fs: change Config callback into state based callback #3455

This is a very large change which turns the post Config function in
backends into a state based call and response system so that
alternative user interfaces can be added.

The existing config logic has been converted, but it is quite
complicated and folloup commits will likely be needed to fix it!

Follow up commits will add a command line and API based way of using
this configuration system.

backend/drive/drive.go

@@ -182,32 +182,64 @@ func init() {
 		Description: "Google Drive",
 		NewFs:       NewFs,
 		CommandHelp: commandHelp,
-		Config: func(ctx context.Context, name string, m configmap.Mapper) error {
+		Config: func(ctx context.Context, name string, m configmap.Mapper, config fs.ConfigIn) (*fs.ConfigOut, error) {
 			// Parse config into Options struct
 			opt := new(Options)
 			err := configstruct.Set(m, opt)
 			if err != nil {
-				return errors.Wrap(err, "couldn't parse config into struct")
+				return nil, errors.Wrap(err, "couldn't parse config into struct")
 			}
 
-			// Fill in the scopes
-			driveConfig.Scopes = driveScopes(opt.Scope)
-			// Set the root_folder_id if using drive.appfolder
-			if driveScopesContainsAppFolder(driveConfig.Scopes) {
-				m.Set("root_folder_id", "appDataFolder")
-			}
+			switch config.State {
+			case "":
+				// Fill in the scopes
+				driveConfig.Scopes = driveScopes(opt.Scope)
 
-			if opt.ServiceAccountFile == "" && opt.ServiceAccountCredentials == "" {
-				err = oauthutil.Config(ctx, "drive", name, m, driveConfig, nil)
-				if err != nil {
-					return errors.Wrap(err, "failed to configure token")
+				// Set the root_folder_id if using drive.appfolder
+				if driveScopesContainsAppFolder(driveConfig.Scopes) {
+					m.Set("root_folder_id", "appDataFolder")
 				}
+
+				if opt.ServiceAccountFile == "" && opt.ServiceAccountCredentials == "" {
+					return oauthutil.ConfigOut("teamdrive", &oauthutil.Options{
+						OAuth2Config: driveConfig,
+					})
+				}
+				return fs.ConfigGoto("teamdrive")
+			case "teamdrive":
+				if opt.TeamDriveID == "" {
+					return fs.ConfigConfirm("teamdrive_ok", false, "Configure this as a Shared Drive (Team Drive)?\n")
+				}
+				return fs.ConfigConfirm("teamdrive_ok", false, fmt.Sprintf("Change current Shared Drive (Team Drive) ID %q?\n", opt.TeamDriveID))
+			case "teamdrive_ok":
+				if config.Result == "false" {
+					m.Set("team_drive", "")
+					return nil, nil
+				}
+				f, err := newFs(ctx, name, "", m)
+				if err != nil {
+					return nil, errors.Wrap(err, "failed to make Fs to list Shared Drives")
+				}
+				teamDrives, err := f.listTeamDrives(ctx)
+				if err != nil {
+					return nil, err
+				}
+				if len(teamDrives) == 0 {
+					return fs.ConfigError("", "No Shared Drives found in your account")
+				}
+				return fs.ConfigChoose("teamdrive_final", "Shared Drive", len(teamDrives), func(i int) (string, string) {
+					teamDrive := teamDrives[i]
+					return teamDrive.Id, teamDrive.Name
+				})
+			case "teamdrive_final":
+				driveID := config.Result
+				m.Set("team_drive", driveID)
+				m.Set("root_folder_id", "")
+				opt.TeamDriveID = driveID
+				opt.RootFolderID = ""
+				return nil, nil
 			}
-			err = configTeamDrive(ctx, opt, m, name)
-			if err != nil {
-				return errors.Wrap(err, "failed to configure Shared Drive")
-			}
-			return nil
+			return nil, fmt.Errorf("unknown state %q", config.State)
 		},
 		Options: append(driveOAuthOptions(), []fs.Option{{
 			Name: "scope",
@@ -948,48 +980,6 @@ func parseExtensions(extensionsIn ...string) (extensions, mimeTypes []string, er
 	return
 }
 
-// Figure out if the user wants to use a team drive
-func configTeamDrive(ctx context.Context, opt *Options, m configmap.Mapper, name string) error {
-	ci := fs.GetConfig(ctx)
-
-	// Stop if we are running non-interactive config
-	if ci.AutoConfirm {
-		return nil
-	}
-	if opt.TeamDriveID == "" {
-		fmt.Printf("Configure this as a Shared Drive (Team Drive)?\n")
-	} else {
-		fmt.Printf("Change current Shared Drive (Team Drive) ID %q?\n", opt.TeamDriveID)
-	}
-	if !config.Confirm(false) {
-		return nil
-	}
-	f, err := newFs(ctx, name, "", m)
-	if err != nil {
-		return errors.Wrap(err, "failed to make Fs to list Shared Drives")
-	}
-	fmt.Printf("Fetching Shared Drive list...\n")
-	teamDrives, err := f.listTeamDrives(ctx)
-	if err != nil {
-		return err
-	}
-	if len(teamDrives) == 0 {
-		fmt.Printf("No Shared Drives found in your account")
-		return nil
-	}
-	var driveIDs, driveNames []string
-	for _, teamDrive := range teamDrives {
-		driveIDs = append(driveIDs, teamDrive.Id)
-		driveNames = append(driveNames, teamDrive.Name)
-	}
-	driveID := config.Choose("Enter a Shared Drive ID", driveIDs, driveNames, true)
-	m.Set("team_drive", driveID)
-	m.Set("root_folder_id", "")
-	opt.TeamDriveID = driveID
-	opt.RootFolderID = ""
-	return nil
-}
-
 // getClient makes an http client according to the options
 func getClient(ctx context.Context, opt *Options) *http.Client {
 	t := fshttp.NewTransportCustom(ctx, func(t *http.Transport) {
@@ -1168,7 +1158,7 @@ func NewFs(ctx context.Context, name, path string, m configmap.Mapper) (fs.Fs, e
 			}
 		}
 		f.rootFolderID = rootID
-		fs.Debugf(f, "root_folder_id = %q - save this in the config to speed up startup", rootID)
+		fs.Debugf(f, "'root_folder_id = %s' - save this in the config to speed up startup", rootID)
 	}
 
 	f.dirCache = dircache.New(f.root, f.rootFolderID, f)