using Ryujinx.Cpu.Tracking;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Ryujinx.Graphics.Gpu.Image
{
    /// <summary>
    /// A tracking handle for a texture group, which represents a range of views in a storage texture.
    /// Retains a list of overlapping texture views, a modified flag, and tracking for each
    /// CPU VA range that the views cover.
    /// Also tracks copy dependencies for the handle - references to other handles that must be kept 
    /// in sync with this one before use.
    /// </summary>
    class TextureGroupHandle : IDisposable
    {
        private TextureGroup _group;
        private int _bindCount;
        private int _firstLevel;
        private int _firstLayer;

        /// <summary>
        /// The byte offset from the start of the storage of this handle.
        /// </summary>
        public int Offset { get; }

        /// <summary>
        /// The size in bytes covered by this handle.
        /// </summary>
        public int Size { get; }

        /// <summary>
        /// The textures which this handle overlaps with.
        /// </summary>
        public List<Texture> Overlaps { get; }

        /// <summary>
        /// The CPU memory tracking handles that cover this handle.
        /// </summary>
        public CpuRegionHandle[] Handles { get; }

        /// <summary>
        /// True if a texture overlapping this handle has been modified. Is set false when the flush action is called.
        /// </summary>
        public bool Modified { get; set; }

        /// <summary>
        /// Dependencies to handles from other texture groups.
        /// </summary>
        public List<TextureDependency> Dependencies { get; }

        /// <summary>
        /// A flag indicating that a copy is required from one of the dependencies.
        /// </summary>
        public bool NeedsCopy => DeferredCopy != null;

        /// <summary>
        /// A data copy that must be acknowledged the next time this handle is used.
        /// </summary>
        public TextureGroupHandle DeferredCopy { get; set; }

        /// <summary>
        /// Create a new texture group handle, representing a range of views in a storage texture.
        /// </summary>
        /// <param name="group">The TextureGroup that the handle belongs to</param>
        /// <param name="offset">The byte offset from the start of the storage of the handle</param>
        /// <param name="size">The size in bytes covered by the handle</param>
        /// <param name="views">All views of the storage texture, used to calculate overlaps</param>
        /// <param name="firstLayer">The first layer of this handle in the storage texture</param>
        /// <param name="firstLevel">The first level of this handle in the storage texture</param>
        /// <param name="handles">The memory tracking handles that cover this handle</param>
        public TextureGroupHandle(TextureGroup group, int offset, ulong size, List<Texture> views, int firstLayer, int firstLevel, CpuRegionHandle[] handles)
        {
            _group = group;
            _firstLayer = firstLayer;
            _firstLevel = firstLevel;

            Offset = offset;
            Size = (int)size;
            Overlaps = new List<Texture>();
            Dependencies = new List<TextureDependency>();

            if (views != null)
            {
                RecalculateOverlaps(group, views);
            }

            Handles = handles;
        }

        /// <summary>
        /// Calculate a list of which views overlap this handle.
        /// </summary>
        /// <param name="group">The parent texture group, used to find a view's base CPU VA offset</param>
        /// <param name="views">The list of views to search for overlaps</param>
        public void RecalculateOverlaps(TextureGroup group, List<Texture> views)
        {
            // Overlaps can be accessed from the memory tracking signal handler, so access must be atomic.
            lock (Overlaps)
            {
                int endOffset = Offset + Size;

                Overlaps.Clear();

                foreach (Texture view in views)
                {
                    int viewOffset = group.FindOffset(view);
                    if (viewOffset < endOffset && Offset < viewOffset + (int)view.Size)
                    {
                        Overlaps.Add(view);
                    }
                }
            }
        }

        /// <summary>
        /// Signal that this handle has been modified to any existing dependencies, and set the modified flag.
        /// </summary>
        public void SignalModified()
        {
            Modified = true;

            // If this handle has any copy dependencies, notify the other handle that a copy needs to be performed.

            foreach (TextureDependency dependency in Dependencies)
            {
                dependency.SignalModified();
            }
        }

        /// <summary>
        /// Signal that this handle has either started or ended being modified.
        /// </summary>
        /// <param name="bound">True if this handle is being bound, false if unbound</param>
        public void SignalModifying(bool bound)
        {
            SignalModified();

            // Note: Bind count currently resets to 0 on inherit for safety, as the handle <-> view relationship can change.
            _bindCount = Math.Max(0, _bindCount + (bound ? 1 : -1));
        }

        /// <summary>
        /// Signal that a copy dependent texture has been modified, and must have its data copied to this one.
        /// </summary>
        /// <param name="copyFrom">The texture handle that must defer a copy to this one</param>
        public void DeferCopy(TextureGroupHandle copyFrom)
        {
            DeferredCopy = copyFrom;

            _group.Storage.SignalGroupDirty();

            foreach (Texture overlap in Overlaps)
            {
                overlap.SignalGroupDirty();
            }
        }

