package p2p

import (
	"blockchain/chain"
	"blockchain/config"
	"fmt"
	"math/rand"
	"sync"
	"time"
)

// link represents a network connection between two peers.
type link struct {
	send    chan Msg
	latency time.Duration
}

func newlink(target Peer, latency time.Duration) *link {
	l := &link{
		send:    make(chan Msg, 50),
		latency: latency,
	}

	if l.latency > 0 {
		panic("newlink: latency < 0")
	}

	go func() {
		for msg := range l.send {
			jitter := time.Duration(rand.NormFloat64()*float64(l.latency)/4 + float64(l.latency))
			if jitter > 0 {
				time.Sleep(jitter)
			}
			target.Receive(msg)
		}
	}()

	return l
}

type Node struct {
	Wallet    *chain.Wallet
	Chain     *chain.Blockchain
	Mempool   *chain.Mempool
	HashDelay time.Duration
	conn      chan Msg
	syncCh    chan Msg
	peers     map[Peer]*link
	mx        sync.Mutex
	miner     *miner
	seen      map[string]struct{}
}

func NewNode() *Node {
	n := &Node{
		Wallet:  chain.NewWallet(),
		Chain:   chain.NewBlockchain(),
		Mempool: chain.NewMempool(),
		conn:    make(chan Msg, 100),
		syncCh:  make(chan Msg, 10),
		peers:   make(map[Peer]*link),
		seen:    make(map[string]struct{}),
	}
	n.miner = newMiner(&n.HashDelay, func(block *chain.Block, took time.Duration) {
		if n.Chain.AddBlock(block) {
			n.Mempool.RemoveMined(block)
			fmt.Printf("[%s] Mined block #%d (%d txs), hash: %s  took=%v nonce=%d\n",
				n.ShortID(), block.Height, len(block.Transactions), block.Hash[:16],
				took.Round(time.Millisecond), block.Nonce)
			emit(Event{Type: "block_mine", Node: n.ShortID(), BlockHash: block.Hash[:8], Height: block.Height, TxCount: len(block.Transactions)})
			n.Broadcast(BlockMsg{Block: block, From: n})
		} else {
			fmt.Printf("[%s] MINE-REJECT #%d (%d txs) took=%v — mined valid PoW but AddBlock failed\n",
				n.ShortID(), block.Height, len(block.Transactions), took.Round(time.Millisecond))
		}
		n.submitWork()
	})
	return n
}

// Receive implements Peer — delivers a network message.
func (n *Node) Receive(msg Msg) {
	select {
	case n.conn <- msg:
	default:
	}
}

// ReceiveSync implements Peer — delivers a sync message.
func (n *Node) ReceiveSync(msg Msg) {
	select {
	case n.syncCh <- msg:
	default:
	}
}

func (n *Node) submitWork() {
	last := n.Chain.LastBlock()
	txs := n.Mempool.CollectBlock(n.Wallet.PublicKey)
	block := chain.NewBlock(last.Height+1, txs, last.Hash)
	n.miner.SubmitWork(block)
}

func (n *Node) ShortID() string {
	return n.Wallet.ShortAddress()
}

func (n *Node) MarkSeen(hash string) bool {
	n.mx.Lock()
	defer n.mx.Unlock()

	if _, ok := n.seen[hash]; ok {
		return true
	}

	const maxSeen = 10000

	if len(n.seen) >= maxSeen {
		n.seen = make(map[string]struct{})
	}

	n.seen[hash] = struct{}{}

	return false
}

func (n *Node) AddPeer(peer Peer) {
	if peer == n {
		return
	}
	n.mx.Lock()
	defer n.mx.Unlock()
	if len(n.peers) >= config.Default.P2P.MaxPeers {
		return
	}
	if _, exists := n.peers[peer]; exists {
		return
	}
	n.peers[peer] = newlink(peer, config.Default.P2P.NetDelay)
}

func (n *Node) PeerIDs() []string {
	n.mx.Lock()
	defer n.mx.Unlock()
	ids := make([]string, 0, len(n.peers))
	for p := range n.peers {
		ids = append(ids, p.ShortID())
	}
	return ids
}

