package blocksync

import (
	"fmt"
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"

	"github.com/cometbft/cometbft/libs/log"
	cmtrand "github.com/cometbft/cometbft/libs/rand"
	"github.com/cometbft/cometbft/p2p"
	"github.com/cometbft/cometbft/types"
)

func init() {
	peerTimeout = 2 * time.Second
}

type testPeer struct {
	id        p2p.ID
	base      int64
	height    int64
	inputChan chan inputData // make sure each peer's data is sequential
	malicious bool
}

type inputData struct {
	t       *testing.T
	pool    *BlockPool
	request BlockRequest
}

// Malicious nodes parameters
const MaliciousLie = 5  // This is how much the malicious node claims to be higher than the real height
const BlackholeSize = 3 // This is how many blocks the malicious node will not return (missing) above real height
const MaliciousTestMaximumLength = 5 * time.Minute

func (p testPeer) runInputRoutine() {
	go func() {
		for input := range p.inputChan {
			p.simulateInput(input)
		}
	}()
}

// Request desired, pretend like we got the block immediately.
func (p testPeer) simulateInput(input inputData) {
	block := &types.Block{Header: types.Header{Height: input.request.Height}, LastCommit: &types.Commit{}} // real blocks have LastCommit
	extCommit := &types.ExtendedCommit{
		Height: input.request.Height,
	}
	// If this peer is malicious
	if p.malicious {
		realHeight := p.height - MaliciousLie
		// And the requested height is above the real height
		if input.request.Height > realHeight {
			// Then provide a fake block
			block.LastCommit = nil // Fake block, no LastCommit
			// or provide no block at all, if we are close to the real height
			if input.request.Height <= realHeight+BlackholeSize {
				input.pool.RedoRequestFrom(input.request.Height, p.id)
				return
			}
		}
	}
	err := input.pool.AddBlock(input.request.PeerID, block, extCommit, 123)
	require.NoError(input.t, err)
	// TODO: uncommenting this creates a race which is detected by:
	// https://github.com/golang/go/blob/2bd767b1022dd3254bcec469f0ee164024726486/src/testing/testing.go#L854-L856
	// see: https://github.com/tendermint/tendermint/issues/3390#issue-418379890
	// input.t.Logf("Added block from peer %v (height: %v)", input.request.PeerID, input.request.Height)
}

type testPeers map[p2p.ID]*testPeer

func (ps testPeers) start() {
	for _, v := range ps {
		v.runInputRoutine()
	}
}

func (ps testPeers) stop() {
	for _, v := range ps {
		close(v.inputChan)
	}
}

func makePeers(numPeers int, minHeight, maxHeight int64) testPeers {
	peers := make(testPeers, numPeers)
	for i := 0; i < numPeers; i++ {
		peerID := p2p.ID(cmtrand.Str(12))
		height := minHeight + cmtrand.Int63n(maxHeight-minHeight)
		base := minHeight + int64(i)
		if base > height {
			base = height
		}
		peers[peerID] = &testPeer{peerID, base, height, make(chan inputData, 10), false}
	}
	return peers
}

func TestBlockPoolBasic(t *testing.T) {
	var (
		start      = int64(42)
		peers      = makePeers(10, start, 1000)
		errorsCh   = make(chan peerError)
		requestsCh = make(chan BlockRequest)
	)
	pool := NewBlockPool(start, requestsCh, errorsCh)
	pool.SetLogger(log.TestingLogger())

	err := pool.Start()
	if err != nil {
		t.Error(err)
	}

	t.Cleanup(func() {
		if err := pool.Stop(); err != nil {
			t.Error(err)
		}
	})

	peers.start()
	defer peers.stop()

	// Introduce each peer.
	go func() {
		for _, peer := range peers {
			pool.SetPeerRange(peer.id, peer.base, peer.height)
		}
	}()

	// Start a goroutine to pull blocks
	go func() {
		for {
			if !pool.IsRunning() {
				return
			}
			first, second, _ := pool.PeekTwoBlocks()
			if first != nil && second != nil {
				pool.PopRequest()
			} else {
				time.Sleep(1 * time.Second)
			}
		}
	}()

