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

namespace Unity.Collections
{
    /// <summary>
    /// The keys and values of a hash map copied into two parallel arrays.
    /// </summary>
    /// <remarks>For each key-value pair copied from the hash map, the key is stored in `Keys[i]` while the value is stored in `Values[i]` (for the same `i`).
    ///
    /// NativeKeyValueArrays is not actually itself a native collection: it contains a NativeArray for the keys and a NativeArray for the values,
    /// but a NativeKeyValueArrays does not have its own safety handles.</remarks>
    /// <typeparam name="TKey">The type of the keys.</typeparam>
    /// <typeparam name="TValue">The type of the values.</typeparam>
    [GenerateTestsForBurstCompatibility(GenericTypeArguments = new [] { typeof(int), typeof(int) })]
    public struct NativeKeyValueArrays<TKey, TValue>
        : INativeDisposable
        where TKey : unmanaged
        where TValue : unmanaged
    {
        /// <summary>
        /// The keys.
        /// </summary>
        /// <value>The keys. The key at `Keys[i]` is paired with the value at `Values[i]`.</value>
        public NativeArray<TKey> Keys;

        /// <summary>
        /// The values.
        /// </summary>
        /// <value>The values. The value at `Values[i]` is paired with the key at `Keys[i]`.</value>
        public NativeArray<TValue> Values;

        /// <summary>
        /// The number of key-value pairs.
        /// </summary>
        /// <value>The number of key-value pairs.</value>
        public int Length => Keys.Length;

        /// <summary>
        /// Initializes and returns an instance of NativeKeyValueArrays.
        /// </summary>
        /// <param name="length">The number of keys-value pairs.</param>
        /// <param name="allocator">The allocator to use.</param>
        /// <param name="options">Whether newly allocated bytes should be zeroed out.</param>
        public NativeKeyValueArrays(int length, AllocatorManager.AllocatorHandle allocator, NativeArrayOptions options)
        {
            Keys = CollectionHelper.CreateNativeArray<TKey>(length, allocator, options);
            Values = CollectionHelper.CreateNativeArray<TValue>(length, allocator, options);
        }

        /// <summary>
        /// Releases all resources (memory and safety handles).
        /// </summary>
        public void Dispose()
        {
            Keys.Dispose();
            Values.Dispose();
        }

        /// <summary>
        /// Creates and schedules a job that will dispose this collection's key and value arrays.
        /// </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 collection's key and value arrays.</returns>
        public JobHandle Dispose(JobHandle inputDeps)
        {
            return Keys.Dispose(Values.Dispose(inputDeps));
        }
    }

    /// <summary>
    /// An unordered, expandable associative array.
    /// </summary>
    /// <typeparam name="TKey">The type of the keys.</typeparam>
    /// <typeparam name="TValue">The type of the values.</typeparam>
    [StructLayout(LayoutKind.Sequential)]
    [NativeContainer]
    [DebuggerDisplay("Count = {m_HashMapData.Count()}, Capacity = {m_HashMapData.Capacity}, IsCreated = {m_HashMapData.IsCreated}, IsEmpty = {IsEmpty}")]
    [DebuggerTypeProxy(typeof(NativeParallelHashMapDebuggerTypeProxy<,>))]
    [GenerateTestsForBurstCompatibility(GenericTypeArguments = new [] { typeof(int), typeof(int) })]
    public unsafe struct NativeParallelHashMap<TKey, TValue>
        : INativeDisposable
        , IEnumerable<KeyValue<TKey, TValue>> // Used by collection initializers.
        where TKey : unmanaged, IEquatable<TKey>
        where TValue : unmanaged
    {
        internal UnsafeParallelHashMap<TKey, TValue> m_HashMapData;

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

        /// <summary>
        /// Initializes and returns an instance of NativeParallelHashMap.
        /// </summary>
        /// <param name="capacity">The number of key-value pairs that should fit in the initial allocation.</param>
        /// <param name="allocator">The allocator to use.</param>
        public NativeParallelHashMap(int capacity, AllocatorManager.AllocatorHandle allocator)
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            m_Safety = CollectionHelper.CreateSafetyHandle(allocator);

            if (UnsafeUtility.IsNativeContainerType<TKey>() || UnsafeUtility.IsNativeContainerType<TValue>())
                AtomicSafetyHandle.SetNestedContainer(m_Safety, true);

