// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

/*============================================================
**
**
**
** Purpose: Allows developers to view the base data types as 
**          an arbitrary array of bits.
**
** 
===========================================================*/
namespace System {
    
    using System;
    using System.Runtime.CompilerServices;
    using System.Diagnostics;
    using System.Diagnostics.Contracts;
    using System.Security;

    // The BitConverter class contains methods for
    // converting an array of bytes to one of the base data 
    // types, as well as for converting a base data type to an
    // array of bytes.
    // 
    // Only statics, does not need to be marked with the serializable attribute
    public static class BitConverter {

        // This field indicates the "endianess" of the architecture.
        // The value is set to true if the architecture is
        // little endian; false if it is big endian.
#if BIGENDIAN
        public static readonly bool IsLittleEndian /* = false */;
#else
        public static readonly bool IsLittleEndian = true;
#endif

        // Converts a byte into an array of bytes with length one.
        public static byte[] GetBytes(bool value) {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 1);

            byte[] r = new byte[1];
            r[0] = (value ? (byte)Boolean.True : (byte)Boolean.False );
            return r;
        }
    
        // Converts a char into an array of bytes with length two.
        public static byte[] GetBytes(char value)
        {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 2);

            return GetBytes((short)value);
        }
      
        // Converts a short into an array of bytes with length
        // two.
        public unsafe static byte[] GetBytes(short value)
        {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 2);

            byte[] bytes = new byte[2];
            fixed(byte* b = &bytes[0])
                *((short*)b) = value;
            return bytes;
        }

        // Converts an int into an array of bytes with length 
        // four.
        public unsafe static byte[] GetBytes(int value)
        {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 4);

            byte[] bytes = new byte[4];
            fixed(byte* b = &bytes[0])
                *((int*)b) = value;
            return bytes;
        }
      
        // Converts a long into an array of bytes with length 
        // eight.
        public unsafe static byte[] GetBytes(long value)
        {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 8);

            byte[] bytes = new byte[8];
            fixed(byte* b = &bytes[0])
                *((long*)b) = value;
            return bytes;
        }
    
        // Converts an ushort into an array of bytes with
        // length two.
        [CLSCompliant(false)]
        public static byte[] GetBytes(ushort value) {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 2);

            return GetBytes((short)value);
        }
        
        // Converts an uint into an array of bytes with
        // length four.
        [CLSCompliant(false)]
        public static byte[] GetBytes(uint value) {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 4);

            return GetBytes((int)value);
        }
        
        // Converts an unsigned long into an array of bytes with
        // length eight.
        [CLSCompliant(false)]
        public static byte[] GetBytes(ulong value) {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 8);

            return GetBytes((long)value);
        }
      
        // Converts a float into an array of bytes with length 
        // four.
        public unsafe static byte[] GetBytes(float value)
        {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 4);

            return GetBytes(*(int*)&value);
        }
      
        // Converts a double into an array of bytes with length 
        // eight.
        public unsafe static byte[] GetBytes(double value)
        {
            Contract.Ensures(Contract.Result<byte[]>() != null);
            Contract.Ensures(Contract.Result<byte[]>().Length == 8);

            return GetBytes(*(long*)&value);
        }

        // Converts an array of bytes into a char.  
        public static char ToChar(byte[] value, int startIndex)
        {
            if (value == null) {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            }

            if ((uint)startIndex >= value.Length) {
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            }

            if (startIndex > value.Length - 2) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            }
            Contract.EndContractBlock();

            return (char)ToInt16(value, startIndex);
        }
      
        // Converts an array of bytes into a short.  
        public static unsafe short ToInt16(byte[] value, int startIndex) {
            if( value == null)  {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            }
            
            if ((uint) startIndex >= value.Length) {
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            }
        
            if (startIndex > value.Length -2) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            }
            Contract.EndContractBlock();

            fixed( byte * pbyte = &value[startIndex]) {
                if( startIndex % 2 == 0) { // data is aligned 
                    return *((short *) pbyte);
                }
                else {
                    if( IsLittleEndian) { 
                        return (short)((*pbyte) | (*(pbyte + 1) << 8)) ;
                    }
                    else {
                        return (short)((*pbyte << 8) | (*(pbyte + 1)));                        
                    }
                }
            }
            
