// This is Free Software under GNU Affero General Public License v >= 3.0
// without warranty, see README.md and license for details.
//
// SPDX-License-Identifier: AGPL-3.0-or-later
// License-Filename: LICENSES/AGPL-3.0.txt
//
// Copyright (C) 2024 by via donau
//   – Österreichische Wasserstraßen-Gesellschaft mbH
// Software engineering by Intevation GmbH
//
// Author(s):
//  * Sascha L. Teichmann <sascha.teichmann@intevation.de>

package mesh

func (s *STRTree) optimizeForSerializationV2() {
	s.removeUnusedTriangles()
	// TODO: Implement me!
}

// removeUnusedTriangles removes all triangles from the
// TIN that are not registered in the spatial index.
func (s *STRTree) removeUnusedTriangles() {
	used := make([]bool, len(s.tin.Triangles))
	unused := len(used)
	s.allTriangleIndices(func(indices []int32) {
		for _, idx := range indices {
			used[idx] = true
			unused-- // They only occur once in the spatial index.
		}
	})
	if unused <= 0 {
		return
	}
	newTris := make([][]int32, 0, len(s.tin.Triangles)-unused)
	remap := map[int32]int32{}
	for idx, tri := range s.tin.Triangles {
		if used[idx] {
			remap[int32(idx)] = int32(len(newTris))
			newTris = append(newTris, tri)
		}
	}
	s.tin.Triangles = newTris
	// Update the spatial index as the gaps are now closed.
	s.allTriangleIndices(func(indices []int32) {
		for i, idx := range indices {
			indices[i] = remap[idx]
		}
	})
}