gdg-counter-website/main.go

package main

import (
	"encoding/json"
	"log"
	"net/http"
)

func main() {
	mux := http.NewServeMux()

	setupRoutes(mux)

	server := http.Server{
		Addr:    ":4000",
		Handler: mux,
	}

	log.Printf("Starting server on port 4000...")
	log.Fatal(server.ListenAndServe())
}

type Store interface {
	Count() (int, error)
	Increment() (int, error)
	Decrement() (int, error)
}

const StoreFilename = "store.local.json"

type fileStore struct {
	Counter int `json:"counter"`
}

func (db *fileStore) Count() (int, error) {
	if err := readOrCreateJson(StoreFilename, db); err != nil {
		return 0, err
	}

	return db.Counter, nil
}

func (db *fileStore) Increment() (int, error) {
	if err := readOrCreateJson(StoreFilename, db); err != nil {
		return 0, err
	}

	db.Counter++

	if err := writeJson(StoreFilename, db); err != nil {
		return 0, err
	}

	return db.Counter, nil
}

func (db *fileStore) Decrement() (int, error) {
	if err := readOrCreateJson(StoreFilename, db); err != nil {
		return 0, err
	}

	db.Counter--

	if err := writeJson(StoreFilename, db); err != nil {
		return 0, err
	}

	return db.Counter, nil
}

func setupRoutes(mux *http.ServeMux) {
	var db Store = &fileStore{Counter: 0}
	{
		initialCount, err := db.Count()
		if err != nil {
			log.Fatalf(`Unable to create store: %v`, err)
			return
		}

		log.Printf(`Store correctly initialized, count: %v`, initialCount)
	}

	// API Routes

	mux.HandleFunc("/api/status", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
			return
		}

		w.Header().Set("Content-Type", "application/json")

		err := json.NewEncoder(w).Encode("ok")
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	})

	mux.HandleFunc("/api/value", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
			return
		}

		count, err := db.Count()
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		w.Header().Set("Content-Type", "application/json")
		if err := json.NewEncoder(w).Encode(count); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	})

	mux.HandleFunc("/api/increment", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
			return
		}

		newCount, err := db.Increment()
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		w.Header().Set("Content-Type", "application/json")
		if err := json.NewEncoder(w).Encode(newCount); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	})

	mux.HandleFunc("/api/decrement", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
			return
		}

		newCount, err := db.Decrement()
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		w.Header().Set("Content-Type", "application/json")
		if err := json.NewEncoder(w).Encode(newCount); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	})

	// Static Files
	mux.Handle("/", http.FileServer(http.Dir("./dist/")))
}