mcp/internal/tools/scaffold.go

package tools

import (
	"context"
	"fmt"
	"strings"

	"code.nochebuena.dev/einherjar/mcp/internal/envspec"
	"code.nochebuena.dev/einherjar/mcp/internal/index"
	"github.com/modelcontextprotocol/go-sdk/mcp"
)

type getScaffoldInput struct {
	Module  string `json:"module,omitempty" jsonschema:"the go.mod module path of the new app, e.g. code.nochebuena.dev/org/myapp; used to fill import paths. Defaults to 'myapp'."`
	Service string `json:"service,omitempty" jsonschema:"short service name for the cmd/ dir and the logz service tag, e.g. myapp. Defaults to the last path segment of module."`
}

type scaffoldFile struct {
	Path    string `json:"path"`
	Content string `json:"content"`
}

type getScaffoldOutput struct {
	Layout string         `json:"layout"`
	Files  []scaffoldFile `json:"files"`
	Notes  []string       `json:"notes"`
}

func registerGetScaffold(s *mcp.Server, idx *index.Index) {
	mcp.AddTool(s, &mcp.Tool{
		Name: "get_scaffold",
		Description: "Return the canonical MINIMUM Einherjar application scaffold as ready-to-write files: " +
			"a clean main.go (godotenv autoload + wire.Run), internal/wire/wire.go (the launcher assembly), " +
			"internal/config/config.go (one Config composing the framework's component configs via caarlos0/env), " +
			"a health feature hook, and .env.example. This is the one opinionated starting point — call it when " +
			"creating a new Einherjar service so main.go and the launcher stay clean instead of being hand-rolled. " +
			"Migrations and seeding are deliberately excluded — those are the developer's choice, not a framework convention.",
	}, func(ctx context.Context, req *mcp.CallToolRequest, args getScaffoldInput) (*mcp.CallToolResult, getScaffoldOutput, error) {
		module := strings.TrimSpace(args.Module)
		if module == "" {
			module = "myapp"
		}
		service := strings.TrimSpace(args.Service)
		if service == "" {
			service = module
			if i := strings.LastIndex(module, "/"); i >= 0 {
				service = module[i+1:]
			}
		}
		repl := strings.NewReplacer("%%MODULE%%", module, "%%APP%%", service)

		out := getScaffoldOutput{
			Layout: scaffoldLayout,
			Files: []scaffoldFile{
				{Path: "cmd/" + service + "/main.go", Content: repl.Replace(tplMain)},
				{Path: "internal/wire/wire.go", Content: repl.Replace(tplWire)},
				{Path: "internal/wire/health.go", Content: repl.Replace(tplHealth)},
				{Path: "internal/config/config.go", Content: repl.Replace(tplConfig)},
				{Path: ".env.example", Content: renderEnvExample(idx, service)},
			},
			Notes: []string{
				"main.go contains ONLY the godotenv autoload blank import and wire.Run() — never construct components there.",
				".env.example is DERIVED from the framework's real component-config tags (web/server + db-postgres), so the EINHERJAR_* names and defaults are always correct. When you compose another component, add its section — get_config_env(module) lists the exact vars, and check_env catches drift.",
				"App-owned config fields use the APP_* prefix; framework component configs load their own EINHERJAR_* tags through the same env.Parse.",
				"Add one internal/wire/<feature>.go per feature (a with<Feature> hook) plus its internal/<feature>/{dto,handler,repository,service} layers; call validate_snippet / get_example(\"wire\") for the hook shape.",
				"Migrations and seeding are the developer's choice — not part of this scaffold.",
			},
		}
		return jsonText(out), out, nil
	})
}

const scaffoldLayout = `cmd/%%APP%%/main.go              godotenv autoload + wire.Run()
internal/wire/wire.go          Run() — config, infra, feature hooks
internal/wire/<feature>.go     one file per feature (with<Feature> hook)
internal/wire/middleware.go    authz / skip helpers (add when you add authz'd routes)
internal/config/config.go      Config composing framework component configs
.env.example                   every env var the config reads, in sync
internal/<feature>/{dto,handler,repository,service}/`

const tplMain = `package main

import (
	"fmt"
	"os"

	_ "github.com/joho/godotenv/autoload"

	"%%MODULE%%/internal/wire"
)

func main() {
	if err := wire.Run(); err != nil {
		fmt.Fprintln(os.Stderr, "fatal:", err)
		os.Exit(1)
	}
}
`

const tplWire = `package wire

import (
	"github.com/google/uuid"

	"code.nochebuena.dev/einherjar/core/launcher"
	"code.nochebuena.dev/einherjar/core/logz"
	"code.nochebuena.dev/einherjar/db-postgres"
	"code.nochebuena.dev/einherjar/web/mw"
	"code.nochebuena.dev/einherjar/web/server"

	"%%MODULE%%/internal/config"
)

// Run loads configuration, builds infrastructure, registers feature hooks, and
// blocks until shutdown. Order is load-bearing: config, logger, infra, launcher
// with every component appended, then feature hooks, then lc.Run().
func Run() error {
	cfg, err := config.Load()
	if err != nil {
		return err
	}

