package sipguardian

import (
	"regexp"
	"strings"
	"sync"
	"time"

	"go.uber.org/zap"
)

// SIPMethod represents a SIP request method
type SIPMethod string

const (
	MethodREGISTER  SIPMethod = "REGISTER"
	MethodINVITE    SIPMethod = "INVITE"
	MethodOPTIONS   SIPMethod = "OPTIONS"
	MethodACK       SIPMethod = "ACK"
	MethodBYE       SIPMethod = "BYE"
	MethodCANCEL    SIPMethod = "CANCEL"
	MethodINFO      SIPMethod = "INFO"
	MethodNOTIFY    SIPMethod = "NOTIFY"
	MethodSUBSCRIBE SIPMethod = "SUBSCRIBE"
	MethodMESSAGE   SIPMethod = "MESSAGE"
	MethodUPDATE    SIPMethod = "UPDATE"
	MethodPRACK     SIPMethod = "PRACK"
	MethodREFER     SIPMethod = "REFER"
	MethodPUBLISH   SIPMethod = "PUBLISH"
)

// MethodRateLimit defines rate limits per SIP method
type MethodRateLimit struct {
	// Method to rate limit
	Method SIPMethod `json:"method"`

	// MaxRequests per time window
	MaxRequests int `json:"max_requests"`

	// Window is the time window for rate limiting
	Window time.Duration `json:"window"`

	// BurstSize allows temporary bursts above the rate
	BurstSize int `json:"burst_size,omitempty"`
}

// RateLimiter provides per-IP, per-method rate limiting
type RateLimiter struct {
	limits  map[SIPMethod]*MethodRateLimit
	buckets map[string]*methodBuckets
	logger  *zap.Logger
	mu      sync.RWMutex

	// Default limits (used when no specific limit configured)
	defaultMaxRequests int
	defaultWindow      time.Duration
}

// methodBuckets tracks request counts per method for an IP
type methodBuckets struct {
	methods   map[SIPMethod]*tokenBucket
	lastReset time.Time
	mu        sync.Mutex
}

// tokenBucket implements a simple token bucket algorithm
type tokenBucket struct {
	tokens     float64
	lastUpdate time.Time
	maxTokens  float64
	refillRate float64 // tokens per second
}

// Global rate limiter instance
var (
	globalRateLimiter *RateLimiter
	rateLimiterMu     sync.Mutex
)

// DefaultMethodLimits provides reasonable default rate limits per method
var DefaultMethodLimits = map[SIPMethod]*MethodRateLimit{
	MethodREGISTER: {
		Method:      MethodREGISTER,
		MaxRequests: 10,
		Window:      time.Minute,
		BurstSize:   3,
	},
	MethodINVITE: {
		Method:      MethodINVITE,
		MaxRequests: 30,
		Window:      time.Minute,
		BurstSize:   5,
	},
	MethodOPTIONS: {
		Method:      MethodOPTIONS,
		MaxRequests: 60,
		Window:      time.Minute,
		BurstSize:   10,
	},
	MethodSUBSCRIBE: {
		Method:      MethodSUBSCRIBE,
		MaxRequests: 20,
		Window:      time.Minute,
		BurstSize:   5,
	},
	MethodMESSAGE: {
		Method:      MethodMESSAGE,
		MaxRequests: 100,
		Window:      time.Minute,
		BurstSize:   20,
	},
}

// NewRateLimiter creates a new rate limiter
func NewRateLimiter(logger *zap.Logger) *RateLimiter {
	return &RateLimiter{
		limits:             make(map[SIPMethod]*MethodRateLimit),
		buckets:            make(map[string]*methodBuckets),
		logger:             logger,
		defaultMaxRequests: 100,
		defaultWindow:      time.Minute,
	}
}

// GetRateLimiter returns the global rate limiter
func GetRateLimiter(logger *zap.Logger) *RateLimiter {
	rateLimiterMu.Lock()
	defer rateLimiterMu.Unlock()

	if globalRateLimiter == nil {
		globalRateLimiter = NewRateLimiter(logger)
		// Apply default limits
		for method, limit := range DefaultMethodLimits {
			globalRateLimiter.SetLimit(method, limit)
		}
	}

	return globalRateLimiter
}

// SetLimit configures a rate limit for a specific method
func (rl *RateLimiter) SetLimit(method SIPMethod, limit *MethodRateLimit) {
	rl.mu.Lock()
	defer rl.mu.Unlock()
	rl.limits[method] = limit
}

// GetLimit returns the rate limit for a method
func (rl *RateLimiter) GetLimit(method SIPMethod) *MethodRateLimit {
	rl.mu.RLock()
	defer rl.mu.RUnlock()

	if limit, ok := rl.limits[method]; ok {
		return limit
	}

	// Return default limit
	return &MethodRateLimit{
		Method:      method,
		MaxRequests: rl.defaultMaxRequests,
		Window:      rl.defaultWindow,
	}
}

// Allow checks if a request should be allowed based on rate limits
// Returns (allowed, reason) - if not allowed, reason explains why
func (rl *RateLimiter) Allow(ip string, method SIPMethod) (bool, string) {
	rl.mu.Lock()
	bucket, exists := rl.buckets[ip]
	if !exists {
		bucket = &methodBuckets{
			methods:   make(map[SIPMethod]*tokenBucket),
			lastReset: time.Now(),
		}
		rl.buckets[ip] = bucket
	}
	rl.mu.Unlock()

	limit := rl.GetLimit(method)

	bucket.mu.Lock()
	defer bucket.mu.Unlock()

	tb, exists := bucket.methods[method]
	if !exists {
		// Create new token bucket for this method
		burstSize := limit.BurstSize
		if burstSize == 0 {
			burstSize = limit.MaxRequests / 5 // Default burst is 20% of max
			if burstSize < 1 {
				burstSize = 1
			}
		}

		tb = &tokenBucket{
			tokens:     float64(burstSize),
			lastUpdate: time.Now(),
			maxTokens:  float64(burstSize),
			refillRate: float64(limit.MaxRequests) / limit.Window.Seconds(),
		}
		bucket.methods[method] = tb
	}

