nau-sidewalks/main.go

package main

import (
	"context"
	"embed"
	"encoding/json"
	"flag"
	"fmt"
	"io/fs"
	"log"
	"net/http"
	"os"
	"os/signal"
	"runtime/debug"
	"strconv"
	"sync"
	"syscall"
	"time"

	"git.chandlerswift.com/chandlerswift/nau-sidewalks/sidewalk"
)

//go:embed static
var embeddedFiles embed.FS

var buildInfoJSON []byte

func main() {
	devel := flag.Bool("devel", false, "Serve from ./static instead of embedded")
	port := flag.Int("port", 8000, "Port to listen on")
	dataFile := flag.String("datafile", "", "File to read sidewalk data from (required)")
	flag.Parse()
	if *dataFile == "" {
		panic("datafile arg is required")
	}

	sidewalkData, err := os.ReadFile(*dataFile)
	if err != nil {
		panic(err)
	}

	// Decode the JSON data
	var sidewalks []sidewalk.Sidewalk
	var sidewalksMutex sync.RWMutex
	if err := json.Unmarshal(sidewalkData, &sidewalks); err != nil {
		log.Fatalf("Error decoding JSON: %v", err)
	}
	sidewalksLen := len(sidewalks)

	// Serve static content
	if *devel {
		http.Handle("GET /", http.FileServer(http.Dir("./static")))
	} else {
		frontend, err := fs.Sub(embeddedFiles, "static")
		if err != nil {
			panic(err)
		}
		http.Handle("GET /", http.FileServer(http.FS(frontend)))
	}

	initializeBuildInfoJSON()
	http.HandleFunc("GET /api/version", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		w.Write(buildInfoJSON)
	})

	http.HandleFunc("GET /api/sidewalks", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		sidewalksMutex.RLock()
		json.NewEncoder(w).Encode(sidewalks)
		sidewalksMutex.RUnlock()
	})

	http.HandleFunc("POST /api/sidewalks/{id}", func(w http.ResponseWriter, r *http.Request) {
		err := r.ParseForm()
		if err != nil {
			http.Error(w, "Could not parse form", http.StatusInternalServerError)
			return
		}
		sidewalkID, err := strconv.Atoi(r.PathValue("id"))
		if err != nil || sidewalkID < 0 || sidewalkID >= sidewalksLen {
			http.Error(w, "Invalid id", http.StatusBadRequest)
			return
		}
		condition, err := strconv.Atoi(r.Form.Get("condition"))
		if err != nil {
			http.Error(w, "Invalid condition", http.StatusBadRequest)
			return
		}
		sidewalksMutex.Lock()
		sidewalks[sidewalkID].Condition = sidewalk.Condition(condition)
		sidewalks[sidewalkID].LastUpdated = time.Now()
		sidewalksMutex.Unlock()
		http.Redirect(w, r, "/", http.StatusSeeOther)
	})

	server := &http.Server{Addr: fmt.Sprintf(":%v", *port)}

	go func() {
		fmt.Printf("Serving %v sidewalks on :%v\n", sidewalksLen, *port)
		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			log.Fatalf("HTTP server error: %v", err)
		}
	}()

	// Listen for OS termination signals
	stop := make(chan os.Signal, 1)
	signal.Notify(stop, os.Interrupt, syscall.SIGTERM)
	<-stop // Block until signal is received

	fmt.Println("\nShutting down server...")

	// write out JSON
	sidewalksMutex.RLock()
	f, err := os.Create(*dataFile)
	if err != nil {
		panic(err)
	}
	defer f.Close()
	err = json.NewEncoder(f).Encode(sidewalks)
	if err != nil {
		panic(err)
	}
	sidewalksMutex.RUnlock()

	// graceful shutdown
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := server.Shutdown(ctx); err != nil {
		log.Fatalf("Server forced to shutdown: %v", err)
	}

}

func initializeBuildInfoJSON() {
	rawBuildInfo, _ := debug.ReadBuildInfo()
	var revision, time string
	var dirty bool
	for _, buildSetting := range rawBuildInfo.Settings {
		if buildSetting.Key == "vcs.revision" {
			revision = buildSetting.Value
		} else if buildSetting.Key == "vcs.time" {
			time = buildSetting.Value
		} else if buildSetting.Key == "vcs.modified" {
			dirty = buildSetting.Value == "true"
		}
	}
	buildInfo := map[string]interface{}{
		"GitRev":       revision,
		"GitDirty":     dirty,
		"GitTime":      time,
		"GoVersion":    rawBuildInfo.GoVersion,
		"AllBuildInfo": rawBuildInfo.String(),
	}

	var err error
	buildInfoJSON, err = json.Marshal(buildInfo)
	if err != nil {
		panic(err)
	}
}