package sipguardian

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
)

// ViaHeader represents a parsed Via header
type ViaHeader struct {
	Protocol  string // SIP/2.0
	Transport string // UDP, TCP, TLS, WS, WSS
	Host      string
	Port      int
	Branch    string
	Received  string
	RPort     int
	Params    map[string]string // Other parameters
}

// ContactHeader represents a parsed Contact header
type ContactHeader struct {
	DisplayName string
	URI         string
	Params      map[string]string
}

// FromToHeader represents a parsed From or To header
type FromToHeader struct {
	DisplayName string
	URI         string
	Tag         string
	Params      map[string]string
}

// SensitiveHeaders lists headers that may leak internal topology
var SensitiveHeaders = []string{
	"P-Preferred-Identity",
	"P-Asserted-Identity",
	"Remote-Party-ID",
	"P-Charging-Vector",
	"P-Charging-Function-Addresses",
	"Server",
	"User-Agent",
	"X-Asterisk-HangupCause",
	"X-Asterisk-HangupCauseCode",
}

// ParseViaHeader parses a Via header value into structured form
// Example: "SIP/2.0/UDP 192.168.1.1:5060;branch=z9hG4bK123;received=10.0.0.1"
func ParseViaHeader(value string) (*ViaHeader, error) {
	via := &ViaHeader{
		Params: make(map[string]string),
	}

	// Split by semicolons to get parameters
	parts := strings.Split(value, ";")
	if len(parts) == 0 {
		return nil, fmt.Errorf("empty Via header")
	}

	// First part: SIP/2.0/UDP host:port
	mainPart := strings.TrimSpace(parts[0])
	fields := strings.Fields(mainPart)
	if len(fields) < 2 {
		return nil, fmt.Errorf("invalid Via header format")
	}

	// Parse protocol/transport
	protoTransport := strings.Split(fields[0], "/")
	if len(protoTransport) >= 2 {
		via.Protocol = protoTransport[0] + "/" + protoTransport[1]
	}
	if len(protoTransport) >= 3 {
		via.Transport = protoTransport[2]
	}

	// Parse host:port
	hostPort := fields[1]
	if colonIdx := strings.LastIndex(hostPort, ":"); colonIdx > 0 {
		via.Host = hostPort[:colonIdx]
		port, _ := strconv.Atoi(hostPort[colonIdx+1:])
		via.Port = port
	} else {
		via.Host = hostPort
		via.Port = 5060 // Default SIP port
	}

	// Parse parameters
	for i := 1; i < len(parts); i++ {
		param := strings.TrimSpace(parts[i])
		if eqIdx := strings.Index(param, "="); eqIdx > 0 {
			key := strings.ToLower(param[:eqIdx])
			val := param[eqIdx+1:]

			switch key {
			case "branch":
				via.Branch = val
			case "received":
				via.Received = val
			case "rport":
				via.RPort, _ = strconv.Atoi(val)
			default:
				via.Params[key] = val
			}
		} else {
			// Flag parameter (no value)
			via.Params[strings.ToLower(param)] = ""
		}
	}

	return via, nil
}

// Serialize converts ViaHeader back to string format
func (v *ViaHeader) Serialize() string {
	var buf strings.Builder

	// Protocol and transport
	buf.WriteString(v.Protocol)
	buf.WriteByte('/')
	buf.WriteString(v.Transport)
	buf.WriteByte(' ')

	// Host and port
	buf.WriteString(v.Host)
	if v.Port > 0 && v.Port != 5060 {
		buf.WriteByte(':')
		buf.WriteString(strconv.Itoa(v.Port))
	}

	// Branch (required for RFC 3261 compliance)
	if v.Branch != "" {
		buf.WriteString(";branch=")
		buf.WriteString(v.Branch)
	}

	// Received parameter
	if v.Received != "" {
		buf.WriteString(";received=")
		buf.WriteString(v.Received)
	}

	// RPort parameter
	if v.RPort > 0 {
		buf.WriteString(";rport=")
		buf.WriteString(strconv.Itoa(v.RPort))
	}

