using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.InteropServices;
using Unity.Collections.LowLevel.Unsafe;
using Unity.Jobs;
using Unity.Burst;
using System.Runtime.CompilerServices;

namespace Unity.Collections
{
    /// <summary>
    /// An unordered, expandable set of unique values.
    /// </summary>
    /// <remarks>
    /// Not suitable for parallel write access. Use <see cref="NativeParallelHashSet{T}"/> instead.
    /// </remarks>
    /// <typeparam name="T">The type of the values.</typeparam>
    [StructLayout(LayoutKind.Sequential)]
    [NativeContainer]
    [DebuggerTypeProxy(typeof(NativeHashSetDebuggerTypeProxy<>))]
    [GenerateTestsForBurstCompatibility(GenericTypeArguments = new[] { typeof(int) })]
    public unsafe struct NativeHashSet<T>
        : INativeDisposable
        , IEnumerable<T> // Used by collection initializers.
        where T : unmanaged, IEquatable<T>
    {
        [NativeDisableUnsafePtrRestriction]
        internal HashMapHelper<T>* m_Data;

#if ENABLE_UNITY_COLLECTIONS_CHECKS
        internal AtomicSafetyHandle m_Safety;
        internal static readonly SharedStatic<int> s_staticSafetyId = SharedStatic<int>.GetOrCreate<NativeHashSet<T>>();
#endif

        /// <summary>
        /// Initializes and returns an instance of NativeParallelHashSet.
        /// </summary>
        /// <param name="initialCapacity">The number of values that should fit in the initial allocation.</param>
        /// <param name="allocator">The allocator to use.</param>
        public NativeHashSet(int initialCapacity, AllocatorManager.AllocatorHandle allocator)
        {
            m_Data = HashMapHelper<T>.Alloc(initialCapacity, 0, HashMapHelper<T>.kMinimumCapacity, allocator);

#if ENABLE_UNITY_COLLECTIONS_CHECKS
            m_Safety = CollectionHelper.CreateSafetyHandle(allocator);

            if (UnsafeUtility.IsNativeContainerType<T>())
                AtomicSafetyHandle.SetNestedContainer(m_Safety, true);

            CollectionHelper.SetStaticSafetyId<NativeHashSet<T>>(ref m_Safety, ref s_staticSafetyId.Data);
            AtomicSafetyHandle.SetBumpSecondaryVersionOnScheduleWrite(m_Safety, true);
#endif
        }

        /// <summary>
        /// Whether this set is empty.
        /// </summary>
        /// <value>True if this set is empty or if the set has not been constructed.</value>
        public readonly bool IsEmpty
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get
            {
                if (!IsCreated)
                {
                    return true;
                }

                CheckRead();
                return m_Data->IsEmpty;
            }
        }

        /// <summary>
        /// Returns the current number of values in this set.
        /// </summary>
        /// <returns>The current number of values in this set.</returns>
        public readonly int Count
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get
            {
                CheckRead();
                return m_Data->Count;
            }
        }

        /// <summary>
        /// The number of values that fit in the current allocation.
        /// </summary>
        /// <value>The number of values that fit in the current allocation.</value>
        /// <param name="value">A new capacity. Must be larger than current capacity.</param>
        public int Capacity
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            readonly get
            {
                CheckRead();
                return m_Data->Capacity;
            }

            set
            {
                CheckWrite();
                m_Data->Resize(value);
            }
        }

        /// <summary>
        /// Whether this set has been allocated (and not yet deallocated).
        /// </summary>
        /// <value>True if this set has been allocated (and not yet deallocated).</value>
        public readonly bool IsCreated
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            get => m_Data != null && m_Data->IsCreated;
        }

        /// <summary>
        /// Releases all resources (memory and safety handles).
        /// </summary>
        public void Dispose()
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            if (!AtomicSafetyHandle.IsDefaultValue(m_Safety))
            {
                AtomicSafetyHandle.CheckExistsAndThrow(m_Safety);
            }
#endif
            if (!IsCreated)
            {
                return;
            }

