// Package protocol defines the communication protocol between proxy and agent.
package protocol

import (
	"errors"
	"net"
)

// Protocol error codes for agent-server communication.
// Uses byte values to minimize binary size and network traffic.
const (
	// General errors (0-9)
	ErrNone            byte = 0 // Operation completed successfully
	ErrInvalidCommand  byte = 1 // Command type is not recognized
	ErrContextCanceled byte = 2 // Context canceled

	// Connection errors (10-19)
	ErrConnectionClosed   byte = 10 // Connection was terminated
	ErrConnectionNotFound byte = 11 // Connection ID does not exist
	ErrConnectionExists   byte = 12 // Connection ID already in use
	ErrInvalidState       byte = 13 // Connection in wrong state for operation
	ErrPacketSendFailed   byte = 14 // Packet transmission failed
	ErrHandlerStopped     byte = 15 // Protocol handler is not running
	ErrUnexpectedPacket   byte = 16 // Received unexpected packet type
	ErrBufferFull         byte = 17 // Per-connection delivery buffer is full

	// Transport errors (20-29)
	ErrTransportClosed  byte = 20 // Transport layer terminated
	ErrTransportTimeout byte = 21 // Transport operation timed out
	ErrTransportError   byte = 22 // Transport operation failed

	// SOCKS errors (30-39)
	ErrInvalidSocksVersion byte = 30 // Unsupported SOCKS protocol version
	ErrUnsupportedCommand  byte = 31 // SOCKS command not implemented
	ErrHostUnreachable     byte = 32 // Target host not accessible
	ErrConnectionRefused   byte = 33 // Target refused connection
	ErrNetworkUnreachable  byte = 34 // Network path not accessible
	ErrAddressNotSupported byte = 35 // Address format not supported
	ErrTTLExpired          byte = 36 // Time-to-live exceeded
	ErrGeneralSocksFailure byte = 37 // Unspecified SOCKS failure
	ErrAuthFailed          byte = 38 // Authentication rejected

	// Packet errors (40-49)
	ErrInvalidPacket byte = 40 // Malformed packet structure
)

// MapNetError converts a network error to an appropriate protocol error code.
// This consolidates error mapping logic used throughout the codebase.
func MapNetError(err error) byte {
	if err == nil {
		return ErrNone
	}

	// Check for timeout
	if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
		return ErrTTLExpired
	}

	// Check for net.OpError (most common network error type)
	if opErr, ok := err.(*net.OpError); ok {
		if errors.Is(opErr, net.ErrClosed) {
			return ErrTransportClosed
		}
		switch opErr.Op {
		case "dial":
			return ErrNetworkUnreachable
		case "read", "write":
			return ErrHostUnreachable
		case "listen":
			return ErrNetworkUnreachable
		}
	}

	// Check for DNS errors
	if _, ok := err.(*net.DNSError); ok {
		return ErrHostUnreachable
	}

	// Check for closed connection
	if errors.Is(err, net.ErrClosed) {
		return ErrTransportClosed
	}

	// Default to connection refused
	return ErrConnectionRefused
}