	// Pull from channels
	for {
		select {
		case err := <-errorsCh:
			t.Error(err)
		case request := <-requestsCh:
			t.Logf("Pulled new BlockRequest %v", request)
			if request.Height == 300 {
				return // Done!
			}

			peers[request.PeerID].inputChan <- inputData{t, pool, request}
		}
	}
}

func TestBlockPoolTimeout(t *testing.T) {
	var (
		start      = int64(42)
		peers      = makePeers(10, start, 1000)
		errorsCh   = make(chan peerError)
		requestsCh = make(chan BlockRequest)
	)

	pool := NewBlockPool(start, requestsCh, errorsCh)
	pool.SetLogger(log.TestingLogger())
	err := pool.Start()
	if err != nil {
		t.Error(err)
	}
	t.Cleanup(func() {
		if err := pool.Stop(); err != nil {
			t.Error(err)
		}
	})

	for _, peer := range peers {
		t.Logf("Peer %v", peer.id)
	}

	// Introduce each peer.
	go func() {
		for _, peer := range peers {
			pool.SetPeerRange(peer.id, peer.base, peer.height)
		}
	}()

	// Start a goroutine to pull blocks
	go func() {
		for {
			if !pool.IsRunning() {
				return
			}
			first, second, _ := pool.PeekTwoBlocks()
			if first != nil && second != nil {
				pool.PopRequest()
			} else {
				time.Sleep(1 * time.Second)
			}
		}
	}()

	// Pull from channels
	counter := 0
	timedOut := map[p2p.ID]struct{}{}
	for {
		select {
		case err := <-errorsCh:
			t.Log(err)
			// consider error to be always timeout here
			if _, ok := timedOut[err.peerID]; !ok {
				counter++
				if counter == len(peers) {
					return // Done!
				}
			}
		case request := <-requestsCh:
			t.Logf("Pulled new BlockRequest %+v", request)
		}
	}
}

func TestBlockPoolRemovePeer(t *testing.T) {
	peers := make(testPeers, 10)
	for i := 0; i < 10; i++ {
		peerID := p2p.ID(fmt.Sprintf("%d", i+1))
		height := int64(i + 1)
		peers[peerID] = &testPeer{peerID, 0, height, make(chan inputData), false}
	}
	requestsCh := make(chan BlockRequest)
	errorsCh := make(chan peerError)

	pool := NewBlockPool(1, requestsCh, errorsCh)
	pool.SetLogger(log.TestingLogger())
	err := pool.Start()
	require.NoError(t, err)
	t.Cleanup(func() {
		if err := pool.Stop(); err != nil {
			t.Error(err)
		}
	})

	// add peers
	for peerID, peer := range peers {
		pool.SetPeerRange(peerID, peer.base, peer.height)
	}
	assert.EqualValues(t, 10, pool.MaxPeerHeight())

	// remove not-existing peer
	assert.NotPanics(t, func() { pool.RemovePeer(p2p.ID("Superman")) })

	// remove peer with biggest height
	pool.RemovePeer(p2p.ID("10"))
	assert.EqualValues(t, 9, pool.MaxPeerHeight())

