package consul

import (
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/hashicorp/consul/consul/agent"
	"github.com/hashicorp/consul/consul/servers"
	"github.com/hashicorp/consul/consul/structs"
	"github.com/hashicorp/consul/lib"
	"github.com/hashicorp/serf/coordinate"
	"github.com/hashicorp/serf/serf"
)

const (
	// clientRPCConnMaxIdle controls how long we keep an idle connection
	// open to a server.  127s was chosen as the first prime above 120s
	// (arbitrarily chose to use a prime) with the intent of reusing
	// connections who are used by once-a-minute cron(8) jobs *and* who
	// use a 60s jitter window (e.g. in vixie cron job execution can
	// drift by up to 59s per job, or 119s for a once-a-minute cron job).
	clientRPCConnMaxIdle = 127 * time.Second

	// clientMaxStreams controls how many idle streams we keep
	// open to a server
	clientMaxStreams = 32

	// serfEventBacklog is the maximum number of unprocessed Serf Events
	// that will be held in queue before new serf events block.  A
	// blocking serf event queue is a bad thing.
	serfEventBacklog = 256

	// serfEventBacklogWarning is the threshold at which point log
	// warnings will be emitted indicating a problem when processing serf
	// events.
	serfEventBacklogWarning = 200
)

// Interface is used to provide either a Client or Server,
// both of which can be used to perform certain common
// Consul methods
type Interface interface {
	RPC(method string, args interface{}, reply interface{}) error
	LANMembers() []serf.Member
	LocalMember() serf.Member
}

// Client is Consul client which uses RPC to communicate with the
// services for service discovery, health checking, and DC forwarding.
type Client struct {
	config *Config

	// Connection pool to consul servers
	connPool *ConnPool

	// servers is responsible for the selection and maintenance of
	// Consul servers this agent uses for RPC requests
	servers *servers.Manager

	// eventCh is used to receive events from the
	// serf cluster in the datacenter
	eventCh chan serf.Event

	// Logger uses the provided LogOutput
	logger *log.Logger

	// serf is the Serf cluster maintained inside the DC
	// which contains all the DC nodes
	serf *serf.Serf

	shutdown     bool
	shutdownCh   chan struct{}
	shutdownLock sync.Mutex
}

// NewClient is used to construct a new Consul client from the
// configuration, potentially returning an error
func NewClient(config *Config) (*Client, error) {
	// Check the protocol version
	if err := config.CheckVersion(); err != nil {
		return nil, err
	}

	// Check for a data directory!
	if config.DataDir == "" {
		return nil, fmt.Errorf("Config must provide a DataDir")
	}

	// Sanity check the ACLs
	if err := config.CheckACL(); err != nil {
		return nil, err
	}

	// Ensure we have a log output
	if config.LogOutput == nil {
		config.LogOutput = os.Stderr
	}

	// Create the tls Wrapper
	tlsWrap, err := config.tlsConfig().OutgoingTLSWrapper()
	if err != nil {
		return nil, err
	}

	// Create a logger
	logger := log.New(config.LogOutput, "", log.LstdFlags)

	// Create server
	c := &Client{
		config:     config,
		connPool:   NewPool(config.LogOutput, clientRPCConnMaxIdle, clientMaxStreams, tlsWrap),
		eventCh:    make(chan serf.Event, serfEventBacklog),
		logger:     logger,
		shutdownCh: make(chan struct{}),
	}

	// Start lan event handlers before lan Serf setup to prevent deadlock
	go c.lanEventHandler()

	// Initialize the lan Serf
	c.serf, err = c.setupSerf(config.SerfLANConfig,
		c.eventCh, serfLANSnapshot)
	if err != nil {
		c.Shutdown()
		return nil, fmt.Errorf("Failed to start lan serf: %v", err)
	}

