// Copyright 2016 The Netstack Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package header

import (
	"encoding/binary"

	"github.com/google/netstack/tcpip"
)

// ICMPv4 represents an ICMPv4 header stored in a byte array.
type ICMPv4 []byte

const (
	// ICMPv4MinimumSize is the minimum size of a valid ICMP packet.
	ICMPv4MinimumSize = 4

	// ICMPv4EchoMinimumSize is the minimum size of a valid ICMP echo packet.
	ICMPv4EchoMinimumSize = 6

	// ICMPv4ProtocolNumber is the ICMP transport protocol number.
	ICMPv4ProtocolNumber tcpip.TransportProtocolNumber = 1
)

// ICMPv4Type is the ICMP type field described in RFC 792.
type ICMPv4Type byte

// Typical values of ICMPv4Type defined in RFC 792.
const (
	ICMPv4EchoReply      ICMPv4Type = 0
	ICMPv4DstUnreachable ICMPv4Type = 3
	ICMPv4SrcQuench      ICMPv4Type = 4
	ICMPv4Redirect       ICMPv4Type = 5
	ICMPv4Echo           ICMPv4Type = 8
	ICMPv4TimeExceeded   ICMPv4Type = 11
	ICMPv4ParamProblem   ICMPv4Type = 12
	ICMPv4Timestamp      ICMPv4Type = 13
	ICMPv4TimestampReply ICMPv4Type = 14
	ICMPv4InfoRequest    ICMPv4Type = 15
	ICMPv4InfoReply      ICMPv4Type = 16
)

// Type is the ICMP type field.
func (b ICMPv4) Type() ICMPv4Type { return ICMPv4Type(b[0]) }

// SetType sets the ICMP type field.
func (b ICMPv4) SetType(t ICMPv4Type) { b[0] = byte(t) }

// Code is the ICMP code field. Its meaning depends on the value of Type.
func (b ICMPv4) Code() byte { return b[1] }

// SetCode sets the ICMP code field.
func (b ICMPv4) SetCode(c byte) { b[1] = c }

// SetChecksum sets the ICMP checksum field.
func (b ICMPv4) SetChecksum(checksum uint16) {
	binary.BigEndian.PutUint16(b[2:], checksum)
}

// CalculateChecksum calculates the checksum of the ipv4 header.
func (b ICMPv4) CalculateChecksum(prev uint16) uint16 {
	return Checksum(b[:], prev)
}