// Demos a trivial key-value database backed by a file.
package main

import (
	"context"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"syscall"
)

func main() {
	if len(os.Args) != 3 {
		log.Fatalf("Usage: %s LISTEN-ADDRESS DATABASE-FILE\n", os.Args[0])
	}

	listenAddr, dbFilename := os.Args[1], os.Args[2]
	db, err := OpenDB(dbFilename)
	if err != nil && os.IsNotExist(err) {
		log.Println("database file does not exist, creating")
		db, err = CreateDB(dbFilename)
	}
	if err != nil {
		log.Fatalln(err)
	}

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if _, ok := r.URL.Query()["checkpoint"]; ok && r.Method == "GET" {
			if err := db.Checkpoint(); err != nil {
				w.WriteHeader(http.StatusInternalServerError)
			}
			return
		}

		byteValue, err := ioutil.ReadAll(r.Body)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			return
		}

		key, value := strings.TrimPrefix(r.URL.Path, "/"), string(byteValue)
		switch r.Method {
		case "GET":
			if value, ok, err := db.Get(key); err != nil {
				w.WriteHeader(http.StatusInternalServerError)
			} else if ok {
				w.WriteHeader(http.StatusOK)
				w.Write([]byte(value))
			} else {
				w.WriteHeader(http.StatusNotFound)
			}
		case "PUT":
			if err := db.Put(key, value); err != nil {
				w.WriteHeader(http.StatusInternalServerError)
			}
		case "DELETE":
			if err := db.Delete(key); err != nil {
				w.WriteHeader(http.StatusInternalServerError)
			}
		default:
			w.WriteHeader(http.StatusMethodNotAllowed)
		}
	})

	server := &http.Server{Addr: listenAddr}
	errs := make(chan error, 1)
	go func() { errs <- server.ListenAndServe() }()

	sig := make(chan os.Signal)
	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
	select {
	case <-sig:
	case err := <-errs:
		log.Println(err)
	}

	// For simplicity, we'll wait for everything to finish, including snapshots.
	if err := server.Shutdown(context.Background()); err != nil {
		log.Fatalln(err)
	}
	if err := db.Close(); err != nil {
		log.Fatalln(err)
	}
}