handle_map_style.go

package server

import (
	"encoding/json"

	"net/http"
	"net/url"
	"strconv"
	"strings"

	"github.com/dimfeld/httptreemux"
	"gopkg.in/go-playground/colors.v1"

	"github.com/go-spatial/geom"
	"github.com/go-spatial/tegola/atlas"
	"github.com/go-spatial/tegola/internal/log"
	"github.com/go-spatial/tegola/mapbox/style"
)

type HandleMapStyle struct {
	// required
	mapName string
	// the requests extension defaults to "json"
	extension string
}

// returns details about a map according to the
// tileJSON spec (https://github.com/mapbox/tilejson-spec/tree/master/2.1.0)
//
// URI scheme: /capabilities/:map_name.json
// 	map_name - map name in the config file
func (req HandleMapStyle) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	var err error

	params := httptreemux.ContextParams(r.Context())

	// read the map_name value from the request
	mapName := params["map_name"]
	mapNameParts := strings.Split(mapName, ".")

	req.mapName = mapNameParts[0]
	// check if we have a provided extension
	if len(mapNameParts) > 2 {
		req.extension = mapNameParts[len(mapNameParts)-1]
	} else {
		req.extension = "json"
	}

	// lookup our Map
	m, err := atlas.GetMap(req.mapName)
	if err != nil {
		log.Errorf("map (%v) not configured. check your config file", req.mapName)
		http.Error(w, "map ("+req.mapName+") not configured. check your config file", http.StatusNotFound)
		return
	}

	// if we have a debug param add it to our URLs
	debugQuery := url.Values{}
	if r.URL.Query().Get("debug") == "true" {
		debugQuery.Set("debug", "true")

		// update our map to include the debug layers
		m = m.AddDebugLayers()
	}

	mapboxStyle := style.Root{
		Name:    m.Name,
		Version: style.Version,
		Center:  [2]float64{m.Center[0], m.Center[1]},
		Zoom:    m.Center[2],
		Sources: map[string]style.Source{
			req.mapName: {
				Type: style.SourceTypeVector,
				URL:  buildCapabilitiesURL(r, []string{"capabilities", req.mapName + ".json"}, debugQuery),
			},
		},
		Layers: []style.Layer{},
	}

	// determining the min and max zoom for this map
	for _, l := range m.Layers {
		// check if the layer already exists in our slice. this can happen if the config
		// is using the "name" param for a layer to override the providerLayerName
		var skip bool
		for i := range mapboxStyle.Layers {
			if mapboxStyle.Layers[i].ID == l.MVTName() {
				skip = true
				break
			}
		}
		// entry for layer already exists. move on
		if skip {
			continue
		}

		// build our vector layer details
		layer := style.Layer{
			ID:          l.MVTName(),
			Source:      req.mapName,
			SourceLayer: l.MVTName(),
			Layout: &style.LayerLayout{
				Visibility: style.LayoutVisible,
			},
		}

		// chose our paint type based on the geometry type
		switch l.GeomType.(type) {
		case geom.Point, geom.MultiPoint:
			layer.Type = style.LayerTypeCircle
			layer.Paint = &style.LayerPaint{
				CircleRadius: 3,
				CircleColor:  stringToColorHex(l.MVTName()),
			}
		case geom.Line, geom.LineString, geom.MultiLineString:
			layer.Type = style.LayerTypeLine
			layer.Paint = &style.LayerPaint{
				LineColor: stringToColorHex(l.MVTName()),
			}
		case geom.Polygon, geom.MultiPolygon:
			layer.Type = style.LayerTypeFill
			hexColor := stringToColorHex(l.MVTName())

			hex, err := colors.ParseHEX(hexColor)
			if err != nil {
				log.Errorf("error parsing hex color (%v)", hexColor)
				hex, _ = colors.ParseHEX("#fff") // default to white on error
			}

			rgba := hex.ToRGBA()
			// set the opacity to 10%
			rgba.A = 0.10

			layer.Paint = &style.LayerPaint{
				FillColor:        rgba.String(),
				FillOutlineColor: hexColor,
			}
		default:
			log.Infof("unable to infer geometry type for providerLayerName: %v. style definition not generated", l.ProviderLayerName)
			continue
		}

		// add our layer to our tile layer response
		mapboxStyle.Layers = append(mapboxStyle.Layers, layer)
	}

	// mimetype for protocol buffers
	w.Header().Add("Content-Type", "application/json")

	// cache control headers (no-cache)
	w.Header().Add("Cache-Control", "no-cache, no-store, must-revalidate")
	w.Header().Add("Pragma", "no-cache")
	w.Header().Add("Expires", "0")

	if err = json.NewEncoder(w).Encode(mapboxStyle); err != nil {
		log.Errorf("error encoding tileJSON for map (%v)", req.mapName)
	}
}

// port of https://stackoverflow.com/questions/3426404/create-a-hexadecimal-colour-based-on-a-string-with-javascript
func stringToColorHex(str string) string {
	var hash uint
	for i := range []rune(str) {
		hash = uint(str[i]) + ((hash << 5) - hash)
	}
	var color string
	for i := 0; i < 3; i++ {
		value := (hash >> (uint(i) * 8)) & 0xFF
		val := "00" + strconv.FormatUint(uint64(value), 16)
		color += val[len(val)-2:]
	}
	return "#" + color
}