validation/validator.go - KorAP/KorAP-MCP - Gitiles

 package validation

 import (
 	"fmt"
 	"net/url"
 	"regexp"
 	"strings"

 	"slices"

 	"github.com/korap/korap-mcp/service"
 	"github.com/rs/zerolog"
 )

 // Validator provides input validation and response schema validation
 type Validator struct {
 	logger zerolog.Logger
 }

 // New creates a new validator instance
 func New(logger zerolog.Logger) *Validator {
 	return &Validator{
 		logger: logger.With().Str("component", "validator").Logger(),
 	}
 }

 // SearchRequest holds the parameters for a search request validation
 type SearchRequest struct {
 	Query         string `json:"query"`
 	QueryLanguage string `json:"query_language,omitempty"`
 	Corpus        string `json:"corpus,omitempty"`
 	Count         int    `json:"count,omitempty"`
 }

 // MetadataRequest holds the parameters for a metadata request validation
 type MetadataRequest struct {
 	Action string `json:"action"`
 	Corpus string `json:"corpus,omitempty"`
 }

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

 func (e ValidationError) Error() string {
 	return fmt.Sprintf("validation error for field '%s' (value: '%s'): %s", e.Field, e.Value, e.Message)
 }

 // ValidationErrors represents multiple validation errors
 type ValidationErrors struct {
 	Errors []ValidationError `json:"errors"`
 }

 func (e ValidationErrors) Error() string {
 	if len(e.Errors) == 0 {
 		return "validation errors occurred"
 	}
 	var messages []string
 	for _, err := range e.Errors {
 		messages = append(messages, err.Error())
 	}
 	return strings.Join(messages, "; ")
 }

 // Regular expressions for validation
 var (
 	// Query language validation
 	validQueryLanguages = []string{"poliqarp", "poliqarpplus", "cosmas2", "annis", "cql", "cqp", "fcsql"}

 	// Corpus ID validation - KorAP collection queries with metadata fields, operators, and regex
 	corpusIDRegex = regexp.MustCompile(`^[a-zA-Z0-9._\-\s&|!=<>()/*"']+$`)

 	// Action validation for metadata requests
 	validMetadataActions = map[string]bool{
 		"list":       true,
 		"statistics": true,
 	}
 )

 // ValidateSearchRequest validates a search request
 func (v *Validator) ValidateSearchRequest(req SearchRequest) error {
 	var errors []ValidationError

 	// Validate query - required and non-empty
 	if strings.TrimSpace(req.Query) == "" {
 		errors = append(errors, ValidationError{
 			Field:   "query",
 			Value:   req.Query,
 			Message: "query is required and cannot be empty",
 		})
 	} else {
 		// Basic query validation - check for potentially dangerous patterns
 		if err := v.validateQuerySafety(req.Query); err != nil {
 			errors = append(errors, ValidationError{
 				Field:   "query",
 				Value:   req.Query,
 				Message: err.Error(),
 			})
 		}
 	}

 	// Validate query language if provided
 	if req.QueryLanguage != "" && !slices.Contains(validQueryLanguages, req.QueryLanguage) {
 		errors = append(errors, ValidationError{
 			Field:   "query_language",
 			Value:   req.QueryLanguage,
 			Message: fmt.Sprintf("invalid query language, must be one of: %s", strings.Join(validQueryLanguages, ", ")),
 		})
 	}

 	// Validate corpus if provided
 	if req.Corpus != "" {
 		if err := v.validateCorpusID(req.Corpus); err != nil {
 			errors = append(errors, ValidationError{
 				Field:   "corpus",
 				Value:   req.Corpus,
 				Message: err.Error(),
 			})
 		}
 	}

 	// Validate count if provided (0 means use default, so only validate non-zero values)
 	if req.Count < 0 || req.Count > 10000 {
 		errors = append(errors, ValidationError{
 			Field:   "count",
 			Value:   fmt.Sprintf("%d", req.Count),
 			Message: "count must be between 0 and 10000 (0 means use default)",
 		})
 	}

 	if len(errors) > 0 {
 		v.logger.Warn().Interface("errors", errors).Msg("Search request validation failed")
 		return ValidationErrors{Errors: errors}
 	}

 	v.logger.Debug().Interface("request", req).Msg("Search request validation passed")
 	return nil
 }

 // ValidateMetadataRequest validates a metadata request
 func (v *Validator) ValidateMetadataRequest(req MetadataRequest) error {
 	var errors []ValidationError

