package proxy

import (
	"crypto/tls"
	"fmt"
	"io"
	"net"
	"sync"
	"time"

	"git.secnex.io/secnex/masterlog"
)

// peekConn wraps a connection to allow peeking at data without consuming it
type peekConn struct {
	net.Conn
	peeked       []byte
	peekedOffset int
}

func newPeekConn(conn net.Conn) *peekConn {
	return &peekConn{Conn: conn}
}

func (p *peekConn) Read(b []byte) (int, error) {
	if p.peekedOffset < len(p.peeked) {
		n := copy(b, p.peeked[p.peekedOffset:])
		p.peekedOffset += n
		return n, nil
	}
	return p.Conn.Read(b)
}

func (p *peekConn) peek(n int) ([]byte, error) {
	if len(p.peeked) >= n {
		return p.peeked[:n], nil
	}

	needed := n - len(p.peeked)
	buf := make([]byte, needed)
	read, err := io.ReadFull(p.Conn, buf)
	if err != nil && err != io.EOF {
		return nil, err
	}

	p.peeked = append(p.peeked, buf[:read]...)
	return p.peeked[:len(p.peeked)], nil
}

// handleConnection handles a new client connection
func (p *Proxy) handleConnection(clientConn net.Conn) {
	defer clientConn.Close()

	remoteAddr := clientConn.RemoteAddr().String()
	masterlog.Info("New connection", map[string]interface{}{"remoteAddr": remoteAddr})

	var hostname string
	var peekConn *peekConn

	// Create peek connection to inspect first bytes
	tempPeekConn := newPeekConn(clientConn)

	// Check if this is a TLS handshake (first byte is 0x16)
	firstByte, err := tempPeekConn.peek(1)
	if err != nil {
		masterlog.Error("Failed to peek connection", map[string]interface{}{"error": err, "remoteAddr": remoteAddr})
		return
	}

	// If TLS is enabled and this looks like a TLS handshake, upgrade to TLS
	if p.config.TLS.Enabled && len(firstByte) > 0 && firstByte[0] == 0x16 {
		// Get TLS config
		var tlsConfig *tls.Config
		if p.certmagic != nil {
			// Use Let's Encrypt certmagic
			tlsConfig = createTLSConfigWithLetsEncrypt(p.certmagic)
		} else if p.certificate != nil {
			// Use stored certificate for regular TLS
			tlsConfig = &tls.Config{
				Certificates: []tls.Certificate{*p.certificate},
				ClientAuth:   tls.NoClientCert,
			}
		} else {
			// Fallback: get certificate on demand
			cert, err := getCertificateForMappings(p.config)
			if err != nil {
				masterlog.Error("Failed to get TLS certificate", map[string]interface{}{"error": err})
				return
			}
			tlsConfig = &tls.Config{
				Certificates: []tls.Certificate{cert},
				ClientAuth:   tls.NoClientCert,
			}
		}

		// Upgrade connection to TLS
		tlsConn := tls.Server(clientConn, tlsConfig)
		if err := tlsConn.Handshake(); err != nil {
			masterlog.Error("TLS handshake failed", map[string]interface{}{"error": err, "remoteAddr": remoteAddr})
			return
		}

		// Extract SNI from connection state
		state := tlsConn.ConnectionState()
		if state.ServerName != "" {
			hostname = state.ServerName
			masterlog.Info("Extracted hostname from TLS SNI", map[string]interface{}{"hostname": hostname})
		}
		peekConn = newPeekConn(tlsConn)
	} else {
		// Non-TLS connection
		peekConn = tempPeekConn
		// Try to extract hostname from raw connection (won't work for non-TLS, but that's OK)
		hostname = p.extractHostname(peekConn)
	}
	var (
		targetMapping struct {
			host string
			port int
		}
		ok bool
	)

	// If we have a hostname (e.g. from TLS SNI), try to use it first
	if hostname != "" {
		targetMapping, ok = p.mappings[hostname]
		if !ok {
			masterlog.Info("No mapping found for hostname", map[string]interface{}{"hostname": hostname})
		}
	}

	// Fallback: if we couldn't determine a hostname or no mapping exists,
	// but there is exactly one mapping configured, use it as a default backend.
	if !ok {
		if len(p.mappings) == 1 {
			for _, m := range p.mappings {
				targetMapping = m
				break
			}
			masterlog.Info("Using default backend", map[string]interface{}{"host": targetMapping.host, "port": targetMapping.port, "remoteAddr": remoteAddr, "hostname": hostname})
			ok = true
		}
	}

	if !ok {
		masterlog.Error("No suitable backend found", map[string]interface{}{"remoteAddr": remoteAddr, "hostname": hostname})
		return
	}

	masterlog.Info("Proxying", map[string]interface{}{"hostname": hostname, "host": targetMapping.host, "port": targetMapping.port})

