package main

import (
	"context"
	"database/sql"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

	"github.com/joho/godotenv"
	_ "github.com/lib/pq"
)

// Declare a string containing the application version number. Later in the book we'll
// generate this automatically at build time, but for now we'll just store the version
// number as a hard-coded global constant.
const version = "1.0.0"

// Define a config struct to hold all the configuration settings for our application.
// For now, the only configuration settings will be the network port that we want the
// server to listen on, and the name of the current operating environment for the
// application (development, staging, production, etc.). We will read in these
// configuration settings from command-line flags when the application starts.
type config struct {
	port int
	env  string
	db   struct {
		dsn string
	}
}

// Define an application struct to hold the dependencies for our HTTP handlers, helpers,
// and middleware. At the moment this only contains a copy of the config struct and a
// logger, but it will grow to include a lot more as our build progresses.
type application struct {
	config config
	logger *log.Logger
}

func main() {
	logger := log.New(os.Stdout, "", log.Ldate|log.Ltime)
	var cfg config

	err := godotenv.Load()
	if err != nil {
		logger.Fatal(err)
	}
	dsn := os.Getenv("DATABASE_DSN")

	flag.IntVar(&cfg.port, "port", 4000, "API server port")
	flag.StringVar(&cfg.env, "env", "development", "Environment (development|staging|production)")
	// Read the DSN value from the db-dsn command-line flag into the config struct. We
	// default to using our development DSN if no flag is provided.
	flag.StringVar(&cfg.db.dsn, "db-dsn", dsn, "PostgreSQL DSN (From DATABASE_DSN in .env)")

	flag.Parse()

	// Call the openDB() helper function (see below) to create the connection pool,
	// passing in the config struct. If this returns an error, we log it and exit the
	// application immediately.
	db, err := openDB(cfg)
	if err != nil {
		logger.Fatal(err)
	}

	// Defer a call to db.Close() so that the connection pool is closed before the
	// main() function exits.
	defer func() {
		if closeErr := db.Close(); closeErr != nil && err == nil {
			err = closeErr
		}
	}()
	// Also log a message to say that the connection pool has been successfully
	// established.
	logger.Printf("database connection pool established")

	app := &application{
		config: cfg,
		logger: logger,
	}

	// Use the httprouter instance returned by app.routes() as the server handler.
	srv := &http.Server{
		Addr:         fmt.Sprintf(":%d", cfg.port),
		Handler:      app.routes(),
		IdleTimeout:  time.Minute,
		ReadTimeout:  10 * time.Second,
		WriteTimeout: 30 * time.Second,
	}

	logger.Printf("starting %s server on %s", cfg.env, srv.Addr)
	err = srv.ListenAndServe()
	logger.Fatal(err)
}

func openDB(cfg config) (*sql.DB, error) {
	// Use sql.Open() to create an empty connection pool, using the DSN from the config
	// struct.
	db, err := sql.Open("postgres", cfg.db.dsn)
	if err != nil {
		return nil, err
	}

	// Create a context with a 5-second timeout deadline.
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	// Use PingContext() to establish a new connection to the database, passing in the
	// context we created above as a parameter. If the connection couldn't be
	// established successfully within the 5 second deadline, then this will return an
	// error.
	err = db.PingContext(ctx)
	if err != nil {
		return nil, err
	}

	// Return the sql.DB connection pool.
	return db, nil
}