package statesync

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"

	dbm "github.com/tendermint/tm-db"

	"github.com/tendermint/tendermint/internal/p2p"
	sm "github.com/tendermint/tendermint/internal/state"
	"github.com/tendermint/tendermint/libs/log"
	"github.com/tendermint/tendermint/light"
	lightprovider "github.com/tendermint/tendermint/light/provider"
	lighthttp "github.com/tendermint/tendermint/light/provider/http"
	lightrpc "github.com/tendermint/tendermint/light/rpc"
	lightdb "github.com/tendermint/tendermint/light/store/db"
	ssproto "github.com/tendermint/tendermint/proto/tendermint/statesync"
	rpchttp "github.com/tendermint/tendermint/rpc/client/http"
	"github.com/tendermint/tendermint/types"
	"github.com/tendermint/tendermint/version"
)

//go:generate ../../scripts/mockery_generate.sh StateProvider

// StateProvider is a provider of trusted state data for bootstrapping a node. This refers
// to the state.State object, not the state machine. There are two implementations. One
// uses the P2P layer and the other uses the RPC layer. Both use light client verification.
type StateProvider interface {
	// AppHash returns the app hash after the given height has been committed.
	AppHash(ctx context.Context, height uint64) ([]byte, error)
	// Commit returns the commit at the given height.
	Commit(ctx context.Context, height uint64) (*types.Commit, error)
	// State returns a state object at the given height.
	State(ctx context.Context, height uint64) (sm.State, error)
}

type stateProviderRPC struct {
	sync.Mutex    // light.Client is not concurrency-safe
	lc            *light.Client
	initialHeight int64
	providers     map[lightprovider.Provider]string
	logger        log.Logger
}

// NewRPCStateProvider creates a new StateProvider using a light client and RPC clients.
func NewRPCStateProvider(
	ctx context.Context,
	chainID string,
	initialHeight int64,
	servers []string,
	trustOptions light.TrustOptions,
	logger log.Logger,
) (StateProvider, error) {
	if len(servers) < 2 {
		return nil, fmt.Errorf("at least 2 RPC servers are required, got %d", len(servers))
	}

	providers := make([]lightprovider.Provider, 0, len(servers))
	providerRemotes := make(map[lightprovider.Provider]string)
	for _, server := range servers {
		client, err := rpcClient(server)
		if err != nil {
			return nil, fmt.Errorf("failed to set up RPC client: %w", err)
		}
		provider := lighthttp.NewWithClient(chainID, client)
		providers = append(providers, provider)
		// We store the RPC addresses keyed by provider, so we can find the address of the primary
		// provider used by the light client and use it to fetch consensus parameters.
		providerRemotes[provider] = server
	}

	lc, err := light.NewClient(ctx, chainID, trustOptions, providers[0], providers[1:],
		lightdb.New(dbm.NewMemDB()), light.Logger(logger))
	if err != nil {
		return nil, err
	}
	return &stateProviderRPC{
		logger:        logger,
		lc:            lc,
		initialHeight: initialHeight,
		providers:     providerRemotes,
	}, nil
}

func (s *stateProviderRPC) verifyLightBlockAtHeight(ctx context.Context, height uint64, ts time.Time) (*types.LightBlock, error) {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	return s.lc.VerifyLightBlockAtHeight(ctx, int64(height), ts)
}

// AppHash implements part of StateProvider. It calls the application to verify the
// light blocks at heights h+1 and h+2 and, if verification succeeds, reports the app
// hash for the block at height h+1 which correlates to the state at height h.
func (s *stateProviderRPC) AppHash(ctx context.Context, height uint64) ([]byte, error) {
	s.Lock()
	defer s.Unlock()

	// We have to fetch the next height, which contains the app hash for the previous height.
	header, err := s.verifyLightBlockAtHeight(ctx, height+1, time.Now())
	if err != nil {
		return nil, err
	}

	// We also try to fetch the blocks at H+2, since we need these
	// when building the state while restoring the snapshot. This avoids the race
	// condition where we try to restore a snapshot before H+2 exists.
	_, err = s.verifyLightBlockAtHeight(ctx, height+2, time.Now())
	if err != nil {
		return nil, err
	}
	return header.AppHash, nil
}

// Commit implements StateProvider.
func (s *stateProviderRPC) Commit(ctx context.Context, height uint64) (*types.Commit, error) {
	s.Lock()
	defer s.Unlock()
	header, err := s.verifyLightBlockAtHeight(ctx, height, time.Now())
	if err != nil {
		return nil, err
	}
	return header.Commit, nil
}

// State implements StateProvider.
func (s *stateProviderRPC) State(ctx context.Context, height uint64) (sm.State, error) {
	s.Lock()
	defer s.Unlock()

	state := sm.State{
		ChainID:       s.lc.ChainID(),
		InitialHeight: s.initialHeight,
	}
	if state.InitialHeight == 0 {
		state.InitialHeight = 1
	}

