using System;
using System.Text;

namespace StackExchange.Redis
{
    /// <summary>
    /// Represents values that can be stored in redis
    /// </summary>
    public struct RedisValue : IEquatable<RedisValue>, IComparable<RedisValue>, IComparable, IConvertible
    {
        internal static readonly RedisValue[] EmptyArray = new RedisValue[0];
        private static readonly byte[] EmptyByteArr = new byte[0];
        private static readonly byte[] IntegerSentinel = new byte[0];
        private readonly byte[] valueBlob;
        private readonly long valueInt64;

        // internal bool IsNullOrDefaultValue {  get { return (valueBlob == null && valueInt64 == 0L) || ((object)valueBlob == (object)NullSentinel); } }
        private RedisValue(long valueInt64, byte[] valueBlob)
        {
            this.valueInt64 = valueInt64;
            this.valueBlob = valueBlob;
        }

        /// <summary>
        /// Represents the string <c>""</c>
        /// </summary>
        public static RedisValue EmptyString { get; } = new RedisValue(0, EmptyByteArr);

        /// <summary>
        /// A null value
        /// </summary>
        public static RedisValue Null { get; } = new RedisValue(0, null);

        /// <summary>
        /// Indicates whether the value is a primitive integer
        /// </summary>
        public bool IsInteger => valueBlob == IntegerSentinel;

        /// <summary>
        /// Indicates whether the value should be considered a null value
        /// </summary>
        public bool IsNull => valueBlob == null;

        /// <summary>
        /// Indicates whether the value is either null or a zero-length value
        /// </summary>
        public bool IsNullOrEmpty => valueBlob == null || (valueBlob.Length == 0 && !(valueBlob == IntegerSentinel));

        /// <summary>
        /// Indicates whether the value is greater than zero-length or has an integer value
        /// </summary>
        public bool HasValue => !IsNullOrEmpty;

        /// <summary>
        /// Indicates whether two RedisValue values are equivalent
        /// </summary>
        /// <param name="x">The first <see cref="RedisValue"/> to compare.</param>
        /// <param name="y">The second <see cref="RedisValue"/> to compare.</param>
        public static bool operator !=(RedisValue x, RedisValue y) => !(x == y);

        /// <summary>
        /// Indicates whether two RedisValue values are equivalent
        /// </summary>
        /// <param name="x">The first <see cref="RedisValue"/> to compare.</param>
        /// <param name="y">The second <see cref="RedisValue"/> to compare.</param>
        public static bool operator ==(RedisValue x, RedisValue y)
        {
            if (x.valueBlob == null) return y.valueBlob == null;

            if (x.valueBlob == IntegerSentinel)
            {
                if (y.valueBlob == IntegerSentinel)
                {
                    return x.valueInt64 == y.valueInt64;
                }
                else
                {
                    return Equals((byte[])x, (byte[])y);
                }
            }
            else if (y.valueBlob == IntegerSentinel)
            {
                return Equals((byte[])x, (byte[])y);
            }

            return Equals(x.valueBlob, y.valueBlob);
        }

        /// <summary>
        /// See Object.Equals()
        /// </summary>
        /// <param name="obj">The other <see cref="RedisValue"/> to compare.</param>
        public override bool Equals(object obj)
        {
            if (obj == null) return valueBlob == null;

            if (obj is RedisValue)
            {
                return Equals((RedisValue)obj);
            }
            if (obj is string)
            {
                return (string)obj == (string)this;
            }
            if (obj is byte[])
            {
                return Equals((byte[])obj, (byte[])this);
            }
            if (obj is long)
            {
                return (long)obj == (long)this;
            }
            if (obj is int)
            {
                return (int)obj == (int)this;
            }
            return false;
        }

        /// <summary>
        /// Indicates whether two RedisValue values are equivalent
        /// </summary>
        /// <param name="other">The <see cref="RedisValue"/> to compare to.</param>
        public bool Equals(RedisValue other) => this == other;

