package redis

import (
	"context"
	"crypto/tls"
	"errors"
	"net"
	"strings"
	"sync"
	"time"

	"github.com/go-redis/redis/v8/internal"
	"github.com/go-redis/redis/v8/internal/pool"
)

//------------------------------------------------------------------------------

// FailoverOptions are used to configure a failover client and should
// be passed to NewFailoverClient.
type FailoverOptions struct {
	// The master name.
	MasterName string
	// A seed list of host:port addresses of sentinel nodes.
	SentinelAddrs    []string
	SentinelPassword string

	// Following options are copied from Options struct.

	Dialer    func(ctx context.Context, network, addr string) (net.Conn, error)
	OnConnect func(*Conn) error

	Password string
	DB       int

	MaxRetries      int
	MinRetryBackoff time.Duration
	MaxRetryBackoff time.Duration

	DialTimeout  time.Duration
	ReadTimeout  time.Duration
	WriteTimeout time.Duration

	PoolSize           int
	MinIdleConns       int
	MaxConnAge         time.Duration
	PoolTimeout        time.Duration
	IdleTimeout        time.Duration
	IdleCheckFrequency time.Duration

	TLSConfig *tls.Config
}

func (opt *FailoverOptions) options() *Options {
	return &Options{
		Addr:      "FailoverClient",
		Dialer:    opt.Dialer,
		OnConnect: opt.OnConnect,

		DB:       opt.DB,
		Password: opt.Password,

		MaxRetries:      opt.MaxRetries,
		MinRetryBackoff: opt.MinRetryBackoff,
		MaxRetryBackoff: opt.MaxRetryBackoff,

		DialTimeout:  opt.DialTimeout,
		ReadTimeout:  opt.ReadTimeout,
		WriteTimeout: opt.WriteTimeout,

		PoolSize:           opt.PoolSize,
		PoolTimeout:        opt.PoolTimeout,
		IdleTimeout:        opt.IdleTimeout,
		IdleCheckFrequency: opt.IdleCheckFrequency,
		MinIdleConns:       opt.MinIdleConns,
		MaxConnAge:         opt.MaxConnAge,

		TLSConfig: opt.TLSConfig,
	}
}

// NewFailoverClient returns a Redis client that uses Redis Sentinel
// for automatic failover. It's safe for concurrent use by multiple
// goroutines.
func NewFailoverClient(failoverOpt *FailoverOptions) *Client {
	opt := failoverOpt.options()
	opt.init()

	failover := &sentinelFailover{
		masterName:    failoverOpt.MasterName,
		sentinelAddrs: failoverOpt.SentinelAddrs,
		password:      failoverOpt.SentinelPassword,

		opt: opt,
	}

	c := Client{
		baseClient: newBaseClient(opt, failover.Pool()),
		ctx:        context.Background(),
	}
	c.cmdable = c.Process
	c.onClose = failover.Close

	return &c
}

//------------------------------------------------------------------------------

type SentinelClient struct {
	*baseClient
	ctx context.Context
}

func NewSentinelClient(opt *Options) *SentinelClient {
	opt.init()
	c := &SentinelClient{
		baseClient: &baseClient{
			opt:      opt,
			connPool: newConnPool(opt),
		},
		ctx: context.Background(),
	}
	return c
}

func (c *SentinelClient) Context() context.Context {
	return c.ctx
}

func (c *SentinelClient) WithContext(ctx context.Context) *SentinelClient {
	if ctx == nil {
		panic("nil context")
	}
	clone := *c
	clone.ctx = ctx
	return &clone
}

func (c *SentinelClient) Process(ctx context.Context, cmd Cmder) error {
	return c.baseClient.process(ctx, cmd)
}

func (c *SentinelClient) pubSub() *PubSub {
	pubsub := &PubSub{
		opt: c.opt,

		newConn: func(ctx context.Context, channels []string) (*pool.Conn, error) {
			return c.newConn(ctx)
		},
		closeConn: c.connPool.CloseConn,
	}
	pubsub.init()
	return pubsub
}

// Ping is used to test if a connection is still alive, or to
// measure latency.
func (c *SentinelClient) Ping(ctx context.Context) *StringCmd {
	cmd := NewStringCmd(ctx, "ping")
	_ = c.Process(ctx, cmd)
	return cmd
}

// Subscribe subscribes the client to the specified channels.
// Channels can be omitted to create empty subscription.
func (c *SentinelClient) Subscribe(ctx context.Context, channels ...string) *PubSub {
	pubsub := c.pubSub()
	if len(channels) > 0 {
		_ = pubsub.Subscribe(ctx, channels...)
	}
	return pubsub
}

// PSubscribe subscribes the client to the given patterns.
// Patterns can be omitted to create empty subscription.
func (c *SentinelClient) PSubscribe(ctx context.Context, channels ...string) *PubSub {
	pubsub := c.pubSub()
	if len(channels) > 0 {
		_ = pubsub.PSubscribe(ctx, channels...)
	}
	return pubsub
}

func (c *SentinelClient) GetMasterAddrByName(ctx context.Context, name string) *StringSliceCmd {
	cmd := NewStringSliceCmd(ctx, "sentinel", "get-master-addr-by-name", name)
	_ = c.Process(ctx, cmd)
	return cmd
}

func (c *SentinelClient) Sentinels(ctx context.Context, name string) *SliceCmd {
	cmd := NewSliceCmd(ctx, "sentinel", "sentinels", name)
	_ = c.Process(ctx, cmd)
	return cmd
}