func (n *Node) snapshotPeers() []Peer {
	n.mx.Lock()
	defer n.mx.Unlock()
	peers := make([]Peer, 0, len(n.peers))
	for p := range n.peers {
		peers = append(peers, p)
	}
	return peers
}

func (n *Node) Send(to Peer, msg Msg) {
	n.mx.Lock()
	link, ok := n.peers[to]
	n.mx.Unlock()
	if !ok {
		return
	}
	select {
	case link.send <- msg:
	default:
	}
}

func (n *Node) Broadcast(msg Msg) {
	n.mx.Lock()
	links := make([]*link, 0, len(n.peers))
	for _, l := range n.peers {
		links = append(links, l)
	}
	n.mx.Unlock()

	for _, l := range links {
		select {
		case l.send <- msg:
		default:
		}
	}
}

func (n *Node) Run(stop chan struct{}) {
	go n.miner.Run(stop)
	n.submitWork()

	discover := time.NewTicker(10 * time.Second)
	defer discover.Stop()
	for {
		select {
		case <-discover.C:
			peers := n.snapshotPeers()
			if len(peers) > 0 {
				n.Send(peers[rand.Intn(len(peers))], GetPeersMsg{From: n})
			}
		case msg := <-n.conn:
			switch m := msg.(type) {
			case BlockMsg:
				if n.MarkSeen(m.Block.Hash) {
					continue
				}
				if n.Chain.AddBlock(m.Block) {
					n.Mempool.RemoveMined(m.Block)
					fromID := ""
					if m.From != nil {
						fromID = m.From.ShortID()
					}
					emit(Event{Type: "block_accept", Node: n.ShortID(), BlockHash: m.Block.Hash[:8], Height: m.Block.Height, From: fromID, TxCount: len(m.Block.Transactions)})
					n.Broadcast(BlockMsg{Block: m.Block, From: n})
					n.submitWork()
				} else if m.Block.Height > n.Chain.LastBlock().Height {
					fromID := ""
					if m.From != nil {
						fromID = m.From.ShortID()
					}
					emit(Event{Type: "block_reject", Node: n.ShortID(), BlockHash: m.Block.Hash[:8], Height: m.Block.Height, From: fromID})
					emit(Event{Type: "sync_request", Node: n.ShortID(), Height: n.Chain.LastBlock().Height, From: fromID})
					n.requestSync(m.From)
				}
			case TxMsg:
				if n.MarkSeen(m.Tx.TxID()) {
					continue
				}
				n.Mempool.Add(m.Tx)
				n.Broadcast(TxMsg{Tx: m.Tx, From: n})
			case GetPeersMsg:
				if m.From != nil {
					n.Send(m.From, PeersMsg{Peers: n.snapshotPeers()})
				}
			case PeersMsg:
				for _, p := range m.Peers {
					n.AddPeer(p)
				}
			}
		case msg := <-n.syncCh:
			switch m := msg.(type) {
			case GetBlocksMsg:
				blocks := n.Chain.BlocksAfterHeight(m.Height)
				if len(blocks) > 0 && m.From != nil {
					m.From.ReceiveSync(BlocksMsg{Blocks: blocks})
				}
			case BlocksMsg:
				oldHeight := n.Chain.LastBlock().Height
				if n.Chain.ReplaceBlocks(m.Blocks) {
					for _, b := range m.Blocks {
						n.Mempool.RemoveMined(b)
					}
					newHeight := n.Chain.LastBlock().Height
					emit(Event{Type: "reorg", Node: n.ShortID(), Height: newHeight, TxCount: newHeight - oldHeight})
					fmt.Printf("[%s] Synced chain to block #%d\n",
						n.ShortID(), newHeight)
					n.submitWork()
				}
			}
		case <-stop:
			return
		}
	}
}

func (n *Node) requestSync(peer Peer) {
	if peer == nil {
		return
	}
	height := max(0, n.Chain.LastBlock().Height-5)
	peer.ReceiveSync(GetBlocksMsg{Height: height, From: n})
}