using System;
using System.Runtime.CompilerServices;
using Microsoft.Xna.Framework;

namespace MonoGame.Extended
{
    public static class Vector2Extensions
    {
        /// <summary>
        /// Computes the 2D pseudo cross product (perp-dot product) of two vectors.
        /// </summary>
        /// <param name="value1">The first vector.</param>
        /// <param name="value2">The second vector.</param>
        /// <returns>
        /// A scalar value representing twice the signed area of the parallelogram formed by the vectors.
        /// Positive if <paramref name="value2"/> is clockwise from <paramref name="value1"/>,
        /// negative if clockwise, zero if parallel.
        /// </returns>
        public static float PerpDot(Vector2 value1, Vector2 value2)
        {
            // C. Ericson, Real-Time Collision Detection, Morgan Kaufmann, 2005
            // Section 3.3.5 The Cross Product

            return (value1.X * value2.Y) - (value1.Y * value2.X);
        }

        /// <summary>
        /// Computes the 2D pseudo cross products (perp-dot product) of two vectors.
        /// </summary>
        /// <param name="value1">The first vector.</param>
        /// <param name="value2">The second vector.</param>
        /// <param name="result">
        /// A scalar value representing twice the signed area of the parallelogram formed by the vectors.
        /// Positive if <paramref name="value2"/> is clockwise from <paramref name="value1"/>,
        /// negative if clockwise, zero if parallel.
        /// </param>
        public static void PerpDot(ref Vector2 value1, ref Vector2 value2, out float result)
        {
            // C. Ericson, Real-Time Collision Detection, Morgan Kaufmann, 2005
            // Section 3.3.5 The Cross Product

            result = (value1.X * value2.Y) - (value1.Y * value2.X);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 SetX(this Vector2 vector2, float x) => new Vector2(x, vector2.Y);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 SetY(this Vector2 vector2, float y) => new Vector2(vector2.X, y);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 Translate(this Vector2 vector2, float x, float y) => new Vector2(vector2.X + x, vector2.Y + y);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static SizeF ToSize(this Vector2 value) => new SizeF(value.X, value.Y);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static SizeF ToAbsoluteSize(this Vector2 value)
        {
            var x = Math.Abs(value.X);
            var y = Math.Abs(value.Y);
            return new SizeF(x, y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 Round(this Vector2 value, int digits, MidpointRounding mode)
        {
            var x = (float)Math.Round(value.X, digits, mode);
            var y = (float)Math.Round(value.Y, digits, mode);
            return new Vector2(x, y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 Round(this Vector2 value, int digits)
        {
            var x = (float)Math.Round(value.X, digits);
            var y = (float)Math.Round(value.Y, digits);
            return new Vector2(x, y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 Round(this Vector2 value)
        {
            var x = (float)Math.Round(value.X);
            var y = (float)Math.Round(value.Y);
            return new Vector2(x, y);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static bool EqualsWithTolerence(this Vector2 value, Vector2 otherValue, float tolerance = 0.00001f)
        {
            return Math.Abs(value.X - otherValue.X) <= tolerance && (Math.Abs(value.Y - otherValue.Y) <= tolerance);
        }

#if FNA || KNI
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
#else
        [Obsolete("Use native Vector2.Rotate provided by MonoGame instead.  This will be removed in a future release.", false)]
#endif
        public static Vector2 Rotate(this Vector2 value, float radians)
        {
            var cos = (float) Math.Cos(radians);
            var sin = (float) Math.Sin(radians);
            return new Vector2(value.X*cos - value.Y*sin, value.X*sin + value.Y*cos);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 NormalizedCopy(this Vector2 value)
        {
            var newVector2 = new Vector2(value.X, value.Y);
            newVector2.Normalize();
            return newVector2;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 PerpendicularClockwise(this Vector2 value) => new Vector2(value.Y, -value.X);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 PerpendicularCounterClockwise(this Vector2 value) => new Vector2(-value.Y, value.X);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 Truncate(this Vector2 value, float maxLength)
        {
            if (value.LengthSquared() > maxLength*maxLength)
                return value.NormalizedCopy()*maxLength;

            return value;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static bool IsNaN(this Vector2 value) => float.IsNaN(value.X) || float.IsNaN(value.Y);

