/* Copyright 2010-2015 MongoDB Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License. 
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
* See the License for the specific language governing permissions and
* limitations under the License. 
*/

using System;
using System. IO;
using MongoDB.Bson. IO;
using MongoDB.Bson. Serialization. Attributes;
using MongoDB.Bson. Serialization. Options;

namespace MongoDB.Bson. Serialization. Serializers
{
    /// <summary>
    /// Represents a serializer for Timespans. 
    /// </summary>
    public class TimeSpanSerializer : StructSerializerBase<TimeSpan>, IRepresentationConfigurable<TimeSpanSerializer>
    {
        // private fields
        private readonly BsonType _representation;
        private readonly TimeSpanUnits _units;

        // constructors
        /// <summary>
        /// Initializes a new instance of the <see cref="TimeSpanSerializer"/> class. 
        /// </summary>
        public TimeSpanSerializer()
            : this(BsonType. String)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="TimeSpanSerializer"/> class. 
        /// </summary>
        /// <param name="representation">The representation.</param>
        public TimeSpanSerializer(BsonType representation)
            : this(representation, TimeSpanUnits. Ticks)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="TimeSpanSerializer"/> class. 
        /// </summary>
        /// <param name="representation">The representation.</param>
        /// <param name="units">The units.</param>
        public TimeSpanSerializer(BsonType representation, TimeSpanUnits units)
        {
            switch (representation)
            {
                case BsonType. Double:
                case BsonType. Int32:
                case BsonType. Int64:
                case BsonType. String:
                    break;

                default:
                    var message = string. Format("{0} is not a valid representation for a TimeSpanSerializer.",  representation);
                    throw new ArgumentException(message);
            }

            _representation = representation;
            _units = units;
        }

        // public properties
        /// <summary>
        /// Gets the representation. 
        /// </summary>
        /// <value>
        /// The representation. 
        /// </value>
        public BsonType Representation
        {
            get { return _representation; }
        }

        /// <summary>
        /// Gets the units. 
        /// </summary>
        /// <value>
        /// The units. 
        /// </value>
        public TimeSpanUnits Units
        {
            get { return _units; }
        }

        // public methods
        /// <summary>
        /// Deserializes a value. 
        /// </summary>
        /// <param name="context">The deserialization context.</param>
        /// <param name="args">The deserialization args.</param>
        /// <returns>A deserialized value.</returns>
        public override TimeSpan Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
        {
            var bsonReader = context. Reader;

            BsonType bsonType = bsonReader. GetCurrentBsonType();
            switch (bsonType)
            {
                case BsonType. Double:
                    return FromDouble(bsonReader. ReadDouble(), _units);

                case BsonType. Int32:
                    return FromInt32(bsonReader. ReadInt32(), _units);

                case BsonType. Int64:
                    return FromInt64(bsonReader. ReadInt64(), _units);

                case BsonType. String:
                    return TimeSpan. Parse(bsonReader. ReadString()); // not XmlConvert. ToTimeSpan (we're using .NET's format for TimeSpan)

                default:
                    throw CreateCannotDeserializeFromBsonTypeException(bsonType);
            }
        }

        /// <summary>
        /// Serializes a value. 
        /// </summary>
        /// <param name="context">The serialization context.</param>
        /// <param name="args">The serialization args.</param>
        /// <param name="value">The object.</param>
        public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, TimeSpan value)
        {
            var bsonWriter = context. Writer;

            switch (_representation)
            {
                case BsonType. Double:
                    bsonWriter. WriteDouble(ToDouble(value, _units));
                    break;

                case BsonType. Int32:
                    bsonWriter. WriteInt32(ToInt32(value, _units));
                    break;

                case BsonType. Int64:
                    bsonWriter. WriteInt64(ToInt64(value, _units));
                    break;

                case BsonType. String:
                    bsonWriter. WriteString(value. ToString()); // not XmlConvert. ToString (we're using .NET's format for TimeSpan)
                    break;

                default:
                    var message = string. Format("'{0}' is not a valid TimeSpan representation.", _ representation);
                    throw new BsonSerializationException(message);
            }
        }