	// remove all peers
	for peerID := range peers {
		pool.RemovePeer(peerID)
	}

	assert.EqualValues(t, 0, pool.MaxPeerHeight())
}

func TestBlockPoolMaliciousNode(t *testing.T) {
	// Setup:
	// * each peer has blocks 1..N but the malicious peer reports 1..N+5 (block N+1,N+2,N+3 missing, N+4,N+5 fake)
	// * The malicious peer is ahead of the network but not by much, so it does not get dropped from the pool
	//   with a timeout error. (If a peer does not send blocks after 2 seconds, they are disconnected.)
	// * The network creates new blocks every second. The malicious peer will also get ahead with another fake block.
	// * The pool verifies blocks every half second. This ensures that the pool catches up with the network.
	// * When the pool encounters a fake block sent by the malicious peer and has the previous block from a good peer,
	//   it can prove that the block is fake. The malicious peer gets banned, together with the sender of the previous (valid) block.
	// Additional notes:
	// * After a minute of ban, the malicious peer is unbanned. If the pool IsCaughtUp() by then and consensus started,
	//   there is no impact. If blocksync did not catch up yet, the malicious peer can continue its lie until the next ban.
	// * The pool has an initial 3 seconds spin-up time before it starts verifying peers. (So peers have a chance to
	//   connect.) If the initial height is 7 and the block creation is 1/second, verification will start at height 10.
	// * Testing with height 7, the main functionality of banning a malicious peer is tested.
	//   Testing with height 127, a malicious peer can reconnect and the subsequent banning is also tested.
	//   This takes a couple of minutes to complete, so we don't run it.
	const InitialHeight = 7
	peers := testPeers{
		p2p.ID("good"):  &testPeer{p2p.ID("good"), 1, InitialHeight, make(chan inputData), false},
		p2p.ID("bad"):   &testPeer{p2p.ID("bad"), 1, InitialHeight + MaliciousLie, make(chan inputData), true},
		p2p.ID("good1"): &testPeer{p2p.ID("good1"), 1, InitialHeight, make(chan inputData), false},
	}
	errorsCh := make(chan peerError)
	requestsCh := make(chan BlockRequest)

	pool := NewBlockPool(1, requestsCh, errorsCh)
	pool.SetLogger(log.TestingLogger())

	err := pool.Start()
	if err != nil {
		t.Error(err)
	}

	t.Cleanup(func() {
		if err := pool.Stop(); err != nil {
			t.Error(err)
		}
	})

	peers.start()
	t.Cleanup(func() { peers.stop() })

	// Simulate blocks created on each peer regularly and update pool max height.
	go func() {
		// Introduce each peer
		for _, peer := range peers {
			pool.SetPeerRange(peer.id, peer.base, peer.height)
		}
		for {
			time.Sleep(1 * time.Second) // Speed of new block creation
			for _, peer := range peers {
				peer.height += 1                                   // Network height increases on all peers
				pool.SetPeerRange(peer.id, peer.base, peer.height) // Tell the pool that a new height is available
			}
		}
	}()

	// Start a goroutine to verify blocks
	go func() {
		for {
			time.Sleep(500 * time.Millisecond) // Speed of block verification
			if !pool.IsRunning() {
				return
			}
			first, second, _ := pool.PeekTwoBlocks()
			if first != nil && second != nil {
				if second.LastCommit == nil {
					// Second block is fake
					pool.RemovePeerAndRedoAllPeerRequests(second.Height)
				} else {
					pool.PopRequest()
				}
			}
		}
	}()

	testTicker := time.NewTicker(200 * time.Millisecond) // speed of test execution
	t.Cleanup(func() { testTicker.Stop() })

	bannedOnce := false // true when the malicious peer was banned at least once
	startTime := time.Now()

	// Pull from channels
	for {
		select {
		case err := <-errorsCh:
			t.Error(err)
		case request := <-requestsCh:
			// Process request
			peers[request.PeerID].inputChan <- inputData{t, pool, request}
		case <-testTicker.C:
			banned := pool.isPeerBanned("bad")
			bannedOnce = bannedOnce || banned // Keep bannedOnce true, even if the malicious peer gets unbanned
			caughtUp := pool.IsCaughtUp()
			// Success: pool caught up and malicious peer was banned at least once
			if caughtUp && bannedOnce {
				t.Logf("Pool caught up, malicious peer was banned at least once, start consensus.")
				return
			}
			// Failure: the pool caught up without banning the bad peer at least once
			require.False(t, caughtUp, "Network caught up without banning the malicious peer at least once.")
			// Failure: the network could not catch up in the allotted time
			require.True(t, time.Since(startTime) < MaliciousTestMaximumLength, "Network ran too long, stopping test.")
		}
	}
}