 	// Validate action - required
 	if strings.TrimSpace(req.Action) == "" {
 		errors = append(errors, ValidationError{
 			Field:   "action",
 			Value:   req.Action,
 			Message: "action is required and cannot be empty",
 		})
 	} else if !validMetadataActions[req.Action] {
 		var validActions []string
 		for action := range validMetadataActions {
 			validActions = append(validActions, action)
 		}
 		errors = append(errors, ValidationError{
 			Field:   "action",
 			Value:   req.Action,
 			Message: fmt.Sprintf("invalid action, must be one of: %s", strings.Join(validActions, ", ")),
 		})
 	}

 	// Validate corpus if provided
 	if req.Corpus != "" {
 		if err := v.validateCorpusID(req.Corpus); err != nil {
 			errors = append(errors, ValidationError{
 				Field:   "corpus",
 				Value:   req.Corpus,
 				Message: err.Error(),
 			})
 		}
 	}

 	if len(errors) > 0 {
 		v.logger.Warn().Interface("errors", errors).Msg("Metadata request validation failed")
 		return ValidationErrors{Errors: errors}
 	}

 	v.logger.Debug().Interface("request", req).Msg("Metadata request validation passed")
 	return nil
 }

 // ValidateSearchResponse validates a search response
 func (v *Validator) ValidateSearchResponse(resp *service.SearchResponse) error {
 	if resp == nil {
 		return fmt.Errorf("search response is nil")
 	}

 	var errors []ValidationError

 	// Validate meta structure
 	if resp.Meta.TotalResults < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "meta.totalResults",
 			Value:   fmt.Sprintf("%d", resp.Meta.TotalResults),
 			Message: "totalResults cannot be negative",
 		})
 	}

 	if resp.Meta.Count < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "meta.count",
 			Value:   fmt.Sprintf("%d", resp.Meta.Count),
 			Message: "count cannot be negative",
 		})
 	}

 	if resp.Meta.StartIndex < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "meta.startIndex",
 			Value:   fmt.Sprintf("%d", resp.Meta.StartIndex),
 			Message: "startIndex cannot be negative",
 		})
 	}

 	if resp.Meta.ItemsPerPage < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "meta.itemsPerPage",
 			Value:   fmt.Sprintf("%d", resp.Meta.ItemsPerPage),
 			Message: "itemsPerPage cannot be negative",
 		})
 	}

 	// Validate matches if present
 	if resp.Matches != nil {
 		for i, match := range resp.Matches {
 			if match.MatchID == "" {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("matches[%d].matchID", i),
 					Value:   "",
 					Message: "match ID is required",
 				})
 			}

 			if match.TextSigle == "" {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("matches[%d].textSigle", i),
 					Value:   "",
 					Message: "textSigle is required",
 				})
 			}

 			if match.Position < 0 {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("matches[%d].position", i),
 					Value:   fmt.Sprintf("%d", match.Position),
 					Message: "position cannot be negative",
 				})
 			}
 		}
 	}

 	if len(errors) > 0 {
 		v.logger.Warn().Interface("errors", errors).Msg("Search response validation failed")
 		return ValidationErrors{Errors: errors}
 	}

 	v.logger.Debug().Msg("Search response validation passed")
 	return nil
 }

 // ValidateCorpusListResponse validates a corpus list response
 func (v *Validator) ValidateCorpusListResponse(resp *service.CorpusListResponse) error {
 	if resp == nil {
 		return fmt.Errorf("corpus list response is nil")
 	}

 	var errors []ValidationError

 	// Validate corpus entries
 	if resp.Corpora != nil {
 		for i, corpus := range resp.Corpora {
 			if corpus.ID == "" {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("corpora[%d].id", i),
 					Value:   "",
 					Message: "corpus ID is required",
 				})
 			} else if err := v.validateCorpusID(corpus.ID); err != nil {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("corpora[%d].id", i),
 					Value:   corpus.ID,
 					Message: err.Error(),
 				})
 			}

 			if corpus.Name == "" {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("corpora[%d].name", i),
 					Value:   "",
 					Message: "corpus name is required",
 				})
 			}

 			if corpus.Documents < 0 {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("corpora[%d].documents", i),
 					Value:   fmt.Sprintf("%d", corpus.Documents),
 					Message: "document count cannot be negative",
 				})
 			}

