// This source code is property of the Computer Graphics and Visualization
// chair of the TU Dresden. Do not distribute!
// Copyright (C) CGV TU Dresden - All Rights Reserved

#include "SurfaceArea.h"

#include <iostream>

struct SimpleFace {
	std::vector<OpenMesh::HalfedgeHandle> he_handles;

	bool is_triangulated() {
		if (he_handles.size() != 3) {
			return false;
		}

		return true;
	}
};

struct Triangle {
	Triangle(std::vector<OpenMesh::Vec3f> vpoints)  {
		if (vpoints.size() != 3) {
			abort();
		}

		for (int i = 0; i < 3; i++) {
			points[i] = vpoints[i];
		}
	}

	OpenMesh::Vec3f points[3];
};

struct Triangles {
	Triangles(std::vector<SimpleFace> simple_faces, const HEMesh& m) {
		for (auto simple_face: simple_faces) {
			std::vector<OpenMesh::Vec3f> points = face_points(simple_face, m);
			triangles.emplace_back(points);
		}
	}

	std::vector<OpenMesh::Vec3f> face_points(SimpleFace& simple_face, const HEMesh& m) {
		std::vector<OpenMesh::Vec3f> points;

		for (auto he : simple_face.he_handles) {
			OpenMesh::VertexHandle vertex_handle = m.from_vertex_handle(he);

			points.emplace_back(m.point(vertex_handle));
		}

		return points;
	}

	float surface_area() {
		float surface_area = 0.0f;

		for (Triangle& triangle : triangles) {
			OpenMesh::Vec3f p1 = triangle.points[0];
			OpenMesh::Vec3f p2 = triangle.points[1];
			OpenMesh::Vec3f p3 = triangle.points[2];

			/*

						3
					  /	|  \
				    /	|h   \
				  /		|	   \
				1 -------------- 2
						  g

				surface area = (g * h) / 2;
			*/

			OpenMesh::Vec3f g_vec = p1 - p2;
			float g = g_vec.length();

			float h = 0.0f;

			surface_area += (g * h) / 2;
		}

		return surface_area;
	}

	std::vector<Triangle> triangles;
};

bool gather_faces(const HEMesh& m, std::vector<SimpleFace>& simple_faces) {
	auto faces = m.all_faces();

	for (auto face_handle : faces) {
		HEMesh::ConstFaceHalfedgeIter fh_it = m.cfh_iter(face_handle);

		SimpleFace simple_face;

		for (; fh_it.is_valid(); ++fh_it) {
			simple_face.he_handles.emplace_back(*fh_it);
		}

		if (!simple_face.is_triangulated()) {
			return false;
		}

		simple_faces.emplace_back(simple_face);
	}

	return true;
}

float ComputeSurfaceArea(const HEMesh& _m)
{
	float area = 0;
	/* Task 2.2.2 */
	std::cout << "Area computation is not implemented." << std::endl;

	// copy mesh for mutability
	HEMesh private_mesh = _m;

	std::vector<SimpleFace> simple_faces;

	if (!gather_faces(private_mesh, simple_faces)) {
		simple_faces.clear();
		private_mesh.triangulate();

		if (!gather_faces(private_mesh, simple_faces)) {
			abort();
		}
	}

	Triangles triangles(simple_faces, private_mesh);

	area = triangles.surface_area();

	return area;
}