	// If TLS is enabled, handle PostgreSQL SSL request
	// After TLS handshake, PostgreSQL clients may send an SSL request
	// We respond with 'S' (SSL supported) since encryption is already handled by TLS
	if p.config.TLS.Enabled {
		if err := p.handlePostgresSSLRequest(peekConn); err != nil {
			masterlog.Error("Failed to handle PostgreSQL SSL request", map[string]interface{}{"error": err})
			return
		}
	}

	// Connect to backend PostgreSQL server
	backendAddr := net.JoinHostPort(targetMapping.host, fmt.Sprintf("%d", targetMapping.port))
	backendConn, err := net.DialTimeout("tcp", backendAddr, 10*time.Second)
	if err != nil {
		masterlog.Error("Failed to connect to backend", map[string]interface{}{"backendAddr": backendAddr, "error": err})
		return
	}
	defer backendConn.Close()

	// Start bidirectional proxying
	var wg sync.WaitGroup
	wg.Add(2)

	// Copy from client to backend
	go func() {
		defer wg.Done()
		io.Copy(backendConn, peekConn)
		backendConn.Close()
	}()

	// Copy from backend to client
	go func() {
		defer wg.Done()
		io.Copy(peekConn, backendConn)
		peekConn.Close()
	}()

	wg.Wait()
	masterlog.Info("Connection closed", map[string]interface{}{"hostname": hostname, "host": targetMapping.host, "port": targetMapping.port})
}

// extractHostname extracts hostname from connection (TLS SNI or PostgreSQL startup)
func (p *Proxy) extractHostname(conn *peekConn) string {
	// Peek at first byte to determine protocol
	firstBytes, err := conn.peek(1)
	if err != nil {
		return ""
	}

	// TLS handshake starts with 0x16
	if len(firstBytes) > 0 && firstBytes[0] == 0x16 {
		return p.extractHostnameFromTLS(conn)
	}

	// Otherwise, try PostgreSQL startup message
	return p.extractHostnameFromPostgresStartup(conn)
}

// extractHostnameFromTLS extracts hostname by parsing TLS ClientHello manually
func (p *Proxy) extractHostnameFromTLS(conn *peekConn) string {
	// Read enough bytes to parse TLS ClientHello
	// TLS Record Header: 5 bytes (type, version, length)
	peekBuf, err := conn.peek(5)
	if err != nil || len(peekBuf) < 5 {
		return ""
	}

	// Check TLS record type (should be 0x16 for Handshake)
	if peekBuf[0] != 0x16 {
		return ""
	}

	// Get record length
	recordLength := int(peekBuf[3])<<8 | int(peekBuf[4])

	// Read the full TLS record (5 bytes header + recordLength bytes)
	fullRecord, err := conn.peek(5 + recordLength)
	if err != nil || len(fullRecord) < 5+recordLength {
		return ""
	}

	// Parse ClientHello to extract SNI
	// Skip TLS record header (5 bytes)
	handshake := fullRecord[5:]
	if len(handshake) < 4 {
		return ""
	}

	// Handshake message type (should be 0x01 for ClientHello)
	if handshake[0] != 0x01 {
		return ""
	}

	// Handshake message length (3 bytes)
	handshakeLength := int(handshake[1])<<16 | int(handshake[2])<<8 | int(handshake[3])
	if len(handshake) < 4+handshakeLength {
		return ""
	}

	// Skip handshake header (4 bytes) and protocol version (2 bytes)
	offset := 4 + 2

	// Read random (32 bytes)
	if len(handshake) < offset+32 {
		return ""
	}
	offset += 32

	// Read session ID length (1 byte) and session ID
	if len(handshake) < offset+1 {
		return ""
	}
	sessionIDLength := int(handshake[offset])
	offset++
	if len(handshake) < offset+sessionIDLength {
		return ""
	}
	offset += sessionIDLength

	// Read cipher suites length (2 bytes) and cipher suites
	if len(handshake) < offset+2 {
		return ""
	}
	cipherSuitesLength := int(handshake[offset])<<8 | int(handshake[offset+1])
	offset += 2
	if len(handshake) < offset+cipherSuitesLength {
		return ""
	}
	offset += cipherSuitesLength

	// Read compression methods length (1 byte) and compression methods
	if len(handshake) < offset+1 {
		return ""
	}
	compressionMethodsLength := int(handshake[offset])
	offset++
	if len(handshake) < offset+compressionMethodsLength {
		return ""
	}
	offset += compressionMethodsLength

	// Read extensions length (2 bytes)
	if len(handshake) < offset+2 {
		return ""
	}
	extensionsLength := int(handshake[offset])<<8 | int(handshake[offset+1])
	offset += 2