 			if corpus.Tokens < 0 {
 				errors = append(errors, ValidationError{
 					Field:   fmt.Sprintf("corpora[%d].tokens", i),
 					Value:   fmt.Sprintf("%d", corpus.Tokens),
 					Message: "token count cannot be negative",
 				})
 			}
 		}
 	}

 	if len(errors) > 0 {
 		v.logger.Warn().Interface("errors", errors).Msg("Corpus list response validation failed")
 		return ValidationErrors{Errors: errors}
 	}

 	v.logger.Debug().Msg("Corpus list response validation passed")
 	return nil
 }

 // ValidateStatisticsResponse validates a statistics response
 func (v *Validator) ValidateStatisticsResponse(resp *service.StatisticsResponse) error {
 	if resp == nil {
 		return fmt.Errorf("statistics response is nil")
 	}

 	var errors []ValidationError

 	if resp.Documents < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "documents",
 			Value:   fmt.Sprintf("%d", resp.Documents),
 			Message: "document count cannot be negative",
 		})
 	}

 	if resp.Tokens < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "tokens",
 			Value:   fmt.Sprintf("%d", resp.Tokens),
 			Message: "token count cannot be negative",
 		})
 	}

 	if resp.Sentences < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "sentences",
 			Value:   fmt.Sprintf("%d", resp.Sentences),
 			Message: "sentence count cannot be negative",
 		})
 	}

 	if resp.Paragraphs < 0 {
 		errors = append(errors, ValidationError{
 			Field:   "paragraphs",
 			Value:   fmt.Sprintf("%d", resp.Paragraphs),
 			Message: "paragraph count cannot be negative",
 		})
 	}

 	if len(errors) > 0 {
 		v.logger.Warn().Interface("errors", errors).Msg("Statistics response validation failed")
 		return ValidationErrors{Errors: errors}
 	}

 	v.logger.Debug().Msg("Statistics response validation passed")
 	return nil
 }

 // validateQuerySafety performs basic security validation on queries
 func (v *Validator) validateQuerySafety(query string) error {
 	// Check for extremely long queries that could cause DoS
 	if len(query) > 10000 {
 		return fmt.Errorf("query is too long (max 10000 characters)")
 	}

 	// Check for potentially dangerous URL patterns
 	if strings.Contains(query, "://") {
 		if _, err := url.Parse(query); err == nil {
 			return fmt.Errorf("query appears to contain a URL which is not allowed")
 		}
 	}

 	// Check for excessive nesting that could cause parser issues
 	openParens := strings.Count(query, "(")
 	closeParens := strings.Count(query, ")")
 	if openParens != closeParens {
 		return fmt.Errorf("unmatched parentheses in query")
 	}
 	if openParens > 100 {
 		return fmt.Errorf("query has too many nested levels (max 100)")
 	}

 	return nil
 }

 // validateCorpusID validates a corpus identifier or collection query
 // This supports both simple corpus sigles (e.g., "DeReKo-2023-I") and complex
 // collection queries with metadata fields (e.g., "textClass = \"politics\" & pubDate in 2020")
 func (v *Validator) validateCorpusID(corpusID string) error {
 	if len(corpusID) == 0 {
 		return fmt.Errorf("corpus ID cannot be empty")
 	}

 	if len(corpusID) > 100 {
 		return fmt.Errorf("corpus ID is too long (max 100 characters)")
 	}

 	if !corpusIDRegex.MatchString(corpusID) {
 		return fmt.Errorf("collection query contains invalid characters (supports alphanumeric, dots, hyphens, underscores, spaces, quotes, operators & | ! = < > in, parentheses, and regex /pattern/)")
 	}

 	return nil
 }

 // SanitizeQuery performs basic sanitization on search queries
 func (v *Validator) SanitizeQuery(query string) string {
 	// Trim whitespace
 	sanitized := strings.TrimSpace(query)

 	// Remove any null bytes
 	sanitized = strings.ReplaceAll(sanitized, "\x00", "")

 	// Normalize whitespace
 	sanitized = regexp.MustCompile(`\s+`).ReplaceAllString(sanitized, " ")

 	v.logger.Debug().
 		Str("original", query).
 		Str("sanitized", sanitized).
 		Msg("Query sanitized")

 	return sanitized
 }

 // SanitizeCorpusID performs basic sanitization on corpus IDs
 func (v *Validator) SanitizeCorpusID(corpusID string) string {
 	// Trim whitespace
 	sanitized := strings.TrimSpace(corpusID)

 	// Remove any null bytes
 	sanitized = strings.ReplaceAll(sanitized, "\x00", "")

