porting - part 1 and 2 completed and working

garth/errors/errors.go

@@ -0,0 +1,69 @@
+package errors
+
+import "fmt"
+
+// AuthenticationError represents authentication failures
+type AuthenticationError struct {
+	Message string
+	Cause   error
+}
+
+func (e *AuthenticationError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("authentication error: %s: %v", e.Message, e.Cause)
+	}
+	return fmt.Sprintf("authentication error: %s", e.Message)
+}
+
+// OAuthError represents OAuth token-related errors
+type OAuthError struct {
+	Message string
+	Cause   error
+}
+
+func (e *OAuthError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("OAuth error: %s: %v", e.Message, e.Cause)
+	}
+	return fmt.Sprintf("OAuth error: %s", e.Message)
+}
+
+// APIError represents errors from API calls
+type APIError struct {
+	StatusCode int
+	Response   string
+	Cause      error
+}
+
+func (e *APIError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("API error (status %d): %s: %v", e.StatusCode, e.Response, e.Cause)
+	}
+	return fmt.Sprintf("API error (status %d): %s", e.StatusCode, e.Response)
+}
+
+// IOError represents file I/O errors
+type IOError struct {
+	Message string
+	Cause   error
+}
+
+func (e *IOError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("I/O error: %s: %v", e.Message, e.Cause)
+	}
+	return fmt.Sprintf("I/O error: %s", e.Message)
+}
+
+// ValidationError represents input validation failures
+type ValidationError struct {
+	Message string
+	Field   string
+}
+
+func (e *ValidationError) Error() string {
+	if e.Field != "" {
+		return fmt.Sprintf("validation error for %s: %s", e.Field, e.Message)
+	}
+	return fmt.Sprintf("validation error: %s", e.Message)
+}