package wire

import (
	"fmt"
	"io"
)

// defaultInvListAlloc is the default size used for the backing array for an inventory list. The array will dynamically
// grow as needed, but this figure is intended to provide enough space for the max number of inventory vectors in a
// *typical* inventory message without needing to grow the backing array multiple times. Technically, the list can grow
// to MaxInvPerMsg, but rather than using that large figure, this figure more accurately reflects the typical case.
const defaultInvListAlloc = 1000

// MsgInv implements the Message interface and represents a bitcoin inv message. It is used to advertise a peer's known
// data such as blocks and transactions through inventory vectors. It may be sent unsolicited to inform other peers of
// the data or in response to a getblocks message (MsgGetBlocks). Each message is limited to a maximum number of
// inventory vectors, which is currently 50,000. Use the AddInvVect function to podbuild up the list of inventory vectors
// when sending an inv message to another peer.
type MsgInv struct {
	InvList []*InvVect
}

// AddInvVect adds an inventory vector to the message.
func (msg *MsgInv) AddInvVect(iv *InvVect) (e error) {
	if len(msg.InvList)+1 > MaxInvPerMsg {
		str := fmt.Sprintf(
			"too many invvect in message [max %v]",
			MaxInvPerMsg,
		)
		return messageError("MsgInv.AddInvVect", str)
	}
	msg.InvList = append(msg.InvList, iv)
	return
}

// BtcDecode decodes r using the bitcoin protocol encoding into the receiver. This is part of the Message interface
// implementation.
func (msg *MsgInv) BtcDecode(r io.Reader, pver uint32, enc MessageEncoding) (e error) {
	var count uint64
	if count, e = ReadVarInt(r, pver); E.Chk(e) {
		return
	}
	// Limit to max inventory vectors per message.
	if count > MaxInvPerMsg {
		str := fmt.Sprintf("too many invvect in message [%v]", count)
		return messageError("MsgInv.BtcDecode", str)
	}
	// Create a contiguous slice of inventory vectors to deserialize into in order to reduce the number of allocations.
	invList := make([]InvVect, count)
	msg.InvList = make([]*InvVect, 0, count)
	for i := uint64(0); i < count; i++ {
		iv := &invList[i]
		if e = readInvVect(r, pver, iv); E.Chk(e) {
			return
		}
		if e = msg.AddInvVect(iv); E.Chk(e) {
		}
	}
	return
}

// BtcEncode encodes the receiver to w using the bitcoin protocol encoding. This is part of the Message interface
// implementation.
func (msg *MsgInv) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) (e error) {
	// Limit to max inventory vectors per message.
	count := len(msg.InvList)
	if count > MaxInvPerMsg {
		str := fmt.Sprintf("too many invvect in message [%v]", count)
		return messageError("MsgInv.BtcEncode", str)
	}
	if e = WriteVarInt(w, pver, uint64(count)); E.Chk(e) {
		return
	}
	for _, iv := range msg.InvList {
		if e = writeInvVect(w, pver, iv); E.Chk(e) {
			return
		}
	}
	return
}

// Command returns the protocol command string for the message. This is part of the Message interface implementation.
func (msg *MsgInv) Command() string {
	return CmdInv
}

// MaxPayloadLength returns the maximum length the payload can be for the receiver. This is part of the Message
// interface implementation.
func (msg *MsgInv) MaxPayloadLength(pver uint32) uint32 {
	// Num inventory vectors (varInt) + max allowed inventory vectors.
	return MaxVarIntPayload + (MaxInvPerMsg * maxInvVectPayload)
}

// NewMsgInv returns a new bitcoin inv message that conforms to the Message interface. See MsgInv for details.
func NewMsgInv() *MsgInv {
	return &MsgInv{
		InvList: make([]*InvVect, 0, defaultInvListAlloc),
	}
}

// NewMsgInvSizeHint returns a new bitcoin inv message that conforms to the Message interface. See MsgInv for details.
// This function differs from NewMsgInv in that it allows a default allocation size for the backing array which houses
// the inventory vector list. This allows callers who know in advance how large the inventory list will grow to avoid
// the overhead of growing the internal backing array several times when appending large amounts of inventory vectors
// with AddInvVect. Note that the specified hint is just that - a hint that is used for the default allocation size.
// Adding more (or less) inventory vectors will still work properly. The size hint is limited to MaxInvPerMsg.
func NewMsgInvSizeHint(sizeHint uint) *MsgInv {
	// Limit the specified hint to the maximum allow per message.
	if sizeHint > MaxInvPerMsg {
		sizeHint = MaxInvPerMsg
	}
	return &MsgInv{
		InvList: make([]*InvVect, 0, sizeHint),
	}
}