            CollectionHelper.SetStaticSafetyId<NativeParallelHashMap<TKey, TValue>>(ref m_Safety, ref s_staticSafetyId.Data);
            AtomicSafetyHandle.SetBumpSecondaryVersionOnScheduleWrite(m_Safety, true);
#endif

            m_HashMapData = new UnsafeParallelHashMap<TKey, TValue>(capacity, allocator);
        }

        /// <summary>
        /// Whether this hash map is empty.
        /// </summary>
        /// <value>True if this hash map 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_HashMapData.IsEmpty;
            }
        }

        /// <summary>
        /// The current number of key-value pairs in this hash map.
        /// </summary>
        /// <returns>The current number of key-value pairs in this hash map.</returns>
        public int Count()
        {
            CheckRead();
            return m_HashMapData.Count();
        }

        /// <summary>
        /// The number of key-value pairs that fit in the current allocation.
        /// </summary>
        /// <value>The number of key-value pairs that fit in the current allocation.</value>
        /// <param name="value">A new capacity. Must be larger than the current capacity.</param>
        /// <exception cref="InvalidOperationException">Thrown if `value` is less than the current capacity.</exception>
        public int Capacity
        {
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            readonly get
            {
                CheckRead();
                return m_HashMapData.Capacity;
            }

            set
            {
                CheckWrite();
                m_HashMapData.Capacity = value;
            }
        }

        /// <summary>
        /// Removes all key-value pairs.
        /// </summary>
        /// <remarks>Does not change the capacity.</remarks>
        public void Clear()
        {
            CheckWrite();
            m_HashMapData.Clear();
        }


        /// <summary>
        /// Adds a new key-value pair.
        /// </summary>
        /// <remarks>If the key is already present, this method returns false without modifying the hash map.</remarks>
        /// <param name="key">The key to add.</param>
        /// <param name="item">The value to add.</param>
        /// <returns>True if the key-value pair was added.</returns>
        public bool TryAdd(TKey key, TValue item)
        {
            CheckWrite();
            return UnsafeParallelHashMapBase<TKey, TValue>.TryAdd(m_HashMapData.m_Buffer, key, item, false, m_HashMapData.m_AllocatorLabel);
        }

        /// <summary>
        /// Adds a new key-value pair.
        /// </summary>
        /// <remarks>If the key is already present, this method throws without modifying the hash map.</remarks>
        /// <param name="key">The key to add.</param>
        /// <param name="item">The value to add.</param>
        /// <exception cref="ArgumentException">Thrown if the key was already present.</exception>
        public void Add(TKey key, TValue item)
        {
            CheckWrite();
            var added = UnsafeParallelHashMapBase<TKey, TValue>.TryAdd(m_HashMapData.m_Buffer, key, item, false, m_HashMapData.m_AllocatorLabel);

            if (!added)
            {
                ThrowKeyAlreadyAdded(key);
            }
        }

        /// <summary>
        /// Removes a key-value pair.
        /// </summary>
        /// <param name="key">The key to remove.</param>
        /// <returns>True if a key-value pair was removed.</returns>
        public bool Remove(TKey key)
        {
            CheckWrite();
            return m_HashMapData.Remove(key);
        }

        /// <summary>
        /// Returns the value associated with a key.
        /// </summary>
        /// <param name="key">The key to look up.</param>
        /// <param name="item">Outputs the value associated with the key. Outputs default if the key was not present.</param>
        /// <returns>True if the key was present.</returns>
        public bool TryGetValue(TKey key, out TValue item)
        {
            CheckRead();
            return m_HashMapData.TryGetValue(key, out item);
        }

        /// <summary>
        /// Returns true if a given key is present in this hash map.
        /// </summary>
        /// <param name="key">The key to look up.</param>
        /// <returns>True if the key was present.</returns>
        public bool ContainsKey(TKey key)
        {
            CheckRead();
            return m_HashMapData.ContainsKey(key);
        }