        /// <summary>
        /// See Object.GetHashCode()
        /// </summary>
        public override int GetHashCode()
        {
            if (valueBlob == IntegerSentinel) return valueInt64.GetHashCode();
            if (valueBlob == null) return -1;
            return GetHashCode(valueBlob);
        }

        /// <summary>
        /// Returns a string representation of the value
        /// </summary>
        public override string ToString() => (string)this;

        internal static unsafe bool Equals(byte[] x, byte[] y)
        {
            if ((object)x == (object)y) return true; // ref equals
            if (x == null || y == null) return false;
            int len = x.Length;
            if (len != y.Length) return false;

            int octets = len / 8, spare = len % 8;
            fixed (byte* x8 = x, y8 = y)
            {
                long* x64 = (long*)x8, y64 = (long*)y8;
                for (int i = 0; i < octets; i++)
                {
                    if (x64[i] != y64[i]) return false;
                }
                int offset = len - spare;
                while (spare-- != 0)
                {
                    if (x8[offset] != y8[offset++]) return false;
                }
            }
            return true;
        }

        internal static unsafe int GetHashCode(byte[] value)
        {
            unchecked
            {
                if (value == null) return -1;
                int len = value.Length;
                if (len == 0) return 0;
                int octets = len / 8, spare = len % 8;
                int acc = 728271210;
                fixed (byte* ptr8 = value)
                {
                    long* ptr64 = (long*)ptr8;
                    for (int i = 0; i < octets; i++)
                    {
                        long val = ptr64[i];
                        int valHash = (((int)val) ^ ((int)(val >> 32)));
                        acc = (((acc << 5) + acc) ^ valHash);
                    }
                    int offset = len - spare;
                    while (spare-- != 0)
                    {
                        acc = (((acc << 5) + acc) ^ ptr8[offset++]);
                    }
                }
                return acc;
            }
        }
        internal static bool TryParseInt64(byte[] value, int offset, int count, out long result)
            => TryParseInt64(new ReadOnlySpan<byte>(value, offset, count), out result);
        internal static bool TryParseInt64(ReadOnlySpan<byte> value, out long result)
        {
            result = 0;
            if (value.IsEmpty) return false;
            checked
            {
                int max = value.Length;
                if (value[0] == '-')
                {
                    for (int i = 1; i < max; i++)
                    {
                        var b = value[i];
                        if (b < '0' || b > '9') return false;
                        result = (result * 10) - (b - '0');
                    }
                    return true;
                }
                else
                {
                    for (int i = 0; i < max; i++)
                    {
                        var b = value[i];
                        if (b < '0' || b > '9') return false;
                        result = (result * 10) + (b - '0');
                    }
                    return true;
                }
            }
        }

        internal void AssertNotNull()
        {
            if (IsNull) throw new ArgumentException("A null value is not valid in this context");
        }

        private enum CompareType
        {
            Null, Int64, Double, Raw
        }

        private CompareType ResolveType(out long i64, out double r8)
        {
            byte[] blob = valueBlob;
            if (blob == IntegerSentinel)
            {
                i64 = valueInt64;
                r8 = default(double);
                return CompareType.Int64;
            }
            if (blob == null)
            {
                i64 = default(long);
                r8 = default(double);
                return CompareType.Null;
            }
            if (TryParseInt64(blob, 0, blob.Length, out i64))
            {
                r8 = default(double);
                return CompareType.Int64;
            }
            if (TryParseDouble(blob, out r8))
            {
                i64 = default(long);
                return CompareType.Double;
            }
            i64 = default(long);
            r8 = default(double);
            return CompareType.Raw;
        }