#if ENABLE_UNITY_COLLECTIONS_CHECKS
            CollectionHelper.DisposeSafetyHandle(ref m_Safety);
#endif

            HashMapHelper<T>.Free(m_Data);
            m_Data = null;
        }

        /// <summary>
        /// Creates and schedules a job that will dispose this set.
        /// </summary>
        /// <param name="inputDeps">A job handle. The newly scheduled job will depend upon this handle.</param>
        /// <returns>The handle of a new job that will dispose this set.</returns>
        public JobHandle Dispose(JobHandle inputDeps)
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            if (!AtomicSafetyHandle.IsDefaultValue(m_Safety))
            {
                AtomicSafetyHandle.CheckExistsAndThrow(m_Safety);
            }
#endif
            if (!IsCreated)
            {
                return inputDeps;
            }

#if ENABLE_UNITY_COLLECTIONS_CHECKS
            var jobHandle = new NativeHashMapDisposeJob { Data = new NativeHashMapDispose { m_HashMapData = (UnsafeHashMap<int, int>*)m_Data, m_Safety = m_Safety } }.Schedule(inputDeps);
            AtomicSafetyHandle.Release(m_Safety);
#else
            var jobHandle = new NativeHashMapDisposeJob { Data = new NativeHashMapDispose { m_HashMapData = (UnsafeHashMap<int, int>*)m_Data } }.Schedule(inputDeps);
#endif
            m_Data = null;

            return jobHandle;
        }

        /// <summary>
        /// Removes all values.
        /// </summary>
        /// <remarks>Does not change the capacity.</remarks>
        public void Clear()
        {
            CheckWrite();
            m_Data->Clear();
        }

        /// <summary>
        /// Adds a new value (unless it is already present).
        /// </summary>
        /// <param name="item">The value to add.</param>
        /// <returns>True if the value was not already present.</returns>
        public bool Add(T item)
        {
            CheckWrite();
            return -1 != m_Data->TryAdd(item);
        }

        /// <summary>
        /// Removes a particular value.
        /// </summary>
        /// <param name="item">The value to remove.</param>
        /// <returns>True if the value was present.</returns>
        public bool Remove(T item)
        {
            CheckWrite();
            return -1 != m_Data->TryRemove(item);
        }

        /// <summary>
        /// Returns true if a particular value is present.
        /// </summary>
        /// <param name="item">The item to look up.</param>
        /// <returns>True if the value was present.</returns>
        public bool Contains(T item)
        {
            CheckRead();
            return -1 != m_Data->Find(item);
        }

        /// <summary>
        /// Sets the capacity to match what it would be if it had been originally initialized with all its entries.
        /// </summary>
        public void TrimExcess()
        {
            CheckWrite();
            m_Data->TrimExcess();
        }

        /// <summary>
        /// Returns an array with a copy of this set's values (in no particular order).
        /// </summary>
        /// <param name="allocator">The allocator to use.</param>
        /// <returns>An array with a copy of the set's values.</returns>
        public NativeArray<T> ToNativeArray(AllocatorManager.AllocatorHandle allocator)
        {
            CheckRead();
            return m_Data->GetKeyArray(allocator);
        }

        /// <summary>
        /// Returns an enumerator over the values of this set.
        /// </summary>
        /// <returns>An enumerator over the values of this set.</returns>
        public Enumerator GetEnumerator()
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            AtomicSafetyHandle.CheckGetSecondaryDataPointerAndThrow(m_Safety);
            var ash = m_Safety;
            AtomicSafetyHandle.UseSecondaryVersion(ref ash);
#endif
            return new Enumerator
            {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                m_Safety = ash,
#endif
                m_Enumerator = new HashMapHelper<T>.Enumerator(m_Data),
            };
        }

        /// <summary>
        /// This method is not implemented. Use <see cref="GetEnumerator"/> instead.
        /// </summary>
        /// <returns>Throws NotImplementedException.</returns>
        /// <exception cref="NotImplementedException">Method is not implemented.</exception>
        IEnumerator<T> IEnumerable<T>.GetEnumerator()
        {
            throw new NotImplementedException();
        }

