// 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) 2018 by via donau
//   – Österreichische Wasserstraßen-Gesellschaft mbH
// Software engineering by Intevation GmbH
//
// Author(s):
//  * Sascha L. Teichmann <sascha.teichmann@intevation.de>

package octree

import (
	"math"
	"sort"
)

const numEntries = 8

type STRTree struct {
	tin    *Tin
	index  []int32
	bboxes []Box2D
}

func (s *STRTree) Build(t *Tin) {

	s.tin = t

	all := make([]int32, len(t.Triangles))

	for i := range all {
		all[i] = int32(i)
	}

	s.index = append(s.index, 0)

	root := s.build(all)

	s.index[0] = root
}

func (s *STRTree) Clip(p *Polygon) map[int32]struct{} {

	removed := make(map[int32]struct{})

	stack := []int32{s.index[0]}

	vertices := s.tin.Vertices

	for len(stack) > 0 {
		top := stack[len(stack)-1]
		stack = stack[:len(stack)-1]

		if top > 0 { // node
			switch p.IntersectionBox2D(s.bbox(top)) {
			case IntersectionInside:
				// all triangles are inside polygon
			case IntersectionOutSide:
				// all triangles are outside polygon
				s.allTriangles(top, removed)
			default:
				// mixed bag
				for i, n := int32(0), s.index[top+1]; i < n; i++ {
					stack = append(stack, s.index[top+2+i])
				}
			}
		} else { // leaf
			top = -top - 1
			for i, n := int32(0), s.index[top+1]; i < n; i++ {
				idx := s.index[top+2+i]
				ti := s.tin.Triangles[idx]
				t := Triangle{
					vertices[ti[0]],
					vertices[ti[1]],
					vertices[ti[2]],
				}
				if p.IntersectionWithTriangle(&t) != IntersectionInside {
					removed[idx] = struct{}{}
				}
			}
		}
	}

	return removed
}

func (s *STRTree) allTriangles(pos int32, tris map[int32]struct{}) {
	stack := []int32{pos}
	for len(stack) > 0 {
		top := stack[len(stack)-1]
		stack = stack[:len(stack)-1]
		if top > 0 { // node
			for i, n := int32(0), s.index[top+1]; i < n; i++ {
				stack = append(stack, s.index[top+2+i])
			}
		} else { // leaf
			top = -top - 1
			for i, n := int32(0), s.index[top+1]; i < n; i++ {
				tris[s.index[top+2+i]] = struct{}{}
			}
		}
	}
}

func (s *STRTree) build(items []int32) int32 {
	sort.Slice(items, func(i, j int) bool {
		ti := s.tin.Triangles[items[i]]
		tj := s.tin.Triangles[items[j]]
		return s.tin.Vertices[ti[0]].X < s.tin.Vertices[tj[0]].X
	})

	P := int(math.Ceil(float64(len(items)) / float64(numEntries)))
	S := int(math.Ceil(math.Sqrt(float64(P))))

	slices := strSplit(items, S)

	leaves := strJoin(
		slices, S,
		func(i, j int32) bool {
			ti := s.tin.Triangles[i]
			tj := s.tin.Triangles[j]
			return s.tin.Vertices[ti[0]].Y < s.tin.Vertices[tj[0]].Y
		},
		s.allocLeaf,
	)

	return s.buildNodes(leaves)
}

func (s *STRTree) buildNodes(items []int32) int32 {

	if len(items) <= numEntries {
		return s.allocNode(items)
	}

	sort.Slice(items, func(i, j int) bool {
		return s.bbox(items[i]).X1 < s.bbox(items[j]).X1
	})

	P := int(math.Ceil(float64(len(items)) / float64(numEntries)))
	S := int(math.Ceil(math.Sqrt(float64(P))))

	slices := strSplit(items, S)

	nodes := strJoin(
		slices, S,
		func(i, j int32) bool { return s.bbox(i).Y1 < s.bbox(j).Y1 },
		s.allocNode,
	)

	return s.buildNodes(nodes)
}

func (s *STRTree) bbox(idx int32) Box2D {
	if idx < 0 { // Don't care if leaf or node.
		idx = -idx - 1
	}
	return s.bboxes[s.index[idx]]
}

func strSplit(items []int32, S int) [][]int32 {
	sm := S * numEntries
	slices := make([][]int32, S)
	for i := range slices {
		var n int
		if l := len(items); l < sm {
			n = l
		} else {
			n = sm
		}
		slices[i] = items[:n]
		items = items[n:]
	}
	return slices
}

func strJoin(
	slices [][]int32, S int,
	less func(int32, int32) bool,
	alloc func([]int32) int32,
) []int32 {
	nodes := make([]int32, 0, S*S)

	for _, slice := range slices {
		sort.Slice(slice, func(i, j int) bool {
			return less(slice[i], slice[j])
		})

		for len(slice) > 0 {
			var n int
			if l := len(slice); l >= numEntries {
				n = numEntries
			} else {
				n = l
			}
			nodes = append(nodes, alloc(slice[:n]))
			slice = slice[n:]
		}
	}
	return nodes
}

func (s *STRTree) allocNode(items []int32) int32 {
	pos := len(s.index)
	s.index = append(s.index, 0, int32(len(items)))
	s.index = append(s.index, items...)
	if len(items) > 0 {
		box := s.bbox(items[0])
		for i := 1; i < len(items); i++ {
			box = box.Union(s.bbox(items[i]))
		}
		s.index[pos] = int32(s.allocBBox(box))
	}
	return int32(pos)
}

func (s *STRTree) allocBBox(box Box2D) int {
	pos := len(s.bboxes)
	s.bboxes = append(s.bboxes, box)
	return pos
}

func (s *STRTree) allocLeaf(items []int32) int32 {
	pos := len(s.index)
	s.index = append(s.index, 0, int32(len(items)))
	s.index = append(s.index, items...)
	if len(items) > 0 {
		vertices := s.tin.Vertices
		ti := s.tin.Triangles[items[0]]
		t := Triangle{
			vertices[ti[0]],
			vertices[ti[1]],
			vertices[ti[2]],
		}
		box := t.BBox()
		for i := 1; i < len(items); i++ {
			it := items[i]
			ti := s.tin.Triangles[it]
			t := Triangle{
				vertices[ti[0]],
				vertices[ti[1]],
				vertices[ti[2]],
			}
			box = box.Union(t.BBox())
		}
		s.index[pos] = int32(s.allocBBox(box))
	}
	return int32(-(pos + 1))
}