tilde.club/html/fruitvote/main.go

package main

import (
	"database/sql"
	"encoding/json"
	"flag"
	"fmt"
	_ "github.com/mattn/go-sqlite3"
	"log"
	"math"
	"net"
	"net/http"
	"os"
	"os/exec"
	"os/signal"
	"strings"
	"syscall"
	"text/template"
)

type Fruit struct {
	Name string `json:"name"`
	Img  string `json:"img"`
	Elo  int    `json:"elo"`
}

type Context struct {
	db           *sql.DB
	users        []string
	templatePath string
	socketPath   string
	fruitsPath   string
}

type CurriedContextHandler func(*Context, http.ResponseWriter, *http.Request)

func curryContext(context *Context) func(CurriedContextHandler) http.HandlerFunc {
	return func(handler CurriedContextHandler) http.HandlerFunc {
		return func(w http.ResponseWriter, r *http.Request) {
			log.Println(r.Method, r.URL.Path, r.RemoteAddr)

			handler(context, w, r)
		}
	}
}

func indexHandler(context *Context, resp http.ResponseWriter, req *http.Request) {
	// get from POST
	winner := req.FormValue("winner")
	contestants := req.Form["contestant[]"]

	if winner != "" && len(contestants) == 2 {
		losingFruitName := string(contestants[0])
		if losingFruitName == winner {
			losingFruitName = string(contestants[1])
		}
		winningFruit := fruitByName(context.db, winner)
		losingFruit := fruitByName(context.db, losingFruitName)

		winningFruit.Elo, losingFruit.Elo = updateElo(winningFruit.Elo, losingFruit.Elo)

		updateFruit(context.db, winningFruit)
		updateFruit(context.db, losingFruit)

		log.Println(winningFruit.Name, "won against", losingFruit.Name, "new elo:", winningFruit.Elo, losingFruit.Elo)
	}

	fruitOne := randomFruit(context.db)
	fruitTwo := randomFruit(context.db)
	for fruitOne.Name == fruitTwo.Name {
		fruitTwo = randomFruit(context.db)
	}

	templateFile := context.templatePath + "/vote.html"
	vote, err := template.ParseFiles(templateFile)
	if err != nil {
		panic(err)
	}

	fruits := []Fruit{fruitOne, fruitTwo}
	err = vote.Execute(resp, fruits)
	if err != nil {
		panic(err)
	}
	resp.Header().Set("Content-Type", "text/html")
}

func getStatsHandler(context *Context, resp http.ResponseWriter, _req *http.Request) {
	rows, err := context.db.Query("SELECT name, img, elo FROM fruits ORDER BY elo DESC")
	if err != nil {
		panic(err)
	}
	defer rows.Close()

	fruits := []Fruit{}
	for rows.Next() {
		fruit := Fruit{}
		err = rows.Scan(&fruit.Name, &fruit.Img, &fruit.Elo)
		if err != nil {
			panic(err)
		}
		fruits = append(fruits, fruit)
	}

	templateFile := context.templatePath + "/stats.html"
	stats, err := template.ParseFiles(templateFile)
	if err != nil {
		panic(err)
	}

	err = stats.Execute(resp, fruits)
	if err != nil {
		panic(err)
	}
	resp.Header().Set("Content-Type", "text/html")
}

func healthCheckHandler(context *Context, resp http.ResponseWriter, req *http.Request) {
	resp.WriteHeader(http.StatusOK)
	resp.Write([]byte("healthy"))
}

func main() {
	log.Println("starting server...")
	log.SetFlags(log.LstdFlags | log.Lshortfile)

	context := getArgs()
	log.Println("removing socket file", context.socketPath)
	os.Remove(context.socketPath)

	log.Println("migrating database...")
	migrate(context.db)
	seedFruits(context.db, context.fruitsPath)

	listener, err := net.Listen("unix", context.socketPath)
	if err != nil {
		panic(err)
	}
	log.Println("listening on", context.socketPath)
	os.Chmod(context.socketPath, 0700)

	sigc := make(chan os.Signal, 1)
	signal.Notify(sigc, os.Interrupt, os.Kill, syscall.SIGTERM)
	go func(c chan os.Signal) {
		sig := <-c
		log.Printf("caught signal %s: shutting down.", sig)

		listener.Close()
		os.Exit(0)
	}(sigc)
	defer listener.Close()

	log.Println("setting ACLs for users", context.users)
	for _, user := range context.users {
		setACL(context.socketPath, user)
	}