        /// <summary>
        /// Gets and sets values by key.
        /// </summary>
        /// <remarks>Getting a key that is not present will throw. Setting a key that is not already present will add the key.</remarks>
        /// <param name="key">The key to look up.</param>
        /// <value>The value associated with the key.</value>
        /// <exception cref="ArgumentException">For getting, thrown if the key was not present.</exception>
        public TValue this[TKey key]
        {
            get
            {
                CheckRead();

                TValue res;

                if (m_HashMapData.TryGetValue(key, out res))
                {
                    return res;
                }

                ThrowKeyNotPresent(key);

                return default;
            }

            set
            {
                CheckWrite();
                m_HashMapData[key] = value;
            }
        }

        /// <summary>
        /// Whether this hash map has been allocated (and not yet deallocated).
        /// </summary>
        /// <value>True if this hash map has been allocated (and not yet deallocated).</value>
        public readonly bool IsCreated => m_HashMapData.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
            m_HashMapData.Dispose();
        }

        /// <summary>
        /// Creates and schedules a job that will dispose this hash map.
        /// </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 hash map.</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 UnsafeParallelHashMapDataDisposeJob { Data = new UnsafeParallelHashMapDataDispose { m_Buffer = m_HashMapData.m_Buffer, m_AllocatorLabel = m_HashMapData.m_AllocatorLabel, m_Safety = m_Safety } }.Schedule(inputDeps);

            AtomicSafetyHandle.Release(m_Safety);
#else
            var jobHandle = new UnsafeParallelHashMapDataDisposeJob { Data = new UnsafeParallelHashMapDataDispose { m_Buffer = m_HashMapData.m_Buffer, m_AllocatorLabel = m_HashMapData.m_AllocatorLabel }  }.Schedule(inputDeps);
#endif
            m_HashMapData.m_Buffer = null;

            return jobHandle;
        }

        /// <summary>
        /// Returns an array with a copy of all this hash map's keys (in no particular order).
        /// </summary>
        /// <param name="allocator">The allocator to use.</param>
        /// <returns>An array with a copy of all this hash map's keys (in no particular order).</returns>
        public NativeArray<TKey> GetKeyArray(AllocatorManager.AllocatorHandle allocator)
        {
            CheckRead();
            return m_HashMapData.GetKeyArray(allocator);
        }

        /// <summary>
        /// Returns an array with a copy of all this hash map's values (in no particular order).
        /// </summary>
        /// <param name="allocator">The allocator to use.</param>
        /// <returns>An array with a copy of all this hash map's values (in no particular order).</returns>
        public NativeArray<TValue> GetValueArray(AllocatorManager.AllocatorHandle allocator)
        {
            CheckRead();
            return m_HashMapData.GetValueArray(allocator);
        }

        /// <summary>
        /// Returns a NativeKeyValueArrays with a copy of all this hash map's keys and values.
        /// </summary>
        /// <remarks>The key-value pairs are copied in no particular order. For all `i`, `Values[i]` will be the value associated with `Keys[i]`.</remarks>
        /// <param name="allocator">The allocator to use.</param>
        /// <returns>A NativeKeyValueArrays with a copy of all this hash map's keys and values.</returns>
        public NativeKeyValueArrays<TKey, TValue> GetKeyValueArrays(AllocatorManager.AllocatorHandle allocator)
        {
            CheckRead();
            return m_HashMapData.GetKeyValueArrays(allocator);
        }

        /// <summary>
        /// Returns a parallel writer for this hash map.
        /// </summary>
        /// <returns>A parallel writer for this hash map.</returns>
        public ParallelWriter AsParallelWriter()
        {
            ParallelWriter writer;
            writer.m_Writer = m_HashMapData.AsParallelWriter();
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            writer.m_Safety = m_Safety;
            CollectionHelper.SetStaticSafetyId<ParallelWriter>(ref writer.m_Safety, ref ParallelWriter.s_staticSafetyId.Data);
#endif
            return writer;
        }