        /// <summary>
        /// Returns a serializer that has been reconfigured with the specified representation. 
        /// </summary>
        /// <param name="representation">The representation.</param>
        /// <returns>The reconfigured serializer.</returns>
        public TimeSpanSerializer WithRepresentation(BsonType representation)
        {
            if (representation == _representation)
            {
                return this;
            }
            else
            {
                return new TimeSpanSerializer(representation, _units);
            }
        }

        /// <summary>
        /// Returns a serializer that has been reconfigured with the specified representation and units. 
        /// </summary>
        /// <param name="representation">The representation.</param>
        /// <param name="units">The units.</param>
        /// <returns>
        /// The reconfigured serializer. 
        /// </returns>
        public TimeSpanSerializer WithRepresentation(BsonType representation, TimeSpanUnits units)
        {
            if (representation == _representation && units == _units)
            {
                return this;
            }
            else
            {
                return new TimeSpanSerializer(representation, units);
            }
        }

        // private methods
        private TimeSpan FromDouble(double value, TimeSpanUnits units)
        {
            if (units == TimeSpanUnits. Nanoseconds)
            {
                return TimeSpan. FromTicks((long)(value / 100.0)); // divide first then cast to reduce chance of overflow
            }
            else
            {
                return TimeSpan. FromTicks((long)(value * TicksPerUnit(units))); // multiply first then cast to preserve fractional part of value
            }
        }

        private TimeSpan FromInt32(int value, TimeSpanUnits units)
        {
            if (units == TimeSpanUnits. Nanoseconds)
            {
                return TimeSpan. FromTicks(value / 100);
            }
            else
            {
                return TimeSpan. FromTicks(value * TicksPerUnit(units));
            }
        }

        private TimeSpan FromInt64(long value, TimeSpanUnits units)
        {
            if (units == TimeSpanUnits. Nanoseconds)
            {
                return TimeSpan. FromTicks(value / 100);
            }
            else
            {
                return TimeSpan. FromTicks(value * TicksPerUnit(units));
            }
        }

        private long TicksPerUnit(TimeSpanUnits units)
        {
            switch (units)
            {
                case TimeSpanUnits. Days: return TimeSpan. TicksPerDay;
                case TimeSpanUnits. Hours: return TimeSpan. TicksPerHour;
                case TimeSpanUnits. Minutes: return TimeSpan. TicksPerMinute;
                case TimeSpanUnits. Seconds: return TimeSpan. TicksPerSecond;
                case TimeSpanUnits. Milliseconds: return TimeSpan. TicksPerMillisecond;
                case TimeSpanUnits. Microseconds: return TimeSpan. TicksPerMillisecond / 1000;
                case TimeSpanUnits. Ticks: return 1;
                default:
                    var message = string. Format("Invalid TimeSpanUnits value: {0}.",  units);
                    throw new ArgumentException(message);
            }
        }

        private double ToDouble(TimeSpan timeSpan, TimeSpanUnits units)
        {
            if (units == TimeSpanUnits. Nanoseconds)
            {
                return (double)(timeSpan. Ticks) * 100.0;
            }
            else
            {
                return (double)timeSpan. Ticks / (double)TicksPerUnit(units); // cast first then divide to preserve fractional part of result
            }
        }

        private int ToInt32(TimeSpan timeSpan, TimeSpanUnits units)
        {
            if (units == TimeSpanUnits. Nanoseconds)
            {
                return (int)(timeSpan. Ticks * 100); 
            }
            else
            {
                return (int)(timeSpan. Ticks / TicksPerUnit(units));
            }
        }

        private long ToInt64(TimeSpan timeSpan, TimeSpanUnits units)
        {
            if (units == TimeSpanUnits. Nanoseconds)
            {
                return timeSpan. Ticks * 100;
            }
            else
            {
                return timeSpan. Ticks / TicksPerUnit(units);
            }
        }

        // explicit interface implementations
        IBsonSerializer IRepresentationConfigurable. WithRepresentation(BsonType representation)
        {
            return WithRepresentation(representation);
        }
    }
}
