return va;
        }

        /// <summary>
        /// Frees memory that was previously allocated by a map or reserved.
        /// </summary>
        /// <param name="va">GPU virtual address to free</param>
        /// <param name="size">Size in bytes of the region being freed</param>
        public void Free(ulong va, ulong size)
        {
            lock (_pageTable)
            {
                // Event handlers are not expected to be thread safe.
                MemoryUnmapped?.Invoke(this, new UnmapEventArgs(va, size));

                for (ulong offset = 0; offset < size; offset += PageSize)
                {
                    SetPte(va + offset, PteUnmapped);
                }
            }
        }

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

        /// <summary>
        /// Translates a GPU virtual address to a CPU virtual address.
        /// </summary>
        /// <param name="gpuVa">GPU virtual address to be translated</param>
        /// <returns>CPU virtual address</returns>
        public ulong Translate(ulong gpuVa)
        {
            ulong baseAddress = GetPte(gpuVa);

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

            return baseAddress + (gpuVa & PageMask);
        }

        /// <summary>
        /// Gets the Page Table entry for a given GPU virtual address.
        /// </summary>
        /// <param name="gpuVa">GPU virtual address</param>
        /// <returns>Page table entry (CPU virtual address)</returns>
        private ulong GetPte(ulong gpuVa)
        {
            ulong l0 = (gpuVa >> PtLvl0Bit) & PtLvl0Mask;
            ulong l1 = (gpuVa >> 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="gpuVa">GPU virtual address</param>
        /// <param name="pte">Page table entry (CPU virtual address)</param>
        private void SetPte(ulong gpuVa, ulong pte)
        {
            ulong l0 = (gpuVa >> PtLvl0Bit) & PtLvl0Mask;
            ulong l1 = (gpuVa >> 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;
        }
    }
}