// errors.go provides error classification for AWS Cognito errors.
// It maps AWS error types to appropriate HTTP status codes and sanitized error messages
// suitable for returning in API responses without leaking sensitive information.
package usermanagement

import (
	"errors"
	"fmt"
	"net/http"
	"strings"

	"github.com/aws/aws-sdk-go-v2/service/cognitoidentityprovider/types"
	"github.com/aws/smithy-go"
)

// CognitoErrorType represents a machine-readable error classification.
type CognitoErrorType string

const (
	// ErrTypeUserNotFound indicates the user does not exist in Cognito.
	ErrTypeUserNotFound CognitoErrorType = "UserNotFound"

	// ErrTypeAccessDenied indicates the caller does not have permission to perform the operation.
	ErrTypeAccessDenied CognitoErrorType = "AccessDenied"

	// ErrTypeNotAuthorized indicates the caller is not authorized (e.g., invalid credentials).
	ErrTypeNotAuthorized CognitoErrorType = "NotAuthorized"

	// ErrTypeInvalidParameter indicates an invalid parameter was provided.
	ErrTypeInvalidParameter CognitoErrorType = "InvalidParameter"

	// ErrTypeRateLimited indicates too many requests were made.
	ErrTypeRateLimited CognitoErrorType = "RateLimited"

	// ErrTypeServiceUnavailable indicates the Cognito service is temporarily unavailable.
	ErrTypeServiceUnavailable CognitoErrorType = "ServiceUnavailable"

	// ErrTypeServiceError indicates a general error communicating with Cognito.
	ErrTypeServiceError CognitoErrorType = "ServiceError"

	// ErrTypeUserExists indicates the user already exists in Cognito.
	ErrTypeUserExists CognitoErrorType = "UserExists"
)

// CognitoErrorInfo contains classified error information suitable for HTTP responses.
// The Message and Details fields are sanitized to avoid leaking sensitive information
// like ARNs, internal paths, or request IDs.
type CognitoErrorInfo struct {
	// HTTPStatus is the appropriate HTTP status code for this error type.
	HTTPStatus int

	// ErrorType is a machine-readable error classification.
	ErrorType CognitoErrorType

	// Message is a user-friendly error message safe for HTTP responses.
	Message string

	// Details provides additional error context (sanitized).
	Details string
}

// ClassifyCognitoError analyzes a Cognito error and returns appropriate HTTP response info.
// The returned CognitoErrorInfo contains sanitized messages suitable for API responses.
//
// Parameters:
//   - err: The error returned from a Cognito operation
//   - email: The user's email address for context in error messages
//
// Returns:
//   - CognitoErrorInfo: Classified error information with appropriate HTTP status and messages
func ClassifyCognitoError(err error, email string) CognitoErrorInfo {
	if err == nil {
		return CognitoErrorInfo{
			HTTPStatus: http.StatusOK,
			ErrorType:  "",
			Message:    "",
			Details:    "",
		}
	}

	// Check for specific Cognito SDK error types
	var userNotFoundErr *types.UserNotFoundException
	if errors.As(err, &userNotFoundErr) {
		return CognitoErrorInfo{
			HTTPStatus: http.StatusNotFound,
			ErrorType:  ErrTypeUserNotFound,
			Message:    fmt.Sprintf("User not found: %s", email),
			Details:    "The specified user does not exist in Cognito",
		}
	}

	var notAuthorizedErr *types.NotAuthorizedException
	if errors.As(err, &notAuthorizedErr) {
		return CognitoErrorInfo{
			HTTPStatus: http.StatusUnauthorized,
			ErrorType:  ErrTypeNotAuthorized,
			Message:    "Not authorized to perform this operation",
			Details:    sanitizeErrorMessage(err.Error()),
		}
	}

	var invalidParamErr *types.InvalidParameterException
	if errors.As(err, &invalidParamErr) {
		return CognitoErrorInfo{
			HTTPStatus: http.StatusBadRequest,
			ErrorType:  ErrTypeInvalidParameter,
			Message:    "Invalid parameter in request",
			Details:    sanitizeErrorMessage(err.Error()),
		}
	}

	var tooManyRequestsErr *types.TooManyRequestsException
	if errors.As(err, &tooManyRequestsErr) {
		return CognitoErrorInfo{
			HTTPStatus: http.StatusTooManyRequests,
			ErrorType:  ErrTypeRateLimited,
			Message:    "Too many requests to Cognito",
			Details:    "Rate limit exceeded. Please retry after a short delay.",
		}
	}

	var internalErr *types.InternalErrorException
	if errors.As(err, &internalErr) {
		return CognitoErrorInfo{
			HTTPStatus: http.StatusServiceUnavailable,
			ErrorType:  ErrTypeServiceUnavailable,
			Message:    "Cognito service temporarily unavailable",
			Details:    "Internal service error. Please retry later.",
		}
	}

	var usernameExistsErr *types.UsernameExistsException
	if errors.As(err, &usernameExistsErr) {
		return CognitoErrorInfo{
			HTTPStatus: http.StatusConflict,
			ErrorType:  ErrTypeUserExists,
			Message:    fmt.Sprintf("User already exists: %s", email),
			Details:    "A user with this email already exists in Cognito",
		}
	}

	// Check for generic AWS API errors (including AccessDeniedException)
	var apiErr smithy.APIError
	if errors.As(err, &apiErr) {
		return classifyAPIError(apiErr, email)
	}