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static float ToAngle(this Vector2 value) => (float) Math.Atan2(value.X, -value.Y);

        /// <summary>
        ///     Calculates the dot product of two vectors. If the two vectors are unit vectors, the dot product returns a floating
        ///     point value between -1 and 1 that can be used to determine some properties of the angle between two vectors. For
        ///     example, it can show whether the vectors are orthogonal, parallel, or have an acute or obtuse angle between them.
        /// </summary>
        /// <param name="vector1">The first vector.</param>
        /// <param name="vector2">The second vector.</param>
        /// <returns>The dot product of the two vectors.</returns>
        /// <remarks>
        ///     <para>The dot product is also known as the inner product.</para>
        ///     <para>
        ///         For any two vectors, the dot product is defined as: <c>(vector1.X * vector2.X) + (vector1.Y * vector2.Y).</c>
        ///         The result of this calculation, plus or minus some margin to account for floating point error, is equal to:
        ///         <c>Length(vector1) * Length(vector2) * System.Math.Cos(theta)</c>, where <c>theta</c> is the angle between the
        ///         two vectors.
        ///     </para>
        ///     <para>
        ///         If <paramref name="vector1" /> and <paramref name="vector2" /> are unit vectors, the length of each
        ///         vector will be equal to 1. So, when <paramref name="vector1" /> and <paramref name="vector2" /> are unit
        ///         vectors, the dot product is simply equal to the cosine of the angle between the two vectors. For example, both
        ///         <c>cos</c> values in the following calcuations would be equal in value:
        ///         <c>vector1.Normalize(); vector2.Normalize(); var cos = vector1.Dot(vector2)</c>,
        ///         <c>var cos = System.Math.Cos(theta)</c>, where <c>theta</c> is angle in radians betwen the two vectors.
        ///     </para>
        ///     <para>
        ///         If <paramref name="vector1" /> and <paramref name="vector2" /> are unit vectors, without knowing the value of
        ///         <c>theta</c> or using a potentially processor-intensive trigonometric function, the value of the dot product
        ///         can tell us the
        ///         following things:
        ///         <list type="bullet">
        ///             <item>
        ///                 <description>
        ///                     If <c>vector1.Dot(vector2) &gt; 0</c>, the angle between the two vectors
        ///                     is less than 90 degrees.
        ///                 </description>
        ///             </item>
        ///             <item>
        ///                 <description>
        ///                     If <c>vector1.Dot(vector2) &lt; 0</c>, the angle between the two vectors
        ///                     is more than 90 degrees.
        ///                 </description>
        ///             </item>
        ///             <item>
        ///                 <description>
        ///                     If <c>vector1.Dot(vector2) == 0</c>, the angle between the two vectors
        ///                     is 90 degrees; that is, the vectors are othogonal.
        ///                 </description>
        ///             </item>
        ///             <item>
        ///                 <description>
        ///                     If <c>vector1.Dot(vector2) == 1</c>, the angle between the two vectors
        ///                     is 0 degrees; that is, the vectors point in the same direction and are parallel.
        ///                 </description>
        ///             </item>
        ///             <item>
        ///                 <description>
        ///                     If <c>vector1.Dot(vector2) == -1</c>, the angle between the two vectors
        ///                     is 180 degrees; that is, the vectors point in opposite directions and are parallel.
        ///                 </description>
        ///             </item>
        ///         </list>
        ///     </para>
        ///     <note type="caution">
        ///         Because of floating point error, two orthogonal vectors may not return a dot product that is exactly zero. It
        ///         might be zero plus some amount of floating point error. In your code, you will want to determine what amount of
        ///         error is acceptable in your calculation, and take that into account when you do your comparisons.
        ///     </note>
        /// </remarks>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static float Dot(this Vector2 vector1, Vector2 vector2)
        {
            return vector1.X*vector2.X + vector1.Y*vector2.Y;
        }

