// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package clientv3

import (
	"context"
	"errors"
	"fmt"
	"net"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/google/uuid"
	"go.etcd.io/etcd/clientv3/balancer"
	"go.etcd.io/etcd/clientv3/balancer/picker"
	"go.etcd.io/etcd/clientv3/balancer/resolver/endpoint"
	"go.etcd.io/etcd/clientv3/credentials"
	"go.etcd.io/etcd/etcdserver/api/v3rpc/rpctypes"
	"go.etcd.io/etcd/pkg/logutil"
	"go.uber.org/zap"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	grpccredentials "google.golang.org/grpc/credentials"
	"google.golang.org/grpc/keepalive"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/status"
)

var (
	ErrNoAvailableEndpoints = errors.New("etcdclient: no available endpoints")
	ErrOldCluster           = errors.New("etcdclient: old cluster version")

	roundRobinBalancerName = fmt.Sprintf("etcd-%s", picker.RoundrobinBalanced.String())
)

func init() {
	lg := zap.NewNop()
	if os.Getenv("ETCD_CLIENT_DEBUG") != "" {
		lcfg := logutil.DefaultZapLoggerConfig
		lcfg.Level = zap.NewAtomicLevelAt(zap.DebugLevel)

		var err error
		lg, err = lcfg.Build() // info level logging
		if err != nil {
			panic(err)
		}
	}

	// TODO: support custom balancer
	balancer.RegisterBuilder(balancer.Config{
		Policy: picker.RoundrobinBalanced,
		Name:   roundRobinBalancerName,
		Logger: lg,
	})
}

// Client provides and manages an etcd v3 client session.
type Client struct {
	Cluster
	KV
	Lease
	Watcher
	Auth
	Maintenance

	conn *grpc.ClientConn

	cfg           Config
	creds         grpccredentials.TransportCredentials
	resolverGroup *endpoint.ResolverGroup
	mu            *sync.RWMutex

	ctx    context.Context
	cancel context.CancelFunc

	// Username is a user name for authentication.
	Username string
	// Password is a password for authentication.
	Password        string
	authTokenBundle credentials.Bundle

	callOpts []grpc.CallOption

	lg *zap.Logger
}

// New creates a new etcdv3 client from a given configuration.
func New(cfg Config) (*Client, error) {
	if len(cfg.Endpoints) == 0 {
		return nil, ErrNoAvailableEndpoints
	}

	return newClient(&cfg)
}

// NewCtxClient creates a client with a context but no underlying grpc
// connection. This is useful for embedded cases that override the
// service interface implementations and do not need connection management.
func NewCtxClient(ctx context.Context) *Client {
	cctx, cancel := context.WithCancel(ctx)
	return &Client{ctx: cctx, cancel: cancel}
}

// NewFromURL creates a new etcdv3 client from a URL.
func NewFromURL(url string) (*Client, error) {
	return New(Config{Endpoints: []string{url}})
}

// NewFromURLs creates a new etcdv3 client from URLs.
func NewFromURLs(urls []string) (*Client, error) {
	return New(Config{Endpoints: urls})
}

// Close shuts down the client's etcd connections.
func (c *Client) Close() error {
	c.cancel()
	if c.Watcher != nil {
		c.Watcher.Close()
	}
	if c.Lease != nil {
		c.Lease.Close()
	}
	if c.resolverGroup != nil {
		c.resolverGroup.Close()
	}
	if c.conn != nil {
		return toErr(c.ctx, c.conn.Close())
	}
	return c.ctx.Err()
}

// Ctx is a context for "out of band" messages (e.g., for sending
// "clean up" message when another context is canceled). It is
// canceled on client Close().
func (c *Client) Ctx() context.Context { return c.ctx }

// Endpoints lists the registered endpoints for the client.
func (c *Client) Endpoints() []string {
	// copy the slice; protect original endpoints from being changed
	c.mu.RLock()
	defer c.mu.RUnlock()
	eps := make([]string, len(c.cfg.Endpoints))
	copy(eps, c.cfg.Endpoints)
	return eps
}

// SetEndpoints updates client's endpoints.
func (c *Client) SetEndpoints(eps ...string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.cfg.Endpoints = eps
	c.resolverGroup.SetEndpoints(eps)
}