	// Default: treat as a generic service communication error
	return CognitoErrorInfo{
		HTTPStatus: http.StatusBadGateway,
		ErrorType:  ErrTypeServiceError,
		Message:    "Failed to communicate with Cognito",
		Details:    sanitizeErrorMessage(err.Error()),
	}
}

// classifyAPIError handles generic AWS API errors that may not have specific SDK types.
//
// Parameters:
//   - apiErr: The AWS API error
//   - email: The user's email address for context in error messages
//
// Returns:
//   - CognitoErrorInfo: Classified error information
func classifyAPIError(apiErr smithy.APIError, email string) CognitoErrorInfo {
	code := apiErr.ErrorCode()

	switch code {
	case "AccessDeniedException":
		return CognitoErrorInfo{
			HTTPStatus: http.StatusForbidden,
			ErrorType:  ErrTypeAccessDenied,
			Message:    "Access denied to Cognito user pool",
			Details:    "The service does not have permission to perform this Cognito operation",
		}

	case "UserNotFoundException":
		return CognitoErrorInfo{
			HTTPStatus: http.StatusNotFound,
			ErrorType:  ErrTypeUserNotFound,
			Message:    fmt.Sprintf("User not found: %s", email),
			Details:    "The specified user does not exist in Cognito",
		}

	case "NotAuthorizedException":
		return CognitoErrorInfo{
			HTTPStatus: http.StatusUnauthorized,
			ErrorType:  ErrTypeNotAuthorized,
			Message:    "Not authorized to perform this operation",
			Details:    sanitizeErrorMessage(apiErr.ErrorMessage()),
		}

	case "InvalidParameterException":
		return CognitoErrorInfo{
			HTTPStatus: http.StatusBadRequest,
			ErrorType:  ErrTypeInvalidParameter,
			Message:    "Invalid parameter in request",
			Details:    sanitizeErrorMessage(apiErr.ErrorMessage()),
		}

	case "TooManyRequestsException":
		return CognitoErrorInfo{
			HTTPStatus: http.StatusTooManyRequests,
			ErrorType:  ErrTypeRateLimited,
			Message:    "Too many requests to Cognito",
			Details:    "Rate limit exceeded. Please retry after a short delay.",
		}

	case "ServiceUnavailable", "InternalError", "InternalErrorException":
		return CognitoErrorInfo{
			HTTPStatus: http.StatusServiceUnavailable,
			ErrorType:  ErrTypeServiceUnavailable,
			Message:    "Cognito service temporarily unavailable",
			Details:    "Internal service error. Please retry later.",
		}

	case "UsernameExistsException":
		return CognitoErrorInfo{
			HTTPStatus: http.StatusConflict,
			ErrorType:  ErrTypeUserExists,
			Message:    fmt.Sprintf("User already exists: %s", email),
			Details:    "A user with this email already exists in Cognito",
		}

	default:
		return CognitoErrorInfo{
			HTTPStatus: http.StatusBadGateway,
			ErrorType:  ErrTypeServiceError,
			Message:    "Failed to communicate with Cognito",
			Details:    sanitizeErrorMessage(apiErr.ErrorMessage()),
		}
	}
}

// sanitizeErrorMessage removes sensitive information from error messages.
// It strips out ARNs, request IDs, and internal resource names.
//
// Parameters:
//   - msg: The raw error message
//
// Returns:
//   - string: The sanitized error message
func sanitizeErrorMessage(msg string) string {
	msg = removeARNs(msg)
	msg = removeRequestIDs(msg)
	msg = normalizeWhitespace(msg)
	return msg
}

// removeARNs replaces all AWS ARNs with [REDACTED].
func removeARNs(msg string) string {
	for {
		start := strings.Index(msg, "arn:aws:")
		if start == -1 {
			return msg
		}
		end := findEndOfToken(msg, start)
		msg = msg[:start] + "[REDACTED]" + msg[end:]
	}
}

// removeRequestIDs removes request ID patterns and their values from the message.
func removeRequestIDs(msg string) string {
	patterns := []string{"requestid:", "request-id:", "request id:"}
	msgLower := strings.ToLower(msg)

	for _, pattern := range patterns {
		for {
			idx := strings.Index(msgLower, pattern)
			if idx == -1 {
				break
			}
			end := idx + len(pattern)
			end = skipWhitespace(msg, end)
			end = findEndOfToken(msg, end)
			msg = msg[:idx] + msg[end:]
			msgLower = strings.ToLower(msg)
		}
	}
	return msg
}

// findEndOfToken finds the end of a token (space, comma, or newline delimited).
func findEndOfToken(msg string, start int) int {
	end := start
	for end < len(msg) && !isTokenDelimiter(msg[end]) {
		end++
	}
	return end
}

// isTokenDelimiter returns true if the character is a token delimiter.
func isTokenDelimiter(c byte) bool {
	return c == ' ' || c == ',' || c == '\n' || c == '\r'
}

// skipWhitespace advances past whitespace characters.
func skipWhitespace(msg string, pos int) int {
	for pos < len(msg) && (msg[pos] == ' ' || msg[pos] == '\t') {
		pos++
	}
	return pos
}

// normalizeWhitespace trims and collapses multiple spaces.
func normalizeWhitespace(msg string) string {
	msg = strings.TrimSpace(msg)
	for strings.Contains(msg, "  ") {
		msg = strings.ReplaceAll(msg, "  ", " ")
	}
	return msg
}