// Copyright 2020 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 eth

import (
	"errors"
	"sync"

	"github.com/ledgerwatch/turbo-geth/common"
	"github.com/ledgerwatch/turbo-geth/eth/protocols/eth"
	"github.com/ledgerwatch/turbo-geth/p2p"
)

var (
	// errPeerSetClosed is returned if a peer is attempted to be added or removed
	// from the peer set after it has been terminated.
	errPeerSetClosed = errors.New("peerset closed")

	// errPeerAlreadyRegistered is returned if a peer is attempted to be added
	// to the peer set, but one with the same id already exists.
	errPeerAlreadyRegistered = errors.New("peer already registered")

	// errPeerNotRegistered is returned if a peer is attempted to be removed from
	// a peer set, but no peer with the given id exists.
	errPeerNotRegistered = errors.New("peer not registered")
)

// peerSet represents the collection of active peers currently participating in
// the `eth` protocol, with or without the `snap` extension.
type peerSet struct {
	peers map[string]*ethPeer // Peers connected on the `eth` protocol

	lock   sync.RWMutex
	closed bool
}

// newPeerSet creates a new peer set to track the active participants.
func newPeerSet() *peerSet {
	return &peerSet{
		peers: make(map[string]*ethPeer),
	}
}

// registerPeer injects a new `eth` peer into the working set, or returns an error
// if the peer is already known.
func (ps *peerSet) registerPeer(peer *eth.Peer) error {
	// Start tracking the new peer
	ps.lock.Lock()
	defer ps.lock.Unlock()

	if ps.closed {
		return errPeerSetClosed
	}
	id := peer.ID()
	if _, ok := ps.peers[id]; ok {
		return errPeerAlreadyRegistered
	}
	eth := &ethPeer{
		Peer: peer,
	}
	ps.peers[id] = eth
	return nil
}

// unregisterPeer removes a remote peer from the active set, disabling any further
// actions to/from that particular entity.
func (ps *peerSet) unregisterPeer(id string) error {
	ps.lock.Lock()
	defer ps.lock.Unlock()

	_, ok := ps.peers[id]
	if !ok {
		return errPeerNotRegistered
	}
	delete(ps.peers, id)
	return nil
}

// peer retrieves the registered peer with the given id.
func (ps *peerSet) peer(id string) *ethPeer {
	ps.lock.RLock()
	defer ps.lock.RUnlock()

	return ps.peers[id]
}

// peersWithoutBlock retrieves a list of peers that do not have a given block in
// their set of known hashes so it might be propagated to them.
func (ps *peerSet) peersWithoutBlock(hash common.Hash) []*ethPeer {
	ps.lock.RLock()
	defer ps.lock.RUnlock()

	list := make([]*ethPeer, 0, len(ps.peers))
	for _, p := range ps.peers {
		if !p.KnownBlock(hash) {
			list = append(list, p)
		}
	}
	return list
}

// peersWithoutTransaction retrieves a list of peers that do not have a given
// transaction in their set of known hashes.
func (ps *peerSet) peersWithoutTransaction(hash common.Hash) []*ethPeer {
	ps.lock.RLock()
	defer ps.lock.RUnlock()

	list := make([]*ethPeer, 0, len(ps.peers))
	for _, p := range ps.peers {
		if !p.KnownTransaction(hash) {
			list = append(list, p)
		}
	}
	return list
}

// len returns if the current number of `eth` peers in the set. Since the `snap`
// peers are tied to the existence of an `eth` connection, that will always be a
// subset of `eth`.
func (ps *peerSet) len() int {
	ps.lock.RLock()
	defer ps.lock.RUnlock()

	return len(ps.peers)
}

// peerWithHighestNumber retrieves the known peer with the currently highest block height.
func (ps *peerSet) peerWithHighestNumber() *eth.Peer {
	ps.lock.RLock()
	defer ps.lock.RUnlock()

	var (
		bestPeer   *eth.Peer
		bestNumber uint64
	)
	for _, p := range ps.peers {
		if _, headNumber := p.Head(); bestPeer == nil || headNumber > bestNumber {
			bestPeer, bestNumber = p.Peer, headNumber
		}
	}
	return bestPeer
}

// close disconnects all peers.
func (ps *peerSet) close() {
	ps.lock.Lock()
	defer ps.lock.Unlock()

	for _, p := range ps.peers {
		p.Disconnect(p2p.DiscQuitting)
	}
	ps.closed = true
}