	// Start maintenance task for servers
	c.servers = servers.New(c.logger, c.shutdownCh, c.serf, c.connPool)
	go c.servers.Start()

	return c, nil
}

// setupSerf is used to setup and initialize a Serf
func (c *Client) setupSerf(conf *serf.Config, ch chan serf.Event, path string) (*serf.Serf, error) {
	conf.Init()
	conf.NodeName = c.config.NodeName
	conf.Tags["role"] = "node"
	conf.Tags["dc"] = c.config.Datacenter
	conf.Tags["id"] = string(c.config.NodeID)
	conf.Tags["vsn"] = fmt.Sprintf("%d", c.config.ProtocolVersion)
	conf.Tags["vsn_min"] = fmt.Sprintf("%d", ProtocolVersionMin)
	conf.Tags["vsn_max"] = fmt.Sprintf("%d", ProtocolVersionMax)
	conf.Tags["build"] = c.config.Build
	conf.MemberlistConfig.LogOutput = c.config.LogOutput
	conf.LogOutput = c.config.LogOutput
	conf.EventCh = ch
	conf.SnapshotPath = filepath.Join(c.config.DataDir, path)
	conf.ProtocolVersion = protocolVersionMap[c.config.ProtocolVersion]
	conf.RejoinAfterLeave = c.config.RejoinAfterLeave
	conf.Merge = &lanMergeDelegate{
		dc:       c.config.Datacenter,
		nodeID:   c.config.NodeID,
		nodeName: c.config.NodeName,
	}
	if err := lib.EnsurePath(conf.SnapshotPath, false); err != nil {
		return nil, err
	}
	return serf.Create(conf)
}

// Shutdown is used to shutdown the client
func (c *Client) Shutdown() error {
	c.logger.Printf("[INFO] consul: shutting down client")
	c.shutdownLock.Lock()
	defer c.shutdownLock.Unlock()

	if c.shutdown {
		return nil
	}

	c.shutdown = true
	close(c.shutdownCh)

	if c.serf != nil {
		c.serf.Shutdown()
	}

	// Close the connection pool
	c.connPool.Shutdown()
	return nil
}

// Leave is used to prepare for a graceful shutdown
func (c *Client) Leave() error {
	c.logger.Printf("[INFO] consul: client starting leave")

	// Leave the LAN pool
	if c.serf != nil {
		if err := c.serf.Leave(); err != nil {
			c.logger.Printf("[ERR] consul: Failed to leave LAN Serf cluster: %v", err)
		}
	}
	return nil
}

// JoinLAN is used to have Consul client join the inner-DC pool
// The target address should be another node inside the DC
// listening on the Serf LAN address
func (c *Client) JoinLAN(addrs []string) (int, error) {
	return c.serf.Join(addrs, true)
}

// LocalMember is used to return the local node
func (c *Client) LocalMember() serf.Member {
	return c.serf.LocalMember()
}

// LANMembers is used to return the members of the LAN cluster
func (c *Client) LANMembers() []serf.Member {
	return c.serf.Members()
}

// RemoveFailedNode is used to remove a failed node from the cluster
func (c *Client) RemoveFailedNode(node string) error {
	return c.serf.RemoveFailedNode(node)
}

// KeyManagerLAN returns the LAN Serf keyring manager
func (c *Client) KeyManagerLAN() *serf.KeyManager {
	return c.serf.KeyManager()
}

// Encrypted determines if gossip is encrypted
func (c *Client) Encrypted() bool {
	return c.serf.EncryptionEnabled()
}

// lanEventHandler is used to handle events from the lan Serf cluster
func (c *Client) lanEventHandler() {
	var numQueuedEvents int
	for {
		numQueuedEvents = len(c.eventCh)
		if numQueuedEvents > serfEventBacklogWarning {
			c.logger.Printf("[WARN] consul: number of queued serf events above warning threshold: %d/%d", numQueuedEvents, serfEventBacklogWarning)
		}

		select {
		case e := <-c.eventCh:
			switch e.EventType() {
			case serf.EventMemberJoin:
				c.nodeJoin(e.(serf.MemberEvent))
			case serf.EventMemberLeave, serf.EventMemberFailed:
				c.nodeFail(e.(serf.MemberEvent))
			case serf.EventUser:
				c.localEvent(e.(serf.UserEvent))
			case serf.EventMemberUpdate: // Ignore
			case serf.EventMemberReap: // Ignore
			case serf.EventQuery: // Ignore
			default:
				c.logger.Printf("[WARN] consul: unhandled LAN Serf Event: %#v", e)
			}
		case <-c.shutdownCh:
			return
		}
	}
}

