// 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 mesh

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"math"

	"gemma.intevation.de/gemma/pkg/log"
	"gemma.intevation.de/gemma/pkg/models"
	"gemma.intevation.de/gemma/pkg/wkb"
)

var (
	errNoByteSlice   = errors.New("not a byte slice")
	errTooLessPoints = errors.New("too less points")
)

// Tin stores a mesh of triangles with common vertices.
type Tin struct {
	// EPSG holds the projection.
	EPSG uint32
	// Vertices are the shared vertices.
	Vertices []Vertex
	// Triangles are the triangles.
	Triangles [][]int32

	// Min is the lower left corner of the bbox.
	Min Vertex
	// Max is the upper right corner of the bbox.
	Max Vertex
}

// Clip returns a map of ids of triangles which are not inside the
// given polygon.
func (t *Tin) Clip(polygon *Polygon) map[int32]struct{} {
	var tree STRTree
	tree.Build(t)
	return tree.Clip(polygon)
}

// FromWKB constructs the TIN from a WKB representation.
// Shared vertices are identified and referenced by the
// same index.
func (t *Tin) FromWKB(data []byte) error {
	log.Infof("data length %d\n", len(data))

	r := bytes.NewReader(data)

	endian, err := r.ReadByte()

	var order binary.ByteOrder

	switch {
	case err != nil:
		return err
	case endian == wkb.NDR:
		order = binary.LittleEndian
	case endian == wkb.XDR:
		order = binary.BigEndian
	default:
		return fmt.Errorf("unknown byte order %x", endian)
	}

	var geomType uint32
	err = binary.Read(r, order, &geomType)

	switch {
	case err != nil:
		return err
	case geomType != wkb.TinZ:
		return fmt.Errorf("unknown geometry type %x", geomType)
	}

	var num uint32
	if err = binary.Read(r, order, &num); err != nil {
		return err
	}

	vertices := make([]Vertex, 0, 100000)

	var v Vertex

	v2i := make(map[Vertex]int32, 100000)

	var indexPool []int32

	allocIndices := func() []int32 {
		if len(indexPool) == 0 {
			indexPool = make([]int32, 3*8*1024)
		}
		ids := indexPool[:3]
		indexPool = indexPool[3:]
		return ids
	}

	var triangles [][]int32

	min := Vertex{math.MaxFloat64, math.MaxFloat64, math.MaxFloat64}
	max := Vertex{-math.MaxFloat64, -math.MaxFloat64, -math.MaxFloat64}

	for i := uint32(0); i < num; i++ {

		endian, err = r.ReadByte()
		switch {
		case err != nil:
			return err
		case endian == wkb.NDR:
			order = binary.LittleEndian
		case endian == wkb.XDR:
			order = binary.BigEndian
		default:
			return fmt.Errorf("unknown byte order %x", endian)
		}

		err = binary.Read(r, order, &geomType)
		switch {
		case err != nil:
			return err
		case geomType != wkb.TriangleZ:
			return fmt.Errorf("unknown geometry type %d", geomType)
		}

		var rings uint32
		if err = binary.Read(r, order, &rings); err != nil {
			return err
		}
		triangle := allocIndices()

		for ring := uint32(0); ring < rings; ring++ {
			var npoints uint32
			if err = binary.Read(r, order, &npoints); err != nil {
				return err
			}

			if npoints < 3 {
				return errTooLessPoints
			}

			for p := uint32(0); p < npoints; p++ {
				var x, y, z uint64
				for _, addr := range []*uint64{&x, &y, &z} {
					if err = binary.Read(r, order, addr); err != nil {
						return err
					}
				}
				if p >= 3 || ring >= 1 {
					// Don't store the forth point.
					continue
				}
				// Do this conversion later to spare reflect calls
				// and allocs in binary.Read.
				v.X = math.Float64frombits(x)
				v.Y = math.Float64frombits(y)
				v.Z = math.Float64frombits(z)
				idx, found := v2i[v]
				if !found {
					idx = int32(len(vertices))
					v2i[v] = idx
					vertices = append(vertices, v)
					min.Minimize(v)
					max.Maximize(v)
				}
				triangle[p] = idx
			}
		}
		triangles = append(triangles, triangle)
	}

	log.Infof("bbox: [[%f, %f], [%f, %f]]\n",
		min.X, min.Y, max.X, max.Y)

	*t = Tin{
		EPSG:      models.WGS84,
		Vertices:  vertices,
		Triangles: triangles,
		Min:       min,
		Max:       max,
	}

	return nil
}

// Scan implements the sql.Scanner interface.
func (t *Tin) Scan(raw any) error {
	if raw == nil {
		return nil
	}
	data, ok := raw.([]byte)
	if !ok {
		return errNoByteSlice
	}
	return t.FromWKB(data)
}