	curriedContext := curryContext(context)
	mux := http.NewServeMux()
	mux.HandleFunc("/", curriedContext(indexHandler))
	mux.HandleFunc("/health", curriedContext(healthCheckHandler))
	mux.HandleFunc("/stats", curriedContext(getStatsHandler))

	log.Println("serving http...")
	http.Serve(listener, mux)
}

func calculateRatingDelta(winnerRating int, loserRating int, K int) (int, int) {
	winnerRatingFloat := float64(winnerRating)
	loserRatingFloat := float64(loserRating)

	expectedScoreWinner := 1 / (1 + math.Pow(10, (loserRatingFloat-winnerRatingFloat)/400))
	expectedScoreLoser := 1 - expectedScoreWinner

	changeWinner := int(math.Round(float64(K) * (1 - expectedScoreWinner)))
	changeLoser := -int(math.Round(float64(K) * (expectedScoreLoser)))

	return changeWinner, changeLoser
}

func updateElo(winnerElo int, loserElo int) (int, int) {
	const K = 32

	changeWinner, changeLoser := calculateRatingDelta(winnerElo, loserElo, K)

	newWinnerElo := winnerElo + changeWinner
	newLoserElo := loserElo + changeLoser

	return newWinnerElo, newLoserElo
}

func seedFruits(db *sql.DB, fruitsPath string) {
	log.Println("seeding fruits (haha)...")

	fruitsContents, err := os.ReadFile(fruitsPath)
	if err != nil {
		panic(err)
	}
	jsonFruits := []Fruit{}
	err = json.Unmarshal(fruitsContents, &jsonFruits)
	if err != nil {
		panic(err)
	}

	for _, fruit := range jsonFruits {
		// insert if not exists
		_, err := db.Exec("INSERT OR IGNORE INTO fruits (name, img) VALUES (?, ?)", fruit.Name, fruit.Img)
		if err != nil {
			panic(err)
		}
	}
}

func migrate(db *sql.DB) {
	log.Println("creating fruits table...")
	_, err := db.Exec(`
		CREATE TABLE IF NOT EXISTS fruits (
			name TEXT PRIMARY KEY,
                        img TEXT,
                        elo INTEGER DEFAULT 1400
		);
	`)
	if err != nil {
		panic(err)
	}
}

func randomFruit(db *sql.DB) Fruit {
	fruit := Fruit{}
	err := db.QueryRow("SELECT name, img, elo FROM fruits ORDER BY RANDOM() LIMIT 1").Scan(&fruit.Name, &fruit.Img, &fruit.Elo)
	if err != nil {
		panic(err)
	}
	return fruit
}

func fruitByName(db *sql.DB, name string) Fruit {
	fruit := Fruit{}
	err := db.QueryRow("SELECT name, img, elo FROM fruits WHERE name = ?", name).Scan(&fruit.Name, &fruit.Img, &fruit.Elo)
	if err != nil {
		panic(err)
	}
	return fruit
}

func updateFruit(db *sql.DB, fruit Fruit) {
	_, err := db.Exec("UPDATE fruits SET img = ?, elo = ? WHERE name = ?", fruit.Img, fruit.Elo, fruit.Name)
	if err != nil {
		panic(err)
	}
}

func setACL(socketPath, user string) {
	cmd := exec.Command("setfacl", "-m", "u:"+user+":rwx", socketPath)
	if err := cmd.Run(); err != nil {
		panic("failed to set ACL: " + err.Error())
	}
}

func getArgs() *Context {
	socketPath := flag.String("socket-path", "/tmp/go-server.sock", "Path to the Unix socket")
	users := flag.String("users", "", "Comma-separated list of users for ACL")
	database := flag.String("database-path", "/tmp/go-server.db", "Path to the SQLite database")
	fruitsPath := flag.String("fruits", "/dev/null", "Path to the fruits file")
	templatePath := flag.String("template", "", "Path to the template directory")
	flag.Parse()

	if *users == "" {
		fmt.Println("You must specify at least one user with --users")
		os.Exit(1)
	}
	if *templatePath == "" {
		fmt.Println("You must specify a template directory with --template")
		os.Exit(1)
	}

	log.Println("opening database at", *database, "with foreign keys enabled")
	db, err := sql.Open("sqlite3", *database+"?_foreign_keys=on")
	if err != nil {
		panic(err)
	}

	return &Context{
		db:           db,
		users:        strings.Split(*users, ","),
		socketPath:   *socketPath,
		fruitsPath:   *fruitsPath,
		templatePath: *templatePath,
	}
}