 	// Convert to lowercase for consistency
 	sanitized = strings.ToLower(sanitized)

 	v.logger.Debug().
 		Str("original", corpusID).
 		Str("sanitized", sanitized).
 		Msg("Corpus ID sanitized")

 	return sanitized
 }
	package validation

	import (
	"fmt"
	"net/url"
	"regexp"
	"strings"

	"slices"

	"github.com/korap/korap-mcp/service"
	"github.com/rs/zerolog"
	)

	// Validator provides input validation and response schema validation
	type Validator struct {
	logger zerolog.Logger
	}

	// New creates a new validator instance
	func New(logger zerolog.Logger) *Validator {
	return &Validator{
	logger: logger.With().Str("component", "validator").Logger(),
	}
	}

	// SearchRequest holds the parameters for a search request validation
	type SearchRequest struct {
	Query string `json:"query"`
	QueryLanguage string `json:"query_language,omitempty"`
	Corpus string `json:"corpus,omitempty"`
	Count int `json:"count,omitempty"`
	}

	// MetadataRequest holds the parameters for a metadata request validation
	type MetadataRequest struct {
	Action string `json:"action"`
	Corpus string `json:"corpus,omitempty"`
	}

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

	func (e ValidationError) Error() string {
	return fmt.Sprintf("validation error for field '%s' (value: '%s'): %s", e.Field, e.Value, e.Message)
	}

	// ValidationErrors represents multiple validation errors
	type ValidationErrors struct {
	Errors []ValidationError `json:"errors"`
	}

	func (e ValidationErrors) Error() string {
	if len(e.Errors) == 0 {
	return "validation errors occurred"
	}
	var messages []string
	for _, err := range e.Errors {
	messages = append(messages, err.Error())
	}
	return strings.Join(messages, "; ")
	}

	// Regular expressions for validation
	var (
	// Query language validation
	validQueryLanguages = []string{"poliqarp", "poliqarpplus", "cosmas2", "annis", "cql", "cqp", "fcsql"}

	// Corpus ID validation - KorAP collection queries with metadata fields, operators, and regex
	corpusIDRegex = regexp.MustCompile(`^[a-zA-Z0-9._\-\s&\|!=<>()/*"']+$`)

	// Action validation for metadata requests
	validMetadataActions = map[string]bool{
	"list": true,
	"statistics": true,
	}
	)

	// ValidateSearchRequest validates a search request
	func (v *Validator) ValidateSearchRequest(req SearchRequest) error {
	var errors []ValidationError

	// Validate query - required and non-empty
	if strings.TrimSpace(req.Query) == "" {
	errors = append(errors, ValidationError{
	Field: "query",
	Value: req.Query,
	Message: "query is required and cannot be empty",
	})
	} else {
	// Basic query validation - check for potentially dangerous patterns
	if err := v.validateQuerySafety(req.Query); err != nil {
	errors = append(errors, ValidationError{
	Field: "query",
	Value: req.Query,
	Message: err.Error(),
	})
	}
	}

	// Validate query language if provided
	if req.QueryLanguage != "" && !slices.Contains(validQueryLanguages, req.QueryLanguage) {
	errors = append(errors, ValidationError{
	Field: "query_language",
	Value: req.QueryLanguage,
	Message: fmt.Sprintf("invalid query language, must be one of: %s", strings.Join(validQueryLanguages, ", ")),
	})
	}

	// Validate corpus if provided
	if req.Corpus != "" {
	if err := v.validateCorpusID(req.Corpus); err != nil {
	errors = append(errors, ValidationError{
	Field: "corpus",
	Value: req.Corpus,
	Message: err.Error(),
	})
	}
	}

	// Validate count if provided (0 means use default, so only validate non-zero values)
	if req.Count < 0 \|\| req.Count > 10000 {
	errors = append(errors, ValidationError{
	Field: "count",
	Value: fmt.Sprintf("%d", req.Count),
	Message: "count must be between 0 and 10000 (0 means use default)",
	})
	}

	if len(errors) > 0 {
	v.logger.Warn().Interface("errors", errors).Msg("Search request validation failed")
	return ValidationErrors{Errors: errors}
	}

	v.logger.Debug().Interface("request", req).Msg("Search request validation passed")
	return nil
	}

	// ValidateMetadataRequest validates a metadata request
	func (v *Validator) ValidateMetadataRequest(req MetadataRequest) error {
	var errors []ValidationError

