cli: add encore app init (#861)

This adds a new command, `encore app init`, that initializes
an existing repository by creating a new app on the server
and linking with it.

Stacked on top of #860

cli/cmd/encore/app/initialize.go

@@ -0,0 +1,108 @@
+package app
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"time"
+
+	"github.com/briandowns/spinner"
+	"github.com/fatih/color"
+	"github.com/spf13/cobra"
+
+	"encr.dev/cli/cmd/encore/auth"
+	"encr.dev/cli/cmd/encore/cmdutil"
+	"encr.dev/internal/conf"
+)
+
+// Create a new app from scratch: `encore app create`
+// Link an existing app to an existing repo: `encore app link <app-id>`
+// Link an existing repo to a new app: `encore app init <name>`
+
+func init() {
+	initAppCmd := &cobra.Command{
+		Use:   "init [name]",
+		Short: "Create a new Encore app from an existing repository",
+		Args:  cobra.MaximumNArgs(1),
+
+		DisableFlagsInUseLine: true,
+		Run: func(cmd *cobra.Command, args []string) {
+			var name string
+			if len(args) > 0 {
+				name = args[0]
+			}
+			if err := initializeApp(name); err != nil {
+				cmdutil.Fatal(err)
+			}
+		},
+	}
+
+	appCmd.AddCommand(initAppCmd)
+}
+
+func initializeApp(name string) error {
+	// Check if encore.app file exists
+	_, _, err := cmdutil.MaybeAppRoot()
+	if errors.Is(err, cmdutil.ErrNoEncoreApp) {
+		// expected
+	} else if err != nil {
+		cmdutil.Fatal(err)
+	} else if err == nil {
+		// There is already an app here or in a parent directory.
+		cmdutil.Fatal("an encore.app file already exists (here or in a parent directory)")
+	}
+
+	cyan := color.New(color.FgCyan)
+	if _, err := conf.CurrentUser(); errors.Is(err, fs.ErrNotExist) {
+		_, _ = cyan.Fprint(os.Stderr, "Log in to create your app [press enter to continue]: ")
+		_, _ = fmt.Scanln()
+		if err := auth.DoLogin(auth.AutoFlow); err != nil {
+			cmdutil.Fatal(err)
+		}
+	}
+
+	if name == "" {
+		name, _ = selectTemplate("", "empty")
+	}
+	if err := validateName(name); err != nil {
+		return err
+	}
+
+	// Create the app on the server.
+	if _, err := conf.CurrentUser(); err != nil {
+		cmdutil.Fatal("you must be logged in to initialize a new app")
+	}
+
+	s := spinner.New(spinner.CharSets[14], 100*time.Millisecond)
+	s.Prefix = "Creating app on encore.dev "
+	s.Start()
+
+	app, err := createAppOnServer(name, exampleConfig{})
+	s.Stop()
+	if err != nil {
+		return fmt.Errorf("creating app on encore.dev: %v", err)
+	}
+
+	// Create the encore.app file
+	encoreAppData := []byte(`{
+	"id": "` + app.Slug + `",
+}
+`)
+	if err := os.WriteFile("encore.app", encoreAppData, 0644); err != nil {
+		return err
+	}
+
+	// Update to latest encore.dev release if this looks to be a go module.
+	if _, err := os.Stat("go.mod"); err == nil {
+		s := spinner.New(spinner.CharSets[14], 100*time.Millisecond)
+		s.Prefix = "Running go get encore.dev@latest"
+		s.Start()
+		if err := gogetEncore(name); err != nil {
+			s.FinalMSG = fmt.Sprintf("failed, skipping: %v", err.Error())
+		}
+		s.Stop()
+	}
+
+	return nil
+}