using System;
using System.Collections.Generic;

using Syntriax.Engine.Core;
using Syntriax.Engine.Physics2D.Primitives;

namespace Syntriax.Engine.Physics2D;

public static class PhysicsMath
{


    // Given three collinear points p, q, r, the function checks if 
    // point q lies on line segment 'pr' 
    public static bool OnSegment(Vector2D p, Vector2D q, Vector2D r)
    {
        if (q.X <= MathF.Max(p.X, r.X) && q.X >= MathF.Min(p.X, r.X) &&
            q.Y <= MathF.Max(p.Y, r.Y) && q.Y >= MathF.Min(p.Y, r.Y))
            return true;

        return false;
    }

    // To find orientation of ordered triplet (p, q, r). 
    // The function returns following values 
    // 0 --> p, q and r are collinear 
    // 1 --> Clockwise 
    // 2 --> Counterclockwise 
    public static int Orientation(Vector2D p, Vector2D q, Vector2D r)
    {
        // See https://www.geeksforgeeks.org/orientation-3-ordered-points/ 
        // for details of below formula. 
        float val = (q.Y - p.Y) * (r.X - q.X) -
                (q.X - p.X) * (r.Y - q.Y);

        if (val == 0) return 0; // collinear 

        return (val > 0) ? 1 : 2; // clock or counterclock wise 
    }

    public static float IntersectionParameterT(Vector2D p0, Vector2D p1, Vector2D q0, Vector2D q1)
        => ((q0.X - p0.X) * (p1.Y - p0.Y) - (q0.Y - p0.Y) * (p1.X - p0.X)) /
            ((q1.Y - q0.Y) * (p1.X - p0.X) - (q1.X - q0.X) * (p1.Y - p0.Y));


    public static bool ApproximatelyEquals(this float a, float b)
        => ApproximatelyEquals(a, b, float.Epsilon);
    public static bool ApproximatelyEquals(this Vector2D a, Vector2D b)
        => ApproximatelyEquals(a, b, float.Epsilon);
    public static bool ApproximatelyEquals(this Vector2D a, Vector2D b, float epsilon)
        => ApproximatelyEquals(a.X, b.X, epsilon) && ApproximatelyEquals(a.Y, b.Y, epsilon);
    public static bool ApproximatelyEquals(this float a, float b, float epsilon)
    {
        if (a == b)
            return true;

        const float floatNormal = (1 << 23) * float.Epsilon;
        float absA = MathF.Abs(a);
        float absB = MathF.Abs(b);
        float diff = MathF.Abs(a - b);

        if (a == 0.0f || b == 0.0f || diff < floatNormal)
            return diff < (epsilon * floatNormal);

        return diff / MathF.Min(absA + absB, float.MaxValue) < epsilon;
    }
}