lbc/cmd/fizzbuzz/di.go

package main

import (
	"context"
	"flag"
	"fmt"
	"io"
	"log"
	"time"

	"code.osinet.fr/fgm/izidic"
	"github.com/dcowgill/envflag"

	"code.osinet.fr/fgm/lbc/internal"
	"code.osinet.fr/fgm/lbc/web"
)

// containers wraps an [izidic.Container] to provide typed services accessors,
// obviating the need to type-assert calls to Service.
type container struct {
	*izidic.Container
}

func (c *container) Config() *web.Config {
	return c.MustService("config").(*web.Config)
}

func (c *container) Logger() *log.Logger {
	return c.MustService("logger").(*log.Logger)
}

func (c *container) Stats() *web.Stats {
	return c.MustService("stats").(*web.Stats)
}

func (c *container) Web() *web.Server {
	return c.MustService("web").(*web.Server)
}

// 12-factor/XI: log to stdout.
func loggerService(dic *izidic.Container) (any, error) {
	sw, err := dic.Param("writer")
	if err != nil {
		return nil, err
	}
	w, ok := sw.(io.Writer)
	if !ok {
		return nil, fmt.Errorf("incorrect type for service writer: %T", sw)
	}
	logger := log.New(w, "", log.LstdFlags)
	// Support code not able to use an injected logger
	log.SetOutput(w)
	return logger, nil
}

func configService(dic *izidic.Container) (any, error) {
	name := dic.MustParam("name").(string)
	// Provide fallback configuration.
	c := &web.Config{
		Config: internal.Config{
			Verbose: false,
		},

		Addr:         ":8080",
		Base:         "/",
		WriteTimeout: 100 * time.Millisecond,
	}

	// Build runtime configuration.
	fs := flag.NewFlagSet(name, flag.ContinueOnError)
	fs.StringVar(&c.Addr, "addr", c.Addr, "the address on which to listen")
	fs.StringVar(&c.Base, "base", c.Base, "the base path for the server")
	fs.BoolVar(&c.Verbose, "v", c.Verbose, "be verbose")
	fs.DurationVar(&c.WriteTimeout, "wt", c.WriteTimeout, "the write timeout")
	err := fs.Parse(dic.MustParam("args").([]string))
	if err != nil {
		return nil, err
	}
	vs := envflag.NewVarSet(fs)
	vs.SetPrefix(name)
	vs.Parse()

	return c, nil
}

func statsService(dic *izidic.Container) (any, error) {
	return web.NewStats(), nil
}

func webService(dic *izidic.Container) (any, error) {
	wd := container{dic}
	return &web.Server{
		BaseContext: context.Background(),
		Config:      wd.Config(),
		Logger:      wd.Logger(),
		Stats:       wd.Stats(),
	}, nil
}

// resolve configures dependency injection.
func resolve(w io.Writer, args []string) *izidic.Container {
	dic := izidic.New()
	dic.Register("config", configService)
	dic.Register("logger", loggerService)
	dic.Register("stats", statsService)
	dic.Register("web", webService)

	dic.Store("name", "fizzbuzz")
	dic.Store("args", args[1:])
	dic.Store("writer", w)

	dic.Freeze()
	return dic
}