	// Validate action - required
	if strings.TrimSpace(req.Action) == "" {
	errors = append(errors, ValidationError{
	Field: "action",
	Value: req.Action,
	Message: "action is required and cannot be empty",
	})
	} else if !validMetadataActions[req.Action] {
	var validActions []string
	for action := range validMetadataActions {
	validActions = append(validActions, action)
	}
	errors = append(errors, ValidationError{
	Field: "action",
	Value: req.Action,
	Message: fmt.Sprintf("invalid action, must be one of: %s", strings.Join(validActions, ", ")),
	})
	}

	// Validate corpus if provided
	if req.Corpus != "" {
	if err := v.validateCorpusID(req.Corpus); err != nil {
	errors = append(errors, ValidationError{
	Field: "corpus",
	Value: req.Corpus,
	Message: err.Error(),
	})
	}
	}

	if len(errors) > 0 {
	v.logger.Warn().Interface("errors", errors).Msg("Metadata request validation failed")
	return ValidationErrors{Errors: errors}
	}

	v.logger.Debug().Interface("request", req).Msg("Metadata request validation passed")
	return nil
	}

	// ValidateSearchResponse validates a search response
	func (v Validator) ValidateSearchResponse(resp service.SearchResponse) error {
	if resp == nil {
	return fmt.Errorf("search response is nil")
	}

	var errors []ValidationError

	// Validate meta structure
	if resp.Meta.TotalResults < 0 {
	errors = append(errors, ValidationError{
	Field: "meta.totalResults",
	Value: fmt.Sprintf("%d", resp.Meta.TotalResults),
	Message: "totalResults cannot be negative",
	})
	}

	if resp.Meta.Count < 0 {
	errors = append(errors, ValidationError{
	Field: "meta.count",
	Value: fmt.Sprintf("%d", resp.Meta.Count),
	Message: "count cannot be negative",
	})
	}

	if resp.Meta.StartIndex < 0 {
	errors = append(errors, ValidationError{
	Field: "meta.startIndex",
	Value: fmt.Sprintf("%d", resp.Meta.StartIndex),
	Message: "startIndex cannot be negative",
	})
	}

	if resp.Meta.ItemsPerPage < 0 {
	errors = append(errors, ValidationError{
	Field: "meta.itemsPerPage",
	Value: fmt.Sprintf("%d", resp.Meta.ItemsPerPage),
	Message: "itemsPerPage cannot be negative",
	})
	}

	// Validate matches if present
	if resp.Matches != nil {
	for i, match := range resp.Matches {
	if match.MatchID == "" {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("matches[%d].matchID", i),
	Value: "",
	Message: "match ID is required",
	})
	}

	if match.TextSigle == "" {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("matches[%d].textSigle", i),
	Value: "",
	Message: "textSigle is required",
	})
	}

	if match.Position < 0 {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("matches[%d].position", i),
	Value: fmt.Sprintf("%d", match.Position),
	Message: "position cannot be negative",
	})
	}
	}
	}

	if len(errors) > 0 {
	v.logger.Warn().Interface("errors", errors).Msg("Search response validation failed")
	return ValidationErrors{Errors: errors}
	}

	v.logger.Debug().Msg("Search response validation passed")
	return nil
	}

	// ValidateCorpusListResponse validates a corpus list response
	func (v Validator) ValidateCorpusListResponse(resp service.CorpusListResponse) error {
	if resp == nil {
	return fmt.Errorf("corpus list response is nil")
	}

	var errors []ValidationError

	// Validate corpus entries
	if resp.Corpora != nil {
	for i, corpus := range resp.Corpora {
	if corpus.ID == "" {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("corpora[%d].id", i),
	Value: "",
	Message: "corpus ID is required",
	})
	} else if err := v.validateCorpusID(corpus.ID); err != nil {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("corpora[%d].id", i),
	Value: corpus.ID,
	Message: err.Error(),
	})
	}

	if corpus.Name == "" {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("corpora[%d].name", i),
	Value: "",
	Message: "corpus name is required",
	})
	}

	if corpus.Documents < 0 {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("corpora[%d].documents", i),
	Value: fmt.Sprintf("%d", corpus.Documents),
	Message: "document count cannot be negative",
	})
	}

	if corpus.Tokens < 0 {
	errors = append(errors, ValidationError{
	Field: fmt.Sprintf("corpora[%d].tokens", i),
	Value: fmt.Sprintf("%d", corpus.Tokens),
	Message: "token count cannot be negative",
	})
	}
	}
	}