	// The snapshot height maps onto the state heights as follows:
	//
	// height: last block, i.e. the snapshotted height
	// height+1: current block, i.e. the first block we'll process after the snapshot
	// height+2: next block, i.e. the second block after the snapshot
	//
	// We need to fetch the NextValidators from height+2 because if the application changed
	// the validator set at the snapshot height then this only takes effect at height+2.
	lastLightBlock, err := s.verifyLightBlockAtHeight(ctx, height, time.Now())
	if err != nil {
		return sm.State{}, err
	}
	currentLightBlock, err := s.verifyLightBlockAtHeight(ctx, height+1, time.Now())
	if err != nil {
		return sm.State{}, err
	}
	nextLightBlock, err := s.verifyLightBlockAtHeight(ctx, height+2, time.Now())
	if err != nil {
		return sm.State{}, err
	}

	state.Version = sm.Version{
		Consensus: currentLightBlock.Version,
		Software:  version.TMVersion,
	}
	state.LastBlockHeight = lastLightBlock.Height
	state.LastBlockTime = lastLightBlock.Time
	state.LastBlockID = lastLightBlock.Commit.BlockID
	state.AppHash = currentLightBlock.AppHash
	state.LastResultsHash = currentLightBlock.LastResultsHash
	state.LastValidators = lastLightBlock.ValidatorSet
	state.Validators = currentLightBlock.ValidatorSet
	state.NextValidators = nextLightBlock.ValidatorSet
	state.LastHeightValidatorsChanged = nextLightBlock.Height

	// We'll also need to fetch consensus params via RPC, using light client verification.
	primaryURL, ok := s.providers[s.lc.Primary()]
	if !ok || primaryURL == "" {
		return sm.State{}, fmt.Errorf("could not find address for primary light client provider")
	}
	primaryRPC, err := rpcClient(primaryURL)
	if err != nil {
		return sm.State{}, fmt.Errorf("unable to create RPC client: %w", err)
	}
	rpcclient := lightrpc.NewClient(s.logger, primaryRPC, s.lc)
	result, err := rpcclient.ConsensusParams(ctx, &currentLightBlock.Height)
	if err != nil {
		return sm.State{}, fmt.Errorf("unable to fetch consensus parameters for height %v: %w",
			nextLightBlock.Height, err)
	}
	state.ConsensusParams = result.ConsensusParams
	state.LastHeightConsensusParamsChanged = currentLightBlock.Height

	return state, nil
}

// rpcClient sets up a new RPC client
func rpcClient(server string) (*rpchttp.HTTP, error) {
	if !strings.Contains(server, "://") {
		server = "http://" + server
	}
	return rpchttp.New(server)
}

type stateProviderP2P struct {
	sync.Mutex    // light.Client is not concurrency-safe
	lc            *light.Client
	initialHeight int64
	paramsSendCh  *p2p.Channel
	paramsRecvCh  chan types.ConsensusParams
}

// NewP2PStateProvider creates a light client state
// provider but uses a dispatcher connected to the P2P layer
func NewP2PStateProvider(
	ctx context.Context,
	chainID string,
	initialHeight int64,
	providers []lightprovider.Provider,
	trustOptions light.TrustOptions,
	paramsSendCh *p2p.Channel,
	logger log.Logger,
) (StateProvider, error) {
	if len(providers) < 2 {
		return nil, fmt.Errorf("at least 2 peers are required, got %d", len(providers))
	}

	lc, err := light.NewClient(ctx, chainID, trustOptions, providers[0], providers[1:],
		lightdb.New(dbm.NewMemDB()), light.Logger(logger))
	if err != nil {
		return nil, err
	}

	return &stateProviderP2P{
		lc:            lc,
		initialHeight: initialHeight,
		paramsSendCh:  paramsSendCh,
		paramsRecvCh:  make(chan types.ConsensusParams),
	}, nil
}

func (s *stateProviderP2P) verifyLightBlockAtHeight(ctx context.Context, height uint64, ts time.Time) (*types.LightBlock, error) {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	return s.lc.VerifyLightBlockAtHeight(ctx, int64(height), ts)
}

// AppHash implements StateProvider.
func (s *stateProviderP2P) AppHash(ctx context.Context, height uint64) ([]byte, error) {
	s.Lock()
	defer s.Unlock()

	// We have to fetch the next height, which contains the app hash for the previous height.
	header, err := s.verifyLightBlockAtHeight(ctx, height+1, time.Now())
	if err != nil {
		return nil, err
	}

	// We also try to fetch the blocks at H+2, since we need these
	// when building the state while restoring the snapshot. This avoids the race
	// condition where we try to restore a snapshot before H+2 exists.
	_, err = s.verifyLightBlockAtHeight(ctx, height+2, time.Now())
	if err != nil {
		return nil, err
	}
	return header.AppHash, nil
}

// Commit implements StateProvider.
func (s *stateProviderP2P) Commit(ctx context.Context, height uint64) (*types.Commit, error) {
	s.Lock()
	defer s.Unlock()
	header, err := s.verifyLightBlockAtHeight(ctx, height, time.Now())
	if err != nil {
		return nil, err
	}
	return header.Commit, nil
}

