main.go

package main

import (
	"context"
	"database/sql"
	"expvar"
	"flag"
	"fmt"
	"github.com/ejacobg/greenlight/internal/data"
	"github.com/ejacobg/greenlight/internal/jsonlog"
	"github.com/ejacobg/greenlight/internal/mailer"
	"os"
	"runtime"
	"strings"
	"sync"
	"time"

	_ "github.com/lib/pq"
)

var (
	// buildTime will be populated using the -X linker flag.
	buildTime string
	version   string
)

type config struct {
	port int
	env  string
	db   struct {
		dsn          string
		maxOpenConns int
		maxIdleConns int
		maxIdleTime  string
	}
	// Settings for the rate limiter.
	limiter struct {
		rps     float64 // Requests per second (ie. refill rate)
		burst   int     // Maximum number of simultaneous requests (bucket capacity)
		enabled bool    // Allow enabling/disabling of rate limiter
	}
	// Mailtrap inbox credentials.
	smtp struct {
		host     string
		port     int
		username string
		password string
		sender   string
	}
	// CORS settings.
	cors struct {
		trustedOrigins []string
	}
	// JWT settings.
	jwt struct {
		secret string
	}
}

type application struct {
	config config
	logger *jsonlog.Logger
	models data.Models
	mailer mailer.Mailer
	wg     sync.WaitGroup
}

func main() {
	var cfg config

	flag.IntVar(&cfg.port, "port", 4000, "API server port")
	flag.StringVar(&cfg.env, "env", "development", "Environment (development|staging|production)")

	// Update the default value with your password.
	flag.StringVar(&cfg.db.dsn, "db-dsn", "", "PostgreSQL DSN")

	// Database configuration
	flag.IntVar(&cfg.db.maxOpenConns, "db-max-open-conns", 25, "PostgreSQL max open connections")
	flag.IntVar(&cfg.db.maxIdleConns, "db-max-idle-conns", 25, "PostgreSQL max idle connections")
	flag.StringVar(&cfg.db.maxIdleTime, "db-max-idle-time", "15m", "PostgreSQL max connection idle time")

	// Rate limiter configuration
	flag.Float64Var(&cfg.limiter.rps, "limiter-rps", 2, "Rate limiter maximum requests per second")
	flag.IntVar(&cfg.limiter.burst, "limiter-burst", 4, "Rate limiter maximum burst")
	flag.BoolVar(&cfg.limiter.enabled, "limiter-enabled", true, "Enable rate limiter") // Rate limiter is on by default.

	// Mailtrap configuration
	flag.StringVar(&cfg.smtp.host, "smtp-host", "", "SMTP host")
	flag.IntVar(&cfg.smtp.port, "smtp-port", 0, "SMTP port")
	flag.StringVar(&cfg.smtp.username, "smtp-username", "", "SMTP username")
	flag.StringVar(&cfg.smtp.password, "smtp-password", "", "SMTP password")
	flag.StringVar(&cfg.smtp.sender, "smtp-sender", "", "SMTP sender")

	// CORS configuration
	flag.Func("cors-trusted-origins", "Trusted CORS origins (space separated)", func(val string) error {
		cfg.cors.trustedOrigins = strings.Fields(val)
		return nil
	})

	// JWT configuration
	// If a secret is provided, then the application will use JWTs for authentication. Otherwise, it will default to using stateful tokens.
	flag.StringVar(&cfg.jwt.secret, "jwt-secret", "", "JWT secret")

	displayVersion := flag.Bool("version", false, "Display version and exit")

	flag.Parse()

	if *displayVersion {
		fmt.Printf("Version:\t%s\n", version)
		fmt.Printf("Build time:\t%s\n", buildTime)
		os.Exit(0)
	}

	logger := jsonlog.New(os.Stdout, jsonlog.LevelInfo)

	db, err := openDB(cfg)
	if err != nil {
		logger.PrintFatal(err, nil)
	}
	defer db.Close()

	logger.PrintInfo("database connection pool established", nil)

	// Add the current version number to our debug output.
	expvar.NewString("version").Set(version)

	// Publish the number of active goroutines.
	expvar.Publish("goroutines", expvar.Func(func() interface{} {
		return runtime.NumGoroutine()
	}))
	// Publish the database connection pool statistics.
	expvar.Publish("database", expvar.Func(func() interface{} {
		return db.Stats()
	}))
	// Publish the current Unix timestamp.
	expvar.Publish("timestamp", expvar.Func(func() interface{} {
		return time.Now().Unix()
	}))

	app := &application{
		config: cfg,
		logger: logger,
		models: data.NewModels(db),
		mailer: mailer.New(cfg.smtp.host, cfg.smtp.port, cfg.smtp.username, cfg.smtp.password, cfg.smtp.sender),
	}

	if err = app.serve(); err != nil {
		logger.PrintFatal(err, nil)
	}
}

func openDB(cfg config) (*sql.DB, error) {
	db, err := sql.Open("postgres", cfg.db.dsn)
	if err != nil {
		return nil, err
	}

	db.SetMaxOpenConns(cfg.db.maxOpenConns)

	db.SetMaxIdleConns(cfg.db.maxIdleConns)

	duration, err := time.ParseDuration(cfg.db.maxIdleTime)
	if err != nil {
		return nil, err
	}
	db.SetConnMaxIdleTime(duration)

	// We will wait for 5 seconds for a response from the DB.
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	err = db.PingContext(ctx)
	if err != nil {
		return nil, err
	}

	return db, nil
}