        /// <summary>
        /// Create a copy dependency between this handle, and another.
        /// </summary>
        /// <param name="other">The handle to create a copy dependency to</param>
        /// <param name="copyToOther">True if a copy should be deferred to all of the other handle's dependencies</param>
        public void CreateCopyDependency(TextureGroupHandle other, bool copyToOther = false)
        {
            // Does this dependency already exist?
            foreach (TextureDependency existing in Dependencies)
            {
                if (existing.Other.Handle == other)
                {
                    // Do not need to create it again. May need to set the dirty flag.
                    return;
                }
            }

            _group.HasCopyDependencies = true;
            other._group.HasCopyDependencies = true;

            TextureDependency dependency = new TextureDependency(this);
            TextureDependency otherDependency = new TextureDependency(other);

            dependency.Other = otherDependency;
            otherDependency.Other = dependency;

            Dependencies.Add(dependency);
            other.Dependencies.Add(otherDependency);

            // Recursively create dependency:
            // All of this handle's dependencies must depend on the other.
            foreach (TextureDependency existing in Dependencies.ToArray())
            {
                if (existing != dependency && existing.Other.Handle != other)
                {
                    existing.Other.Handle.CreateCopyDependency(other);
                }
            }

            // All of the other handle's dependencies must depend on this.
            foreach (TextureDependency existing in other.Dependencies.ToArray())
            {
                if (existing != otherDependency && existing.Other.Handle != this)
                {
                    existing.Other.Handle.CreateCopyDependency(this);

                    if (copyToOther)
                    {
                        existing.Other.Handle.DeferCopy(this);
                    }
                }
            }
        }

        /// <summary>
        /// Remove a dependency from this handle's dependency list.
        /// </summary>
        /// <param name="dependency">The dependency to remove</param>
        public void RemoveDependency(TextureDependency dependency)
        {
            Dependencies.Remove(dependency);
        }

        /// <summary>
        /// Check if any of this handle's memory tracking handles are dirty.
        /// </summary>
        /// <returns>True if at least one of the handles is dirty</returns>
        private bool CheckDirty()
        {
            return Handles.Any(handle => handle.Dirty);
        }

        /// <summary>
        /// Perform a copy from the provided handle to this one, or perform a deferred copy if none is provided.
        /// </summary>
        /// <param name="fromHandle">The handle to copy from. If not provided, this method will copy from and clear the deferred copy instead</param>
        /// <returns>True if the copy was performed, false otherwise</returns>
        public bool Copy(TextureGroupHandle fromHandle = null)
        {
            bool result = false;

            if (fromHandle == null)
            {
                fromHandle = DeferredCopy;

                if (fromHandle != null && fromHandle._bindCount == 0)
                {
                    // Repeat the copy in future if the bind count is greater than 0.
                    DeferredCopy = null;
                }
            }

            if (fromHandle != null)
            {
                // If the copy texture is dirty, do not copy. Its data no longer matters, and this handle should also be dirty.
                if (!fromHandle.CheckDirty())
                {
                    Texture from = fromHandle._group.Storage;
                    Texture to = _group.Storage;

                    if (from.ScaleFactor != to.ScaleFactor)
                    {
                        to.PropagateScale(from);
                    }

                    from.HostTexture.CopyTo(
                        to.HostTexture,
                        fromHandle._firstLayer,
                        _firstLayer,
                        fromHandle._firstLevel,
                        _firstLevel);

                    Modified = true;

                    _group.RegisterAction(this);

                    result = true;
                }
            }

            return result;
        }

        /// <summary>
        /// Inherit modified flags and dependencies from another texture handle.
        /// </summary>
        /// <param name="old">The texture handle to inherit from</param>
        public void Inherit(TextureGroupHandle old)
        {
            Modified |= old.Modified;

            foreach (TextureDependency dependency in old.Dependencies.ToArray())
            {
                CreateCopyDependency(dependency.Other.Handle);

                if (dependency.Other.Handle.DeferredCopy == old)
                {
                    dependency.Other.Handle.DeferredCopy = this;
                }
            }

            DeferredCopy = old.DeferredCopy;
        }

        /// <summary>
        /// Check if this region overlaps with another.
        /// </summary>
        /// <param name="address">Base address</param>
        /// <param name="size">Size of the region</param>
        /// <returns>True if overlapping, false otherwise</returns>
        public bool OverlapsWith(int offset, int size)
        {
            return Offset < offset + size && offset < Offset + Size;
        }

        public void Dispose()
        {
            foreach (CpuRegionHandle handle in Handles)
            {
                handle.Dispose();
            }

            foreach (TextureDependency dependency in Dependencies.ToArray())
            {
                dependency.Other.Handle.RemoveDependency(dependency.Other);
            }
        }
    }
}