        /// <summary>
        ///     Calculates the scalar projection of one vector onto another. The scalar projection returns the length of the
        ///     orthogonal projection of the first vector onto a straight line parallel to the second vector, with a negative value
        ///     if the projection has an opposite direction with respect to the second vector.
        /// </summary>
        /// <param name="vector1">The first vector.</param>
        /// <param name="vector2">The second vector.</param>
        /// <returns>The scalar projection of <paramref name="vector1" /> onto <paramref name="vector2" />.</returns>
        /// <remarks>
        ///     <para>
        ///         The scalar projection is also known as the scalar resolute of the first vector in the direction of the second
        ///         vector.
        ///     </para>
        ///     <para>
        ///         For any two vectors, the scalar projection is defined as: <c>vector1.Dot(vector2) / Length(vector2)</c>. The
        ///         result of this calculation, plus or minus some margin to account for floating point error, is equal to:
        ///         <c>Length(vector1) * System.Math.Cos(theta)</c>, where <c>theta</c> is the angle in radians between
        ///         <paramref name="vector1" /> and <paramref name="vector2" />.
        ///     </para>
        ///     <para>
        ///         The value of the scalar projection can tell us the following things:
        ///         <list type="bullet">
        ///             <item>
        ///                 <description>
        ///                     If <c>vector1.ScalarProjectOnto(vector2) &gt;= 0</c>, the angle between <paramref name="vector1" />
        ///                     and <paramref name="vector2" /> is between 0 degrees (exclusive) and 90 degrees (inclusive).
        ///                 </description>
        ///             </item>
        ///             <item>
        ///                 <description>
        ///                     If <c>vector1.ScalarProjectOnto(vector2) &lt; 0</c>, the angle between <paramref name="vector1" />
        ///                     and <paramref name="vector2" /> is between 90 degrees (exclusive) and 180 degrees (inclusive).
        ///                 </description>
        ///             </item>
        ///         </list>
        ///     </para>
        /// </remarks>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static float ScalarProjectOnto(this Vector2 vector1, Vector2 vector2)
        {
            var dotNumerator = vector1.X*vector2.X + vector1.Y*vector2.Y;
            var lengthSquaredDenominator = vector2.X*vector2.X + vector2.Y*vector2.Y;
            return dotNumerator/(float) Math.Sqrt(lengthSquaredDenominator);
        }

        /// <summary>
        ///     Calculates the vector projection of one vector onto another. The vector projection returns the orthogonal
        ///     projection of the first vector onto a straight line parallel to the second vector.
        /// </summary>
        /// <param name="vector1">The first vector.</param>
        /// <param name="vector2">The second vector.</param>
        /// <returns>The vector projection of <paramref name="vector1" /> onto <paramref name="vector2" />.</returns>
        /// <remarks>
        ///     <para>
        ///         The vector projection is also known as the vector component or vector resolute of the first vector in the
        ///         direction of the second vector.
        ///     </para>
        ///     <para>
        ///         For any two vectors, the vector projection is defined as:
        ///         <c>( vector1.Dot(vector2) / Length(vector2)^2 ) * vector2</c>.
        ///         The
        ///         result of this calculation, plus or minus some margin to account for floating point error, is equal to:
        ///         <c>( Length(vector1) * System.Math.Cos(theta) ) * vector2 / Length(vector2)</c>, where <c>theta</c> is the
        ///         angle in radians between <paramref name="vector1" /> and <paramref name="vector2" />.
        ///     </para>
        ///     <para>
        ///         This function is easier to compute than <see cref="ScalarProjectOnto" /> since it does not use a square root.
        ///         When the vector projection and the scalar projection is required, consider using this function; the scalar
        ///         projection can be obtained by taking the length of the projection vector.
        ///     </para>
        /// </remarks>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 ProjectOnto(this Vector2 vector1, Vector2 vector2)
        {
            var dotNumerator = vector1.X*vector2.X + vector1.Y*vector2.Y;
            var lengthSquaredDenominator = vector2.X*vector2.X + vector2.Y*vector2.Y;
            return dotNumerator/lengthSquaredDenominator*vector2;
        }

#if FNA
        // MomoGame compatibility layer

        /// <summary>
        /// Gets a Point representation for this Vector2.
        /// </summary>
        /// <returns>A Point representation for this Vector2.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Point ToPoint(this Vector2 value)
        {
            return new Point((int)value.X, (int)value.Y);
        }

        /// <summary>
        /// Gets a Vector2 representation for this Point.
        /// </summary>
        /// <returns>A Vector2 representation for this Point.</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static Vector2 ToVector2(this Point value)
        {
            return new Vector2(value.X, value.Y);
        }
#endif
    }
}