/*
Copyright 2014 CoreOS Inc.

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 etcdserver

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/url"
	"path"
	"sync"
	"time"

	"github.com/coreos/etcd/raft"
)

var (
	errUnknownPeer = errors.New("unknown peer")
)

type peerGetter interface {
	peer(id int64) (*peer, error)
}

type peerHub struct {
	mu             sync.RWMutex
	stopped        bool
	seeds          map[string]bool
	peers          map[int64]*peer
	c              *http.Client
	followersStats *raftFollowersStats
	serverStats    *raftServerStats
}

func newPeerHub(c *http.Client, followersStats *raftFollowersStats) *peerHub {
	h := &peerHub{
		peers:          make(map[int64]*peer),
		seeds:          make(map[string]bool),
		c:              c,
		followersStats: followersStats,
	}
	return h
}

func (h *peerHub) setServerStats(serverStats *raftServerStats) {
	h.serverStats = serverStats
}

func (h *peerHub) setSeeds(seeds []string) {
	for _, seed := range seeds {
		h.seeds[seed] = true
	}
}

func (h *peerHub) getSeeds() map[string]bool {
	h.mu.RLock()
	defer h.mu.RUnlock()
	s := make(map[string]bool)
	for k, v := range h.seeds {
		s[k] = v
	}
	return s
}

func (h *peerHub) stop() {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.stopped = true
	for _, p := range h.peers {
		p.stop()
	}
	h.followersStats.Reset()
	// http.Transport needs some time to put used connections
	// into idle queues.
	time.Sleep(time.Millisecond)
	tr := h.c.Transport.(*http.Transport)
	tr.CloseIdleConnections()
}

func (h *peerHub) peer(id int64) (*peer, error) {
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.stopped {
		return nil, fmt.Errorf("peerHub stopped")
	}
	if p, ok := h.peers[id]; ok {
		return p, nil
	}
	return nil, fmt.Errorf("peer %d not found", id)
}

func (h *peerHub) add(id int64, rawurl string) (*peer, error) {
	u, err := url.Parse(rawurl)
	if err != nil {
		return nil, err
	}
	u.Path = raftPrefix

	h.mu.Lock()
	defer h.mu.Unlock()
	if h.stopped {
		return nil, fmt.Errorf("peerHub stopped")
	}
	h.peers[id] = newPeer(u.String(), h.c, h.followersStats.Follower(fmt.Sprint(id)))
	return h.peers[id], nil
}

func (h *peerHub) send(msg raft.Message) error {
	if p, err := h.fetch(msg.To); err == nil {
		data, err := json.Marshal(msg)
		if err != nil {
			return err
		}
		if msg.IsMsgApp() {
			h.serverStats.SendAppendReq(len(data))
		}
		p.send(data)
		return nil
	}
	return errUnknownPeer
}

func (h *peerHub) fetch(nodeId int64) (*peer, error) {
	if p, err := h.peer(nodeId); err == nil {
		return p, nil
	}
	for seed := range h.seeds {
		if p, err := h.seedFetch(seed, nodeId); err == nil {
			return p, nil
		}
	}
	return nil, fmt.Errorf("cannot fetch the address of node %d", nodeId)
}

func (h *peerHub) seedFetch(seedurl string, id int64) (*peer, error) {
	u, err := url.Parse(seedurl)
	if err != nil {
		return nil, fmt.Errorf("cannot parse the url of the given seed")
	}

	u.Path = path.Join("/raft/cfg", fmt.Sprint(id))
	resp, err := h.c.Get(u.String())
	if err != nil {
		return nil, fmt.Errorf("cannot reach %v", u)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("cannot find node %d via %s", id, seedurl)
	}

	b, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("cannot reach %v", u)
	}

	return h.add(id, string(b))
}