// nodeJoin is used to handle join events on the serf cluster
func (c *Client) nodeJoin(me serf.MemberEvent) {
	for _, m := range me.Members {
		ok, parts := agent.IsConsulServer(m)
		if !ok {
			continue
		}
		if parts.Datacenter != c.config.Datacenter {
			c.logger.Printf("[WARN] consul: server %s for datacenter %s has joined wrong cluster",
				m.Name, parts.Datacenter)
			continue
		}
		c.logger.Printf("[INFO] consul: adding server %s", parts)
		c.servers.AddServer(parts)

		// Trigger the callback
		if c.config.ServerUp != nil {
			c.config.ServerUp()
		}
	}
}

// nodeFail is used to handle fail events on the serf cluster
func (c *Client) nodeFail(me serf.MemberEvent) {
	for _, m := range me.Members {
		ok, parts := agent.IsConsulServer(m)
		if !ok {
			continue
		}
		c.logger.Printf("[INFO] consul: removing server %s", parts)
		c.servers.RemoveServer(parts)
	}
}

// localEvent is called when we receive an event on the local Serf
func (c *Client) localEvent(event serf.UserEvent) {
	// Handle only consul events
	if !strings.HasPrefix(event.Name, "consul:") {
		return
	}

	switch name := event.Name; {
	case name == newLeaderEvent:
		c.logger.Printf("[INFO] consul: New leader elected: %s", event.Payload)

		// Trigger the callback
		if c.config.ServerUp != nil {
			c.config.ServerUp()
		}
	case isUserEvent(name):
		event.Name = rawUserEventName(name)
		c.logger.Printf("[DEBUG] consul: user event: %s", event.Name)

		// Trigger the callback
		if c.config.UserEventHandler != nil {
			c.config.UserEventHandler(event)
		}
	default:
		c.logger.Printf("[WARN] consul: Unhandled local event: %v", event)
	}
}

// RPC is used to forward an RPC call to a consul server, or fail if no servers
func (c *Client) RPC(method string, args interface{}, reply interface{}) error {
	server := c.servers.FindServer()
	if server == nil {
		return structs.ErrNoServers
	}

	// Forward to remote Consul
	if err := c.connPool.RPC(c.config.Datacenter, server.Addr, server.Version, method, args, reply); err != nil {
		c.servers.NotifyFailedServer(server)
		c.logger.Printf("[ERR] consul: RPC failed to server %s: %v", server.Addr, err)
		return err
	}

	return nil
}

// SnapshotReplyFn gets a peek at the reply before the snapshot streams, which
// is useful for setting headers.
type SnapshotReplyFn func(reply *structs.SnapshotResponse) error

// SnapshotRPC sends the snapshot request to one of the servers, reading from
// the streaming input and writing to the streaming output depending on the
// operation.
func (c *Client) SnapshotRPC(args *structs.SnapshotRequest, in io.Reader, out io.Writer,
	replyFn SnapshotReplyFn) error {

	// Locate a server to make the request to.
	server := c.servers.FindServer()
	if server == nil {
		return structs.ErrNoServers
	}

	// Request the operation.
	var reply structs.SnapshotResponse
	snap, err := SnapshotRPC(c.connPool, c.config.Datacenter, server.Addr, args, in, &reply)
	if err != nil {
		return err
	}
	defer func() {
		if err := snap.Close(); err != nil {
			c.logger.Printf("[WARN] consul: Failed closing snapshot stream: %v", err)
		}
	}()

	// Let the caller peek at the reply.
	if replyFn != nil {
		if err := replyFn(&reply); err != nil {
			return nil
		}
	}

	// Stream the snapshot.
	if out != nil {
		if _, err := io.Copy(out, snap); err != nil {
			return fmt.Errorf("failed to stream snapshot: %v", err)
		}
	}

	return nil
}

// Stats is used to return statistics for debugging and insight
// for various sub-systems
func (c *Client) Stats() map[string]map[string]string {
	numServers := c.servers.NumServers()

	toString := func(v uint64) string {
		return strconv.FormatUint(v, 10)
	}
	stats := map[string]map[string]string{
		"consul": map[string]string{
			"server":        "false",
			"known_servers": toString(uint64(numServers)),
		},
		"serf_lan": c.serf.Stats(),
		"runtime":  runtimeStats(),
	}
	return stats
}

// GetCoordinate returns the network coordinate of the current node, as
// maintained by Serf.
func (c *Client) GetCoordinate() (*coordinate.Coordinate, error) {
	return c.serf.GetCoordinate()
}