fix: command line format for showing followers

CHANGES:

- When viewing followers and followings from an account, the from flag
  must now be set by the user.
    - enbas show --type followers --from account --my-account
    - enbas show --type following --from account --account-name john

- New error type for unsupported show operations: Return an error if
  enbas detects an unsupported show operation (e.g. showing media from a
  list).

internal/executor/errors.go

@@ -52,6 +52,19 @@ func (e UnsupportedRemoveOperationError) Error() string {
 		"' is not supported"
 }
 
+type UnsupportedShowOperationError struct {
+	ResourceType         string
+	ShowFromResourceType string
+}
+
+func (e UnsupportedShowOperationError) Error() string {
+	return "showing '" +
+		e.ResourceType +
+		"' from '" +
+		e.ShowFromResourceType +
+		"' is not supported"
+}
+
 type EmptyContentError struct {
 	ResourceType string
 	Hint         string

internal/executor/show.go

@@ -287,6 +287,26 @@ func (s *ShowExecutor) showLists(gtsClient *client.Client) error {
 }
 
 func (s *ShowExecutor) showFollowers(gtsClient *client.Client) error {
+	if s.fromResourceType == "" {
+		return FlagNotSetError{flagText: flagFrom}
+	}
+
+	funcMap := map[string]func(*client.Client) error{
+		resourceAccount: s.showFollowersFromAccount,
+	}
+
+	doFunc, ok := funcMap[s.fromResourceType]
+	if !ok {
+		return UnsupportedShowOperationError{
+			ResourceType:         s.resourceType,
+			ShowFromResourceType: s.fromResourceType,
+		}
+	}
+
+	return doFunc(gtsClient)
+}
+
+func (s *ShowExecutor) showFollowersFromAccount(gtsClient *client.Client) error {
 	accountID, err := getAccountID(gtsClient, s.myAccount, s.accountName, s.config.CredentialsFile)
 	if err != nil {
 		return fmt.Errorf("received an error while getting the account ID: %w", err)
@@ -307,6 +327,26 @@ func (s *ShowExecutor) showFollowers(gtsClient *client.Client) error {
 }
 
 func (s *ShowExecutor) showFollowing(gtsClient *client.Client) error {
+	if s.fromResourceType == "" {
+		return FlagNotSetError{flagText: flagFrom}
+	}
+
+	funcMap := map[string]func(*client.Client) error{
+		resourceAccount: s.showFollowingFromAccount,
+	}
+
+	doFunc, ok := funcMap[s.fromResourceType]
+	if !ok {
+		return UnsupportedShowOperationError{
+			ResourceType:         s.resourceType,
+			ShowFromResourceType: s.fromResourceType,
+		}
+	}
+
+	return doFunc(gtsClient)
+}
+
+func (s *ShowExecutor) showFollowingFromAccount(gtsClient *client.Client) error {
 	accountID, err := getAccountID(gtsClient, s.myAccount, s.accountName, s.config.CredentialsFile)
 	if err != nil {
 		return fmt.Errorf("received an error while getting the account ID: %w", err)
@@ -449,7 +489,10 @@ func (s *ShowExecutor) showMedia(gtsClient *client.Client) error {
 
 	doFunc, ok := funcMap[s.fromResourceType]
 	if !ok {
-		return fmt.Errorf("do not support viewing media from %s", s.fromResourceType)
+		return UnsupportedShowOperationError{
+			ResourceType:         s.resourceType,
+			ShowFromResourceType: s.fromResourceType,
+		}
 	}
 
 	return doFunc(gtsClient)