// Copyright (c) Xenko contributors (https://xenko.com) and Silicon Studio Corp. (https://www.siliconstudio.co.jp)
// Distributed under the MIT license. See the LICENSE.md file in the project root for more information.
using System;
using System.Globalization;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;

namespace math
{
    /// <summary>
    /// Represents a color in the form of Hue, Saturation, Value, Alpha.
    /// </summary>
    [DataContract( Name = "ColorHSV" )]
    [StructLayout( LayoutKind.Sequential, Pack = 4 )]
    public struct ColorHSV : IEquatable<ColorHSV>, IFormattable
    {
        private const string ToStringFormat = "Hue:{0} Saturation:{1} Value:{2} Alpha:{3}";

        /// <summary>
        /// The Hue of the color.
        /// </summary>
        [DataMember( Order = 0 )]
        public float H;

        /// <summary>
        /// The Saturation of the color.
        /// </summary>
        [DataMember( Order = 1 )]
        public float S;

        /// <summary>
        /// The Value of the color.
        /// </summary>
        [DataMember( Order = 2 )]
        public float V;

        /// <summary>
        /// The alpha component of the color.
        /// </summary>
        [DataMember( Order = 3 )]
        public float A;

        /// <summary>
        /// Initializes a new instance of the <see cref="ColorHSV"/> struct.
        /// </summary>
        /// <param name="h">The h.</param>
        /// <param name="s">The s.</param>
        /// <param name="v">The v.</param>
        /// <param name="a">A.</param>
        public ColorHSV( float h, float s, float v, float a )
        {
            H = h;
            S = s;
            V = v;
            A = a;
        }

        /// <summary>
        /// Converts the color into a three component vector.
        /// </summary>
        /// <returns>A three component vector containing the red, green, and blue components of the color.</returns>
        public Color4 ToColor()
        {
            float hdiv = H / 60;
            int hi = (int)hdiv;
            float f = hdiv - hi;

            float p = V * ( 1 - S );
            float q = V * ( 1 - ( S * f ) );
            float t = V * ( 1 - ( S * ( 1 - f ) ) );

            switch( hi )
            {
                case 0:
                    return new Color4( V, t, p, A );
                case 1:
                    return new Color4( q, V, p, A );
                case 2:
                    return new Color4( p, V, t, A );
                case 3:
                    return new Color4( p, q, V, A );
                case 4:
                    return new Color4( t, p, V, A );
                default:
                    return new Color4( V, p, q, A );
            }
        }

        /// <summary>
        /// Converts the color into a HSV color.
        /// </summary>
        /// <param name="color">The color.</param>
        /// <returns>A HSV color</returns>
        public static ColorHSV FromColor( Color4 color )
        {
            float max = Math.Max( color.R, Math.Max( color.G, color.B ) );
            float min = Math.Min( color.R, Math.Min( color.G, color.B ) );

            float delta = max - min;
            float h = 0.0f;

            if( delta > 0.0f )
            {
                if( color.R >= max )
                    h = ( color.G - color.B ) / delta;
                else if( color.G >= max )
                    h = ( color.B - color.R ) / delta + 2.0f;
                else
                    h = ( color.R - color.G ) / delta + 4.0f;
                h *= 60.0f;

                if( h < 0 )
                    h += 360f;
            }

            float s = MathUtil.IsZero( max ) ? 0.0f : delta / max;

            return new ColorHSV( h, s, max, color.A );
        }

        /// <inheritdoc/>
        public bool Equals( ColorHSV other )
        {
            return other.H.Equals( H ) && other.S.Equals( S ) && other.V.Equals( V ) && other.A.Equals( A );
        }

        /// <inheritdoc/>
        public override bool Equals( object obj )
        {
            if( ReferenceEquals( null, obj ) )
                return false;
            if( obj.GetType() != typeof( ColorHSV ) )
                return false;
            return Equals( (ColorHSV)obj );
        }

        /// <inheritdoc/>
        public override int GetHashCode()
        {
            unchecked
            {
                int result = H.GetHashCode();
                result = ( result * 397 ) ^ S.GetHashCode();
                result = ( result * 397 ) ^ V.GetHashCode();
                result = ( result * 397 ) ^ A.GetHashCode();
                return result;
            }
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public override string ToString()
        {
            return ToString( CultureInfo.CurrentCulture );
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <param name="format">The format.</param>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public string ToString( string format )
        {
            return ToString( format, CultureInfo.CurrentCulture );
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <param name="formatProvider">The format provider.</param>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public string ToString( IFormatProvider formatProvider )
        {
            return string.Format( formatProvider, ToStringFormat, H, S, V, A );
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <param name="format">The format.</param>
        /// <param name="formatProvider">The format provider.</param>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public string ToString( string format, IFormatProvider formatProvider )
        {
            if( format == null )
                return ToString( formatProvider );

            return string.Format( formatProvider, ToStringFormat,
                                 H.ToString( format, formatProvider ),
                                 S.ToString( format, formatProvider ),
                                 V.ToString( format, formatProvider ),
                                 A.ToString( format, formatProvider ) );
        }
    }
}