using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Diagnostics.Contracts;
using System.Threading;
using System.Threading.Tasks;

namespace ZeroLevel.Collections
{
    // A vector of bits.  Use this to store bits efficiently, without having to do bit 
    // shifting yourself.
    [System.Runtime.InteropServices.ComVisible(true)]
    [Serializable()]
    public class FastBitArray : ICollection, ICloneable
    {
        private FastBitArray()
        {
        }

        /*=========================================================================
        ** Allocates space to hold length bit values. All of the values in the bit
        ** array are set to false.

        ** Exceptions: ArgumentException if length < 0.
        =========================================================================*/
        public FastBitArray(int length)
            : this(length, false)

        {
        }

        /*=========================================================================
        ** Allocates space to hold length bit values. All of the values in the bit
        ** array are set to defaultValue.
        **
        ** Exceptions: ArgumentOutOfRangeException if length < 0.
        =========================================================================*/
        public FastBitArray(int length, bool defaultValue)
        {
            if (length < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(length), "The length should be at least zero.");
            }
            Contract.EndContractBlock();
            m_array = new int[GetArrayLength(length, BitsPerInt32)];
            m_length = length;
            int fillValue = defaultValue ? unchecked(((int)0xffffffff)) : 0;
            for (int i = 0; i < m_array.Length; i++)
            {
                m_array[i] = fillValue;
            }
            _version = 0;
        }

        /*=========================================================================
        ** Allocates space to hold the bit values in bytes. bytes[0] represents
        ** bits 0 - 7, bytes[1] represents bits 8 - 15, etc. The LSB of each byte
        ** represents the lowest index value; bytes[0] & 1 represents bit 0,
        ** bytes[0] & 2 represents bit 1, bytes[0] & 4 represents bit 2, etc.

        ** Exceptions: ArgumentException if bytes == null.
        =========================================================================*/
        public FastBitArray(byte[] bytes)
        {
            if (bytes == null!)
            {
                throw new ArgumentNullException(nameof(bytes));
            }
            Contract.EndContractBlock();
            // this value is chosen to prevent overflow when computing m_length.
            // m_length is of type int32 and is exposed as a property, so 
            // type of m_length can't be changed to accommodate.
            if (bytes.Length > Int32.MaxValue / BitsPerByte)
            {
                throw new ArgumentException($"The array is too large {BitsPerByte}", nameof(bytes));
            }
            m_array = new int[GetArrayLength(bytes.Length, BytesPerInt32)];
            m_length = bytes.Length * BitsPerByte;
            Parallel
              .ForEach(
                  Partitioner.Create(0, m_array.Length),
                  (range, state) =>
                  {
                      for (var i = range.Item1; i < range.Item2; i++)
                      {
                          var idx = i * BytesPerInt32;
                          if (idx + 3 < bytes.Length)
                          {
                              m_array[i] = (bytes[idx] & 0xff) |
                                  ((bytes[idx + 1] & 0xff) << 8) |
                                  ((bytes[idx + 2] & 0xff) << 16) |
                                  ((bytes[idx + 3] & 0xff) << 24);
                          }
                      }
                  });

            var j = Math.Max(0, bytes.Length - (bytes.Length % BytesPerInt32));
            var last = Math.Max(0, m_array.Length - 1);
            switch (bytes.Length - j)
            {
                case 3:
                    m_array[last] = ((bytes[j + 2] & 0xff) << 16);
                    goto case 2;
                // fall through
                case 2:
                    m_array[last] |= ((bytes[j + 1] & 0xff) << 8);
                    goto case 1;
                // fall through
                case 1:
                    m_array[last] |= (bytes[j] & 0xff);
                    break;
            }
            _version = 0;
        }

        public FastBitArray(bool[] values)
        {
            SetValues(values);
            _version = 0;
        }

        /*=========================================================================
        ** Allocates space to hold the bit values in values. values[0] represents
        ** bits 0 - 31, values[1] represents bits 32 - 63, etc. The LSB of each
        ** integer represents the lowest index value; values[0] & 1 represents bit
        ** 0, values[0] & 2 represents bit 1, values[0] & 4 represents bit 2, etc.

