// Original CSG.JS library by Evan Wallace (http://madebyevan.com), under the MIT license.
// GitHub: https://github.com/evanw/csg.js/
//
// C++ port by Tomasz Dabrowski (http://28byteslater.com), under the MIT license.
// GitHub: https://github.com/dabroz/csgjs-cpp/
//
// C# port by Karl Henkel (parabox.co), under MIT license.
//
// Constructive Solid Geometry (CSG) is a modeling technique that uses Boolean
// operations like union and intersection to combine 3D solids. This library
// implements CSG operations on meshes elegantly and concisely using BSP trees,
// and is meant to serve as an easily understandable implementation of the
// algorithm. All edge cases involving overlapping coplanar polygons in both
// solids are correctly handled.

using UnityEngine;
using System.Collections.Generic;

namespace UnityEngine.ProBuilder.Csg
{
    /// <summary>
    /// Base class for CSG operations. Contains GameObject level methods for Subtraction, Intersection, and Union operations.
    /// The GameObjects passed to these functions will not be modified.
    /// </summary>
    static class Boolean
    {
        // Tolerance used by `splitPolygon()` to decide if a point is on the plane.
        internal const float k_Epsilon = 0.00001f;

        /// <summary>
        /// Returns a new mesh by merging @lhs with @rhs.
        /// </summary>
        /// <param name="lhs">The base mesh of the boolean operation.</param>
        /// <param name="rhs">The input mesh of the boolean operation.</param>
        /// <returns>A new mesh if the operation succeeds, or null if an error occurs.</returns>
        public static Model Union(GameObject lhs, GameObject rhs)
        {
            Model csg_model_a = new Model(lhs);
            Model csg_model_b = new Model(rhs);

            Node a = new Node(csg_model_a.ToPolygons());
            Node b = new Node(csg_model_b.ToPolygons());

            List<Polygon> polygons = Node.Union(a, b).AllPolygons();

            return new Model(polygons);
        }

        /// <summary>
        /// Returns a new mesh by subtracting @lhs with @rhs.
        /// </summary>
        /// <param name="lhs">The base mesh of the boolean operation.</param>
        /// <param name="rhs">The input mesh of the boolean operation.</param>
        /// <returns>A new mesh if the operation succeeds, or null if an error occurs.</returns>
        public static Model Subtract(GameObject lhs, GameObject rhs)
        {
            Model csg_model_a = new Model(lhs);
            Model csg_model_b = new Model(rhs);

            Node a = new Node(csg_model_a.ToPolygons());
            Node b = new Node(csg_model_b.ToPolygons());

            List<Polygon> polygons = Node.Subtract(a, b).AllPolygons();

            return new Model(polygons);
        }

        /// <summary>
        /// Returns a new mesh by intersecting @lhs with @rhs.
        /// </summary>
        /// <param name="lhs">The base mesh of the boolean operation.</param>
        /// <param name="rhs">The input mesh of the boolean operation.</param>
        /// <returns>A new mesh if the operation succeeds, or null if an error occurs.</returns>
        public static Model Intersect(GameObject lhs, GameObject rhs)
        {
            Model csg_model_a = new Model(lhs);
            Model csg_model_b = new Model(rhs);

            Node a = new Node(csg_model_a.ToPolygons());
            Node b = new Node(csg_model_b.ToPolygons());

            List<Polygon> polygons = Node.Intersect(a, b).AllPolygons();

            return new Model(polygons);
        }
    }
}