package p2p

import (
	"github.com/kaspanet/kaspad/peer"
	"github.com/kaspanet/kaspad/util/daghash"
	"github.com/kaspanet/kaspad/wire"
)

// OnGetData is invoked when a peer receives a getdata kaspa message and
// is used to deliver block and transaction information.
func (sp *Peer) OnGetData(_ *peer.Peer, msg *wire.MsgGetData) {
	numAdded := 0
	notFound := wire.NewMsgNotFound()

	length := len(msg.InvList)
	// A decaying ban score increase is applied to prevent exhausting resources
	// with unusually large inventory queries.
	// Requesting more than the maximum inventory vector length within a short
	// period of time yields a score above the default ban threshold. Sustained
	// bursts of small requests are not penalized as that would potentially ban
	// peers performing IBD.
	// This incremental score decays each minute to half of its value.
	sp.addBanScore(0, uint32(length)*99/wire.MaxInvPerMsg, "getdata")

	// We wait on this wait channel periodically to prevent queuing
	// far more data than we can send in a reasonable time, wasting memory.
	// The waiting occurs after the database fetch for the next one to
	// provide a little pipelining.
	var waitChan chan struct{}
	doneChan := make(chan struct{}, 1)

	for i, iv := range msg.InvList {
		var c chan struct{}
		// If this will be the last message we send.
		if i == length-1 && len(notFound.InvList) == 0 {
			c = doneChan
		} else if (i+1)%3 == 0 {
			// Buffered so as to not make the send goroutine block.
			c = make(chan struct{}, 1)
		}
		var err error
		switch iv.Type {
		case wire.InvTypeTx:
			err = sp.server.pushTxMsg(sp, (*daghash.TxID)(iv.Hash), c, waitChan)
		case wire.InvTypeSyncBlock:
			fallthrough
		case wire.InvTypeMissingAncestor:
			fallthrough
		case wire.InvTypeBlock:
			err = sp.server.pushBlockMsg(sp, iv.Hash, c, waitChan)
		case wire.InvTypeFilteredBlock:
			err = sp.server.pushMerkleBlockMsg(sp, iv.Hash, c, waitChan)
		default:
			peerLog.Warnf("Unknown type in inventory request %d",
				iv.Type)
			continue
		}
		if err != nil {
			notFound.AddInvVect(iv)

			// When there is a failure fetching the final entry
			// and the done channel was sent in due to there
			// being no outstanding not found inventory, consume
			// it here because there is now not found inventory
			// that will use the channel momentarily.
			if i == len(msg.InvList)-1 && c != nil {
				<-c
			}
		}
		numAdded++
		waitChan = c
	}
	if len(notFound.InvList) != 0 {
		sp.QueueMessage(notFound, doneChan)
	}

	// Wait for messages to be sent. We can send quite a lot of data at this
	// point and this will keep the peer busy for a decent amount of time.
	// We don't process anything else by them in this time so that we
	// have an idea of when we should hear back from them - else the idle
	// timeout could fire when we were only half done sending the blocks.
	if numAdded > 0 {
		<-doneChan
	}
}