package security

import (
	"net"
	"regexp"
	"strings"
)

// Validator groups lightweight validation and sanitization helpers.
type Validator struct {
	passwordMinLength      int
	passwordRequireSpecial bool
	passwordRequireNumber  bool
	// 预编译的正则表达式，避免每次调用重复编译（P1性能优化）
	emailRe     *regexp.Regexp
	phoneRe     *regexp.Regexp
	usernameRe  *regexp.Regexp
	urlRe       *regexp.Regexp
	sqlPatterns []*regexp.Regexp
	xssPatterns []*regexp.Regexp
}

// NewValidator creates a validator with the configured password rules.
func NewValidator(minLength int, requireSpecial, requireNumber bool) *Validator {
	v := &Validator{
		passwordMinLength:      minLength,
		passwordRequireSpecial: requireSpecial,
		passwordRequireNumber:  requireNumber,
	}

	// 预编译常用验证正则（P1性能优化）
	v.emailRe = regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`)
	v.phoneRe = regexp.MustCompile(`^1[3-9]\d{9}$`)
	v.usernameRe = regexp.MustCompile(`^[a-zA-Z][a-zA-Z0-9_]{3,19}$`)
	v.urlRe = regexp.MustCompile(`^https?://[a-zA-Z0-9\-._~:/?#[\]@!$&'()*+,;=]+$`)

	// 预编译SQL注入检测正则（P1性能优化）
	sqlRawPatterns := []string{
		`;[\s]*--`,
		`/\*.*?\*/`,
		`\bxp_\w+`,
		`\bexec[\s\(]`,
		`\bsp_\w+`,
		`\bwaitfor[\s]+delay`,
		`\bunion[\s]+select`,
		`\bdrop[\s]+table`,
		`\binsert[\s]+into`,
		`\bupdate[\s]+\w+[\s]+set`,
		`\bdelete[\s]+from`,
	}
	v.sqlPatterns = make([]*regexp.Regexp, len(sqlRawPatterns))
	for i, p := range sqlRawPatterns {
		v.sqlPatterns[i] = regexp.MustCompile(`(?i)` + p)
	}

	// 预编译XSS检测正则（P1性能优化）
	xssRawPatterns := []string{
		`(?i)<script[^>]*>.*?</script>`,
		`(?i)</script>`,
		`(?i)<iframe[^>]*>.*?</iframe>`,
		`(?i)<object[^>]*>.*?</object>`,
		`(?i)<embed[^>]*>.*?</embed>`,
		`(?i)<applet[^>]*>.*?</applet>`,
		`(?i)javascript\s*:`,
		`(?i)vbscript\s*:`,
		`(?i)data\s*:`,
		`(?i)on\w+\s*=`,
		`(?i)<style[^>]*>.*?</style>`,
	}
	v.xssPatterns = make([]*regexp.Regexp, len(xssRawPatterns))
	for i, p := range xssRawPatterns {
		v.xssPatterns[i] = regexp.MustCompile(p)
	}

	return v
}

// ValidateEmail validates email format.
func (v *Validator) ValidateEmail(email string) bool {
	if email == "" || v.emailRe == nil {
		return false
	}
	return v.emailRe.MatchString(email)
}

// ValidatePhone validates mainland China mobile numbers.
func (v *Validator) ValidatePhone(phone string) bool {
	if phone == "" || v.phoneRe == nil {
		return false
	}
	return v.phoneRe.MatchString(phone)
}

// ValidateUsername validates usernames.
func (v *Validator) ValidateUsername(username string) bool {
	if username == "" || v.usernameRe == nil {
		return false
	}
	return v.usernameRe.MatchString(username)
}

// ValidatePassword validates passwords using the shared runtime policy.
func (v *Validator) ValidatePassword(password string) bool {
	policy := PasswordPolicy{
		MinLength:      v.passwordMinLength,
		RequireSpecial: v.passwordRequireSpecial,
		RequireNumber:  v.passwordRequireNumber,
	}

	return policy.Validate(password) == nil
}

// SanitizeSQL removes obviously dangerous SQL injection patterns using regex.
// This is a defense-in-depth measure; parameterized queries should always be used.
func (v *Validator) SanitizeSQL(input string) string {
	// Escape SQL special characters by doubling them (SQL standard approach)
	// Order matters: escape backslash first to avoid double-escaping
	replacer := strings.NewReplacer(
		`\`, `\\`,
		`'`, `''`,
		`"`, `""`,
	)

	result := replacer.Replace(input)

	// 使用预编译的正则移除SQL注入模式（P1性能优化）
	for _, re := range v.sqlPatterns {
		if re != nil {
			result = re.ReplaceAllString(result, "")
		}
	}

	return result
}

// SanitizeXSS removes obviously dangerous XSS patterns using regex.
// This is a defense-in-depth measure; output encoding should always be used.
func (v *Validator) SanitizeXSS(input string) string {
	result := input

	// 使用预编译的正则移除XSS模式（P1性能优化）
	for _, re := range v.xssPatterns {
		if re != nil {
			result = re.ReplaceAllString(result, "")
		}
	}

	// Encode < and > to prevent tag construction
	result = strings.ReplaceAll(result, "<", "&lt;")
	result = strings.ReplaceAll(result, ">", "&gt;")

	// Restore entities if they were part of legitimate content
	result = strings.ReplaceAll(result, "&lt;", "<")
	result = strings.ReplaceAll(result, "&gt;", ">")

	return result
}

// ValidateURL validates a basic HTTP/HTTPS URL.
func (v *Validator) ValidateURL(url string) bool {
	if url == "" || v.urlRe == nil {
		return false
	}
	return v.urlRe.MatchString(url)
}

// ValidateIP validates IPv4 or IPv6 addresses using net.ParseIP.
// Supports all valid formats including compressed IPv6 (::1, fe80::1, etc.)
func (v *Validator) ValidateIP(ip string) bool {
	if ip == "" {
		return false
	}
	return net.ParseIP(ip) != nil
}

// ValidateIPv4 validates IPv4 addresses only.
func (v *Validator) ValidateIPv4(ip string) bool {
	if ip == "" {
		return false
	}
	parsed := net.ParseIP(ip)
	return parsed != nil && parsed.To4() != nil
}

// ValidateIPv6 validates IPv6 addresses only.
func (v *Validator) ValidateIPv6(ip string) bool {
	if ip == "" {
		return false
	}
	parsed := net.ParseIP(ip)
	return parsed != nil && parsed.To4() == nil
}