	// Refill tokens based on elapsed time
	now := time.Now()
	elapsed := now.Sub(tb.lastUpdate).Seconds()
	tb.tokens += elapsed * tb.refillRate
	if tb.tokens > tb.maxTokens {
		tb.tokens = tb.maxTokens
	}
	tb.lastUpdate = now

	// Check if we have tokens
	if tb.tokens >= 1.0 {
		tb.tokens -= 1.0
		return true, ""
	}

	// Rate limited
	return false, "rate_limit_" + string(method)
}

// Cleanup removes old entries
func (rl *RateLimiter) Cleanup() {
	rl.mu.Lock()
	defer rl.mu.Unlock()

	now := time.Now()
	cutoff := now.Add(-10 * time.Minute)

	for ip, bucket := range rl.buckets {
		bucket.mu.Lock()
		if bucket.lastReset.Before(cutoff) {
			delete(rl.buckets, ip)
		}
		bucket.mu.Unlock()
	}
}

// GetStats returns rate limiter statistics
func (rl *RateLimiter) GetStats() map[string]interface{} {
	rl.mu.RLock()
	defer rl.mu.RUnlock()

	limitConfigs := make(map[string]interface{})
	for method, limit := range rl.limits {
		limitConfigs[string(method)] = map[string]interface{}{
			"max_requests": limit.MaxRequests,
			"window":       limit.Window.String(),
			"burst_size":   limit.BurstSize,
		}
	}

	return map[string]interface{}{
		"tracked_ips": len(rl.buckets),
		"limits":      limitConfigs,
	}
}

// SIP method extraction patterns
var (
	sipMethodPattern = regexp.MustCompile(`^(REGISTER|INVITE|OPTIONS|ACK|BYE|CANCEL|INFO|NOTIFY|SUBSCRIBE|MESSAGE|UPDATE|PRACK|REFER|PUBLISH)\s+sip:`)
	// Pattern to extract target extension from Request-URI: METHOD sip:extension@domain
	sipTargetExtPattern = regexp.MustCompile(`^(?:REGISTER|INVITE|OPTIONS|MESSAGE|SUBSCRIBE)\s+sip:([^@\s>]+)@`)
)

// ExtractSIPMethod extracts the SIP method from a message
func ExtractSIPMethod(data []byte) SIPMethod {
	s := string(data)
	if matches := sipMethodPattern.FindStringSubmatch(s); len(matches) > 1 {
		return SIPMethod(matches[1])
	}
	return ""
}

// ExtractTargetExtension extracts the target extension from a SIP message
// It looks at the Request-URI first, then falls back to the To header
func ExtractTargetExtension(data []byte) string {
	s := string(data)

	// First try Request-URI: REGISTER sip:1001@domain.com
	if matches := sipTargetExtPattern.FindStringSubmatch(s); len(matches) > 1 {
		ext := matches[1]
		// Filter out domain-like values and overly long strings
		if !strings.Contains(ext, ".") && len(ext) <= 10 && len(ext) > 0 {
			return ext
		}
	}

	// Fall back to To header
	user, _ := ParseToHeader(data)
	if user != "" && !strings.Contains(user, ".") && len(user) <= 10 {
		return user
	}

	return ""
}

// ParseUserAgent extracts User-Agent from SIP message
func ParseUserAgent(data []byte) string {
	s := string(data)
	lines := strings.Split(s, "\r\n")
	for _, line := range lines {
		lower := strings.ToLower(line)
		if strings.HasPrefix(lower, "user-agent:") {
			return strings.TrimSpace(line[11:])
		}
	}
	return ""
}

// ParseFromHeader extracts From header info
func ParseFromHeader(data []byte) (user, domain string) {
	s := string(data)
	lines := strings.Split(s, "\r\n")
	for _, line := range lines {
		lower := strings.ToLower(line)
		if strings.HasPrefix(lower, "from:") {
			// Extract sip:user@domain from From header
			fromPattern := regexp.MustCompile(`sip:([^@]+)@([^>;\s]+)`)
			if matches := fromPattern.FindStringSubmatch(line); len(matches) > 2 {
				return matches[1], matches[2]
			}
		}
	}
	return "", ""
}

// ParseToHeader extracts To header info
func ParseToHeader(data []byte) (user, domain string) {
	s := string(data)
	lines := strings.Split(s, "\r\n")
	for _, line := range lines {
		lower := strings.ToLower(line)
		if strings.HasPrefix(lower, "to:") {
			// Extract sip:user@domain from To header
			toPattern := regexp.MustCompile(`sip:([^@]+)@([^>;\s]+)`)
			if matches := toPattern.FindStringSubmatch(line); len(matches) > 2 {
				return matches[1], matches[2]
			}
		}
	}
	return "", ""
}

// ParseCallID extracts Call-ID from SIP message
func ParseCallID(data []byte) string {
	s := string(data)
	lines := strings.Split(s, "\r\n")
	for _, line := range lines {
		lower := strings.ToLower(line)
		if strings.HasPrefix(lower, "call-id:") {
			return strings.TrimSpace(line[8:])
		}
		if strings.HasPrefix(lower, "i:") { // Short form
			return strings.TrimSpace(line[2:])
		}
	}
	return ""
}