        }
      
        // Converts an array of bytes into an int.  
        public static unsafe int ToInt32 (byte[] value, int startIndex) {
            if( value == null)  {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            }
        
            if ((uint) startIndex >= value.Length) {
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            }
        
            if (startIndex > value.Length -4) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            }
            Contract.EndContractBlock();

            fixed( byte * pbyte = &value[startIndex]) {
                if( startIndex % 4 == 0) { // data is aligned 
                    return *((int *) pbyte);
                }
                else {
                    if( IsLittleEndian) { 
                        return (*pbyte) | (*(pbyte + 1) << 8)  | (*(pbyte + 2) << 16) | (*(pbyte + 3) << 24);
                    }
                    else {
                        return (*pbyte << 24) | (*(pbyte + 1) << 16)  | (*(pbyte + 2) << 8) | (*(pbyte + 3));                        
                    }
                }
            }
        }
      
        // Converts an array of bytes into a long.  
        public static unsafe long ToInt64 (byte[] value, int startIndex) {
            if (value == null)  {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            }
        
            if ((uint) startIndex >= value.Length) {
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            }
        
            if (startIndex > value.Length -8) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            }
            Contract.EndContractBlock();

            fixed( byte * pbyte = &value[startIndex]) {
                if( startIndex % 8 == 0) { // data is aligned 
                    return *((long *) pbyte);
                }
                else {
                    if( IsLittleEndian) { 
                        int i1 = (*pbyte) | (*(pbyte + 1) << 8)  | (*(pbyte + 2) << 16) | (*(pbyte + 3) << 24);                        
                        int i2  = (*(pbyte+4)) | (*(pbyte + 5) << 8)  | (*(pbyte + 6) << 16) | (*(pbyte + 7) << 24);
                        return (uint)i1 | ((long)i2 << 32);
                    }
                    else {
                        int i1 = (*pbyte << 24) | (*(pbyte + 1) << 16)  | (*(pbyte + 2) << 8) | (*(pbyte + 3));                        
                        int i2  = (*(pbyte+4) << 24) | (*(pbyte + 5) << 16)  | (*(pbyte + 6) << 8) | (*(pbyte + 7));
                        return (uint)i2 | ((long)i1 << 32);
                    }
                }
            }        
        }
      
    
        // Converts an array of bytes into an ushort.
        // 
        [CLSCompliant(false)]
        public static ushort ToUInt16(byte[] value, int startIndex)
        {
            if (value == null)
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            if ((uint)startIndex >= value.Length)
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            if (startIndex > value.Length - 2)
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            Contract.EndContractBlock();

            return (ushort)ToInt16(value, startIndex);
        }
    
        // Converts an array of bytes into an uint.
        // 
        [CLSCompliant(false)]
        public static uint ToUInt32(byte[] value, int startIndex)
        {
            if (value == null)
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            if ((uint)startIndex >= value.Length)
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            if (startIndex > value.Length - 4)
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            Contract.EndContractBlock();

            return (uint)ToInt32(value, startIndex);
        }
    
        // Converts an array of bytes into an unsigned long.
        // 
        [CLSCompliant(false)]
        public static ulong ToUInt64(byte[] value, int startIndex)
        {
            if (value == null)
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            if ((uint)startIndex >= value.Length)
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            if (startIndex > value.Length - 8)
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            Contract.EndContractBlock();

            return (ulong)ToInt64(value, startIndex);
        }
    
        // Converts an array of bytes into a float.  
        unsafe public static float ToSingle (byte[] value, int startIndex)
        {
            if (value == null)
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            if ((uint)startIndex >= value.Length)
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            if (startIndex > value.Length - 4)
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            Contract.EndContractBlock();

            int val = ToInt32(value, startIndex);
            return *(float*)&val;
        }
      