        /// <summary>
        /// Compare against a RedisValue for relative order
        /// </summary>
        /// <param name="other">The other <see cref="RedisValue"/> to compare.</param>
        public int CompareTo(RedisValue other)
        {
            try
            {
                CompareType thisType = ResolveType(out long thisInt64, out double thisDouble),
                            otherType = other.ResolveType(out long otherInt64, out double otherDouble);

                if (thisType == CompareType.Null)
                {
                    return otherType == CompareType.Null ? 0 : -1;
                }
                if (otherType == CompareType.Null)
                {
                    return 1;
                }

                if (thisType == CompareType.Int64)
                {
                    if (otherType == CompareType.Int64) return thisInt64.CompareTo(otherInt64);
                    if (otherType == CompareType.Double) return ((double)thisInt64).CompareTo(otherDouble);
                }
                else if (thisType == CompareType.Double)
                {
                    if (otherType == CompareType.Int64) return thisDouble.CompareTo((double)otherInt64);
                    if (otherType == CompareType.Double) return thisDouble.CompareTo(otherDouble);
                }
                // otherwise, compare as strings
                return StringComparer.InvariantCulture.Compare((string)this, (string)other);
            }
            catch (Exception ex)
            {
                ConnectionMultiplexer.TraceWithoutContext(ex.Message);
            }
            // if all else fails, consider equivalent
            return 0;
        }

        int IComparable.CompareTo(object obj)
        {
            if (obj is RedisValue) return CompareTo((RedisValue)obj);
            if (obj is long) return CompareTo((RedisValue)(long)obj);
            if (obj is double) return CompareTo((RedisValue)(double)obj);
            if (obj is string) return CompareTo((RedisValue)(string)obj);
            if (obj is byte[]) return CompareTo((RedisValue)(byte[])obj);
            if (obj is bool) return CompareTo((RedisValue)(bool)obj);
            return -1;
        }

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="int"/>.
        /// </summary>
        /// <param name="value">The <see cref="int"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(int value) => new RedisValue(value, IntegerSentinel);

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="T:Nullable{int}"/>.
        /// </summary>
        /// <param name="value">The <see cref="T:Nullable{int}"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(int? value) => value == null ? Null : (RedisValue)value.GetValueOrDefault();

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="long"/>.
        /// </summary>
        /// <param name="value">The <see cref="long"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(long value) => new RedisValue(value, IntegerSentinel);

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="T:Nullable{long}"/>.
        /// </summary>
        /// <param name="value">The <see cref="T:Nullable{long}"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(long? value) => value == null ? Null : (RedisValue)value.GetValueOrDefault();

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="double"/>.
        /// </summary>
        /// <param name="value">The <see cref="double"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(double value) => Format.ToString(value);

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="T:Nullable{double}"/>.
        /// </summary>
        /// <param name="value">The <see cref="T:Nullable{double}"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(double? value) => value == null ? Null : (RedisValue)value.GetValueOrDefault();

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="string"/>.
        /// </summary>
        /// <param name="value">The <see cref="string"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(string value)
        {
            byte[] blob;
            if (value == null) blob = null;
            else if (value.Length == 0) blob = EmptyByteArr;
            else blob = Encoding.UTF8.GetBytes(value);
            return new RedisValue(0, blob);
        }

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="T:byte[]"/>.
        /// </summary>
        /// <param name="value">The <see cref="T:byte[]"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(byte[] value)
        {
            byte[] blob;
            if (value == null) blob = null;
            else if (value.Length == 0) blob = EmptyByteArr;
            else blob = value;
            return new RedisValue(0, blob);
        }

        internal static RedisValue Parse(object obj)
        {
            if (obj == null) return RedisValue.Null;
            if (obj is RedisValue) return (RedisValue)obj;
            if (obj is string) return (RedisValue)(string)obj;
            if (obj is int) return (RedisValue)(int)obj;
            if (obj is double) return (RedisValue)(double)obj;
            if (obj is byte[]) return (RedisValue)(byte[])obj;
            if (obj is bool) return (RedisValue)(bool)obj;
            if (obj is long) return (RedisValue)(long)obj;
            if (obj is float) return (RedisValue)(float)obj;

            throw new InvalidOperationException("Unable to format type for redis: " + obj.GetType().FullName);
        }

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="bool"/>.
        /// </summary>
        /// <param name="value">The <see cref="bool"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(bool value) => new RedisValue(value ? 1 : 0, IntegerSentinel);

        /// <summary>
        /// Creates a new <see cref="RedisValue"/> from an <see cref="T:Nullable{bool}"/>.
        /// </summary>
        /// <param name="value">The <see cref="T:Nullable{bool}"/> to convert to a <see cref="RedisValue"/>.</param>
        public static implicit operator RedisValue(bool? value) => value == null ? Null : (RedisValue)value.GetValueOrDefault();

