package dem

import (
	"math"

	"github.com/airbusgeo/godal"
	log "github.com/sirupsen/logrus"
)

type Dem1Km struct {
	File          string
	LT            [][]float32
	width, height int
	wUnit         float32 // degree per pixel
	hUnit         float32 // degree per pixel
}

var Dem1KmLT *Dem1Km

func NewDem1Km(file string) *Dem1Km {
	d := &Dem1Km{
		File: file,
	}

	if err := d.Load(); err != nil {
		log.Error("cannot load DEM file", err)
	}
	return d
}

func (d *Dem1Km) Load() error {
	hDataset, err := godal.Open(d.File)
	if err != nil {
		return err
	}

	band := hDataset.Bands()[0]

	structure := band.Structure()

	for y := 1; y <= structure.SizeY; y++ {
		scanline := make([]float32, structure.SizeX)
		err = band.Read(0, y, scanline, structure.SizeX, 1)
		if err != nil {
			return err
		}
		d.LT = append(d.LT, scanline)
	}

	d.wUnit = 360.0 / float32(structure.SizeX)
	d.hUnit = 180.0 / float32(structure.SizeY)
	d.width = structure.SizeX
	d.height = structure.SizeY

	return nil
}

func (d *Dem1Km) Elevation(lng, lat float64) float32 {
	lng = math.Abs(lng + 180.0)
	lat = math.Abs(lat - 90.0)
	w := int(lng / float64(d.wUnit))
	h := int(lat / float64(d.hUnit))

	if w > d.width-1 || h > d.height-1 {
		return 0.0
	}

	return d.LT[h][w]

}