	if len(errors) > 0 {
	v.logger.Warn().Interface("errors", errors).Msg("Corpus list response validation failed")
	return ValidationErrors{Errors: errors}
	}

	v.logger.Debug().Msg("Corpus list response validation passed")
	return nil
	}

	// ValidateStatisticsResponse validates a statistics response
	func (v Validator) ValidateStatisticsResponse(resp service.StatisticsResponse) error {
	if resp == nil {
	return fmt.Errorf("statistics response is nil")
	}

	var errors []ValidationError

	if resp.Documents < 0 {
	errors = append(errors, ValidationError{
	Field: "documents",
	Value: fmt.Sprintf("%d", resp.Documents),
	Message: "document count cannot be negative",
	})
	}

	if resp.Tokens < 0 {
	errors = append(errors, ValidationError{
	Field: "tokens",
	Value: fmt.Sprintf("%d", resp.Tokens),
	Message: "token count cannot be negative",
	})
	}

	if resp.Sentences < 0 {
	errors = append(errors, ValidationError{
	Field: "sentences",
	Value: fmt.Sprintf("%d", resp.Sentences),
	Message: "sentence count cannot be negative",
	})
	}

	if resp.Paragraphs < 0 {
	errors = append(errors, ValidationError{
	Field: "paragraphs",
	Value: fmt.Sprintf("%d", resp.Paragraphs),
	Message: "paragraph count cannot be negative",
	})
	}

	if len(errors) > 0 {
	v.logger.Warn().Interface("errors", errors).Msg("Statistics response validation failed")
	return ValidationErrors{Errors: errors}
	}

	v.logger.Debug().Msg("Statistics response validation passed")
	return nil
	}

	// validateQuerySafety performs basic security validation on queries
	func (v *Validator) validateQuerySafety(query string) error {
	// Check for extremely long queries that could cause DoS
	if len(query) > 10000 {
	return fmt.Errorf("query is too long (max 10000 characters)")
	}

	// Check for potentially dangerous URL patterns
	if strings.Contains(query, "://") {
	if _, err := url.Parse(query); err == nil {
	return fmt.Errorf("query appears to contain a URL which is not allowed")
	}
	}

	// Check for excessive nesting that could cause parser issues
	openParens := strings.Count(query, "(")
	closeParens := strings.Count(query, ")")
	if openParens != closeParens {
	return fmt.Errorf("unmatched parentheses in query")
	}
	if openParens > 100 {
	return fmt.Errorf("query has too many nested levels (max 100)")
	}

	return nil
	}

	// validateCorpusID validates a corpus identifier or collection query
	// This supports both simple corpus sigles (e.g., "DeReKo-2023-I") and complex
	// collection queries with metadata fields (e.g., "textClass = \"politics\" & pubDate in 2020")
	func (v *Validator) validateCorpusID(corpusID string) error {
	if len(corpusID) == 0 {
	return fmt.Errorf("corpus ID cannot be empty")
	}

	if len(corpusID) > 100 {
	return fmt.Errorf("corpus ID is too long (max 100 characters)")
	}

	if !corpusIDRegex.MatchString(corpusID) {
	return fmt.Errorf("collection query contains invalid characters (supports alphanumeric, dots, hyphens, underscores, spaces, quotes, operators & \| ! = < > in, parentheses, and regex /pattern/)")
	}

	return nil
	}

	// SanitizeQuery performs basic sanitization on search queries
	func (v *Validator) SanitizeQuery(query string) string {
	// Trim whitespace
	sanitized := strings.TrimSpace(query)

	// Remove any null bytes
	sanitized = strings.ReplaceAll(sanitized, "\x00", "")

	// Normalize whitespace
	sanitized = regexp.MustCompile(`\s+`).ReplaceAllString(sanitized, " ")

	v.logger.Debug().
	Str("original", query).
	Str("sanitized", sanitized).
	Msg("Query sanitized")

	return sanitized
	}

	// SanitizeCorpusID performs basic sanitization on corpus IDs
	func (v *Validator) SanitizeCorpusID(corpusID string) string {
	// Trim whitespace
	sanitized := strings.TrimSpace(corpusID)

	// Remove any null bytes
	sanitized = strings.ReplaceAll(sanitized, "\x00", "")

	// Convert to lowercase for consistency
	sanitized = strings.ToLower(sanitized)

	v.logger.Debug().
	Str("original", corpusID).
	Str("sanitized", sanitized).
	Msg("Corpus ID sanitized")

	return sanitized
	}