// Sync synchronizes client's endpoints with the known endpoints from the etcd membership.
func (c *Client) Sync(ctx context.Context) error {
	mresp, err := c.MemberList(ctx)
	if err != nil {
		return err
	}
	var eps []string
	for _, m := range mresp.Members {
		eps = append(eps, m.ClientURLs...)
	}
	c.SetEndpoints(eps...)
	return nil
}

func (c *Client) autoSync() {
	if c.cfg.AutoSyncInterval == time.Duration(0) {
		return
	}

	for {
		select {
		case <-c.ctx.Done():
			return
		case <-time.After(c.cfg.AutoSyncInterval):
			ctx, cancel := context.WithTimeout(c.ctx, 5*time.Second)
			err := c.Sync(ctx)
			cancel()
			if err != nil && err != c.ctx.Err() {
				lg.Lvl(4).Infof("Auto sync endpoints failed: %v", err)
			}
		}
	}
}

func (c *Client) processCreds(scheme string) (creds grpccredentials.TransportCredentials) {
	creds = c.creds
	switch scheme {
	case "unix":
	case "http":
		creds = nil
	case "https", "unixs":
		if creds != nil {
			break
		}
		creds = credentials.NewBundle(credentials.Config{}).TransportCredentials()
	default:
		creds = nil
	}
	return creds
}

// dialSetupOpts gives the dial opts prior to any authentication.
func (c *Client) dialSetupOpts(creds grpccredentials.TransportCredentials, dopts ...grpc.DialOption) (opts []grpc.DialOption, err error) {
	if c.cfg.DialKeepAliveTime > 0 {
		params := keepalive.ClientParameters{
			Time:                c.cfg.DialKeepAliveTime,
			Timeout:             c.cfg.DialKeepAliveTimeout,
			PermitWithoutStream: c.cfg.PermitWithoutStream,
		}
		opts = append(opts, grpc.WithKeepaliveParams(params))
	}
	opts = append(opts, dopts...)

	dialer := endpoint.Dialer
	if creds != nil {
		opts = append(opts, grpc.WithTransportCredentials(creds))
		// gRPC load balancer workaround. See credentials.transportCredential for details.
		if credsDialer, ok := creds.(TransportCredentialsWithDialer); ok {
			dialer = credsDialer.Dialer
		}
	} else {
		opts = append(opts, grpc.WithInsecure())
	}
	opts = append(opts, grpc.WithContextDialer(dialer))

	// Interceptor retry and backoff.
	// TODO: Replace all of clientv3/retry.go with interceptor based retry, or with
	// https://github.com/grpc/proposal/blob/master/A6-client-retries.md#retry-policy
	// once it is available.
	rrBackoff := withBackoff(c.roundRobinQuorumBackoff(defaultBackoffWaitBetween, defaultBackoffJitterFraction))
	opts = append(opts,
		// Disable stream retry by default since go-grpc-middleware/retry does not support client streams.
		// Streams that are safe to retry are enabled individually.
		grpc.WithStreamInterceptor(c.streamClientInterceptor(c.lg, withMax(0), rrBackoff)),
		grpc.WithUnaryInterceptor(c.unaryClientInterceptor(c.lg, withMax(defaultUnaryMaxRetries), rrBackoff)),
	)

	return opts, nil
}

// Dial connects to a single endpoint using the client's config.
func (c *Client) Dial(ep string) (*grpc.ClientConn, error) {
	creds, err := c.directDialCreds(ep)
	if err != nil {
		return nil, err
	}
	// Use the grpc passthrough resolver to directly dial a single endpoint.
	// This resolver passes through the 'unix' and 'unixs' endpoints schemes used
	// by etcd without modification, allowing us to directly dial endpoints and
	// using the same dial functions that we use for load balancer dialing.
	return c.dial(fmt.Sprintf("passthrough:///%s", ep), creds)
}

func (c *Client) getToken(ctx context.Context) error {
	var err error // return last error in a case of fail
	var auth *authenticator

	eps := c.Endpoints()
	for _, ep := range eps {
		// use dial options without dopts to avoid reusing the client balancer
		var dOpts []grpc.DialOption
		_, host, _ := endpoint.ParseEndpoint(ep)
		target := c.resolverGroup.Target(host)
		creds := c.dialWithBalancerCreds(ep)
		dOpts, err = c.dialSetupOpts(creds, c.cfg.DialOptions...)
		if err != nil {
			err = fmt.Errorf("failed to configure auth dialer: %v", err)
			continue
		}
		dOpts = append(dOpts, grpc.WithBalancerName(roundRobinBalancerName))
		auth, err = newAuthenticator(ctx, target, dOpts, c)
		if err != nil {
			continue
		}
		defer auth.close()

