Integrate Notification Service into Tender Management System

- Added a new notification service to handle various notification types (email, SMS, push, OTP).
- Implemented configuration for the notification service, allowing customization via environment variables.
- Updated user and customer services to utilize the notification service for sending welcome emails and status updates.
- Introduced a builder pattern for constructing notification requests, enhancing usability and flexibility.
- Enhanced error handling and logging for notification operations, ensuring robust service integration.
- Updated documentation to include usage examples and configuration details for the new notification SDK.

pkg/notification/errors.go

@@ -0,0 +1,83 @@
+package notification
+
+import (
+	"fmt"
+	"net/http"
+)
+
+// Error types for notification SDK
+var (
+	ErrNotificationServiceUnavailable = fmt.Errorf("notification service unavailable")
+	ErrInvalidRequest                 = fmt.Errorf("invalid notification request")
+	ErrNetworkTimeout                 = fmt.Errorf("network timeout")
+	ErrUnauthorized                   = fmt.Errorf("unauthorized request")
+	ErrInternalError                  = fmt.Errorf("internal notification service error")
+)
+
+// ErrInvalidConfig represents configuration validation errors
+type ErrInvalidConfig struct {
+	Field   string
+	Message string
+}
+
+func (e ErrInvalidConfig) Error() string {
+	return fmt.Sprintf("invalid config field %s: %s", e.Field, e.Message)
+}
+
+// ErrHTTP represents HTTP-related errors with status codes
+type ErrHTTP struct {
+	StatusCode int
+	Message    string
+	Body       string
+}
+
+func (e ErrHTTP) Error() string {
+	return fmt.Sprintf("HTTP %d: %s", e.StatusCode, e.Message)
+}
+
+// ErrValidation represents validation errors
+type ErrValidation struct {
+	Field   string
+	Message string
+}
+
+func (e ErrValidation) Error() string {
+	return fmt.Sprintf("validation error for field %s: %s", e.Field, e.Message)
+}
+
+// ErrRetryExhausted represents retry exhaustion errors
+type ErrRetryExhausted struct {
+	Attempts    int
+	LastError   error
+	ElapsedTime string
+}
+
+func (e ErrRetryExhausted) Error() string {
+	return fmt.Sprintf("retry exhausted after %d attempts (%s): %v", e.Attempts, e.ElapsedTime, e.LastError)
+}
+
+// MapHTTPError maps HTTP status codes to appropriate errors
+func MapHTTPError(statusCode int, body string) error {
+	switch statusCode {
+	case http.StatusBadRequest:
+		return ErrHTTP{StatusCode: statusCode, Message: "bad request", Body: body}
+	case http.StatusUnauthorized:
+		return ErrHTTP{StatusCode: statusCode, Message: "unauthorized", Body: body}
+	case http.StatusForbidden:
+		return ErrHTTP{StatusCode: statusCode, Message: "forbidden", Body: body}
+	case http.StatusNotFound:
+		return ErrHTTP{StatusCode: statusCode, Message: "not found", Body: body}
+	case http.StatusUnprocessableEntity:
+		return ErrHTTP{StatusCode: statusCode, Message: "validation error", Body: body}
+	case http.StatusInternalServerError:
+		return ErrHTTP{StatusCode: statusCode, Message: "internal server error", Body: body}
+	case http.StatusBadGateway:
+		return ErrHTTP{StatusCode: statusCode, Message: "bad gateway", Body: body}
+	case http.StatusServiceUnavailable:
+		return ErrHTTP{StatusCode: statusCode, Message: "service unavailable", Body: body}
+	case http.StatusGatewayTimeout:
+		return ErrHTTP{StatusCode: statusCode, Message: "gateway timeout", Body: body}
+	default:
+		return ErrHTTP{StatusCode: statusCode, Message: "unknown error", Body: body}
+	}
+}