// 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.
 
namespace Roslyn.LanguageServer.Protocol
{
    using System;
    using System.Text.Json.Serialization;
 
    /// <summary>
    /// Class which represents a position on a text document.
    ///
    /// See the <see href="https://microsoft.github.io/language-server-protocol/specifications/specification-current/#position">Language Server Protocol specification</see> for additional information.
    /// </summary>
    internal class Position : IEquatable<Position>
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="Position"/> class.
        /// </summary>
        public Position()
        {
        }
 
        /// <summary>
        /// Initializes a new instance of the <see cref="Position"/> class.
        /// </summary>
        /// <param name="line">Line number.</param>
        /// <param name="character">Character number.</param>
        public Position(int line, int character)
        {
            this.Line = line;
            this.Character = character;
        }
 
        /// <summary>
        /// Gets or sets the line number.
        /// </summary>
        [JsonPropertyName("line")]
        public int Line
        {
            get;
            set;
        }
 
        /// <summary>
        /// Gets or sets the character number.
        /// </summary>
        [JsonPropertyName("character")]
        public int Character
        {
            get;
            set;
        }
 
        /// <summary>
        /// Overrides default equals operator.  Two positions are equal if they are both null or one of them is the object equivalent of the other.
        /// </summary>
        /// <param name="firstPosition">The first position to compare.</param>
        /// <param name="secondPosition">The second position to compare.</param>
        /// <returns>True if both positions are null or one of them is the object equivalent of the other, false otherwise.</returns>
        public static bool operator ==(Position? firstPosition, Position? secondPosition)
        {
            if (firstPosition is null && secondPosition is null)
            {
                return true;
            }
 
            if (firstPosition is null && secondPosition is not null)
            {
                return false;
            }
 
            if (firstPosition is not null && secondPosition is null)
            {
                return false;
            }
 
            return firstPosition!.Equals(secondPosition!);
        }
 
        /// <summary>
        /// Overrides the default not equals operator.
        /// </summary>
        /// <param name="firstPosition">The first position to compare.</param>
        /// <param name="secondPosition">The second position to compare.</param>
        /// <returns>True if first and second positions are not equivalent.</returns>
        public static bool operator !=(Position? firstPosition, Position? secondPosition)
        {
            return !(firstPosition == secondPosition);
        }
 
        /// <summary>
        /// Overrides base class method <see cref="object.Equals(object)"/>. Two positions are equal if their line and character are the same.
        /// </summary>
        /// <param name="obj">Object to compare to.</param>
        /// <returns>True if the given position has the same line and character; false otherwise.</returns>
        public override bool Equals(object obj)
        {
            return this.Equals(obj as Position);
        }
 
        /// <inheritdoc/>
        public bool Equals(Position? other)
        {
            return other != null &&
                   this.Line == other.Line &&
                   this.Character == other.Character;
        }
 
        /// <summary>
        /// Overrides base class method <see cref="object.GetHashCode()"/>.
        /// </summary>
        /// <returns>Hashcode for this object.</returns>
        public override int GetHashCode()
        {
            return this.Line ^ this.Character;
        }
    }
}