	// Parse extensions to find SNI (extension type 0x0000)
	extensionsEnd := offset + extensionsLength
	for offset < extensionsEnd-4 {
		if len(handshake) < offset+4 {
			break
		}

		extType := int(handshake[offset])<<8 | int(handshake[offset+1])
		extLength := int(handshake[offset+2])<<8 | int(handshake[offset+3])
		offset += 4

		if len(handshake) < offset+extLength {
			break
		}

		// SNI extension type is 0x0000
		if extType == 0x0000 {
			// SNI format: list length (2 bytes) + server name list
			if extLength < 2 {
				break
			}
			sniListLength := int(handshake[offset])<<8 | int(handshake[offset+1])
			sniOffset := offset + 2

			if len(handshake) < sniOffset+sniListLength {
				break
			}

			// Parse server name entry
			if sniListLength >= 3 {
				// Name type (1 byte) - 0x00 for hostname
				nameType := handshake[sniOffset]
				if nameType == 0x00 {
					nameLength := int(handshake[sniOffset+1])<<8 | int(handshake[sniOffset+2])
					if len(handshake) >= sniOffset+3+nameLength {
						hostname := string(handshake[sniOffset+3 : sniOffset+3+nameLength])
						return hostname
					}
				}
			}
		}

		offset += extLength
	}

	return ""
}

// extractHostnameFromPostgresStartup extracts hostname from PostgreSQL startup message
func (p *Proxy) extractHostnameFromPostgresStartup(conn *peekConn) string {
	// Peek at first 4 bytes to get message length
	lengthBuf, err := conn.peek(4)
	if err != nil || len(lengthBuf) < 4 {
		return ""
	}

	length := int(lengthBuf[0])<<24 | int(lengthBuf[1])<<16 | int(lengthBuf[2])<<8 | int(lengthBuf[3])
	if length < 8 || length > 10000 {
		return ""
	}

	// Peek at the full startup message
	startupBuf, err := conn.peek(length)
	if err != nil || len(startupBuf) < length {
		return ""
	}

	// Skip length (4 bytes) and protocol version (4 bytes)
	offset := 8

	// Parse key-value pairs
	for offset < len(startupBuf)-1 {
		// Find null terminator for key
		keyEnd := offset
		for keyEnd < len(startupBuf) && startupBuf[keyEnd] != 0 {
			keyEnd++
		}
		if keyEnd >= len(startupBuf) {
			break
		}

		_ = string(startupBuf[offset:keyEnd]) // key (not used, PostgreSQL startup doesn't contain hostname)
		offset = keyEnd + 1

		// Find null terminator for value
		valueEnd := offset
		for valueEnd < len(startupBuf) && startupBuf[valueEnd] != 0 {
			valueEnd++
		}
		if valueEnd >= len(startupBuf) {
			break
		}

		_ = string(startupBuf[offset:valueEnd]) // value (not used, PostgreSQL startup doesn't contain hostname)
		offset = valueEnd + 1

		// PostgreSQL startup message doesn't contain hostname directly
		// Hostname should come from TLS SNI for TLS connections

		// If we hit the final null byte, we're done
		if offset >= len(startupBuf) || startupBuf[offset] == 0 {
			break
		}
	}

	return ""
}

// handlePostgresSSLRequest handles PostgreSQL SSL request after TLS handshake
// PostgreSQL clients may send an SSL request (0x00 0x00 0x00 0x08 0x04 0xD2 0x16 0x2F)
// We respond with 'S' (0x53) to indicate SSL is supported, since encryption is already handled by TLS
func (p *Proxy) handlePostgresSSLRequest(conn *peekConn) error {
	// Peek at first 8 bytes to check for SSL request
	peekBuf, err := conn.peek(8)
	if err != nil {
		// If we can't peek, it's not an SSL request, continue normally
		return nil
	}

	// PostgreSQL SSL request: 4 bytes length (0x00 0x00 0x00 0x08) + 4 bytes code (0x04 0xD2 0x16 0x2F)
	sslRequest := []byte{0x00, 0x00, 0x00, 0x08, 0x04, 0xD2, 0x16, 0x2F}

	if len(peekBuf) >= 8 {
		isSSLRequest := true
		for i := 0; i < 8; i++ {
			if peekBuf[i] != sslRequest[i] {
				isSSLRequest = false
				break
			}
		}

		if isSSLRequest {
			// Consume the SSL request (read it from the connection)
			buf := make([]byte, 8)
			_, err := io.ReadFull(conn, buf)
			if err != nil {
				return fmt.Errorf("failed to read SSL request: %w", err)
			}

			// Respond with 'S' (0x53) - SSL supported
			// Since encryption is already handled by TLS termination, we signal SSL support
			_, err = conn.Write([]byte{'S'})
			if err != nil {
				return fmt.Errorf("failed to write SSL response: %w", err)
			}

			masterlog.Info("Handled PostgreSQL SSL request", map[string]interface{}{"response": "S", "reason": "TLS already enabled"})
		}
	}

	return nil
}