        /// <summary>
        /// Converts a <see cref="RedisValue"/> to a <see cref="bool"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator bool(RedisValue value)
        {
            switch ((long)value)
            {
                case 0: return false;
                case 1: return true;
                default: throw new InvalidCastException();
            }
        }

        /// <summary>
        /// Converts a <see cref="RedisValue"/> to a <see cref="int"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator int(RedisValue value)
        {
            checked
            {
                return (int)(long)value;
            }
        }

        /// <summary>
        /// Converts a <see cref="RedisValue"/> to a <see cref="long"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator long(RedisValue value)
        {
            var blob = value.valueBlob;
            if (blob == IntegerSentinel) return value.valueInt64;
            if (blob == null) return 0; // in redis, an arithmetic zero is kinda the same thing as not-exists (think "incr")
            if (TryParseInt64(blob, 0, blob.Length, out long i64)) return i64;
            throw new InvalidCastException();
        }

        /// <summary>
        /// Converts a <see cref="RedisValue"/> to a <see cref="double"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator double(RedisValue value)
        {
            var blob = value.valueBlob;
            if (blob == IntegerSentinel) return value.valueInt64;
            if (blob == null) return 0; // in redis, an arithmetic zero is kinda the same thing as not-exists (think "incr")

            if (TryParseDouble(blob, out double r8)) return r8;
            throw new InvalidCastException();
        }

        private static bool TryParseDouble(byte[] blob, out double value)
        {
            // simple integer?
            if (blob.Length == 1 && blob[0] >= '0' && blob[0] <= '9')
            {
                value = blob[0] - '0';
                return true;
            }

            return Format.TryParseDouble(Encoding.UTF8.GetString(blob), out value);
        }

        /// <summary>
        /// Converts the <see cref="RedisValue"/> to a <see cref="T:Nullable{double}"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator double? (RedisValue value)
        {
            if (value.valueBlob == null) return null;
            return (double)value;
        }

        /// <summary>
        /// Converts the <see cref="RedisValue"/> to a <see cref="T:Nullable{long}"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator long? (RedisValue value)
        {
            if (value.valueBlob == null) return null;
            return (long)value;
        }

        /// <summary>
        /// Converts the <see cref="RedisValue"/> to a <see cref="T:Nullable{int}"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator int? (RedisValue value)
        {
            if (value.valueBlob == null) return null;
            return (int)value;
        }

        /// <summary>
        /// Converts the <see cref="RedisValue"/> to a <see cref="T:Nullable{bool}"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static explicit operator bool? (RedisValue value)
        {
            if (value.valueBlob == null) return null;
            return (bool)value;
        }

        /// <summary>
        /// Converts a <see cref="RedisValue"/> to a <see cref="string"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static implicit operator string(RedisValue value)
        {
            var valueBlob = value.valueBlob;
            if (valueBlob == IntegerSentinel)
                return Format.ToString(value.valueInt64);
            if (valueBlob == null) return null;

            if (valueBlob.Length == 0) return "";
            if (valueBlob.Length == 2 && valueBlob[0] == (byte)'O' && valueBlob[1] == (byte)'K')
            {
                return "OK"; // special case for +OK status results from modules
            }
            try
            {
                return Encoding.UTF8.GetString(valueBlob);
            }
            catch
            {
                return BitConverter.ToString(valueBlob);
            }
        }

        /// <summary>
        /// Converts a <see cref="RedisValue"/> to a <see cref="T:byte[]"/>.
        /// </summary>
        /// <param name="value">The <see cref="RedisValue"/> to convert.</param>
        public static implicit operator byte[] (RedisValue value)
        {
            var valueBlob = value.valueBlob;
            if (valueBlob == IntegerSentinel)
            {
                return Encoding.UTF8.GetBytes(Format.ToString(value.valueInt64));
            }
            return valueBlob;
        }