        /// <summary>
        /// This method is not implemented. Use <see cref="GetEnumerator"/> instead.
        /// </summary>
        /// <returns>Throws NotImplementedException.</returns>
        /// <exception cref="NotImplementedException">Method is not implemented.</exception>
        IEnumerator IEnumerable.GetEnumerator()
        {
            throw new NotImplementedException();
        }

        /// <summary>
        /// An enumerator over the values of a set.
        /// </summary>
        /// <remarks>
        /// In an enumerator's initial state, <see cref="Current"/> is invalid.
        /// The first <see cref="MoveNext"/> call advances the enumerator to the first value.
        /// </remarks>
        [NativeContainer]
        [NativeContainerIsReadOnly]
        public struct Enumerator : IEnumerator<T>
        {
            [NativeDisableUnsafePtrRestriction]
            internal HashMapHelper<T>.Enumerator m_Enumerator;
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            internal AtomicSafetyHandle m_Safety;
#endif

            /// <summary>
            /// Does nothing.
            /// </summary>
            public void Dispose() { }

            /// <summary>
            /// Advances the enumerator to the next value.
            /// </summary>
            /// <returns>True if `Current` is valid to read after the call.</returns>
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public bool MoveNext()
            {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                AtomicSafetyHandle.CheckReadAndThrow(m_Safety);
#endif
                return m_Enumerator.MoveNext();
            }

            /// <summary>
            /// Resets the enumerator to its initial state.
            /// </summary>
            public void Reset()
            {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                AtomicSafetyHandle.CheckReadAndThrow(m_Safety);
#endif
                m_Enumerator.Reset();
            }

            /// <summary>
            /// The current value.
            /// </summary>
            /// <value>The current value.</value>
            public T Current
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get
                {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                    AtomicSafetyHandle.CheckReadAndThrow(m_Safety);
#endif
                    return m_Enumerator.GetCurrentKey();
                }
            }

            /// <summary>
            /// Gets the element at the current position of the enumerator in the container.
            /// </summary>
            object IEnumerator.Current => Current;
        }

        /// <summary>
        /// Returns a readonly version of this NativeHashSet instance.
        /// </summary>
        /// <remarks>ReadOnly containers point to the same underlying data as the NativeHashSet it is made from.</remarks>
        /// <returns>ReadOnly instance for this.</returns>
        public ReadOnly AsReadOnly()
        {
            return new ReadOnly(ref this);
        }

        /// <summary>
        /// A read-only alias for the value of a NativeHashSet. Does not have its own allocated storage.
        /// </summary>
        [NativeContainer]
        [NativeContainerIsReadOnly]
        [GenerateTestsForBurstCompatibility(GenericTypeArguments = new[] { typeof(int) })]
        public struct ReadOnly
            : IEnumerable<T>
        {
            [NativeDisableUnsafePtrRestriction]
            internal HashMapHelper<T>* m_Data;

#if ENABLE_UNITY_COLLECTIONS_CHECKS
            AtomicSafetyHandle m_Safety;
            internal static readonly SharedStatic<int> s_staticSafetyId = SharedStatic<int>.GetOrCreate<ReadOnly>();
#endif

            internal ReadOnly(ref NativeHashSet<T> data)
            {
                m_Data = data.m_Data;
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                m_Safety = data.m_Safety;
                CollectionHelper.SetStaticSafetyId<ReadOnly>(ref m_Safety, ref s_staticSafetyId.Data);
#endif
            }

            /// <summary>
            /// Whether this hash set has been allocated (and not yet deallocated).
            /// </summary>
            /// <value>True if this hash set has been allocated (and not yet deallocated).</value>
            public readonly bool IsCreated
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get => m_Data != null && m_Data->IsCreated;
            }

            /// <summary>
            /// Whether this hash set is empty.
            /// </summary>
            /// <value>True if this hash set is empty or if the map has not been constructed.</value>
            public readonly bool IsEmpty
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get
                {
                    if (!IsCreated)
                    {
                        return true;
                    }

