// ReSharper disable MemberCanBePrivate.Global

using System;
using RGB.NET.Core;

namespace RGB.NET.Presets.Helper;

/// <summary>
/// Offers some extensions and helper-methods for gradient related things.
/// </summary>
public static class GradientHelper
{
    #region Methods

    // Based on https://web.archive.org/web/20170125201230/https://dotupdate.wordpress.com/2008/01/28/find-the-color-of-a-point-in-a-lineargradientbrush/
    /// <summary>
    /// Calculates the offset of an specified <see cref="Point"/> on an gradient.
    /// </summary>
    /// <param name="startPoint">The start <see cref="Point"/> of the gradient.</param>
    /// <param name="endPoint">The end <see cref="Point"/> of the gradient.</param>
    /// <param name="point">The <see cref="Point"/> on the gradient to which the offset is calculated.</param>
    /// <returns>The offset of the <see cref="Point"/> on the gradient.</returns>
    public static float CalculateLinearGradientOffset(Point startPoint, Point endPoint, Point point)
    {
        Point intersectingPoint;
        if (startPoint.Y.EqualsInTolerance(endPoint.Y)) // Horizontal case
            intersectingPoint = new Point(point.X, startPoint.Y);

        else if (startPoint.X.EqualsInTolerance(endPoint.X)) // Vertical case
            intersectingPoint = new Point(startPoint.X, point.Y);

        else // Diagonal case
        {
            float slope = (endPoint.Y - startPoint.Y) / (endPoint.X - startPoint.X);
            float orthogonalSlope = -1 / slope;

            float startYIntercept = startPoint.Y - (slope * startPoint.X);
            float pointYIntercept = point.Y - (orthogonalSlope * point.X);

            float intersectingPointX = (pointYIntercept - startYIntercept) / (slope - orthogonalSlope);
            float intersectingPointY = (slope * intersectingPointX) + startYIntercept;
            intersectingPoint = new Point(intersectingPointX, intersectingPointY);
        }

        // Calculate distances relative to the vector start
        float intersectDistance = CalculateDistance(intersectingPoint, startPoint, endPoint);
        float gradientLength = CalculateDistance(endPoint, startPoint, endPoint);

        return intersectDistance / gradientLength;
    }

    // Based on https://web.archive.org/web/20170125201230/https://dotupdate.wordpress.com/2008/01/28/find-the-color-of-a-point-in-a-lineargradientbrush/
    /// <summary>
    /// Returns the signed magnitude of a <see cref="Point"/> on a vector.
    /// </summary>
    /// <param name="point">The <see cref="Point"/> on the vector of which the magnitude should be calculated.</param>
    /// <param name="origin">The origin of the vector.</param>
    /// <param name="direction">The direction of the vector.</param>
    /// <returns>The signed magnitude of a <see cref="Point"/> on a vector.</returns>
    public static float CalculateDistance(Point point, Point origin, Point direction)
    {
        float distance = CalculateDistance(point, origin);

        return (((point.Y < origin.Y) && (direction.Y > origin.Y))
             || ((point.Y > origin.Y) && (direction.Y < origin.Y))
             || ((point.Y.EqualsInTolerance(origin.Y)) && (point.X < origin.X) && (direction.X > origin.X))
             || ((point.Y.EqualsInTolerance(origin.Y)) && (point.X > origin.X) && (direction.X < origin.X)))
                   ? -distance : distance;
    }

    /// <summary>
    /// Calculated the distance between two <see cref="Point"/>.
    /// </summary>
    /// <param name="point1">The first <see cref="Point"/>.</param>
    /// <param name="point2">The second <see cref="Point"/>.</param>
    /// <returns>The distance between the two <see cref="Point"/>.</returns>
    public static float CalculateDistance(Point point1, Point point2)
    {
        float x = point1.X - point2.X;
        float y = point1.Y - point2.Y;
        return MathF.Sqrt((y * y) + (x * x));
    }

    #endregion
}