        TypeCode IConvertible.GetTypeCode() => TypeCode.Object;

        bool IConvertible.ToBoolean(IFormatProvider provider) => (bool)this;
        byte IConvertible.ToByte(IFormatProvider provider) => (byte)this;
        char IConvertible.ToChar(IFormatProvider provider) => (char)this;
        DateTime IConvertible.ToDateTime(IFormatProvider provider) => DateTime.Parse((string)this, provider);
        decimal IConvertible.ToDecimal(IFormatProvider provider) => (decimal)this;
        double IConvertible.ToDouble(IFormatProvider provider) => (double)this;
        short IConvertible.ToInt16(IFormatProvider provider) => (short)this;
        int IConvertible.ToInt32(IFormatProvider provider) => (int)this;
        long IConvertible.ToInt64(IFormatProvider provider) => (long)this;
        sbyte IConvertible.ToSByte(IFormatProvider provider) => (sbyte)this;
        float IConvertible.ToSingle(IFormatProvider provider) => (float)this;
        string IConvertible.ToString(IFormatProvider provider) => (string)this;

        object IConvertible.ToType(Type conversionType, IFormatProvider provider)
        {
            if (conversionType == null) throw new ArgumentNullException(nameof(conversionType));
            if (conversionType == typeof(byte[])) return (byte[])this;
            if (conversionType == typeof(RedisValue)) return this;
            switch (Type.GetTypeCode(conversionType))
            {
                case TypeCode.Boolean: return (bool)this;
                case TypeCode.Byte: return (byte)this;
                case TypeCode.Char: return (char)this;
                case TypeCode.DateTime: return DateTime.Parse((string)this, provider);
                case TypeCode.Decimal: return (decimal)this;
                case TypeCode.Double: return (double)this;
                case TypeCode.Int16: return (short)this;
                case TypeCode.Int32: return (int)this;
                case TypeCode.Int64: return (long)this;
                case TypeCode.SByte: return (sbyte)this;
                case TypeCode.Single: return (float)this;
                case TypeCode.String: return (string)this;
                case TypeCode.UInt16: return (ushort)this;
                case TypeCode.UInt32: return (uint)this;
                case TypeCode.UInt64: return (long)this;
                case TypeCode.Object: return this;
                default:
                    throw new NotSupportedException();
            }
        }

        ushort IConvertible.ToUInt16(IFormatProvider provider) => (ushort)this;
        uint IConvertible.ToUInt32(IFormatProvider provider) => (uint)this;
        ulong IConvertible.ToUInt64(IFormatProvider provider) => (ulong)this;

        /// <summary>
        /// Convert to a long if possible, returning true.
        ///
        /// Returns false otherwise.
        /// </summary>
        /// <param name="val">The <see cref="long"/> value, if conversion was possible.</param>
        public bool TryParse(out long val)
        {
            var blob = valueBlob;
            if (blob == IntegerSentinel)
            {
                val = valueInt64;
                return true;
            }

            if (blob == null)
            {
                // in redis-land 0 approx. equal null; so roll with it
                val = 0;
                return true;
            }

            return TryParseInt64(blob, 0, blob.Length, out val);
        }

        /// <summary>
        /// Convert to a int if possible, returning true.
        ///
        /// Returns false otherwise.
        /// </summary>
        /// <param name="val">The <see cref="int"/> value, if conversion was possible.</param>
        public bool TryParse(out int val)
        {
            if (!TryParse(out long l) || l > int.MaxValue || l < int.MinValue)
            {
                val = 0;
                return false;
            }

            val = (int)l;
            return true;
        }

        /// <summary>
        /// Convert to a double if possible, returning true.
        ///
        /// Returns false otherwise.
        /// </summary>
        /// <param name="val">The <see cref="double"/> value, if conversion was possible.</param>
        public bool TryParse(out double val)
        {
            var blob = valueBlob;
            if (blob == IntegerSentinel)
            {
                val = valueInt64;
                return true;
            }
            if (blob == null)
            {
                // in redis-land 0 approx. equal null; so roll with it
                val = 0;
                return true;
            }

            return TryParseDouble(blob, out val);
        }
    }
}