        /// <summary>
        /// Returns a readonly version of this NativeParallelHashMap instance.
        /// </summary>
        /// <remarks>ReadOnly containers point to the same underlying data as the NativeParallelHashMap it is made from.</remarks>
        /// <returns>ReadOnly instance for this.</returns>
        public ReadOnly AsReadOnly()
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            var ash = m_Safety;
            return new ReadOnly(m_HashMapData, ash);
#else
            return new ReadOnly(m_HashMapData);
#endif
        }

        /// <summary>
        /// A read-only alias for the value of a NativeParallelHashMap. Does not have its own allocated storage.
        /// </summary>
        [NativeContainer]
        [NativeContainerIsReadOnly]
        [DebuggerTypeProxy(typeof(NativeParallelHashMapDebuggerTypeProxy<,>))]
        [DebuggerDisplay("Count = {m_HashMapData.Count()}, Capacity = {m_HashMapData.Capacity}, IsCreated = {m_HashMapData.IsCreated}, IsEmpty = {IsEmpty}")]
        [GenerateTestsForBurstCompatibility(GenericTypeArguments = new [] { typeof(int), typeof(int) })]
        public struct ReadOnly
            : IEnumerable<KeyValue<TKey, TValue>>
        {
            internal UnsafeParallelHashMap<TKey, TValue> m_HashMapData;

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

            [GenerateTestsForBurstCompatibility(CompileTarget = GenerateTestsForBurstCompatibilityAttribute.BurstCompatibleCompileTarget.Editor)]
            internal ReadOnly(UnsafeParallelHashMap<TKey, TValue> hashMapData, AtomicSafetyHandle safety)
            {
                m_HashMapData = hashMapData;
                m_Safety = safety;
                CollectionHelper.SetStaticSafetyId<ReadOnly>(ref m_Safety, ref s_staticSafetyId.Data);
            }
#else
            internal ReadOnly(UnsafeParallelHashMap<TKey, TValue> hashMapData)
            {
                m_HashMapData = hashMapData;
            }
#endif

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

            /// <summary>
            /// Whether this hash map is empty.
            /// </summary>
            /// <value>True if this hash map 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_HashMapData.IsEmpty;
                }
            }

            /// <summary>
            /// The current number of key-value pairs in this hash map.
            /// </summary>
            /// <returns>The current number of key-value pairs in this hash map.</returns>
            public readonly int Count()
            {
                CheckRead();
                return m_HashMapData.Count();
            }

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

            /// <summary>
            /// Returns the value associated with a key.
            /// </summary>
            /// <param name="key">The key to look up.</param>
            /// <param name="item">Outputs the value associated with the key. Outputs default if the key was not present.</param>
            /// <returns>True if the key was present.</returns>
            public readonly bool TryGetValue(TKey key, out TValue item)
            {
                CheckRead();
                return m_HashMapData.TryGetValue(key, out item);
            }

            /// <summary>
            /// Returns true if a given key is present in this hash map.
            /// </summary>
            /// <param name="key">The key to look up.</param>
            /// <returns>True if the key was present.</returns>
            public readonly bool ContainsKey(TKey key)
            {
                CheckRead();
                return m_HashMapData.ContainsKey(key);
            }

            /// <summary>
            /// Gets values by key.
            /// </summary>
            /// <remarks>Getting a key that is not present will throw.</remarks>
            /// <param name="key">The key to look up.</param>
            /// <value>The value associated with the key.</value>
            /// <exception cref="ArgumentException">For getting, thrown if the key was not present.</exception>
            public readonly TValue this[TKey key]
            {
                get
                {
                    CheckRead();

                    TValue res;

                    if (m_HashMapData.TryGetValue(key, out res))
                    { 
                        return res;
                    }

                    ThrowKeyNotPresent(key);

                    return default;
                }
            }

            /// <summary>
            /// Returns an array with a copy of all this hash map's keys (in no particular order).
            /// </summary>
            /// <param name="allocator">The allocator to use.</param>
            /// <returns>An array with a copy of all this hash map's keys (in no particular order).</returns>
            public readonly NativeArray<TKey> GetKeyArray(AllocatorManager.AllocatorHandle allocator)
            {
                CheckRead();
                return m_HashMapData.GetKeyArray(allocator);
            }

