backend-service/internal/errors/errors.go

package errors

import (
	"fmt"
	"net/http"
)

// ErrorCode represents application-specific error codes
type ErrorCode string

const (
	// Authentication errors
	ErrCodeInvalidCredentials ErrorCode = "INVALID_CREDENTIALS"
	ErrCodeTokenExpired       ErrorCode = "TOKEN_EXPIRED"
	ErrCodeTokenInvalid       ErrorCode = "TOKEN_INVALID"
	ErrCodeUnauthorized       ErrorCode = "UNAUTHORIZED"
	ErrCodeForbidden          ErrorCode = "FORBIDDEN"

	// Validation errors
	ErrCodeValidationFailed ErrorCode = "VALIDATION_FAILED"
	ErrCodeInvalidInput     ErrorCode = "INVALID_INPUT"
	ErrCodeMissingField     ErrorCode = "MISSING_FIELD"

	// Resource errors
	ErrCodeNotFound      ErrorCode = "NOT_FOUND"
	ErrCodeAlreadyExists ErrorCode = "ALREADY_EXISTS"
	ErrCodeConflict      ErrorCode = "CONFLICT"

	// Business logic errors
	ErrCodeSlotUnavailable     ErrorCode = "SLOT_UNAVAILABLE"
	ErrCodeBookingNotFound     ErrorCode = "BOOKING_NOT_FOUND"
	ErrCodePaymentFailed       ErrorCode = "PAYMENT_FAILED"
	ErrCodePaymentRequired     ErrorCode = "PAYMENT_REQUIRED"
	ErrCodeMeetingCreateFailed ErrorCode = "MEETING_CREATE_FAILED"

	// System errors
	ErrCodeInternalServer     ErrorCode = "INTERNAL_SERVER_ERROR"
	ErrCodeDatabaseError      ErrorCode = "DATABASE_ERROR"
	ErrCodeExternalAPI        ErrorCode = "EXTERNAL_API_ERROR"
	ErrCodeServiceUnavailable ErrorCode = "SERVICE_UNAVAILABLE"

	// Rate limiting errors
	ErrCodeRateLimitExceeded ErrorCode = "RATE_LIMIT_EXCEEDED"
	ErrCodeTooManyRequests   ErrorCode = "TOO_MANY_REQUESTS"
)

// AppError represents an application error with structured information
type AppError struct {
	Code       ErrorCode              `json:"code"`
	Message    string                 `json:"message"`
	Details    string                 `json:"details,omitempty"`
	HTTPStatus int                    `json:"-"`
	Fields     map[string]interface{} `json:"fields,omitempty"`
	Cause      error                  `json:"-"`
}

// Error implements the error interface
func (e *AppError) Error() string {
	if e.Details != "" {
		return fmt.Sprintf("%s: %s - %s", e.Code, e.Message, e.Details)
	}
	return fmt.Sprintf("%s: %s", e.Code, e.Message)
}

// Unwrap returns the underlying cause error
func (e *AppError) Unwrap() error {
	return e.Cause
}

// WithDetails adds details to the error
func (e *AppError) WithDetails(details string) *AppError {
	e.Details = details
	return e
}

// WithField adds a field to the error
func (e *AppError) WithField(key string, value interface{}) *AppError {
	if e.Fields == nil {
		e.Fields = make(map[string]interface{})
	}
	e.Fields[key] = value
	return e
}

// WithFields adds multiple fields to the error
func (e *AppError) WithFields(fields map[string]interface{}) *AppError {
	if e.Fields == nil {
		e.Fields = make(map[string]interface{})
	}
	for k, v := range fields {
		e.Fields[k] = v
	}
	return e
}

// WithCause adds a cause error
func (e *AppError) WithCause(cause error) *AppError {
	e.Cause = cause
	return e
}

// New creates a new AppError
func New(code ErrorCode, message string, httpStatus int) *AppError {
	return &AppError{
		Code:       code,
		Message:    message,
		HTTPStatus: httpStatus,
	}
}

// Wrap wraps an existing error with application error information
func Wrap(err error, code ErrorCode, message string, httpStatus int) *AppError {
	return &AppError{
		Code:       code,
		Message:    message,
		HTTPStatus: httpStatus,
		Cause:      err,
	}
}

// Predefined common errors
var (
	// Authentication errors
	ErrInvalidCredentials = New(ErrCodeInvalidCredentials, "Invalid email or password", http.StatusUnauthorized)
	ErrTokenExpired       = New(ErrCodeTokenExpired, "Authentication token has expired", http.StatusUnauthorized)
	ErrTokenInvalid       = New(ErrCodeTokenInvalid, "Invalid authentication token", http.StatusUnauthorized)
	ErrUnauthorized       = New(ErrCodeUnauthorized, "Authentication required", http.StatusUnauthorized)
	ErrForbidden          = New(ErrCodeForbidden, "Access denied", http.StatusForbidden)

