using System;
using System.Globalization;
using System.Numerics;
using System.Runtime.Serialization;

namespace Python.Runtime
{
    /// <summary>
    /// Represents a Python integer object.
    /// See the documentation at https://docs.python.org/3/c-api/long.html
    /// </summary>
    public class PyInt : PyNumber, IFormattable
    {
        internal PyInt(in StolenReference ptr) : base(ptr)
        {
        }

        internal PyInt(BorrowedReference reference) : base(reference)
        {
            if (!Runtime.PyInt_Check(reference)) throw new ArgumentException("object is not an int");
        }


        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Copy constructor - obtain a PyInt from a generic PyObject. An
        /// ArgumentException will be thrown if the given object is not a
        /// Python int object.
        /// </remarks>
        public PyInt(PyObject o) : base(FromObject(o))
        {
        }

        private static BorrowedReference FromObject(PyObject o)
        {
            if (o is null) throw new ArgumentNullException(nameof(o));
            if (!IsIntType(o))
            {
                throw new ArgumentException("object is not an int");
            }
            return o.Reference;
        }

        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from an int32 value.
        /// </remarks>
        public PyInt(int value) : base(Runtime.PyInt_FromInt32(value).StealOrThrow())
        {
        }


        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from a uint32 value.
        /// </remarks>
        public PyInt(uint value) : this((long)value)
        {
        }


        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from an int64 value.
        /// </remarks>
        public PyInt(long value) : base(Runtime.PyInt_FromInt64(value).StealOrThrow())
        {
        }

        /// <summary>
        /// Creates a new Python int from a <see cref="UInt64"/> value.
        /// </summary>
        public PyInt(ulong value) : base(Runtime.PyLong_FromUnsignedLongLong(value).StealOrThrow())
        {
        }

        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from an int16 value.
        /// </remarks>
        public PyInt(short value) : this((int)value)
        {
        }


        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from a uint16 value.
        /// </remarks>
        public PyInt(ushort value) : this((int)value)
        {
        }


        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from a byte value.
        /// </remarks>
        public PyInt(byte value) : this((int)value)
        {
        }


        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from an sbyte value.
        /// </remarks>
        public PyInt(sbyte value) : this((int)value)
        {
        }

        /// <summary>
        /// PyInt Constructor
        /// </summary>
        /// <remarks>
        /// Creates a new Python int from a string value.
        /// </remarks>
        public PyInt(string value) : base(Runtime.PyLong_FromString(value, 0).StealOrThrow())
        {
        }

        public PyInt(BigInteger value) : this(value.ToString(CultureInfo.InvariantCulture)) { }

        protected PyInt(SerializationInfo info, StreamingContext context)
            : base(info, context) { }


        /// <summary>
        /// IsIntType Method
        /// </summary>
        /// <remarks>
        /// Returns true if the given object is a Python int.
        /// </remarks>
        public static bool IsIntType(PyObject value)
        {
            if (value is null) throw new ArgumentNullException(nameof(value));
            return Runtime.PyInt_Check(value.obj);
        }


        /// <summary>
        /// Convert a Python object to a Python int if possible, raising
        /// a PythonException if the conversion is not possible. This is
        /// equivalent to the Python expression "int(object)".
        /// </summary>
        public static PyInt AsInt(PyObject value)
        {
            if (value is null) throw new ArgumentNullException(nameof(value));
            var op = Runtime.PyNumber_Long(value.Reference);
            PythonException.ThrowIfIsNull(op);
            return new PyInt(op.Steal());
        }


        /// <summary>
        /// ToInt16 Method
        /// </summary>
        /// <remarks>
        /// Return the value of the Python int object as an int16.
        /// </remarks>
        public short ToInt16()
        {
            return Convert.ToInt16(ToInt32());
        }


        /// <summary>
        /// Return the value of the Python int object as an <see cref="Int32"/>.
        /// </summary>
        public int ToInt32() => Converter.ToInt32(Reference);

        /// <summary>
        /// ToInt64 Method
        /// </summary>
        /// <remarks>
        /// Return the value of the Python int object as an int64.
        /// </remarks>
        public long ToInt64()
        {
            long? val = Runtime.PyLong_AsLongLong(obj);
            if (val is null)
            {
                throw PythonException.ThrowLastAsClrException();
            }
            return val.Value;
        }

        public BigInteger ToBigInteger()
        {
            using var pyHex = Runtime.HexCallable.Invoke(this);
            string hex = pyHex.As<string>();
            int offset = 0;
            bool neg = false;
            if (hex[0] == '-')
            {
                offset++;
                neg = true;
            }
            byte[] littleEndianBytes = new byte[(hex.Length - offset + 1) / 2];
            for (; offset < hex.Length; offset++)
            {
                int littleEndianHexIndex = hex.Length - 1 - offset;
                int byteIndex = littleEndianHexIndex / 2;
                int isByteTopHalf = littleEndianHexIndex & 1;
                int valueShift = isByteTopHalf * 4;
                littleEndianBytes[byteIndex] += (byte)(Util.HexToInt(hex[offset]) << valueShift);
            }
            var result = new BigInteger(littleEndianBytes);
            return neg ? -result : result;
        }

        public string ToString(string format, IFormatProvider formatProvider)
        {
            using var _ = Py.GIL();
            return ToBigInteger().ToString(format, formatProvider);
        }

        public override TypeCode GetTypeCode() => TypeCode.Int64;
    }
}
