// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package network

import (
	"context"
	"fmt"
	"sync"

	"github.com/ethereum/go-ethereum/swarm/pot"
)

// discovery bzz extension for requesting and relaying node address records

var sortPeers = noSortPeers

// Peer wraps BzzPeer and embeds Kademlia overlay connectivity driver
type Peer struct {
	*BzzPeer
	kad       *Kademlia
	sentPeers bool            // whether we already sent peer closer to this address
	mtx       sync.RWMutex    //
	peers     map[string]bool // tracks node records sent to the peer
	depth     uint8           // the proximity order advertised by remote as depth of saturation
}

// NewPeer constructs a discovery peer
func NewPeer(p *BzzPeer, kad *Kademlia) *Peer {
	d := &Peer{
		kad:     kad,
		BzzPeer: p,
		peers:   make(map[string]bool),
	}
	// record remote as seen so we never send a peer its own record
	d.seen(p.BzzAddr)
	return d
}

// HandleMsg is the message handler that delegates incoming messages
func (d *Peer) HandleMsg(ctx context.Context, msg interface{}) error {
	switch msg := msg.(type) {

	case *peersMsg:
		return d.handlePeersMsg(msg)

	case *subPeersMsg:
		return d.handleSubPeersMsg(msg)

	default:
		return fmt.Errorf("unknown message type: %T", msg)
	}
}

// NotifyDepth sends a message to all connections if depth of saturation is changed
func NotifyDepth(depth uint8, kad *Kademlia) {
	f := func(val *Peer, po int) bool {
		val.NotifyDepth(depth)
		return true
	}
	kad.EachConn(nil, 255, f)
}

// NotifyPeer informs all peers about a newly added node
func NotifyPeer(p *BzzAddr, k *Kademlia) {
	f := func(val *Peer, po int) bool {
		val.NotifyPeer(p, uint8(po))
		return true
	}
	k.EachConn(p.Address(), 255, f)
}

// NotifyPeer notifies the remote node (recipient) about a peer if
// the peer's PO is within the recipients advertised depth
// OR the peer is closer to the recipient than self
// unless already notified during the connection session
func (d *Peer) NotifyPeer(a *BzzAddr, po uint8) {
	// immediately return
	if (po < d.getDepth() && pot.ProxCmp(d.kad.BaseAddr(), d, a) != 1) || d.seen(a) {
		return
	}
	resp := &peersMsg{
		Peers: []*BzzAddr{a},
	}
	go d.Send(context.TODO(), resp)
}

// NotifyDepth sends a subPeers Msg to the receiver notifying them about
// a change in the depth of saturation
func (d *Peer) NotifyDepth(po uint8) {
	go d.Send(context.TODO(), &subPeersMsg{Depth: po})
}

/*
peersMsg is the message to pass peer information
It is always a response to a peersRequestMsg

The encoding of a peer address is identical the devp2p base protocol peers
messages: [IP, Port, NodeID],
Note that a node's FileStore address is not the NodeID but the hash of the NodeID.

TODO:
To mitigate against spurious peers messages, requests should be remembered
and correctness of responses should be checked

If the proxBin of peers in the response is incorrect the sender should be
disconnected
*/

// peersMsg encapsulates an array of peer addresses
// used for communicating about known peers
// relevant for bootstrapping connectivity and updating peersets
type peersMsg struct {
	Peers []*BzzAddr
}

// String pretty prints a peersMsg
func (msg peersMsg) String() string {
	return fmt.Sprintf("%T: %v", msg, msg.Peers)
}

// handlePeersMsg called by the protocol when receiving peerset (for target address)
// list of nodes ([]PeerAddr in peersMsg) is added to the overlay db using the
// Register interface method
func (d *Peer) handlePeersMsg(msg *peersMsg) error {
	// register all addresses
	if len(msg.Peers) == 0 {
		return nil
	}

	for _, a := range msg.Peers {
		d.seen(a)
		NotifyPeer(a, d.kad)
	}
	return d.kad.Register(msg.Peers...)
}

// subPeers msg is communicating the depth of the overlay table of a peer
type subPeersMsg struct {
	Depth uint8
}

// String returns the pretty printer
func (msg subPeersMsg) String() string {
	return fmt.Sprintf("%T: request peers > PO%02d. ", msg, msg.Depth)
}

// handleSubPeersMsg handles incoming subPeersMsg
// this message represents the saturation depth of the remote peer
// saturation depth is the radius within which the peer subscribes to peers
// the first time this is received we send peer info on all
// our connected peers that fall within peers saturation depth
// otherwise this depth is just recorded on the peer, so that
// subsequent new connections are sent iff they fall within the radius
func (d *Peer) handleSubPeersMsg(msg *subPeersMsg) error {
	d.setDepth(msg.Depth)
	// only send peers after the initial subPeersMsg
	if !d.sentPeers {
		var peers []*BzzAddr
		// iterate connection in ascending order of disctance from the remote address
		d.kad.EachConn(d.Over(), 255, func(p *Peer, po int) bool {
			// terminate if we are beyond the radius
			if uint8(po) < msg.Depth {
				return false
			}
			if !d.seen(p.BzzAddr) { // here just records the peer sent
				peers = append(peers, p.BzzAddr)
			}
			return true
		})
		// if useful  peers are found, send them over
		if len(peers) > 0 {
			go d.Send(context.TODO(), &peersMsg{Peers: sortPeers(peers)})
		}
	}
	d.sentPeers = true
	return nil
}

// seen takes a peer address and checks if it was sent to a peer already
// if not, marks the peer as sent
func (d *Peer) seen(p *BzzAddr) bool {
	d.mtx.Lock()
	defer d.mtx.Unlock()
	k := string(p.Address())
	if d.peers[k] {
		return true
	}
	d.peers[k] = true
	return false
}

func (d *Peer) getDepth() uint8 {
	d.mtx.RLock()
	defer d.mtx.RUnlock()
	return d.depth
}

func (d *Peer) setDepth(depth uint8) {
	d.mtx.Lock()
	defer d.mtx.Unlock()
	d.depth = depth
}

func noSortPeers(peers []*BzzAddr) []*BzzAddr {
	return peers
}