        ** Exceptions: ArgumentException if values == null.
        =========================================================================*/
        public FastBitArray(int[] values)
        {
            SetValues(values);
            _version = 0;
        }

        private void SetValues(int[] values)
        {
            if (values == null!)
            {
                throw new ArgumentNullException(nameof(values));
            }
            Contract.EndContractBlock();
            // this value is chosen to prevent overflow when computing m_length
            if (values.Length > Int32.MaxValue / BitsPerInt32)
            {
                throw new ArgumentException($"The array is too large: {BitsPerInt32}", nameof(values));
            }
            m_array = new int[values.Length];
            m_length = values.Length * BitsPerInt32;
            Array.Copy(values, m_array, values.Length);
        }

        /*=========================================================================
            ** Allocates a new BitArray with the same length and bit values as bits.
            **
            ** Exceptions: ArgumentException if bits == null.
            =========================================================================*/
        public FastBitArray(FastBitArray bits)
        {
            if (bits == null!)
            {
                throw new ArgumentNullException(nameof(bits));
            }
            Contract.EndContractBlock();
            int arrayLength = GetArrayLength(bits.m_length, BitsPerInt32);
            m_array = new int[arrayLength];
            m_length = bits.m_length;
            Array.Copy(bits.m_array, m_array, arrayLength);
            _version = bits._version;
        }

        public bool this[int index]
        {
            get
            {
                return Get(index);
            }
            set
            {
                Set(index, value);
            }
        }

        private void SetValues(bool[] values)
        {
            if (values == null!)
            {
                throw new ArgumentNullException(nameof(values));
            }
            Contract.EndContractBlock();
            m_array = new int[GetArrayLength(values.Length, BitsPerInt32)];
            m_length = values.Length;
            Parallel
               .ForEach(
                   Partitioner.Create(0, m_array.Length),
                   (range, state) =>
                   {
                       for (var i = range.Item1; i < range.Item2; i++)
                       {
                           var idx = i * BitsPerInt32;
                           for (int j = 0; j < BitsPerInt32 && idx < values.Length; j++, idx++)
                           {
                               if (values[idx])
                               {
                                   m_array[i] |= (1 << j);
                               }
                           }
                       }
                   });
        }

        /*=========================================================================
        ** Returns the bit value at position index.

        ** Exceptions: ArgumentOutOfRangeException if index < 0 or
        **             index >= GetLength().
        =========================================================================*/
        public bool Get(int index)
        {
            if (index < 0 || index >= Length)
            {
                throw new ArgumentOutOfRangeException(nameof(index), "Index is out of range");
            }
            Contract.EndContractBlock();
            return (m_array[index / 32] & (1 << (index % 32))) != 0;
        }

        /*=========================================================================
        ** Sets the bit value at position index to value.

        ** Exceptions: ArgumentOutOfRangeException if index < 0 or
        **             index >= GetLength().
        =========================================================================*/
        public void Set(int index, bool value)
        {
            if (index < 0 || index >= Length)
            {
                throw new ArgumentOutOfRangeException(nameof(index), "Index is out of range");
            }
            Contract.EndContractBlock();
            if (value)
            {
                m_array[index / 32] |= (1 << (index % 32));
            }
            else
            {
                m_array[index / 32] &= ~(1 << (index % 32));
            }
            _version++;
        }

        /*=========================================================================
        ** Sets all the bit values to value.
        =========================================================================*/
        public void SetAll(bool value)
        {
            int fillValue = value ? unchecked(((int)0xffffffff)) : 0;
            Parallel
                .ForEach(
                    Partitioner.Create(0, GetArrayLength(m_length, BitsPerInt32)),
                    (range, state) =>
                    {
                        for (var i = range.Item1; i < range.Item2; i++)
                        {
                            m_array[i] = fillValue;
                        }
                    });
            Interlocked.Increment(ref _version);
        }

        /*=========================================================================
        ** Returns a reference to the current instance ANDed with value.

        ** Exceptions: ArgumentException if value == null or
        **             value.Length != this.Length.
        =========================================================================*/
        public FastBitArray And(FastBitArray value)
        {
            if (value == null!)
                throw new ArgumentNullException(nameof(value));
            if (Length != value.Length)
                throw new ArgumentException("The array lengths differ.");
            Contract.EndContractBlock();
            Parallel
             .ForEach(
                 Partitioner.Create(0, GetArrayLength(m_length, BitsPerInt32)),
                 (range, state) =>
                 {
                     for (var i = range.Item1; i < range.Item2; i++)
                     {
                         m_array[i] &= value.m_array[i];
                     }
                 });
            Interlocked.Increment(ref _version);
            return this;
        }

        /*=========================================================================
        ** Returns a reference to the current instance ORed with value.