// Failover forces a failover as if the master was not reachable, and without
// asking for agreement to other Sentinels.
func (c *SentinelClient) Failover(ctx context.Context, name string) *StatusCmd {
	cmd := NewStatusCmd(ctx, "sentinel", "failover", name)
	_ = c.Process(ctx, cmd)
	return cmd
}

// Reset resets all the masters with matching name. The pattern argument is a
// glob-style pattern. The reset process clears any previous state in a master
// (including a failover in progress), and removes every slave and sentinel
// already discovered and associated with the master.
func (c *SentinelClient) Reset(ctx context.Context, pattern string) *IntCmd {
	cmd := NewIntCmd(ctx, "sentinel", "reset", pattern)
	_ = c.Process(ctx, cmd)
	return cmd
}

// FlushConfig forces Sentinel to rewrite its configuration on disk, including
// the current Sentinel state.
func (c *SentinelClient) FlushConfig(ctx context.Context) *StatusCmd {
	cmd := NewStatusCmd(ctx, "sentinel", "flushconfig")
	_ = c.Process(ctx, cmd)
	return cmd
}

// Master shows the state and info of the specified master.
func (c *SentinelClient) Master(ctx context.Context, name string) *StringStringMapCmd {
	cmd := NewStringStringMapCmd(ctx, "sentinel", "master", name)
	_ = c.Process(ctx, cmd)
	return cmd
}

// Masters shows a list of monitored masters and their state.
func (c *SentinelClient) Masters(ctx context.Context) *SliceCmd {
	cmd := NewSliceCmd(ctx, "sentinel", "masters")
	_ = c.Process(ctx, cmd)
	return cmd
}

// Slaves shows a list of slaves for the specified master and their state.
func (c *SentinelClient) Slaves(ctx context.Context, name string) *SliceCmd {
	cmd := NewSliceCmd(ctx, "sentinel", "slaves", name)
	_ = c.Process(ctx, cmd)
	return cmd
}

// CkQuorum checks if the current Sentinel configuration is able to reach the
// quorum needed to failover a master, and the majority needed to authorize the
// failover. This command should be used in monitoring systems to check if a
// Sentinel deployment is ok.
func (c *SentinelClient) CkQuorum(ctx context.Context, name string) *StringCmd {
	cmd := NewStringCmd(ctx, "sentinel", "ckquorum", name)
	_ = c.Process(ctx, cmd)
	return cmd
}

// Monitor tells the Sentinel to start monitoring a new master with the specified
// name, ip, port, and quorum.
func (c *SentinelClient) Monitor(ctx context.Context, name, ip, port, quorum string) *StringCmd {
	cmd := NewStringCmd(ctx, "sentinel", "monitor", name, ip, port, quorum)
	_ = c.Process(ctx, cmd)
	return cmd
}

// Set is used in order to change configuration parameters of a specific master.
func (c *SentinelClient) Set(ctx context.Context, name, option, value string) *StringCmd {
	cmd := NewStringCmd(ctx, "sentinel", "set", name, option, value)
	_ = c.Process(ctx, cmd)
	return cmd
}

// Remove is used in order to remove the specified master: the master will no
// longer be monitored, and will totally be removed from the internal state of
// the Sentinel.
func (c *SentinelClient) Remove(ctx context.Context, name string) *StringCmd {
	cmd := NewStringCmd(ctx, "sentinel", "remove", name)
	_ = c.Process(ctx, cmd)
	return cmd
}

type sentinelFailover struct {
	sentinelAddrs []string

	opt      *Options
	password string

	pool     *pool.ConnPool
	poolOnce sync.Once

	mu          sync.RWMutex
	masterName  string
	_masterAddr string
	sentinel    *SentinelClient
	pubsub      *PubSub
}

func (c *sentinelFailover) Close() error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.sentinel != nil {
		return c.closeSentinel()
	}
	return nil
}

func (c *sentinelFailover) closeSentinel() error {
	firstErr := c.pubsub.Close()
	c.pubsub = nil

	err := c.sentinel.Close()
	if err != nil && firstErr == nil {
		firstErr = err
	}
	c.sentinel = nil

	return firstErr
}

func (c *sentinelFailover) Pool() *pool.ConnPool {
	c.poolOnce.Do(func() {
		opt := *c.opt
		opt.Dialer = c.dial
		c.pool = newConnPool(&opt)
	})
	return c.pool
}

func (c *sentinelFailover) dial(ctx context.Context, network, _ string) (net.Conn, error) {
	addr, err := c.MasterAddr(ctx)
	if err != nil {
		return nil, err
	}
	if c.opt.Dialer != nil {
		return c.opt.Dialer(ctx, network, addr)
	}
	return net.DialTimeout("tcp", addr, c.opt.DialTimeout)
}

