namespace Syntriax.Engine.Core;

/// <summary>
/// Represents an infinite ray in 2D space.
/// </summary>
/// <param name="Origin">The <see cref="Vector2D"/> in 2D space where the ray starts from.</param>
/// <param name="Direction">Normalized <see cref="Vector2D"/> indicating the ray's is direction.</param> 
public readonly struct Ray2D(Vector2D Origin, Vector2D Direction)
{
    /// <summary>
    /// The starting point of the <see cref="Ray2D"/>.
    /// </summary>
    public readonly Vector2D Origin = Origin;

    /// <summary>
    /// The direction in which the <see cref="Ray2D"/> points. Should be a normalized vector.
    /// </summary>
    public readonly Vector2D Direction = Direction;

    /// <summary>
    /// Gets a <see cref="Ray2D"/> with the same origin but with the direction reversed.
    /// </summary>
    public readonly Ray2D Reversed => new(Origin, -Direction);

    public static implicit operator Ray2D(Line2D line) => new(line.From, line.From.FromTo(line.To).Normalized);

    /// <summary>
    /// Constructs a <see cref="Line2D"/> from a <see cref="Ray2D"/>, extending from its origin in the <see cref="Ray2D"/>'s direction for a given distance.
    /// </summary>
    /// <param name="ray">The source <see cref="Ray2D"/>.</param>
    /// <param name="distance">The length of the line segment to create from the <see cref="Ray2D"/>.</param>
    /// <returns>A <see cref="Line2D"/> representing the segment of the <see cref="Ray2D"/>.</returns>
    public static Line2D GetLine(Ray2D ray, float distance)
        => new(ray.Origin, ray.Origin + ray.Direction * distance);

    /// <summary>
    /// Evaluates the point on the <see cref="Ray2D"/> at a specified distance from its origin.
    /// </summary>
    /// <param name="ray">The <see cref="Ray2D"/> to evaluate.</param>
    /// <param name="distanceFromOrigin">The distance from the origin along the <see cref="Ray2D"/>'s direction.</param>
    /// <returns>A <see cref="Vector2D"/> representing the point at the given distance on the <see cref="Ray2D"/>.</returns>
    public static Vector2D Evaluate(Ray2D ray, float distanceFromOrigin)
        => ray.Origin + ray.Direction * distanceFromOrigin;

    /// <summary>
    /// Calculates the closest point on the <see cref="Ray2D"/> to the specified point.
    /// </summary>
    public static Vector2D ClosestPointTo(Ray2D ray, Vector2D point)
    {
        Vector2D originToPoint = ray.Origin.FromTo(point);

        float dot = ray.Direction.Dot(originToPoint);

        return ray.Origin + ray.Direction * dot;
    }
}

/// <summary>
/// Provides extension methods for the <see cref="Ray2D"/> struct.
/// </summary>
public static class Ray2DExtensions
{
    /// <inheritdoc cref="Ray2D.GetLine(Ray2D, float) />
    public static Line2D ToLine(this Ray2D ray, float distance) => Ray2D.GetLine(ray, distance);

    /// <inheritdoc cref="Ray2D.Evaluate(Ray2D, float) />
    public static Vector2D Evaluate(this Ray2D ray, float distanceFromOrigin) => Ray2D.Evaluate(ray, distanceFromOrigin);

    /// <inheritdoc cref="Ray2D.ClosestPointTo(Ray2D, Vector2D) />
    public static Vector2D ClosestPointTo(this Ray2D ray, Vector2D point) => Ray2D.ClosestPointTo(ray, point);
}