            /// <summary>
            /// Returns an array with a copy of all this hash map's values (in no particular order).
            /// </summary>
            /// <param name="allocator">The allocator to use.</param>
            /// <returns>An array with a copy of all this hash map's values (in no particular order).</returns>
            public readonly NativeArray<TValue> GetValueArray(AllocatorManager.AllocatorHandle allocator)
            {
                CheckRead();
                return m_HashMapData.GetValueArray(allocator);
            }

            /// <summary>
            /// Returns a NativeKeyValueArrays with a copy of all this hash map's keys and values.
            /// </summary>
            /// <remarks>The key-value pairs are copied in no particular order. For all `i`, `Values[i]` will be the value associated with `Keys[i]`.</remarks>
            /// <param name="allocator">The allocator to use.</param>
            /// <returns>A NativeKeyValueArrays with a copy of all this hash map's keys and values.</returns>
            public readonly NativeKeyValueArrays<TKey, TValue> GetKeyValueArrays(AllocatorManager.AllocatorHandle allocator)
            {
                CheckRead();
                return m_HashMapData.GetKeyValueArrays(allocator);
            }

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

            [Conditional("ENABLE_UNITY_COLLECTIONS_CHECKS"), Conditional("UNITY_DOTS_DEBUG")]
            readonly void ThrowKeyNotPresent(TKey key)
            {
                throw new ArgumentException($"Key: {key} is not present in the NativeParallelHashMap.");
            }

            /// <summary>
            /// Returns an enumerator over the key-value pairs of this hash map.
            /// </summary>
            /// <returns>An enumerator over the key-value pairs of this hash map.</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 UnsafeParallelHashMapDataEnumerator(m_HashMapData.m_Buffer),
                };
            }

            /// <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<KeyValue<TKey, TValue>> IEnumerable<KeyValue<TKey, TValue>>.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>
        /// A parallel writer for a NativeParallelHashMap.
        /// </summary>
        /// <remarks>
        /// Use <see cref="AsParallelWriter"/> to create a parallel writer for a NativeParallelHashMap.
        /// </remarks>
        [NativeContainer]
        [NativeContainerIsAtomicWriteOnly]
        [DebuggerDisplay("Capacity = {m_Writer.Capacity}")]
        [GenerateTestsForBurstCompatibility(GenericTypeArguments = new [] { typeof(int), typeof(int) })]
        public unsafe struct ParallelWriter
        {
            internal UnsafeParallelHashMap<TKey, TValue>.ParallelWriter m_Writer;

#if ENABLE_UNITY_COLLECTIONS_CHECKS
            internal AtomicSafetyHandle m_Safety;
            internal static readonly SharedStatic<int> s_staticSafetyId = SharedStatic<int>.GetOrCreate<ParallelWriter>();
#endif
            /// <summary>
            /// Returns the index of the current thread.
            /// </summary>
            /// <remarks>In a job, each thread gets its own copy of the ParallelWriter struct, and the job system assigns
            /// each copy the index of its thread.</remarks>
            /// <value>The index of the current thread.</value>
            public int ThreadIndex => m_Writer.m_ThreadIndex;

            /// <summary> **Obsolete. Use <see cref="ThreadIndex"/> instead.</summary>
            [Obsolete("'m_ThreadIndex' has been deprecated; use 'ThreadIndex' instead. (UnityUpgradable) -> ThreadIndex")]
            public int m_ThreadIndex => m_Writer.m_ThreadIndex;

            /// <summary>
            /// The number of key-value pairs that fit in the current allocation.
            /// </summary>
            /// <value>The number of key-value pairs that fit in the current allocation.</value>
            public readonly int Capacity
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get
                {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                    AtomicSafetyHandle.CheckReadAndThrow(m_Safety);
#endif
                    return m_Writer.Capacity;
                }
            }

            /// <summary>
            /// Adds a new key-value pair.
            /// </summary>
            /// <remarks>If the key is already present, this method returns false without modifying this hash map.</remarks>
            /// <param name="key">The key to add.</param>
            /// <param name="item">The value to add.</param>
            /// <returns>True if the key-value pair was added.</returns>
            public bool TryAdd(TKey key, TValue item)
            {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                AtomicSafetyHandle.CheckWriteAndBumpSecondaryVersion(m_Safety);
#endif
                return m_Writer.TryAdd(key, item);
            }

