package server

import (
    "bytes"
    "crypto/tls"
    "encoding/json"
    "fmt"
    "io"
    "net"
    "net/http"
    "time"

    "github.com/coreos/etcd/log"
    "github.com/coreos/go-raft"
)

// Timeout for setup internal raft http connection
// This should not exceed 3 * RTT
var dailTimeout = 3 * HeartbeatTimeout

// Timeout for setup internal raft http connection + receive response header
// This should not exceed 3 * RTT + RTT
var responseHeaderTimeout = 4 * HeartbeatTimeout

// Timeout for receiving the response body from the server
// This should not exceed election timeout
var tranTimeout = ElectionTimeout

// Transporter layer for communication between raft nodes
type transporter struct {
    client     *http.Client
    transport  *http.Transport
    peerServer *PeerServer
}

// Create transporter using by raft server
// Create http or https transporter based on
// whether the user give the server cert and key
func newTransporter(scheme string, tlsConf tls.Config, peerServer *PeerServer) *transporter {
    t := transporter{}

    tr := &http.Transport{
        Dial: dialWithTimeout,
        ResponseHeaderTimeout: responseHeaderTimeout,
    }

    if scheme == "https" {
        tr.TLSClientConfig = &tlsConf
        tr.DisableCompression = true
    }

    t.client = &http.Client{Transport: tr}
    t.transport = tr
    t.peerServer = peerServer

    return &t
}

// Dial with timeout
func dialWithTimeout(network, addr string) (net.Conn, error) {
    return net.DialTimeout(network, addr, dailTimeout)
}

// Sends AppendEntries RPCs to a peer when the server is the leader.
func (t *transporter) SendAppendEntriesRequest(server *raft.Server, peer *raft.Peer, req *raft.AppendEntriesRequest) *raft.AppendEntriesResponse {
    var aersp *raft.AppendEntriesResponse
    var b bytes.Buffer

    json.NewEncoder(&b).Encode(req)

    size := b.Len()

    t.peerServer.serverStats.SendAppendReq(size)

    u, _ := t.peerServer.registry.PeerURL(peer.Name)

    log.Debugf("Send LogEntries to %s ", u)

    thisFollowerStats, ok := t.peerServer.followersStats.Followers[peer.Name]

    if !ok { //this is the first time this follower has been seen
        thisFollowerStats = &raftFollowerStats{}
        thisFollowerStats.Latency.Minimum = 1 << 63
        t.peerServer.followersStats.Followers[peer.Name] = thisFollowerStats
    }

    start := time.Now()

    resp, httpRequest, err := t.Post(fmt.Sprintf("%s/log/append", u), &b)

    end := time.Now()

    if err != nil {
        log.Debugf("Cannot send AppendEntriesRequest to %s: %s", u, err)
        if ok {
            thisFollowerStats.Fail()
        }
    } else {
        if ok {
            thisFollowerStats.Succ(end.Sub(start))
        }
    }

    if resp != nil {
        defer resp.Body.Close()

        t.CancelWhenTimeout(httpRequest)

        aersp = &raft.AppendEntriesResponse{}
        if err := json.NewDecoder(resp.Body).Decode(&aersp); err == nil || err == io.EOF {
            return aersp
        }

    }

    return aersp
}

// Sends RequestVote RPCs to a peer when the server is the candidate.
func (t *transporter) SendVoteRequest(server *raft.Server, peer *raft.Peer, req *raft.RequestVoteRequest) *raft.RequestVoteResponse {
    var rvrsp *raft.RequestVoteResponse
    var b bytes.Buffer
    json.NewEncoder(&b).Encode(req)

    u, _ := t.peerServer.registry.PeerURL(peer.Name)
    log.Debugf("Send Vote to %s", u)

    resp, httpRequest, err := t.Post(fmt.Sprintf("%s/vote", u), &b)

    if err != nil {
        log.Debugf("Cannot send VoteRequest to %s : %s", u, err)
    }

    if resp != nil {
        defer resp.Body.Close()

        t.CancelWhenTimeout(httpRequest)

        rvrsp := &raft.RequestVoteResponse{}
        if err := json.NewDecoder(resp.Body).Decode(&rvrsp); err == nil || err == io.EOF {
            return rvrsp
        }

    }
    return rvrsp
}

// Sends SnapshotRequest RPCs to a peer when the server is the candidate.
func (t *transporter) SendSnapshotRequest(server *raft.Server, peer *raft.Peer, req *raft.SnapshotRequest) *raft.SnapshotResponse {
    var aersp *raft.SnapshotResponse
    var b bytes.Buffer
    json.NewEncoder(&b).Encode(req)

    u, _ := t.peerServer.registry.PeerURL(peer.Name)
    log.Debugf("Send Snapshot to %s [Last Term: %d, LastIndex %d]", u,
        req.LastTerm, req.LastIndex)

    resp, httpRequest, err := t.Post(fmt.Sprintf("%s/snapshot", u), &b)

    if err != nil {
        log.Debugf("Cannot send SendSnapshotRequest to %s : %s", u, err)
    }

    if resp != nil {
        defer resp.Body.Close()

        t.CancelWhenTimeout(httpRequest)

        aersp = &raft.SnapshotResponse{}
        if err = json.NewDecoder(resp.Body).Decode(&aersp); err == nil || err == io.EOF {

            return aersp
        }
    }

    return aersp
}

// Sends SnapshotRecoveryRequest RPCs to a peer when the server is the candidate.
func (t *transporter) SendSnapshotRecoveryRequest(server *raft.Server, peer *raft.Peer, req *raft.SnapshotRecoveryRequest) *raft.SnapshotRecoveryResponse {
    var aersp *raft.SnapshotRecoveryResponse
    var b bytes.Buffer
    json.NewEncoder(&b).Encode(req)

    u, _ := t.peerServer.registry.PeerURL(peer.Name)
    log.Debugf("Send SnapshotRecovery to %s [Last Term: %d, LastIndex %d]", u,
        req.LastTerm, req.LastIndex)

    resp, _, err := t.Post(fmt.Sprintf("%s/snapshotRecovery", u), &b)

    if err != nil {
        log.Debugf("Cannot send SendSnapshotRecoveryRequest to %s : %s", u, err)
    }

    if resp != nil {
        defer resp.Body.Close()
        aersp = &raft.SnapshotRecoveryResponse{}

        if err = json.NewDecoder(resp.Body).Decode(&aersp); err == nil || err == io.EOF {
            return aersp
        }
    }

    return aersp
}

// Send server side POST request
func (t *transporter) Post(urlStr string, body io.Reader) (*http.Response, *http.Request, error) {
    req, _ := http.NewRequest("POST", urlStr, body)
    resp, err := t.client.Do(req)
    return resp, req, err
}

// Send server side GET request
func (t *transporter) Get(urlStr string) (*http.Response, *http.Request, error) {
    req, _ := http.NewRequest("GET", urlStr, nil)
    resp, err := t.client.Do(req)
    return resp, req, err
}

// Cancel the on fly HTTP transaction when timeout happens.
func (t *transporter) CancelWhenTimeout(req *http.Request) {
    go func() {
        time.Sleep(ElectionTimeout)
        t.transport.CancelRequest(req)
    }()
}