	// Other parameters
	for key, val := range v.Params {
		buf.WriteByte(';')
		buf.WriteString(key)
		if val != "" {
			buf.WriteByte('=')
			buf.WriteString(val)
		}
	}

	return buf.String()
}

// ParseContactHeader parses a Contact header value
// Example: "\"Alice\" <sip:alice@example.com>;expires=3600"
func ParseContactHeader(value string) (*ContactHeader, error) {
	contact := &ContactHeader{
		Params: make(map[string]string),
	}

	// Handle * (special Contact for REGISTER)
	if strings.TrimSpace(value) == "*" {
		contact.URI = "*"
		return contact, nil
	}

	// Extract display name if present (quoted)
	if idx := strings.Index(value, "\""); idx >= 0 {
		endIdx := strings.Index(value[idx+1:], "\"")
		if endIdx > 0 {
			contact.DisplayName = value[idx+1 : idx+1+endIdx]
			value = value[idx+1+endIdx+1:]
		}
	}

	// Extract URI (within angle brackets or until semicolon)
	value = strings.TrimSpace(value)
	if strings.HasPrefix(value, "<") {
		endIdx := strings.Index(value, ">")
		if endIdx > 0 {
			contact.URI = value[1:endIdx]
			value = value[endIdx+1:]
		}
	} else {
		// No angle brackets - URI goes until semicolon or end
		semiIdx := strings.Index(value, ";")
		if semiIdx > 0 {
			contact.URI = strings.TrimSpace(value[:semiIdx])
			value = value[semiIdx:]
		} else {
			contact.URI = strings.TrimSpace(value)
			value = ""
		}
	}

	// Parse parameters
	for _, part := range strings.Split(value, ";") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		if eqIdx := strings.Index(part, "="); eqIdx > 0 {
			contact.Params[strings.ToLower(part[:eqIdx])] = part[eqIdx+1:]
		} else if part != "" {
			contact.Params[strings.ToLower(part)] = ""
		}
	}

	return contact, nil
}

// Serialize converts ContactHeader back to string format
func (c *ContactHeader) Serialize() string {
	var buf strings.Builder

	if c.URI == "*" {
		return "*"
	}

	if c.DisplayName != "" {
		buf.WriteByte('"')
		buf.WriteString(c.DisplayName)
		buf.WriteString("\" ")
	}

	buf.WriteByte('<')
	buf.WriteString(c.URI)
	buf.WriteByte('>')

	for key, val := range c.Params {
		buf.WriteByte(';')
		buf.WriteString(key)
		if val != "" {
			buf.WriteByte('=')
			buf.WriteString(val)
		}
	}

	return buf.String()
}

// ParseFromToHeader parses a From or To header value
// Example: "\"Bob\" <sip:bob@example.com>;tag=abc123"
func ParseFromToHeader(value string) (*FromToHeader, error) {
	header := &FromToHeader{
		Params: make(map[string]string),
	}

	// Extract display name if present (quoted)
	if idx := strings.Index(value, "\""); idx >= 0 {
		endIdx := strings.Index(value[idx+1:], "\"")
		if endIdx > 0 {
			header.DisplayName = value[idx+1 : idx+1+endIdx]
			value = value[idx+1+endIdx+1:]
		}
	}

	// Extract URI (within angle brackets)
	value = strings.TrimSpace(value)
	if strings.HasPrefix(value, "<") {
		endIdx := strings.Index(value, ">")
		if endIdx > 0 {
			header.URI = value[1:endIdx]
			value = value[endIdx+1:]
		}
	} else {
		// No angle brackets
		semiIdx := strings.Index(value, ";")
		if semiIdx > 0 {
			header.URI = strings.TrimSpace(value[:semiIdx])
			value = value[semiIdx:]
		} else {
			header.URI = strings.TrimSpace(value)
			value = ""
		}
	}