		var resp *AuthenticateResponse
		resp, err = auth.authenticate(ctx, c.Username, c.Password)
		if err != nil {
			// return err without retrying other endpoints
			if err == rpctypes.ErrAuthNotEnabled {
				return err
			}
			continue
		}

		c.authTokenBundle.UpdateAuthToken(resp.Token)
		return nil
	}

	return err
}

// dialWithBalancer dials the client's current load balanced resolver group.  The scheme of the host
// of the provided endpoint determines the scheme used for all endpoints of the client connection.
func (c *Client) dialWithBalancer(ep string, dopts ...grpc.DialOption) (*grpc.ClientConn, error) {
	_, host, _ := endpoint.ParseEndpoint(ep)
	target := c.resolverGroup.Target(host)
	creds := c.dialWithBalancerCreds(ep)
	return c.dial(target, creds, dopts...)
}

// dial configures and dials any grpc balancer target.
func (c *Client) dial(target string, creds grpccredentials.TransportCredentials, dopts ...grpc.DialOption) (*grpc.ClientConn, error) {
	opts, err := c.dialSetupOpts(creds, dopts...)
	if err != nil {
		return nil, fmt.Errorf("failed to configure dialer: %v", err)
	}

	if c.Username != "" && c.Password != "" {
		c.authTokenBundle = credentials.NewBundle(credentials.Config{})

		ctx, cancel := c.ctx, func() {}
		if c.cfg.DialTimeout > 0 {
			ctx, cancel = context.WithTimeout(ctx, c.cfg.DialTimeout)
		}

		err = c.getToken(ctx)
		if err != nil {
			if toErr(ctx, err) != rpctypes.ErrAuthNotEnabled {
				if err == ctx.Err() && ctx.Err() != c.ctx.Err() {
					err = context.DeadlineExceeded
				}
				cancel()
				return nil, err
			}
		} else {
			opts = append(opts, grpc.WithPerRPCCredentials(c.authTokenBundle.PerRPCCredentials()))
		}
		cancel()
	}

	opts = append(opts, c.cfg.DialOptions...)

	dctx := c.ctx
	if c.cfg.DialTimeout > 0 {
		var cancel context.CancelFunc
		dctx, cancel = context.WithTimeout(c.ctx, c.cfg.DialTimeout)
		defer cancel() // TODO: Is this right for cases where grpc.WithBlock() is not set on the dial options?
	}

	conn, err := grpc.DialContext(dctx, target, opts...)
	if err != nil {
		return nil, err
	}
	return conn, nil
}

func (c *Client) directDialCreds(ep string) (grpccredentials.TransportCredentials, error) {
	_, host, scheme := endpoint.ParseEndpoint(ep)
	creds := c.creds
	if len(scheme) != 0 {
		creds = c.processCreds(scheme)
		if creds != nil {
			clone := creds.Clone()
			// Set the server name must to the endpoint hostname without port since grpc
			// otherwise attempts to check if x509 cert is valid for the full endpoint
			// including the scheme and port, which fails.
			overrideServerName, _, err := net.SplitHostPort(host)
			if err != nil {
				// Either the host didn't have a port or the host could not be parsed. Either way, continue with the
				// original host string.
				overrideServerName = host
			}
			clone.OverrideServerName(overrideServerName)
			creds = clone
		}
	}
	return creds, nil
}

func (c *Client) dialWithBalancerCreds(ep string) grpccredentials.TransportCredentials {
	_, _, scheme := endpoint.ParseEndpoint(ep)
	creds := c.creds
	if len(scheme) != 0 {
		creds = c.processCreds(scheme)
	}
	return creds
}

// WithRequireLeader requires client requests to only succeed
// when the cluster has a leader.
func WithRequireLeader(ctx context.Context) context.Context {
	md := metadata.Pairs(rpctypes.MetadataRequireLeaderKey, rpctypes.MetadataHasLeader)
	return metadata.NewOutgoingContext(ctx, md)
}

func newClient(cfg *Config) (*Client, error) {
	if cfg == nil {
		cfg = &Config{}
	}
	var creds grpccredentials.TransportCredentials
	if cfg.TLS != nil {
		creds = credentials.NewBundle(credentials.Config{TLSConfig: cfg.TLS}).TransportCredentials()
	}