func (c *sentinelFailover) MasterAddr(ctx context.Context) (string, error) {
	addr, err := c.masterAddr(ctx)
	if err != nil {
		return "", err
	}
	c.switchMaster(addr)
	return addr, nil
}

func (c *sentinelFailover) masterAddr(ctx context.Context) (string, error) {
	c.mu.RLock()
	sentinel := c.sentinel
	c.mu.RUnlock()

	if sentinel != nil {
		addr := c.getMasterAddr(ctx, sentinel)
		if addr != "" {
			return addr, nil
		}
	}

	c.mu.Lock()
	defer c.mu.Unlock()

	if c.sentinel != nil {
		addr := c.getMasterAddr(ctx, c.sentinel)
		if addr != "" {
			return addr, nil
		}
		_ = c.closeSentinel()
	}

	for i, sentinelAddr := range c.sentinelAddrs {
		sentinel := NewSentinelClient(&Options{
			Addr:   sentinelAddr,
			Dialer: c.opt.Dialer,

			Password: c.password,

			MaxRetries: c.opt.MaxRetries,

			DialTimeout:  c.opt.DialTimeout,
			ReadTimeout:  c.opt.ReadTimeout,
			WriteTimeout: c.opt.WriteTimeout,

			PoolSize:           c.opt.PoolSize,
			PoolTimeout:        c.opt.PoolTimeout,
			IdleTimeout:        c.opt.IdleTimeout,
			IdleCheckFrequency: c.opt.IdleCheckFrequency,

			TLSConfig: c.opt.TLSConfig,
		})

		masterAddr, err := sentinel.GetMasterAddrByName(ctx, c.masterName).Result()
		if err != nil {
			internal.Logger.Printf("sentinel: GetMasterAddrByName master=%q failed: %s",
				c.masterName, err)
			_ = sentinel.Close()
			continue
		}

		// Push working sentinel to the top.
		c.sentinelAddrs[0], c.sentinelAddrs[i] = c.sentinelAddrs[i], c.sentinelAddrs[0]
		c.setSentinel(ctx, sentinel)

		addr := net.JoinHostPort(masterAddr[0], masterAddr[1])
		return addr, nil
	}

	return "", errors.New("redis: all sentinels are unreachable")
}

func (c *sentinelFailover) getMasterAddr(ctx context.Context, sentinel *SentinelClient) string {
	addr, err := sentinel.GetMasterAddrByName(ctx, c.masterName).Result()
	if err != nil {
		internal.Logger.Printf("sentinel: GetMasterAddrByName name=%q failed: %s",
			c.masterName, err)
		return ""
	}
	return net.JoinHostPort(addr[0], addr[1])
}

func (c *sentinelFailover) switchMaster(addr string) {
	c.mu.RLock()
	masterAddr := c._masterAddr
	c.mu.RUnlock()
	if masterAddr == addr {
		return
	}

	c.mu.Lock()
	defer c.mu.Unlock()

	if c._masterAddr == addr {
		return
	}

	internal.Logger.Printf("sentinel: new master=%q addr=%q",
		c.masterName, addr)
	_ = c.Pool().Filter(func(cn *pool.Conn) bool {
		return cn.RemoteAddr().String() != addr
	})
	c._masterAddr = addr
}

func (c *sentinelFailover) setSentinel(ctx context.Context, sentinel *SentinelClient) {
	if c.sentinel != nil {
		panic("not reached")
	}
	c.sentinel = sentinel
	c.discoverSentinels(ctx)

	c.pubsub = sentinel.Subscribe(ctx, "+switch-master")
	go c.listen(c.pubsub)
}

func (c *sentinelFailover) discoverSentinels(ctx context.Context) {
	sentinels, err := c.sentinel.Sentinels(ctx, c.masterName).Result()
	if err != nil {
		internal.Logger.Printf("sentinel: Sentinels master=%q failed: %s", c.masterName, err)
		return
	}
	for _, sentinel := range sentinels {
		vals := sentinel.([]interface{})
		for i := 0; i < len(vals); i += 2 {
			key := vals[i].(string)
			if key == "name" {
				sentinelAddr := vals[i+1].(string)
				if !contains(c.sentinelAddrs, sentinelAddr) {
					internal.Logger.Printf("sentinel: discovered new sentinel=%q for master=%q",
						sentinelAddr, c.masterName)
					c.sentinelAddrs = append(c.sentinelAddrs, sentinelAddr)
				}
			}
		}
	}
}

func (c *sentinelFailover) listen(pubsub *PubSub) {
	ch := pubsub.Channel()
	for {
		msg, ok := <-ch
		if !ok {
			break
		}

		if msg.Channel == "+switch-master" {
			parts := strings.Split(msg.Payload, " ")
			if parts[0] != c.masterName {
				internal.Logger.Printf("sentinel: ignore addr for master=%q", parts[0])
				continue
			}
			addr := net.JoinHostPort(parts[3], parts[4])
			c.switchMaster(addr)
		}
	}
}

func contains(slice []string, str string) bool {
	for _, s := range slice {
		if s == str {
			return true
		}
	}
	return false
}