// Copyright 2018 The dexon-consensus-core Authors
// This file is part of the dexon-consensus-core library.
//
// The dexon-consensus-core library is free software: you can redistribute it
// and/or modify it under the terms of the GNU Lesser General Public License as
// published by the Free Software Foundation, either version 3 of the License,
// or (at your option) any later version.
//
// The dexon-consensus-core library is distributed in the hope that it will be
// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the dexon-consensus-core library. If not, see
// <http://www.gnu.org/licenses/>.

package simulation

import (
	"context"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"sync"
	"time"

	"github.com/dexon-foundation/dexon-consensus-core/core/types"
	"github.com/dexon-foundation/dexon-consensus-core/simulation/config"
)

// PeerServer is the main object for maintaining peer list.
type PeerServer struct {
	peers            map[types.ValidatorID]string
	peersMu          sync.Mutex
	peerTotalOrder   PeerTotalOrder
	peerTotalOrderMu sync.Mutex
	verifiedLen      uint64
}

// NewPeerServer returns a new peer server.
func NewPeerServer() *PeerServer {
	return &PeerServer{
		peers:          make(map[types.ValidatorID]string),
		peerTotalOrder: make(PeerTotalOrder),
	}
}

// isValidator checks if vID is in p.peers. If peer server restarts but
// validators are not, it will cause panic if validators send message.
func (p *PeerServer) isValidator(vID types.ValidatorID) bool {
	p.peersMu.Lock()
	defer p.peersMu.Unlock()
	_, exist := p.peers[vID]
	return exist
}

// Run starts the peer server.
func (p *PeerServer) Run(configPath string) {
	cfg, err := config.Read(configPath)
	if err != nil {
		panic(err)
	}

	resetHandler := func(w http.ResponseWriter, r *http.Request) {
		p.peersMu.Lock()
		defer p.peersMu.Unlock()

		p.peers = make(map[types.ValidatorID]string)
		log.Printf("Peer server has been reset.")
	}

	joinHandler := func(w http.ResponseWriter, r *http.Request) {
		defer r.Body.Close()

		idString := r.Header.Get("ID")
		portString := r.Header.Get("PORT")

		id := types.ValidatorID{}
		id.UnmarshalText([]byte(idString))

		p.peersMu.Lock()
		defer p.peersMu.Unlock()

		host, _, _ := net.SplitHostPort(r.RemoteAddr)
		p.peers[id] = net.JoinHostPort(host, portString)
		p.peerTotalOrder[id] = NewTotalOrderResult(id)
		log.Printf("Peer %s joined from %s", id, p.peers[id])

		if len(p.peers) == cfg.Validator.Num {
			log.Println("All peers connected.")
		}
		w.WriteHeader(http.StatusOK)
	}

	peersHandler := func(w http.ResponseWriter, r *http.Request) {
		p.peersMu.Lock()
		defer p.peersMu.Unlock()
		defer r.Body.Close()

		if len(p.peers) != cfg.Validator.Num {
			w.WriteHeader(http.StatusNotFound)
			return
		}

		jsonText, err := json.Marshal(p.peers)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			return
		}

		w.WriteHeader(http.StatusOK)
		w.Header().Set("Content-Type", "application/json")
		w.Write(jsonText)
	}

	infoHandler := func(w http.ResponseWriter, r *http.Request) {
		p.peersMu.Lock()
		defer p.peersMu.Unlock()
		defer r.Body.Close()

		msg := InfoMessage{
			Status: statusNormal,
			Peers:  p.peers,
		}

		if len(p.peers) < cfg.Validator.Num {
			msg.Status = statusInit
		}

		// Determine msg.status.
		if p.verifiedLen >= cfg.Validator.MaxBlock {
			msg.Status = statusShutdown
		}

		jsonText, err := json.Marshal(msg)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			return
		}

		w.WriteHeader(http.StatusOK)
		w.Header().Set("Content-Type", "application/json")
		w.Write(jsonText)
	}

	deliveryHandler := func(w http.ResponseWriter, r *http.Request) {
		defer r.Body.Close()

		idString := r.Header.Get("ID")
		body, err := ioutil.ReadAll(r.Body)
		if err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		m := BlockList{}
		if err := json.Unmarshal(body, &m); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		id := types.ValidatorID{}
		if err := id.UnmarshalText([]byte(idString)); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		if !p.isValidator(id) {
			w.WriteHeader(http.StatusForbidden)
			return
		}

		w.WriteHeader(http.StatusOK)

		p.peerTotalOrderMu.Lock()
		defer p.peerTotalOrderMu.Unlock()

		readyForVerify := p.peerTotalOrder[id].PushBlocks(m)
		if !readyForVerify {
			return
		}

		// Verify the total order result.
		go func(id types.ValidatorID) {
			p.peerTotalOrderMu.Lock()
			defer p.peerTotalOrderMu.Unlock()

			var correct bool
			var length int
			p.peerTotalOrder, correct, length = VerifyTotalOrder(id, p.peerTotalOrder)
			if !correct {
				log.Printf("The result of Total Ordering Algorithm has error.\n")
			}
			p.verifiedLen += uint64(length)
		}(id)
	}

	stopServer := make(chan struct{})

	messageHandler := func(w http.ResponseWriter, r *http.Request) {
		defer r.Body.Close()

		idString := r.Header.Get("ID")
		id := types.ValidatorID{}
		id.UnmarshalText([]byte(idString))

		if !p.isValidator(id) {
			w.WriteHeader(http.StatusForbidden)
			return
		}

		body, err := ioutil.ReadAll(r.Body)
		if err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		m := Message{}
		if err := json.Unmarshal(body, &m); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		switch m.Type {
		case shutdownAck:
			func() {
				p.peersMu.Lock()
				defer p.peersMu.Unlock()

				delete(p.peers, id)
				log.Printf("%v shutdown, %d remains.\n", id, len(p.peers))
				if len(p.peers) == 0 {
					stopServer <- struct{}{}
				}
			}()
			break
		case blockTimestamp:
			msgs := []TimestampMessage{}
			if err := json.Unmarshal(m.Payload, &msgs); err != nil {
				w.WriteHeader(http.StatusBadRequest)
				return
			}
			for _, msg := range msgs {
				if ok := p.peerTotalOrder[id].PushTimestamp(msg); !ok {
					w.WriteHeader(http.StatusBadRequest)
					return
				}
			}
			break
		default:
			w.WriteHeader(http.StatusBadRequest)
			return
		}
		w.WriteHeader(http.StatusOK)
	}

	http.HandleFunc("/reset", resetHandler)
	http.HandleFunc("/join", joinHandler)
	http.HandleFunc("/peers", peersHandler)
	http.HandleFunc("/info", infoHandler)
	http.HandleFunc("/delivery", deliveryHandler)
	http.HandleFunc("/message", messageHandler)

	addr := fmt.Sprintf("0.0.0.0:%d", peerPort)
	log.Printf("Peer server started at %s", addr)

	server := &http.Server{Addr: addr}

	go func() {
		<-stopServer

		LogStatus(p.peerTotalOrder)

		log.Printf("Shutting down peerServer.\n")
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := server.Shutdown(ctx); err != nil {
			log.Printf("Error shutting down peerServer: %v\n", err)
		}
	}()

	if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
		log.Fatalf("Error starting server %v\n", err)
	}

	// Do not exit when we are in TCP node, since k8s will restart the pod and
	// cause confusions.
	if cfg.Networking.Type == config.NetworkTypeTCP {
		select {}
	}
}