package validation

import (
	"fmt"
	"regexp"
	"strings"
	"unicode"
)

var MaxLengths = map[string]int{
	"title":       200,
	"description": 5000,
	"subject":     100,
	"priority":    20,
}

var xssPatterns = []*regexp.Regexp{
	regexp.MustCompile(`(?i)<\s*script`),               // <script with optional space
	regexp.MustCompile(`(?i)</\s*script`),              // </script
	regexp.MustCompile(`(?i)javascript\s*:`),           // javascript:
	regexp.MustCompile(`(?i)on\w+\s*=`),                // onclick=, onerror=, etc.
	regexp.MustCompile(`(?i)<\s*iframe`),               // <iframe
	regexp.MustCompile(`(?i)<\s*object`),               // <object
	regexp.MustCompile(`(?i)<\s*embed`),                // <embed
	regexp.MustCompile(`(?i)<\s*svg[^>]*on\w+\s*=`),    // <svg with event handler
	regexp.MustCompile(`(?i)data\s*:\s*text/html`),     // data:text/html
	regexp.MustCompile(`(?i)<\s*img[^>]*on\w+\s*=`),    // <img with event handler
	regexp.MustCompile(`(?i)expression\s*\(`),          // CSS expression()
	regexp.MustCompile(`(?i)alert\s*\(`),               // alert()
	regexp.MustCompile(`(?i)confirm\s*\(`),             // confirm()
	regexp.MustCompile(`(?i)prompt\s*\(`),              // prompt()
	regexp.MustCompile(`(?i)document\s*\.\s*cookie`),   // document.cookie
	regexp.MustCompile(`(?i)document\s*\.\s*location`), // document.location
	regexp.MustCompile(`(?i)window\s*\.\s*location`),   // window.location
}

// SQL injection detection patterns (common attack signatures)
var sqlInjectionPatterns = []*regexp.Regexp{
	regexp.MustCompile(`(?i)'\s*or\s+`),                                         // ' OR (simplified)
	regexp.MustCompile(`(?i)'\s*and\s+`),                                        // ' AND
	regexp.MustCompile(`(?i)"\s*or\s+`),                                         // " OR
	regexp.MustCompile(`(?i)"\s*and\s+`),                                        // " AND
	regexp.MustCompile(`(?i)union\s+(all\s+)?select`),                           // UNION SELECT
	regexp.MustCompile(`(?i);\s*(drop|delete|update|insert|alter|truncate)\s+`), // ; DROP etc
	regexp.MustCompile(`(?i)--\s*$`),                                            // SQL comment at end
	regexp.MustCompile(`(?i)/\*.*\*/`),                                          // SQL block comment
	regexp.MustCompile(`(?i)'\s*;\s*`),                                          // '; (statement termination)
	regexp.MustCompile(`(?i)exec\s*\(`),                                         // EXEC(
	regexp.MustCompile(`(?i)xp_\w+`),                                            // xp_cmdshell etc.
	regexp.MustCompile(`(?i)load_file\s*\(`),                                    // MySQL LOAD_FILE
	regexp.MustCompile(`(?i)into\s+(out|dump)file`),                             // MySQL file operations
	regexp.MustCompile(`(?i)benchmark\s*\(`),                                    // MySQL BENCHMARK
	regexp.MustCompile(`(?i)sleep\s*\(\s*\d`),                                   // SLEEP()
	regexp.MustCompile(`(?i)waitfor\s+delay`),                                   // WAITFOR DELAY
	regexp.MustCompile(`(?i)1\s*=\s*1`),                                         // 1=1
	regexp.MustCompile(`(?i)'1'\s*=\s*'1`),                                      // '1'='1
}

// Path traversal detection patterns
var pathTraversalPatterns = []*regexp.Regexp{
	regexp.MustCompile(`\.\.[\\/]`),
	regexp.MustCompile(`\.\.%2[fF]`),
	regexp.MustCompile(`%2e%2e[\\/]`),
	regexp.MustCompile(`\.\./`),  // ../
	regexp.MustCompile(`\.\.\\`), // ..\
}

// Command injection detection patterns
var commandInjectionPatterns = []*regexp.Regexp{
	regexp.MustCompile(`^\s*;`),       // starts with semicolon
	regexp.MustCompile(`;\s*\w+`),     // ; followed by command
	regexp.MustCompile(`\|\s*\w+`),    // | pipe to command
	regexp.MustCompile("`[^`]+`"),     // backtick execution
	regexp.MustCompile(`\$\([^)]+\)`), // $(command) execution
	regexp.MustCompile(`&&\s*\w+`),    // && chained command
	regexp.MustCompile(`\|\|\s*\w+`),  // || chained command
}

// ValidationError represents a validation failure
type ValidationError struct {
	Field   string
	Message string
}

func (e *ValidationError) Error() string {
	return fmt.Sprintf("%s: %s", e.Field, e.Message)
}

// ValidateAssignmentInput validates assignment creation/update input
func ValidateAssignmentInput(title, description, subject, priority string) error {
	// Validate title
	if err := ValidateField("title", title, true); err != nil {
		return err
	}

	// Validate description
	if err := ValidateField("description", description, false); err != nil {
		return err
	}

	// Validate subject
	if err := ValidateField("subject", subject, false); err != nil {
		return err
	}

	// Validate priority
	if err := ValidateField("priority", priority, false); err != nil {
		return err
	}

	return nil
}

// ValidateField validates a single field
func ValidateField(fieldName, value string, required bool) error {
	// Check required
	if required && strings.TrimSpace(value) == "" {
		return &ValidationError{Field: fieldName, Message: "必須項目です"}
	}

	// Skip further validation if empty and not required
	if value == "" {
		return nil
	}

	// Check max length
	if maxLen, ok := MaxLengths[fieldName]; ok {
		if len(value) > maxLen {
			return &ValidationError{
				Field:   fieldName,
				Message: fmt.Sprintf("最大%d文字までです", maxLen),
			}
		}
	}

	// Check for control characters (except newline in description)
	if fieldName != "description" {
		for _, r := range value {
			if unicode.IsControl(r) && r != '\n' && r != '\r' && r != '\t' {
				return &ValidationError{
					Field:   fieldName,
					Message: "不正な制御文字が含まれています",
				}
			}
		}
	}

	// Check for XSS patterns
	for _, pattern := range xssPatterns {
		if pattern.MatchString(value) {
			return &ValidationError{
				Field:   fieldName,
				Message: "潜在的に危険なHTMLタグまたはスクリプトが含まれています",
			}
		}
	}

	// Check for SQL injection patterns
	for _, pattern := range sqlInjectionPatterns {
		if pattern.MatchString(value) {
			return &ValidationError{
				Field:   fieldName,
				Message: "潜在的に危険なSQL構文が含まれています",
			}
		}
	}

	// Check for path traversal patterns
	for _, pattern := range pathTraversalPatterns {
		if pattern.MatchString(value) {
			return &ValidationError{
				Field:   fieldName,
				Message: "不正なパス文字列が含まれています",
			}
		}
	}

	// Check for command injection patterns
	for _, pattern := range commandInjectionPatterns {
		if pattern.MatchString(value) {
			return &ValidationError{
				Field:   fieldName,
				Message: "潜在的に危険なコマンド構文が含まれています",
			}
		}
	}

	return nil
}

// SanitizeString removes potentially dangerous characters while preserving readability
// This is a secondary defense - validation should catch issues first
func SanitizeString(s string) string {
	// Remove null bytes
	s = strings.ReplaceAll(s, "\x00", "")

	// Normalize whitespace
	s = strings.TrimSpace(s)

	return s
}