	// use a temporary skeleton client to bootstrap first connection
	baseCtx := context.TODO()
	if cfg.Context != nil {
		baseCtx = cfg.Context
	}

	ctx, cancel := context.WithCancel(baseCtx)
	client := &Client{
		conn:     nil,
		cfg:      *cfg,
		creds:    creds,
		ctx:      ctx,
		cancel:   cancel,
		mu:       new(sync.RWMutex),
		callOpts: defaultCallOpts,
	}

	lcfg := logutil.DefaultZapLoggerConfig
	if cfg.LogConfig != nil {
		lcfg = *cfg.LogConfig
	}
	var err error
	client.lg, err = lcfg.Build()
	if err != nil {
		return nil, err
	}

	if cfg.Username != "" && cfg.Password != "" {
		client.Username = cfg.Username
		client.Password = cfg.Password
	}
	if cfg.MaxCallSendMsgSize > 0 || cfg.MaxCallRecvMsgSize > 0 {
		if cfg.MaxCallRecvMsgSize > 0 && cfg.MaxCallSendMsgSize > cfg.MaxCallRecvMsgSize {
			return nil, fmt.Errorf("gRPC message recv limit (%d bytes) must be greater than send limit (%d bytes)", cfg.MaxCallRecvMsgSize, cfg.MaxCallSendMsgSize)
		}
		callOpts := []grpc.CallOption{
			defaultFailFast,
			defaultMaxCallSendMsgSize,
			defaultMaxCallRecvMsgSize,
		}
		if cfg.MaxCallSendMsgSize > 0 {
			callOpts[1] = grpc.MaxCallSendMsgSize(cfg.MaxCallSendMsgSize)
		}
		if cfg.MaxCallRecvMsgSize > 0 {
			callOpts[2] = grpc.MaxCallRecvMsgSize(cfg.MaxCallRecvMsgSize)
		}
		client.callOpts = callOpts
	}

	// Prepare a 'endpoint://<unique-client-id>/' resolver for the client and create a endpoint target to pass
	// to dial so the client knows to use this resolver.
	client.resolverGroup, err = endpoint.NewResolverGroup(fmt.Sprintf("client-%s", uuid.New().String()))
	if err != nil {
		client.cancel()
		return nil, err
	}
	client.resolverGroup.SetEndpoints(cfg.Endpoints)

	if len(cfg.Endpoints) < 1 {
		return nil, fmt.Errorf("at least one Endpoint must is required in client config")
	}
	dialEndpoint := cfg.Endpoints[0]

	// Use a provided endpoint target so that for https:// without any tls config given, then
	// grpc will assume the certificate server name is the endpoint host.
	conn, err := client.dialWithBalancer(dialEndpoint, grpc.WithBalancerName(roundRobinBalancerName))
	if err != nil {
		client.cancel()
		client.resolverGroup.Close()
		return nil, err
	}
	// TODO: With the old grpc balancer interface, we waited until the dial timeout
	// for the balancer to be ready. Is there an equivalent wait we should do with the new grpc balancer interface?
	client.conn = conn

	client.Cluster = NewCluster(client)
	client.KV = NewKV(client)
	client.Lease = NewLease(client)
	client.Watcher = NewWatcher(client)
	client.Auth = NewAuth(client)
	client.Maintenance = NewMaintenance(client)

	if cfg.RejectOldCluster {
		if err := client.checkVersion(); err != nil {
			client.Close()
			return nil, err
		}
	}

	go client.autoSync()
	return client, nil
}

// roundRobinQuorumBackoff retries against quorum between each backoff.
// This is intended for use with a round robin load balancer.
func (c *Client) roundRobinQuorumBackoff(waitBetween time.Duration, jitterFraction float64) backoffFunc {
	return func(attempt uint) time.Duration {
		// after each round robin across quorum, backoff for our wait between duration
		n := uint(len(c.Endpoints()))
		quorum := (n/2 + 1)
		if attempt%quorum == 0 {
			c.lg.Debug("backoff", zap.Uint("attempt", attempt), zap.Uint("quorum", quorum), zap.Duration("waitBetween", waitBetween), zap.Float64("jitterFraction", jitterFraction))
			return jitterUp(waitBetween, jitterFraction)
		}
		c.lg.Debug("backoff skipped", zap.Uint("attempt", attempt), zap.Uint("quorum", quorum))
		return 0
	}
}