                    CheckRead();
                    return m_Data->IsEmpty;
                }
            }

            /// <summary>
            /// The current number of items in this hash set.
            /// </summary>
            /// <returns>The current number of items in this hash set.</returns>
            public readonly int Count
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get
                {
                    CheckRead();
                    return m_Data->Count;
                }
            }

            /// <summary>
            /// The number of items that fit in the current allocation.
            /// </summary>
            /// <value>The number of items that fit in the current allocation.</value>
            public readonly int Capacity
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get
                {
                    CheckRead();
                    return m_Data->Capacity;
                }
            }

            /// <summary>
            /// Returns true if a given item is present in this hash set.
            /// </summary>
            /// <param name="item">The item to look up.</param>
            /// <returns>True if the item was present.</returns>
            public readonly bool Contains(T item)
            {
                CheckRead();
                return -1 != m_Data->Find(item);
            }

            /// <summary>
            /// Returns an array with a copy of all this hash set's items (in no particular order).
            /// </summary>
            /// <param name="allocator">The allocator to use.</param>
            /// <returns>An array with a copy of all this hash set's items (in no particular order).</returns>
            public readonly NativeArray<T> ToNativeArray(AllocatorManager.AllocatorHandle allocator)
            {
                CheckRead();
                return m_Data->GetKeyArray(allocator);
            }

            /// <summary>
            /// Returns an enumerator over the items of this hash set.
            /// </summary>
            /// <returns>An enumerator over the items of this hash set.</returns>
            public readonly Enumerator GetEnumerator()
            {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                AtomicSafetyHandle.CheckGetSecondaryDataPointerAndThrow(m_Safety);
                var ash = m_Safety;
                AtomicSafetyHandle.UseSecondaryVersion(ref ash);
#endif
                return new Enumerator
                {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                    m_Safety = ash,
#endif
                    m_Enumerator = new HashMapHelper<T>.Enumerator(m_Data),
                };
            }

            /// <summary>
            /// This method is not implemented. Use <see cref="GetEnumerator"/> instead.
            /// </summary>
            /// <returns>Throws NotImplementedException.</returns>
            /// <exception cref="NotImplementedException">Method is not implemented.</exception>
            IEnumerator<T> IEnumerable<T>.GetEnumerator()
            {
                throw new NotImplementedException();
            }

            /// <summary>
            /// This method is not implemented. Use <see cref="GetEnumerator"/> instead.
            /// </summary>
            /// <returns>Throws NotImplementedException.</returns>
            /// <exception cref="NotImplementedException">Method is not implemented.</exception>
            IEnumerator IEnumerable.GetEnumerator()
            {
                throw new NotImplementedException();
            }

            [Conditional("ENABLE_UNITY_COLLECTIONS_CHECKS")]
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            readonly void CheckRead()
            {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                AtomicSafetyHandle.CheckReadAndThrow(m_Safety);
#endif
            }
        }

        [Conditional("ENABLE_UNITY_COLLECTIONS_CHECKS")]
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        readonly void CheckRead()
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            AtomicSafetyHandle.CheckReadAndThrow(m_Safety);
#endif
        }

        [Conditional("ENABLE_UNITY_COLLECTIONS_CHECKS")]
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        void CheckWrite()
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            AtomicSafetyHandle.CheckWriteAndBumpSecondaryVersion(m_Safety);
#endif
        }
    }

    sealed internal unsafe class NativeHashSetDebuggerTypeProxy<T>
        where T : unmanaged, IEquatable<T>
    {
        HashMapHelper<T>* Data;

        public NativeHashSetDebuggerTypeProxy(NativeHashSet<T> data)
        {
            Data = data.m_Data;
        }

        public List<T> Items
        {
            get
            {
                if (Data == null)
                {
                    return default;
                }

                var result = new List<T>();
                using (var items = Data->GetKeyArray(Allocator.Temp))
                {
                    for (var k = 0; k < items.Length; ++k)
                    {
                        result.Add(items[k]);
                    }
                }

                return result;
            }
        }
    }
}