            /// <summary>
            /// Adds a new key-value pair.
            /// </summary>
            /// <remarks>If the key is already present, this method returns false without modifying this hash map.</remarks>
            /// <param name="key">The key to add.</param>
            /// <param name="item">The value to add.</param>
            /// <param name="threadIndexOverride">The thread index which must be set by a field from a job struct with the <see cref="NativeSetThreadIndexAttribute"/> attribute.</param>
            /// <returns>True if the key-value pair was added.</returns>
            internal bool TryAdd(TKey key, TValue item, int threadIndexOverride)
            {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
                AtomicSafetyHandle.CheckWriteAndBumpSecondaryVersion(m_Safety);
#endif
                return m_Writer.TryAdd(key, item, threadIndexOverride);
            }
        }

        /// <summary>
        /// Returns an enumerator over the key-value pairs of this hash map.
        /// </summary>
        /// <returns>An enumerator over the key-value pairs of this hash map.</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 UnsafeParallelHashMapDataEnumerator(m_HashMapData.m_Buffer),
            };
        }

        /// <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<KeyValue<TKey, TValue>> IEnumerable<KeyValue<TKey, TValue>>.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 key-value pairs of a hash map.
        /// </summary>
        /// <remarks>
        /// In an enumerator's initial state, <see cref="Current"/> is not valid to read.
        /// From this state, the first <see cref="MoveNext"/> call advances the enumerator to the first key-value pair.
        /// </remarks>
        [NativeContainer]
        [NativeContainerIsReadOnly]
        public struct Enumerator : IEnumerator<KeyValue<TKey, TValue>>
        {
#if ENABLE_UNITY_COLLECTIONS_CHECKS
            internal AtomicSafetyHandle m_Safety;
#endif
            internal UnsafeParallelHashMapDataEnumerator m_Enumerator;

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

            /// <summary>
            /// Advances the enumerator to the next key-value pair.
            /// </summary>
            /// <returns>True if <see cref="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 key-value pair.
            /// </summary>
            /// <value>The current key-value pair.</value>
            public KeyValue<TKey, TValue> Current
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get => m_Enumerator.GetCurrent<TKey, TValue>();
            }

            object IEnumerator.Current => Current;
        }

        [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
        }

        [Conditional("ENABLE_UNITY_COLLECTIONS_CHECKS"), Conditional("UNITY_DOTS_DEBUG")]
        void ThrowKeyNotPresent(TKey key)
        {
            throw new ArgumentException($"Key: {key} is not present in the NativeParallelHashMap.");
        }

        [Conditional("ENABLE_UNITY_COLLECTIONS_CHECKS"), Conditional("UNITY_DOTS_DEBUG")]
        void ThrowKeyAlreadyAdded(TKey key)
        {
            throw new ArgumentException("An item with the same key has already been added", nameof(key));
        }
    }

    internal sealed class NativeParallelHashMapDebuggerTypeProxy<TKey, TValue>
        where TKey : unmanaged, IEquatable<TKey>
        where TValue : unmanaged
    {
        UnsafeParallelHashMap<TKey, TValue> m_Target;

        public NativeParallelHashMapDebuggerTypeProxy(NativeParallelHashMap<TKey, TValue> target)
        {
            m_Target = target.m_HashMapData;
        }

        internal NativeParallelHashMapDebuggerTypeProxy(NativeParallelHashMap<TKey, TValue>.ReadOnly target)
        {
            m_Target = target.m_HashMapData;
        }

        public List<Pair<TKey, TValue>> Items
        {
            get
            {
                var result = new List<Pair<TKey, TValue>>();
                using (var kva = m_Target.GetKeyValueArrays(Allocator.Temp))
                {
                    for (var i = 0; i < kva.Length; ++i)
                    {
                        result.Add(new Pair<TKey, TValue>(kva.Keys[i], kva.Values[i]));
                    }
                }
                return result;
            }
        }
    }
}