	// Parse parameters
	for _, part := range strings.Split(value, ";") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		if eqIdx := strings.Index(part, "="); eqIdx > 0 {
			key := strings.ToLower(part[:eqIdx])
			val := part[eqIdx+1:]
			if key == "tag" {
				header.Tag = val
			} else {
				header.Params[key] = val
			}
		}
	}

	return header, nil
}

// Serialize converts FromToHeader back to string format
func (f *FromToHeader) Serialize() string {
	var buf strings.Builder

	if f.DisplayName != "" {
		buf.WriteByte('"')
		buf.WriteString(f.DisplayName)
		buf.WriteString("\" ")
	}

	buf.WriteByte('<')
	buf.WriteString(f.URI)
	buf.WriteByte('>')

	if f.Tag != "" {
		buf.WriteString(";tag=")
		buf.WriteString(f.Tag)
	}

	for key, val := range f.Params {
		buf.WriteByte(';')
		buf.WriteString(key)
		if val != "" {
			buf.WriteByte('=')
			buf.WriteString(val)
		}
	}

	return buf.String()
}

// ExtractHostFromURI extracts the host part from a SIP URI
// Example: "sip:user@host:5060;transport=udp" -> "host"
func ExtractHostFromURI(uri string) string {
	// Remove scheme
	if idx := strings.Index(uri, ":"); idx >= 0 {
		uri = uri[idx+1:]
	}

	// Remove user part
	if idx := strings.Index(uri, "@"); idx >= 0 {
		uri = uri[idx+1:]
	}

	// Remove port and parameters
	if idx := strings.Index(uri, ":"); idx >= 0 {
		uri = uri[:idx]
	}
	if idx := strings.Index(uri, ";"); idx >= 0 {
		uri = uri[:idx]
	}

	return uri
}

// ExtractPortFromURI extracts the port from a SIP URI (default 5060)
func ExtractPortFromURI(uri string) int {
	// Remove scheme and user part
	if idx := strings.Index(uri, "@"); idx >= 0 {
		uri = uri[idx+1:]
	} else if idx := strings.Index(uri, ":"); idx >= 0 {
		uri = uri[idx+1:]
	}

	// Extract port
	if colonIdx := strings.Index(uri, ":"); colonIdx >= 0 {
		portStr := uri[colonIdx+1:]
		if semiIdx := strings.Index(portStr, ";"); semiIdx >= 0 {
			portStr = portStr[:semiIdx]
		}
		port, err := strconv.Atoi(portStr)
		if err == nil {
			return port
		}
	}

	return 5060 // Default SIP port
}

// RewriteURIHost replaces the host in a SIP URI
func RewriteURIHost(uri, newHost string, newPort int) string {
	// Pattern to match SIP URI
	re := regexp.MustCompile(`^(sips?:)([^@]+@)?([^:;>]+)(:\d+)?(.*)$`)
	matches := re.FindStringSubmatch(uri)
	if matches == nil {
		return uri
	}

	// Rebuild URI with new host
	result := matches[1] + matches[2] + newHost
	if newPort > 0 && newPort != 5060 {
		result += ":" + strconv.Itoa(newPort)
	}
	result += matches[5]

	return result
}

// GenerateBranch generates an RFC 3261 compliant branch parameter
func GenerateBranch() string {
	// Must start with z9hG4bK for RFC 3261 compliance
	return "z9hG4bK" + generateRandomHex(16)
}

// generateRandomHex generates a random hex string of given length
func generateRandomHex(length int) string {
	const chars = "0123456789abcdef"
	result := make([]byte, length)
	for i := range result {
		// Use uint64 modulo to avoid negative index from int conversion
		result[i] = chars[pseudoRand()%uint64(len(chars))]
	}
	return string(result)
}

// Simple pseudo-random number generator (not cryptographically secure)
var prngState uint64 = 0xdeadbeef

func pseudoRand() uint64 {
	prngState ^= prngState << 13
	prngState ^= prngState >> 7
	prngState ^= prngState << 17
	return prngState
}

// InitPRNG seeds the pseudo-random number generator
func InitPRNG(seed uint64) {
	prngState = seed
	if prngState == 0 {
		prngState = 0xdeadbeef
	}
}

// Note: IsPrivateIP is defined in geoip.go with proper CIDR parsing

// NormalizeHeaderName converts header name to canonical form
func NormalizeHeaderName(name string) string {
	// Map compact forms to full names
	compactToFull := map[string]string{
		"i": "Call-ID",
		"m": "Contact",
		"e": "Content-Encoding",
		"l": "Content-Length",
		"c": "Content-Type",
		"f": "From",
		"s": "Subject",
		"k": "Supported",
		"t": "To",
		"v": "Via",
	}

	lower := strings.ToLower(name)
	if full, ok := compactToFull[lower]; ok {
		return full
	}

	// Title case for standard headers
	return strings.Title(lower)
}