package sctp

import (
	"encoding/binary"
	"errors"
)

const (
	paramOutgoingResetRequestStreamIdentifiersOffset = 12
)

// This parameter is used by the sender to request the reset of some or
// all outgoing streams.
//  0                   1                   2                   3
//  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |     Parameter Type = 13       | Parameter Length = 16 + 2 * N |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |           Re-configuration Request Sequence Number            |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |           Re-configuration Response Sequence Number           |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |                Sender's Last Assigned TSN                     |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |  Stream Number 1 (optional)   |    Stream Number 2 (optional) |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// /                            ......                             /
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |  Stream Number N-1 (optional) |    Stream Number N (optional) |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

type paramOutgoingResetRequest struct {
	paramHeader
	// reconfigRequestSequenceNumber is used to identify the request.  It is a monotonically
	// increasing number that is initialized to the same value as the
	// initial TSN.  It is increased by 1 whenever sending a new Re-
	// configuration Request Parameter.
	reconfigRequestSequenceNumber uint32
	// When this Outgoing SSN Reset Request Parameter is sent in response
	// to an Incoming SSN Reset Request Parameter, this parameter is also
	// an implicit response to the incoming request.  This field then
	// holds the Re-configuration Request Sequence Number of the incoming
	// request.  In other cases, it holds the next expected
	// Re-configuration Request Sequence Number minus 1.
	reconfigResponseSequenceNumber uint32
	// This value holds the next TSN minus 1 -- in other words, the last
	// TSN that this sender assigned.
	senderLastTSN uint32
	// This optional field, if included, is used to indicate specific
	// streams that are to be reset.  If no streams are listed, then all
	// streams are to be reset.
	streamIdentifiers []uint16
}

var errSSNResetRequestParamTooShort = errors.New("outgoing SSN reset request parameter too short")

func (r *paramOutgoingResetRequest) marshal() ([]byte, error) {
	r.typ = outSSNResetReq
	r.raw = make([]byte, paramOutgoingResetRequestStreamIdentifiersOffset+2*len(r.streamIdentifiers))
	binary.BigEndian.PutUint32(r.raw, r.reconfigRequestSequenceNumber)
	binary.BigEndian.PutUint32(r.raw[4:], r.reconfigResponseSequenceNumber)
	binary.BigEndian.PutUint32(r.raw[8:], r.senderLastTSN)
	for i, sID := range r.streamIdentifiers {
		binary.BigEndian.PutUint16(r.raw[paramOutgoingResetRequestStreamIdentifiersOffset+2*i:], sID)
	}
	return r.paramHeader.marshal()
}

func (r *paramOutgoingResetRequest) unmarshal(raw []byte) (param, error) {
	err := r.paramHeader.unmarshal(raw)
	if err != nil {
		return nil, err
	}
	if len(r.raw) < paramOutgoingResetRequestStreamIdentifiersOffset {
		return nil, errSSNResetRequestParamTooShort
	}
	r.reconfigRequestSequenceNumber = binary.BigEndian.Uint32(r.raw)
	r.reconfigResponseSequenceNumber = binary.BigEndian.Uint32(r.raw[4:])
	r.senderLastTSN = binary.BigEndian.Uint32(r.raw[8:])

	lim := (len(r.raw) - paramOutgoingResetRequestStreamIdentifiersOffset) / 2
	r.streamIdentifiers = make([]uint16, lim)
	for i := 0; i < lim; i++ {
		r.streamIdentifiers[i] = binary.BigEndian.Uint16(r.raw[paramOutgoingResetRequestStreamIdentifiersOffset+2*i:])
	}

	return r, nil
}