        ** Exceptions: ArgumentException if value == null or
        **             value.Length != this.Length.
        =========================================================================*/
        public FastBitArray Or(FastBitArray value)
        {
            if (value == null!)
                throw new ArgumentNullException(nameof(value));
            if (Length != value.Length)
                throw new ArgumentException("The array lengths differ");
            Contract.EndContractBlock();
            Parallel
             .ForEach(
                 Partitioner.Create(0, GetArrayLength(m_length, BitsPerInt32)),
                 (range, state) =>
                 {
                     for (var i = range.Item1; i < range.Item2; i++)
                     {
                         m_array[i] |= value.m_array[i];
                     }
                 });
            Interlocked.Increment(ref _version);
            return this;
        }

        public FastBitArray Fold(uint factor, bool inPlace)
        {
            if (factor <= 0)
                throw new ArgumentException($"Fold factor should be a positive number (given value was {factor}.");
            if (Length % factor != 0)
            {
                throw new ArgumentException(
                    $"Fast bit array of size {Length} cannot be folded by a factor {factor}.", nameof(factor));
            }
            Contract.EndContractBlock();
            if (factor == 1) return this;
            int newLength = (int)(Length / factor);
            int arrayLength = GetArrayLength(newLength, BitsPerInt32);
            var newValues = new int[arrayLength];
            Parallel
                   .ForEach(
                       Partitioner.Create(0, arrayLength),
                       (range, state) =>
                       {
                           for (var i = range.Item1; i < range.Item2; i++)
                           {
                               var idx = i * BitsPerInt32;
                               for (var j = 0; j < BitsPerInt32 && idx < newLength; j++, idx++)
                               {
                                   if (GetFolded(this, idx, factor, newLength))
                                   {
                                       newValues[i] |= (1 << j);
                                   }

                               }
                           }
                       });
            if (!inPlace)
            {
                var res = new FastBitArray(newValues);
                res.m_length = newLength;
                return res;
            }
            SetValues(newValues);
            m_length = newLength;
            Interlocked.Increment(ref _version);
            return this;
        }

        private static bool GetFolded(FastBitArray bitArray, int position, uint foldFactor, int foldedSize)
        {
            if (foldFactor == 1) return bitArray[position];
            for (var i = 0; i < foldFactor; i++)
            {
                if (bitArray.Get(position + i * foldedSize))
                    return true;
            }
            return false;
        }

        /*=========================================================================
        ** Returns a reference to the current instance XORed with value.

        ** Exceptions: ArgumentException if value == null or
        **             value.Length != this.Length.
        =========================================================================*/
        public FastBitArray Xor(FastBitArray value)
        {
            if (value == null!)
                throw new ArgumentNullException(nameof(value));
            if (Length != value.Length)
                throw new ArgumentException("The array lengths differ");
            Contract.EndContractBlock();
            Parallel.ForEach(
                           Partitioner.Create(0, GetArrayLength(m_length, BitsPerInt32)),
                           (range, state) =>
                           {
                               for (var i = range.Item1; i < range.Item2; i++)
                               {
                                   m_array[i] ^= value.m_array[i];
                               }
                           });
            Interlocked.Increment(ref _version);
            return this;
        }

        /*=========================================================================
        ** Inverts all the bit values. On/true bit values are converted to
        ** off/false. Off/false bit values are turned on/true. The current instance
        ** is updated and returned.
        =========================================================================*/
        public FastBitArray Not()
        {
            Parallel.ForEach(
               Partitioner.Create(0, GetArrayLength(m_length, BitsPerInt32)),
               (range, state) =>
               {
                   for (var i = range.Item1; i < range.Item2; i++)
                   {
                       m_array[i] = ~m_array[i];
                   }
               });
            Interlocked.Increment(ref _version);
            return this;
        }

        public int Length
        {
            get
            {
                Contract.Ensures(Contract.Result<int>() >= 0);
                return m_length;
            }
            set
            {
                if (value < 0)
                {
                    throw new ArgumentOutOfRangeException(nameof(value), "The length cannot be less than 0.");
                }
                Contract.EndContractBlock();
                int newints = GetArrayLength(value, BitsPerInt32);
                if (newints > m_array.Length || newints + _ShrinkThreshold < m_array.Length)
                {
                    // grow or shrink (if wasting more than _ShrinkThreshold ints)
                    int[] newarray = new int[newints];
                    Array.Copy(m_array, newarray, newints > m_array.Length ? m_array.Length : newints);
                    m_array = newarray;
                }
                if (value > m_length)
                {
                    // clear high bit values in the last int
                    int last = GetArrayLength(m_length, BitsPerInt32) - 1;
                    int bits = m_length % 32;
                    if (bits > 0)
                    {
                        m_array[last] &= (1 << bits) - 1;
                    }
                    // clear remaining int values
                    Array.Clear(m_array, last + 1, newints - last - 1);
                }
                m_length = value;
                _version++;
            }
        }

