/* Copyright 2010-present 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;

namespace MongoDB.Bson
{
    /// <summary>
    /// Represents the BSON undefined value.
    /// </summary>
#if NET452
    [Serializable]
#endif
    public class BsonUndefined : BsonValue, IComparable<BsonUndefined>, IEquatable<BsonUndefined>
    {
        // private static fields
        private static BsonUndefined __value = new BsonUndefined();

        // constructors
        // private so only the singleton instance can be created
        private BsonUndefined()
        {
        }

        // public operators
        /// <summary>
        /// Compares two BsonUndefined values.
        /// </summary>
        /// <param name="lhs">The first BsonUndefined.</param>
        /// <param name="rhs">The other BsonUndefined.</param>
        /// <returns>True if the two BsonUndefined values are not equal according to ==.</returns>
        public static bool operator !=(BsonUndefined lhs, BsonUndefined rhs)
        {
            return !(lhs == rhs);
        }

        /// <summary>
        /// Compares two BsonUndefined values.
        /// </summary>
        /// <param name="lhs">The first BsonUndefined.</param>
        /// <param name="rhs">The other BsonUndefined.</param>
        /// <returns>True if the two BsonUndefined values are equal according to ==.</returns>
        public static bool operator ==(BsonUndefined lhs, BsonUndefined rhs)
        {
            if (object.ReferenceEquals(lhs, null)) { return object.ReferenceEquals(rhs, null); }
            return lhs.Equals(rhs);
        }

        // public static properties
        /// <summary>
        /// Gets the singleton instance of BsonUndefined.
        /// </summary>
        public static BsonUndefined Value { get { return __value; } }

        // public properties
        /// <summary>
        /// Gets the BsonType of this BsonValue.
        /// </summary>
        public override BsonType BsonType
        {
            get { return BsonType.Undefined; }
        }

        // public methods
        /// <summary>
        /// Compares this BsonUndefined to another BsonUndefined.
        /// </summary>
        /// <param name="other">The other BsonUndefined.</param>
        /// <returns>A 32-bit signed integer that indicates whether this BsonUndefined is less than, equal to, or greather than the other.</returns>
        public int CompareTo(BsonUndefined other)
        {
            if (other == null) { return 1; }
            return 0; // it's a singleton
        }

        /// <summary>
        /// Compares the BsonUndefined to another BsonValue.
        /// </summary>
        /// <param name="other">The other BsonValue.</param>
        /// <returns>A 32-bit signed integer that indicates whether this BsonUndefined is less than, equal to, or greather than the other BsonValue.</returns>
        public override int CompareTo(BsonValue other)
        {
            if (other == null) { return 1; }
            if (other is BsonMinKey) { return 1; }
            if (other is BsonUndefined) { return 0; }
            return -1;
        }

        /// <summary>
        /// Compares this BsonUndefined to another BsonUndefined.
        /// </summary>
        /// <param name="rhs">The other BsonUndefined.</param>
        /// <returns>True if the two BsonUndefined values are equal.</returns>
        public bool Equals(BsonUndefined rhs)
        {
            if (object.ReferenceEquals(rhs, null) || GetType() != rhs.GetType()) { return false; }
            return true; // it's a singleton
        }

        /// <summary>
        /// Compares this BsonUndefined to another object.
        /// </summary>
        /// <param name="obj">The other object.</param>
        /// <returns>True if the other object is a BsonUndefined and equal to this one.</returns>
        public override bool Equals(object obj)
        {
            return Equals(obj as BsonUndefined); // works even if obj is null or of a different type
        }

        /// <summary>
        /// Gets the hash code.
        /// </summary>
        /// <returns>The hash code.</returns>
        public override int GetHashCode()
        {
            return BsonType.GetHashCode();
        }

        /// <summary>
        /// Converts this BsonValue to a Boolean (using the JavaScript definition of truthiness).
        /// </summary>
        /// <returns>A Boolean.</returns>
        public override bool ToBoolean()
        {
            return false;
        }

        /// <summary>
        /// Returns a string representation of the value.
        /// </summary>
        /// <returns>A string representation of the value.</returns>
        public override string ToString()
        {
            return "BsonUndefined";
        }
    }
}