	// Validation errors
	ErrValidationFailed = New(ErrCodeValidationFailed, "Request validation failed", http.StatusBadRequest)
	ErrInvalidInput     = New(ErrCodeInvalidInput, "Invalid input provided", http.StatusBadRequest)
	ErrMissingField     = New(ErrCodeMissingField, "Required field is missing", http.StatusBadRequest)

	// Resource errors
	ErrNotFound      = New(ErrCodeNotFound, "Resource not found", http.StatusNotFound)
	ErrAlreadyExists = New(ErrCodeAlreadyExists, "Resource already exists", http.StatusConflict)
	ErrConflict      = New(ErrCodeConflict, "Resource conflict", http.StatusConflict)

	// Business logic errors
	ErrSlotUnavailable     = New(ErrCodeSlotUnavailable, "Selected time slot is not available", http.StatusConflict)
	ErrBookingNotFound     = New(ErrCodeBookingNotFound, "Booking not found", http.StatusNotFound)
	ErrPaymentFailed       = New(ErrCodePaymentFailed, "Payment processing failed", http.StatusPaymentRequired)
	ErrPaymentRequired     = New(ErrCodePaymentRequired, "Payment is required", http.StatusPaymentRequired)
	ErrMeetingCreateFailed = New(ErrCodeMeetingCreateFailed, "Failed to create meeting room", http.StatusInternalServerError)

	// System errors
	ErrInternalServer     = New(ErrCodeInternalServer, "Internal server error", http.StatusInternalServerError)
	ErrDatabaseError      = New(ErrCodeDatabaseError, "Database operation failed", http.StatusInternalServerError)
	ErrExternalAPI        = New(ErrCodeExternalAPI, "External API error", http.StatusBadGateway)
	ErrServiceUnavailable = New(ErrCodeServiceUnavailable, "Service temporarily unavailable", http.StatusServiceUnavailable)

	// Rate limiting errors
	ErrRateLimitExceeded = New(ErrCodeRateLimitExceeded, "Rate limit exceeded", http.StatusTooManyRequests)
	ErrTooManyRequests   = New(ErrCodeTooManyRequests, "Too many requests", http.StatusTooManyRequests)
)

// IsAppError checks if an error is an AppError
func IsAppError(err error) bool {
	_, ok := err.(*AppError)
	return ok
}

// GetAppError extracts AppError from error, returns nil if not an AppError
func GetAppError(err error) *AppError {
	if appErr, ok := err.(*AppError); ok {
		return appErr
	}
	return nil
}

// ErrorResponse represents the JSON error response structure
type ErrorResponse struct {
	Error ErrorInfo `json:"error"`
}

// ErrorInfo contains error information for API responses
type ErrorInfo struct {
	Code    ErrorCode              `json:"code"`
	Message string                 `json:"message"`
	Details string                 `json:"details,omitempty"`
	Fields  map[string]interface{} `json:"fields,omitempty"`
}

// ToErrorResponse converts an AppError to an ErrorResponse
func (e *AppError) ToErrorResponse() ErrorResponse {
	return ErrorResponse{
		Error: ErrorInfo{
			Code:    e.Code,
			Message: e.Message,
			Details: e.Details,
			Fields:  e.Fields,
		},
	}
}

// ValidationError represents a field validation error
type ValidationError struct {
	Field   string      `json:"field"`
	Message string      `json:"message"`
	Value   interface{} `json:"value,omitempty"`
}

// ValidationErrors represents multiple validation errors
type ValidationErrors []ValidationError

// Error implements the error interface for ValidationErrors
func (ve ValidationErrors) Error() string {
	if len(ve) == 0 {
		return "validation failed"
	}
	if len(ve) == 1 {
		return fmt.Sprintf("validation failed: %s %s", ve[0].Field, ve[0].Message)
	}
	return fmt.Sprintf("validation failed: %d errors", len(ve))
}

// ToAppError converts ValidationErrors to AppError
func (ve ValidationErrors) ToAppError() *AppError {
	fields := make(map[string]interface{})
	for _, err := range ve {
		fields[err.Field] = err.Message
	}

	return ErrValidationFailed.WithFields(fields).WithDetails(ve.Error())
}

// NewValidationError creates a new validation error
func NewValidationError(field, message string, value interface{}) ValidationError {
	return ValidationError{
		Field:   field,
		Message: message,
		Value:   value,
	}
}