package middleware

import (
	"encoding/json"
	"log"
	"net/http"
	"os"
	"strings"
	"time"
)

// SecurityEvent represents a security-related event
type SecurityEvent struct {
	Timestamp time.Time `json:"timestamp"`
	EventType string    `json:"event_type"`
	Severity  string    `json:"severity"`
	IP        string    `json:"ip"`
	UserAgent string    `json:"user_agent"`
	Method    string    `json:"method"`
	Path      string    `json:"path"`
	Details   string    `json:"details"`
}

// EventSeverity levels
const (
	SeverityCritical = "CRITICAL"
	SeverityHigh     = "HIGH"
	SeverityMedium   = "MEDIUM"
	SeverityLow      = "LOW"
	SeverityInfo     = "INFO"
)

// Event types
const (
	EventBlocked              = "BLOCKED"
	EventCSRFViolation        = "CSRF_VIOLATION"
	EventOriginViolation      = "ORIGIN_VIOLATION"
	EventRateLimitExceeded    = "RATE_LIMIT_EXCEEDED"
	EventValidationFailed     = "VALIDATION_FAILED"
	EventSuspiciousUserAgent  = "SUSPICIOUS_USER_AGENT"
	EventContactFormSent      = "CONTACT_FORM_SENT"
	EventContactFormFailed    = "CONTACT_FORM_FAILED"
	EventPDFGenerated         = "PDF_GENERATED"
	EventPDFGenerationFailed  = "PDF_GENERATION_FAILED"
	EventEmailSendFailed      = "EMAIL_SEND_FAILED"
	EventBotDetected          = "BOT_DETECTED"
)

// LogSecurityEvent logs a security event in structured JSON format
func LogSecurityEvent(eventType string, r *http.Request, details string) {
	severity := getSeverity(eventType)

	event := SecurityEvent{
		Timestamp: time.Now(),
		EventType: eventType,
		Severity:  severity,
		IP:        getClientIP(r),
		UserAgent: r.Header.Get("User-Agent"),
		Method:    r.Method,
		Path:      r.URL.Path,
		Details:   details,
	}

	// JSON format for easy parsing by SIEM systems
	eventJSON, err := json.Marshal(event)
	if err != nil {
		log.Printf("ERROR: Failed to marshal security event: %v", err)
		return
	}

	// Log to stdout (captured by systemd/Docker)
	log.Printf("[SECURITY] %s", eventJSON)

	// Also log to separate security log file in production
	if os.Getenv("GO_ENV") == "production" {
		logToSecurityFile(eventJSON)
	}
}

// getSeverity determines the severity level based on event type
func getSeverity(eventType string) string {
	switch eventType {
	case EventBlocked, EventCSRFViolation, EventOriginViolation:
		return SeverityHigh
	case EventRateLimitExceeded, EventValidationFailed, EventSuspiciousUserAgent,
		EventContactFormFailed, EventPDFGenerationFailed, EventEmailSendFailed:
		return SeverityMedium
	case EventBotDetected:
		return SeverityLow
	case EventContactFormSent, EventPDFGenerated:
		return SeverityInfo
	default:
		return SeverityLow
	}
}

// getClientIP extracts the real client IP from request headers
func getClientIP(r *http.Request) string {
	// Check X-Forwarded-For header (proxy/load balancer)
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		// Take first IP from comma-separated list
		ips := strings.Split(xff, ",")
		return strings.TrimSpace(ips[0])
	}

	// Check X-Real-IP header
	if xri := r.Header.Get("X-Real-IP"); xri != "" {
		return xri
	}

	// Fallback to RemoteAddr (remove port)
	ip := r.RemoteAddr
	if idx := strings.LastIndex(ip, ":"); idx != -1 {
		ip = ip[:idx]
	}
	return ip
}

// logToSecurityFile appends security events to a dedicated log file
func logToSecurityFile(eventJSON []byte) {
	// Create log directory if it doesn't exist
	logDir := "/var/log/cv-app"
	if err := os.MkdirAll(logDir, 0755); err != nil {
		log.Printf("WARNING: Failed to create log directory: %v", err)
		return
	}

	// Open security log file (append mode)
	logPath := logDir + "/security.log"
	f, err := os.OpenFile(logPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		log.Printf("WARNING: Failed to open security log file: %v", err)
		return
	}
	defer func() {
		if err := f.Close(); err != nil {
			log.Printf("WARNING: Failed to close security log file: %v", err)
		}
	}()

	// Write event with newline
	if _, err := f.Write(eventJSON); err != nil {
		log.Printf("WARNING: Failed to write to security log: %v", err)
		return
	}
	if _, err := f.WriteString("\n"); err != nil {
		log.Printf("WARNING: Failed to write newline to security log: %v", err)
	}
}

// SecurityLogger middleware logs all requests with security context
func SecurityLogger(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		// Wrap response writer to capture status
		wrapped := &responseWriter{
			ResponseWriter: w,
			status:         http.StatusOK,
		}

		// Process request
		next.ServeHTTP(wrapped, r)

		// Log security-relevant requests
		duration := time.Since(start)

		// Log high-value endpoints
		if isSecurityRelevantPath(r.URL.Path) {
			details := map[string]interface{}{
				"status":      wrapped.status,
				"duration_ms": duration.Milliseconds(),
				"bytes":       wrapped.written,
			}
			detailsJSON, _ := json.Marshal(details)

			event := SecurityEvent{
				Timestamp: time.Now(),
				EventType: "REQUEST",
				Severity:  SeverityInfo,
				IP:        getClientIP(r),
				UserAgent: r.Header.Get("User-Agent"),
				Method:    r.Method,
				Path:      r.URL.Path,
				Details:   string(detailsJSON),
			}

			eventJSON, _ := json.Marshal(event)
			log.Printf("[SECURITY] %s", eventJSON)
		}

		// Log errors and security failures
		if wrapped.status >= 400 {
			severity := SeverityLow
			if wrapped.status == 403 || wrapped.status == 429 {
				severity = SeverityMedium
			}

			event := SecurityEvent{
				Timestamp: time.Now(),
				EventType: "HTTP_ERROR",
				Severity:  severity,
				IP:        getClientIP(r),
				UserAgent: r.Header.Get("User-Agent"),
				Method:    r.Method,
				Path:      r.URL.Path,
				Details:   http.StatusText(wrapped.status),
			}

			eventJSON, _ := json.Marshal(event)
			log.Printf("[SECURITY] %s", eventJSON)
		}
	})
}

// isSecurityRelevantPath determines if a path should be logged for security
func isSecurityRelevantPath(path string) bool {
	securityPaths := []string{
		"/api/contact",
		"/export/pdf",
		"/toggle/",
		"/switch-language",
	}

	for _, sp := range securityPaths {
		if strings.HasPrefix(path, sp) {
			return true
		}
	}

	return false
}