        // Converts an array of bytes into a double.  
        unsafe public static double ToDouble (byte[] value, int startIndex)
        {
            if (value == null)
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            if ((uint)startIndex >= value.Length)
                ThrowHelper.ThrowStartIndexArgumentOutOfRange_ArgumentOutOfRange_Index();
            if (startIndex > value.Length - 8)
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            Contract.EndContractBlock();

            long val = ToInt64(value, startIndex);
            return *(double*)&val;
        }
      
        private static char GetHexValue(int i) {
            Debug.Assert( i >=0 && i <16, "i is out of range.");
            if (i<10) {
                return (char)(i + '0');
            }
    
            return (char)(i - 10 + 'A');
        }

        // Converts an array of bytes into a String.  
        public static String ToString (byte[] value, int startIndex, int length) {            
            if (value == null) {
                throw new ArgumentNullException(nameof(value));
            }

            if (startIndex < 0 || startIndex >= value.Length && startIndex > 0) {  // Don't throw for a 0 length array.
                throw new ArgumentOutOfRangeException(nameof(startIndex), Environment.GetResourceString("ArgumentOutOfRange_StartIndex")); 
            }

            if (length < 0) {
                throw new ArgumentOutOfRangeException(nameof(length), Environment.GetResourceString("ArgumentOutOfRange_GenericPositive"));
            }

            if (startIndex > value.Length - length) {
                throw new ArgumentException(Environment.GetResourceString("Arg_ArrayPlusOffTooSmall"));
            }
            Contract.EndContractBlock();

            if (length == 0) {
                return string.Empty;
            }

            if (length > (Int32.MaxValue / 3)) {
                // (Int32.MaxValue / 3) == 715,827,882 Bytes == 699 MB
                throw new ArgumentOutOfRangeException(nameof(length), Environment.GetResourceString("ArgumentOutOfRange_LengthTooLarge", (Int32.MaxValue / 3)));
            }

            int chArrayLength = length * 3;
            
            char[] chArray = new char[chArrayLength];
            int i = 0;
            int index = startIndex;
            for (i = 0; i < chArrayLength; i += 3) {
                byte b = value[index++];
                chArray[i]= GetHexValue(b/16);
                chArray[i+1] = GetHexValue(b%16);
                chArray[i+2] = '-';
            }

            // We don't need the last '-' character
            return new String(chArray, 0, chArray.Length - 1);
        }
    
        // Converts an array of bytes into a String.  
        public static String ToString(byte [] value) {
            if (value == null)
                throw new ArgumentNullException(nameof(value));
            Contract.Ensures(Contract.Result<String>() != null);            
            Contract.EndContractBlock();
            return ToString(value, 0, value.Length);
        }
    
        // Converts an array of bytes into a String.  
        public static String ToString (byte [] value, int startIndex) {
            if (value == null)
                throw new ArgumentNullException(nameof(value));
            Contract.Ensures(Contract.Result<String>() != null);
            Contract.EndContractBlock();
            return ToString(value, startIndex, value.Length - startIndex);
        }
      
        /*==================================ToBoolean===================================
        **Action:  Convert an array of bytes to a boolean value.  We treat this array 
        **         as if the first 4 bytes were an Int4 an operate on this value.
        **Returns: True if the Int4 value of the first 4 bytes is non-zero.
        **Arguments: value -- The byte array
        **           startIndex -- The position within the array.
        **Exceptions: See ToInt4.
        ==============================================================================*/
        // Converts an array of bytes into a boolean.  
        public static bool ToBoolean(byte[] value, int startIndex) {
            if (value==null)
                throw new ArgumentNullException(nameof(value));
            if (startIndex < 0)
                throw new ArgumentOutOfRangeException(nameof(startIndex), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (startIndex > value.Length - 1)
                throw new ArgumentOutOfRangeException(nameof(startIndex), Environment.GetResourceString("ArgumentOutOfRange_Index"));
            Contract.EndContractBlock();
    
            return (value[startIndex]==0)?false:true;
        }

        public static unsafe long DoubleToInt64Bits(double value) {
            return *((long *)&value);
        }

        public static unsafe double Int64BitsToDouble(long value) {
            return *((double*)&value);
        }

        public static unsafe int SingleToInt32Bits(float value) {
            return *((int*)&value);
        }

        public static unsafe float Int32BitsToSingle(int value) {
            return *((float*)&value);
        }
    }
}