        // ICollection implementation
        public void CopyTo(Array array, int index)
        {
            if (array == null!)
                throw new ArgumentNullException(nameof(array));
            if (index < 0)
                throw new ArgumentOutOfRangeException(nameof(index), "The index cannot be less than 0.");
            if (array.Rank != 1)
                throw new ArgumentException("Multi dimensional arrays are not supported.");
            Contract.EndContractBlock();
            if (array is int[])
            {
                Array.Copy(m_array, 0, array, index, GetArrayLength(m_length, BitsPerInt32));
            }
            else if (array is byte[])
            {
                int arrayLength = GetArrayLength(m_length, BitsPerByte);
                if ((array.Length - index) < arrayLength)
                    throw new ArgumentException("The offset is invalid.");
                byte[] b = (byte[])array;
                for (int i = 0; i < arrayLength; i++)
                    b[index + i] = (byte)((m_array[i / 4] >> ((i % 4) * 8)) & 0x000000FF); // Shift to bring the required byte to LSB, then mask
            }
            else if (array is bool[])
            {
                if (array.Length - index < m_length)
                    throw new ArgumentException("The offset is invalid.");
                bool[] b = (bool[])array;
                for (int i = 0; i < m_length; i++)
                    b[index + i] = ((m_array[i / 32] >> (i % 32)) & 0x00000001) != 0;
            }
            else
                throw new ArgumentException("The offset is invalid.");
        }

        public int Count
        {
            get
            {
                Contract.Ensures(Contract.Result<int>() >= 0);
                return m_length;
            }
        }

        public Object Clone()
        {
            Contract.Ensures(Contract.Result<Object>() != null!);
            Contract.Ensures(((FastBitArray)Contract.Result<Object>()).Length == this.Length);
            return new FastBitArray(this);
        }

        public Object SyncRoot
        {
            get
            {
                if (_syncRoot == null!)
                {
                    System.Threading.Interlocked.CompareExchange<Object>(ref _syncRoot!, new Object(), null!);
                }
                return _syncRoot;
            }
        }

        public bool IsReadOnly
        {
            get
            {
                return false;
            }
        }

        public bool IsSynchronized
        {
            get
            {
                return false;
            }
        }

        public IEnumerator GetEnumerator()
        {
            return new BitArrayEnumeratorSimple(this);
        }

        // XPerY=n means that n Xs can be stored in 1 Y. 
        private const int BitsPerInt32 = 32;
        private const int BytesPerInt32 = 4;
        private const int BitsPerByte = 8;

        /// <summary>
        /// Used for conversion between different representations of bit array. 
        /// Returns (n+(div-1))/div, rearranged to avoid arithmetic overflow. 
        /// For example, in the bit to int case, the straightforward calc would 
        /// be (n+31)/32, but that would cause overflow. So instead it's 
        /// rearranged to ((n-1)/32) + 1, with special casing for 0.
        /// 
        /// Usage:
        /// GetArrayLength(77, BitsPerInt32): returns how many ints must be 
        /// allocated to store 77 bits.
        /// </summary>
        /// <param name="n"></param>
        /// <param name="div">use a conversion constant, e.g. BytesPerInt32 to get
        /// how many ints are required to store n bytes</param>
        /// <returns></returns>
        private static int GetArrayLength(int n, int div)
        {
            Contract.Assert(div > 0, "GetArrayLength: div arg must be greater than 0");
            return n > 0 ? (((n - 1) / div) + 1) : 0;
        }

        [Serializable]
        private class BitArrayEnumeratorSimple : IEnumerator, ICloneable
        {
            private FastBitArray bitarray;
            private int index;
            private int version;
            private bool currentElement;

            internal BitArrayEnumeratorSimple(FastBitArray bitarray)
            {
                this.bitarray = bitarray;
                this.index = -1;
                version = bitarray._version;
            }

            public Object Clone()
            {
                return MemberwiseClone();
            }

            public virtual bool MoveNext()
            {
                if (version != bitarray._version) throw new InvalidOperationException("The version changed during enumeration");
                if (index < (bitarray.Count - 1))
                {
                    index++;
                    currentElement = bitarray.Get(index);
                    return true;
                }
                else
                    index = bitarray.Count;
                return false;
            }

            public virtual Object Current
            {
                get
                {
                    if (index == -1)
                        throw new InvalidOperationException("Enumeration was not started");
                    if (index >= bitarray.Count)
                        throw new InvalidOperationException("Enumeration was ended");
                    return currentElement;
                }
            }

            public void Reset()
            {
                if (version != bitarray._version) throw new InvalidOperationException("The bit array was modified during enumeration.");
                index = -1;
            }
        }

        private int[] m_array;
        private int m_length;
        private int _version;

        [NonSerialized]
        private Object _syncRoot;
        private const int _ShrinkThreshold = 256;
    }
}
