mtsatellite/cmd/mtwebmapper/players.go

package main

import (
	"bufio"
	"bytes"
	"encoding/json"
	"html/template"
	"log"
	"net/http"
	"os"
	"sync"
	"time"
)

const sleepInterval = time.Second * 5

var geoJSONTmpl = template.Must(template.New("geojson").Parse(
	`{ "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates": [{{.Z}}, {{.X}}]
  },
  "properties": {
	  "name": "{{.Name | html }}"
  }
}`))

type player struct {
	X    float64 `json:"x"`
	Y    float64 `json:"y"`
	Z    float64 `json:"z"`
	Name string  `json:"name"`
}

type players struct {
	fifo string
	wsf  *websocketForwarder
	pls  []*player
	mu   sync.RWMutex
}

func newPlayers(fifo string, wsf *websocketForwarder) *players {
	return &players{fifo: fifo, wsf: wsf, pls: []*player{}}
}

func (p *player) MarshalJSON() ([]byte, error) {
	var buf bytes.Buffer
	if err := geoJSONTmpl.Execute(&buf, p); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

func (ps *players) readFromFIFO() ([]*player, error) {
	file, err := os.Open(ps.fifo)
	if err != nil {
		return nil, err
	}
	defer file.Close()
	reader := bufio.NewReader(file)
	decoder := json.NewDecoder(reader)
	var pls []*player

	if err = decoder.Decode(&pls); err != nil {
		return nil, err
	}
	return pls, nil
}

func (ps *players) run() {
	for {
		pls, err := ps.readFromFIFO()
		if err != nil {
			time.Sleep(sleepInterval)
			continue
		}
		ps.mu.Lock()
		ps.pls = pls
		ps.mu.Unlock()
		if ps.wsf != nil {
			// TODO: Throttle this!
			ps.wsf.BroadcastPlayers(pls)
		}
	}
}

func (ps *players) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
	rw.Header().Set("Content-Type", "application/json")
	var pls []*player
	ps.mu.RLock()
	pls = ps.pls
	ps.mu.RUnlock()
	encoder := json.NewEncoder(rw)
	if err := encoder.Encode(pls); err != nil {
		log.Printf("error: sending JSON failed: %s\n", err)
	}
}