	// logz.Config is composed in config.Config, so EINHERJAR_LOG_LEVEL / _JSON load
	// from the environment; StaticArgs are set here in code (they carry no env tag).
	logCfg := cfg.Log
	logCfg.StaticArgs = []any{"service", "%%APP%%", "env", cfg.AppEnv}
	logger := logz.New(logCfg)

	db := postgres.New(logger, cfg.PG)
	srv := server.New(logger, cfg.Server,
		server.WithMiddleware(
			mw.RequestID(uuid.NewString),
			mw.Recover(logger),
			mw.CORS(cfg.CORSOrigins),
			mw.RequestLogger(logger),
		),
	)

	lc := launcher.New(logger)
	lc.Append(db, srv)

	withHealth(lc, srv)
	// … one withFeature(lc, srv, …) call per feature in your domain.

	return lc.Run()
}
`

const tplHealth = `package wire

import (
	"net/http"

	"code.nochebuena.dev/einherjar/core/launcher"
	"code.nochebuena.dev/einherjar/web/server"
)

// withHealth registers a liveness endpoint — the simplest with<Feature> hook.
// A real feature hook takes its deps (logging.Logger, postgres.Provider, …) and
// wires repo→service→handler inside the closure; see get_example("wire").
func withHealth(lc launcher.Launcher, srv server.Server) {
	lc.BeforeStart(func() error {
		srv.Get("/health", func(w http.ResponseWriter, r *http.Request) {
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusOK)
			_, _ = w.Write([]byte(` + "`" + `{"status":"ok"}` + "`" + `))
		})
		return nil
	})
}
`

const tplConfig = `// Package config loads %%APP%%'s startup configuration from the environment.
//
// Einherjar component configs (server.Config, postgres.Config, …) are composed
// verbatim as nested fields so their EINHERJAR_* env tags load alongside the
// app-owned APP_* fields through a single caarlos0/env parse. Every env var
// declared here must also be documented in .env.example, kept in lock-step.
package config

import (
	"github.com/caarlos0/env/v11"

	"code.nochebuena.dev/einherjar/core/logz"
	"code.nochebuena.dev/einherjar/db-postgres"
	"code.nochebuena.dev/einherjar/web/server"
)

// Config is the fully-resolved startup configuration. caarlos0/env recurses into
// the nested framework configs, populating their EINHERJAR_LOG_* / EINHERJAR_SERVER_* /
// EINHERJAR_PG_* tags from the environment next to the app-owned APP_* fields.
type Config struct {
	AppEnv      string   ` + "`" + `env:"APP_ENV"          envDefault:"local"` + "`" + `
	CORSOrigins []string ` + "`" + `env:"APP_CORS_ORIGINS" envSeparator:","` + "`" + `

	// Framework component configs — composed verbatim; their EINHERJAR_* tags
	// load through this same env.Parse call.
	Log    logz.Config     // EINHERJAR_LOG_*
	Server server.Config   // EINHERJAR_SERVER_*
	PG     postgres.Config // EINHERJAR_PG_*
}

func Load() (Config, error) {
	var cfg Config
	if err := env.Parse(&cfg); err != nil {
		return Config{}, err
	}
	return cfg, nil
}
`

// renderEnvExample builds .env.example from the framework's real component-config
// tags rather than a hand-maintained string, so the EINHERJAR_* names and defaults
// can never drift from the modules the scaffold composes (web/server + db-postgres).
// Required vars (no default) are emitted uncommented with a runnable dev value;
// vars that carry a framework default are emitted commented — documented, inert
// until overridden.
func renderEnvExample(idx *index.Index, app string) string {
	var b strings.Builder
	b.WriteString("# .env.example — copy to .env for local dev (godotenv autoloads it).\n")
	b.WriteString("# Derived from the framework's real config tags. Required vars are uncommented;\n")
	b.WriteString("# a commented line documents that var's framework default — uncomment to override.\n\n")

	b.WriteString("# ── App (APP_*) ────────────────────────────────────────────────────────────\n")
	b.WriteString("APP_ENV=local\n")
	b.WriteString("APP_CORS_ORIGINS=*\n\n")

	writeEnvSection(&b, "Einherjar: logging", envspec.FindStruct(idx, "core", "logz", "Config"), app)
	writeEnvSection(&b, "Einherjar: HTTP server", envspec.FindStruct(idx, "web", "server", "Config"), app)
	writeEnvSection(&b, "Einherjar: PostgreSQL", envspec.FindStruct(idx, "db-postgres", "", "Config"), app)
	return b.String()
}

// envDevDefaults gives required vars (which carry no framework default) a value
// that runs against the local devtools stack out of the box.
var envDevDefaults = map[string]string{
	"EINHERJAR_PG_HOST":     "localhost",
	"EINHERJAR_PG_USER":     "postgres",
	"EINHERJAR_PG_PASSWORD": "postgres",
}

func envDevValue(v envspec.Var, app string) string {
	if v.Name == "EINHERJAR_PG_NAME" {
		return app
	}
	return envDevDefaults[v.Name]
}

func writeEnvSection(b *strings.Builder, title string, vars []envspec.Var, app string) {
	if len(vars) == 0 {
		return
	}
	fmt.Fprintf(b, "# ── %s ──────────────────────────────────────\n", title)
	for _, v := range vars {
		switch {
		case v.HasDefault:
			fmt.Fprintf(b, "# %s=%s\n", v.Name, v.Default)
		case v.Required:
			fmt.Fprintf(b, "%s=%s\n", v.Name, envDevValue(v, app))
		default:
			fmt.Fprintf(b, "# %s=%s\n", v.Name, envDevValue(v, app))
		}
	}
	b.WriteString("\n")
}