func (c *Client) checkVersion() (err error) {
	var wg sync.WaitGroup

	eps := c.Endpoints()
	errc := make(chan error, len(eps))
	ctx, cancel := context.WithCancel(c.ctx)
	if c.cfg.DialTimeout > 0 {
		cancel()
		ctx, cancel = context.WithTimeout(c.ctx, c.cfg.DialTimeout)
	}

	wg.Add(len(eps))
	for _, ep := range eps {
		// if cluster is current, any endpoint gives a recent version
		go func(e string) {
			defer wg.Done()
			resp, rerr := c.Status(ctx, e)
			if rerr != nil {
				errc <- rerr
				return
			}
			vs := strings.Split(resp.Version, ".")
			maj, min := 0, 0
			if len(vs) >= 2 {
				var serr error
				if maj, serr = strconv.Atoi(vs[0]); serr != nil {
					errc <- serr
					return
				}
				if min, serr = strconv.Atoi(vs[1]); serr != nil {
					errc <- serr
					return
				}
			}
			if maj < 3 || (maj == 3 && min < 2) {
				rerr = ErrOldCluster
			}
			errc <- rerr
		}(ep)
	}
	// wait for success
	for range eps {
		if err = <-errc; err == nil {
			break
		}
	}
	cancel()
	wg.Wait()
	return err
}

// ActiveConnection returns the current in-use connection
func (c *Client) ActiveConnection() *grpc.ClientConn { return c.conn }

// isHaltErr returns true if the given error and context indicate no forward
// progress can be made, even after reconnecting.
func isHaltErr(ctx context.Context, err error) bool {
	if ctx != nil && ctx.Err() != nil {
		return true
	}
	if err == nil {
		return false
	}
	ev, _ := status.FromError(err)
	// Unavailable codes mean the system will be right back.
	// (e.g., can't connect, lost leader)
	// Treat Internal codes as if something failed, leaving the
	// system in an inconsistent state, but retrying could make progress.
	// (e.g., failed in middle of send, corrupted frame)
	// TODO: are permanent Internal errors possible from grpc?
	return ev.Code() != codes.Unavailable && ev.Code() != codes.Internal
}

// isUnavailableErr returns true if the given error is an unavailable error
func isUnavailableErr(ctx context.Context, err error) bool {
	if ctx != nil && ctx.Err() != nil {
		return false
	}
	if err == nil {
		return false
	}
	ev, ok := status.FromError(err)
	if ok {
		// Unavailable codes mean the system will be right back.
		// (e.g., can't connect, lost leader)
		return ev.Code() == codes.Unavailable
	}
	return false
}

func toErr(ctx context.Context, err error) error {
	if err == nil {
		return nil
	}
	err = rpctypes.Error(err)
	if _, ok := err.(rpctypes.EtcdError); ok {
		return err
	}
	if ev, ok := status.FromError(err); ok {
		code := ev.Code()
		switch code {
		case codes.DeadlineExceeded:
			fallthrough
		case codes.Canceled:
			if ctx.Err() != nil {
				err = ctx.Err()
			}
		}
	}
	return err
}

func canceledByCaller(stopCtx context.Context, err error) bool {
	if stopCtx.Err() == nil || err == nil {
		return false
	}

	return err == context.Canceled || err == context.DeadlineExceeded
}

// IsConnCanceled returns true, if error is from a closed gRPC connection.
// ref. https://github.com/grpc/grpc-go/pull/1854
func IsConnCanceled(err error) bool {
	if err == nil {
		return false
	}

	// >= gRPC v1.23.x
	s, ok := status.FromError(err)
	if ok {
		// connection is canceled or server has already closed the connection
		return s.Code() == codes.Canceled || s.Message() == "transport is closing"
	}

	// >= gRPC v1.10.x
	if err == context.Canceled {
		return true
	}

	// <= gRPC v1.7.x returns 'errors.New("grpc: the client connection is closing")'
	return strings.Contains(err.Error(), "grpc: the client connection is closing")
}

// TransportCredentialsWithDialer is for a gRPC load balancer workaround. See credentials.transportCredential for details.
type TransportCredentialsWithDialer interface {
	grpccredentials.TransportCredentials
	Dialer(ctx context.Context, dialEp string) (net.Conn, error)
}
