devsim/cmd/web/main.go

package main

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"os"
	"os/signal"
	"time"

	"golang.org/x/sync/errgroup"

	"git.loyso.art/frx/devsim"
	"git.loyso.art/frx/devsim/internal/api/http"
	"git.loyso.art/frx/devsim/internal/probe"
	"git.loyso.art/frx/devsim/internal/store"
	"git.loyso.art/frx/devsim/internal/store/memory"
	"git.loyso.art/frx/devsim/internal/store/mongo"
	"git.loyso.art/frx/devsim/internal/store/pg"
	"git.loyso.art/frx/devsim/pkg/collections"
)

var availableStoreTypes = collections.NewSet([]string{
	"pg", "mongo", "memory",
}...)

func main() {
	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
	defer cancel()

	log := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
		Level: slog.LevelDebug,
	}))

	log.InfoContext(
		ctx, "running application",
		slog.Int("pid", os.Getpid()),
		slog.String("version", devsim.Version()),
		slog.String("revision", devsim.Revision()),
		slog.String("buildtime", devsim.BuildTime()),
	)

	settings := loadConfigFromEnv()
	err := settings.validate()
	if err != nil {
		log.ErrorContext(ctx, "unable to validate settings", slog.String("err", err.Error()))
		os.Exit(1)
	}

	log.InfoContext(
		ctx, "config parsed",
		slog.Any("settings", settings),
	)

	err = app(ctx, settings, log)
	if err != nil {
		log.ErrorContext(ctx, "unable to run app", slog.String("err", err.Error()))
		os.Exit(1)
	}
}

type mongoSettings struct {
	DSN string
}

func (s *mongoSettings) fromEnv() {
	*s = mongoSettings{
		DSN: os.Getenv("DEVSIM_MONGO_DSN"),
	}
}

type pgSettings struct {
	DSN string
}

func (s *pgSettings) fromEnv() {
	*s = pgSettings{
		DSN: os.Getenv("DEVSIM_PG_DSN"),
	}
}

type applicationSettings struct {
	listenAddr  string
	monitorAddr string
	storeType   string

	pg    pgSettings
	mongo mongoSettings
}

func loadConfigFromEnv() applicationSettings {
	const webaddr = ":9123"
	const monitoraddr = ":9124"

	var cfg applicationSettings
	cfg.listenAddr = valueOrDefault(os.Getenv("DEVSIM_HTTP_ADDR"), webaddr)
	cfg.monitorAddr = valueOrDefault(os.Getenv("DEVSIM_MONITOR_ADDR"), monitoraddr)
	cfg.storeType = os.Getenv("DEVSIM_STORE_TYPE")

	cfg.pg.fromEnv()
	cfg.mongo.fromEnv()

	return cfg
}

func (s applicationSettings) validate() (err error) {
	if !availableStoreTypes.Contains(s.storeType) {
		err = errors.Join(err, errors.New("store_type value is unsupported"))
	}

	switch s.storeType {
	case "pg":
		if s.pg.DSN == "" {
			err = errors.Join(err, errors.New("no postgres dsn provided"))
		}
	case "mongo":
		if s.mongo.DSN == "" {
			err = errors.Join(err, errors.New("no mongo dsn provided"))
		}
	case "memory":
		// no things to validate
	}

	if s.listenAddr == "" {
		err = errors.Join(err, errors.New("no listen address provided"))
	}

	return err
}

type namedCloser struct {
	closer io.Closer
	name   string
}

func app(ctx context.Context, settings applicationSettings, log *slog.Logger) (err error) {
	var repo store.Stats
	var closers []namedCloser

	livenessBase, livenessToggle := probe.SimpleLivenessSwitcher()
	readinessBase, readinessToggle := probe.SimpleReadinessSwitcher()

	pr := probe.NewReporter(time.Second * 15)
	pr.RegisterLiveness(livenessBase)
	pr.RegisterReadiness(readinessBase)

	mb := http.NewHandlersBuilder()
	mb.MountProbeHandlers(pr)

	monitorServer := http.NewServer(settings.monitorAddr)
	closers = append(closers, namedCloser{
		name:   "monitorhttp",
		closer: monitorServer,
	})
	monitorServer.RegisterHandler(mb.Build())

	eg, _ := errgroup.WithContext(ctx)
	eg.Go(func() error {
		return monitorServer.Run()
	})

	switch settings.storeType {
	case "pg":
		pgconn, errDial := pg.Dial(ctx, settings.pg.DSN)
		if errDial != nil {
			return fmt.Errorf("connecting to postgres: %w", errDial)
		}

		repo = pgconn.StatsRepository()
		closers = append(closers, namedCloser{
			name:   "postgres",
			closer: pgconn,
		})
	case "mongo":
		mongoconn, errDial := mongo.Dial(ctx, settings.mongo.DSN)
		if errDial != nil {
			return fmt.Errorf("connecting to mongo: %w", errDial)
		}

		repo = mongoconn.StatsRepository()
		closers = append(closers, namedCloser{
			name:   "mongo",
			closer: mongoconn,
		})
	case "memory":
		repo = memory.NewStore()
	}

	hb := http.NewHandlersBuilder()
	hb.MountStatsHandlers(repo, log)

	httpServer := http.NewServer(settings.listenAddr)
	closers = append(closers, namedCloser{
		name:   "http",
		closer: httpServer,
	})
	httpServer.RegisterHandler(hb.Build())

	eg.Go(func() error {
		return httpServer.Run()
	})
	eg.Go(func() error {
		<-ctx.Done()
		log.InfoContext(ctx, "got interruption signal")
		for _, closer := range closers {
			name := closer.name
			closerUnit := closer.closer
			errClose := closerUnit.Close()
			if errClose != nil {
				log.ErrorContext(ctx, "unable to close component", slog.String("component", name), slog.Any("err", errClose))
			}
		}
		return nil
	})

	livenessToggle()
	readinessToggle(probe.ReadinessOk)

	err = eg.Wait()
	if err != nil {
		if !errors.Is(err, context.Canceled) {
			log.ErrorContext(ctx, "unable to proceed the app", slog.Any("err", err))
		} else {
			log.InfoContext(ctx, "finished processing apps")
		}
	}

	return nil
}

func valueOrDefault[x comparable](value, fallback x) x {
	var v x
	if value == v {
		return fallback
	}

	return value
}