// State implements StateProvider.
func (s *stateProviderP2P) State(ctx context.Context, height uint64) (sm.State, error) {
	s.Lock()
	defer s.Unlock()

	state := sm.State{
		ChainID:       s.lc.ChainID(),
		InitialHeight: s.initialHeight,
	}
	if state.InitialHeight == 0 {
		state.InitialHeight = 1
	}

	// The snapshot height maps onto the state heights as follows:
	//
	// height: last block, i.e. the snapshotted height
	// height+1: current block, i.e. the first block we'll process after the snapshot
	// height+2: next block, i.e. the second block after the snapshot
	//
	// We need to fetch the NextValidators from height+2 because if the application changed
	// the validator set at the snapshot height then this only takes effect at height+2.
	lastLightBlock, err := s.verifyLightBlockAtHeight(ctx, height, time.Now())
	if err != nil {
		return sm.State{}, err
	}
	currentLightBlock, err := s.verifyLightBlockAtHeight(ctx, height+1, time.Now())
	if err != nil {
		return sm.State{}, err
	}
	nextLightBlock, err := s.verifyLightBlockAtHeight(ctx, height+2, time.Now())
	if err != nil {
		return sm.State{}, err
	}

	state.Version = sm.Version{
		Consensus: currentLightBlock.Version,
		Software:  version.TMVersion,
	}
	state.LastBlockHeight = lastLightBlock.Height
	state.LastBlockTime = lastLightBlock.Time
	state.LastBlockID = lastLightBlock.Commit.BlockID
	state.AppHash = currentLightBlock.AppHash
	state.LastResultsHash = currentLightBlock.LastResultsHash
	state.LastValidators = lastLightBlock.ValidatorSet
	state.Validators = currentLightBlock.ValidatorSet
	state.NextValidators = nextLightBlock.ValidatorSet
	state.LastHeightValidatorsChanged = nextLightBlock.Height

	// We'll also need to fetch consensus params via P2P.
	state.ConsensusParams, err = s.consensusParams(ctx, currentLightBlock.Height)
	if err != nil {
		return sm.State{}, err
	}
	// validate the consensus params
	if !bytes.Equal(nextLightBlock.ConsensusHash, state.ConsensusParams.HashConsensusParams()) {
		return sm.State{}, fmt.Errorf("consensus params hash mismatch at height %d. Expected %v, got %v",
			currentLightBlock.Height, nextLightBlock.ConsensusHash, state.ConsensusParams.HashConsensusParams())
	}
	// set the last height changed to the current height
	state.LastHeightConsensusParamsChanged = currentLightBlock.Height

	return state, nil
}

// addProvider dynamically adds a peer as a new witness. A limit of 6 providers is kept as a
// heuristic. Too many overburdens the network and too little compromises the second layer of security.
func (s *stateProviderP2P) addProvider(p lightprovider.Provider) {
	if len(s.lc.Witnesses()) < 6 {
		s.lc.AddProvider(p)
	}
}

// consensusParams sends out a request for consensus params blocking
// until one is returned.
//
// If it fails to get a valid set of consensus params from any of the
// providers it returns an error; however, it will retry indefinitely
// (with backoff) until the context is canceled.
func (s *stateProviderP2P) consensusParams(ctx context.Context, height int64) (types.ConsensusParams, error) {
	iterCount := 0
	for {
		params, err := s.tryGetConsensusParamsFromWitnesses(ctx, height)
		if err != nil {
			return types.ConsensusParams{}, err
		}
		if params != nil {
			return *params, nil
		}
		iterCount++

		select {
		case <-ctx.Done():
			return types.ConsensusParams{}, ctx.Err()
		case <-time.After(time.Duration(iterCount) * consensusParamsResponseTimeout):
		}
	}
}

// tryGetConsensusParamsFromWitnesses attempts to get consensus
// parameters from the light clients available witnesses. If both
// return parameters are nil, then it can be retried.
func (s *stateProviderP2P) tryGetConsensusParamsFromWitnesses(
	ctx context.Context,
	height int64,
) (*types.ConsensusParams, error) {
	for _, provider := range s.lc.Witnesses() {
		p, ok := provider.(*BlockProvider)
		if !ok {
			panic("expected p2p state provider to use p2p block providers")
		}

		// extract the nodeID of the provider
		peer, err := types.NewNodeID(p.String())
		if err != nil {
			return nil, fmt.Errorf("invalid provider (%s) node id: %w", p.String(), err)
		}

		if err := s.paramsSendCh.Send(ctx, p2p.Envelope{
			To: peer,
			Message: &ssproto.ParamsRequest{
				Height: uint64(height),
			},
		}); err != nil {
			return nil, err
		}

		select {
		// if we get no response from this provider we move on to the next one
		case <-time.After(consensusParamsResponseTimeout):
			continue
		case <-ctx.Done():
			return nil, ctx.Err()
		case params, ok := <-s.paramsRecvCh:
			if !ok {
				return nil, errors.New("params channel closed")
			}
			return &params, nil
		}
	}

	// signal to caller to retry.
	return nil, nil
}