// Copyright (C) 2015 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.

// Package rc provides remote control of a Syncthing process via the REST API.
package rc

import (
	"bufio"
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"os/exec"
	"path/filepath"
	stdsync "sync"
	"time"

	"github.com/syncthing/protocol"
	"github.com/syncthing/syncthing/internal/config"
	"github.com/syncthing/syncthing/internal/sync"
)

// We set the API key via the STGUIAPIKEY variable when we launch the binary,
// to ensure that we have API access regardless of authentication settings.
const APIKey = "592A47BC-A7DF-4C2F-89E0-A80B3E5094EE"

type Process struct {
	// Set at initialization
	addr string

	// Set by eventLoop()
	eventMut          sync.Mutex
	id                protocol.DeviceID
	folders           []string
	startComplete     bool
	startCompleteCond *stdsync.Cond
	stop              bool
	localVersion      map[string]map[string]int64 // Folder ID => Device ID => LocalVersion
	done              map[string]bool             // Folder ID => 100%

	cmd   *exec.Cmd
	logfd *os.File
}

// NewProcess returns a new Process talking to Syncthing at the specified address.
// Example: NewProcess("127.0.0.1:8082")
func NewProcess(addr string) *Process {
	p := &Process{
		addr:         addr,
		localVersion: make(map[string]map[string]int64),
		done:         make(map[string]bool),
		eventMut:     sync.NewMutex(),
	}
	p.startCompleteCond = stdsync.NewCond(p.eventMut)
	return p
}

// LogTo creates the specified log file and ensures that stdout and stderr
// from the Start()ed process is redirected there. Must be called before
// Start().
func (p *Process) LogTo(filename string) error {
	if p.cmd != nil {
		panic("logfd cannot be set with an existing cmd")
	}

	if p.logfd != nil {
		p.logfd.Close()
	}

	fd, err := os.Create(filename)
	if err != nil {
		return err
	}
	p.logfd = fd
	return nil
}

// Start runs the specified Syncthing binary with the given arguments.
// Syncthing should be configured to provide an API on the address given to
// NewProcess. Event processing is started.
func (p *Process) Start(bin string, args ...string) error {
	cmd := exec.Command(bin, args...)
	if p.logfd != nil {
		cmd.Stdout = p.logfd
		cmd.Stderr = p.logfd
	}
	cmd.Env = append(os.Environ(), "STNORESTART=1", "STGUIAPIKEY="+APIKey)

	err := cmd.Start()
	if err != nil {
		return err
	}

	p.cmd = cmd
	go p.eventLoop()

	return nil
}

// AwaitStartup waits for the Syncthing process to start and perform initial
// scans of all folders.
func (p *Process) AwaitStartup() {
	p.eventMut.Lock()
	for !p.startComplete {
		p.startCompleteCond.Wait()
	}
	p.eventMut.Unlock()
	return
}

// Stop stops the running Syncthing process. If the process was logging to a
// local file (set by LogTo), the log file will be opened and checked for
// panics and data races. The presence of either will be signalled in the form
// of a returned error.
func (p *Process) Stop() (*os.ProcessState, error) {
	p.eventMut.Lock()
	if p.stop {
		p.eventMut.Unlock()
		return p.cmd.ProcessState, nil
	}
	p.stop = true
	p.eventMut.Unlock()

	if err := p.cmd.Process.Signal(os.Kill); err != nil {
		return nil, err
	}
	p.cmd.Wait()

	var err error
	if p.logfd != nil {
		err = p.checkForProblems(p.logfd)
	}

	return p.cmd.ProcessState, err
}

// Get performs an HTTP GET and returns the bytes and/or an error. Any non-200
// return code is returned as an error.
func (p *Process) Get(path string) ([]byte, error) {
	client := &http.Client{
		Timeout: 30 * time.Second,
		Transport: &http.Transport{
			DisableKeepAlives: true,
		},
	}

	url := fmt.Sprintf("http://%s%s", p.addr, path)
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return nil, err
	}

	req.Header.Add("X-API-Key", APIKey)

	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}

	return p.readResponse(resp)
}

// Post performs an HTTP POST and returns the bytes and/or an error. Any
// non-200 return code is returned as an error.
func (p *Process) Post(path string, data io.Reader) ([]byte, error) {
	client := &http.Client{
		Timeout: 600 * time.Second,
		Transport: &http.Transport{
			DisableKeepAlives: true,
		},
	}
	url := fmt.Sprintf("http://%s%s", p.addr, path)
	req, err := http.NewRequest("POST", url, data)
	if err != nil {
		return nil, err
	}

	req.Header.Add("X-API-Key", APIKey)
	req.Header.Add("Content-Type", "application/json")

	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}

	return p.readResponse(resp)
}

type Event struct {
	ID   int
	Time time.Time
	Type string
	Data interface{}
}

func (p *Process) Events(since int) ([]Event, error) {
	bs, err := p.Get(fmt.Sprintf("/rest/events?since=%d", since))
	if err != nil {
		return nil, err
	}

	var evs []Event
	dec := json.NewDecoder(bytes.NewReader(bs))
	dec.UseNumber()
	err = dec.Decode(&evs)
	if err != nil {
		return nil, fmt.Errorf("Events: %s in %q", err, bs)
	}
	return evs, err
}

func (p *Process) Rescan(folder string) error {
	_, err := p.Post("/rest/db/scan?folder="+folder, nil)
	return err
}

func (p *Process) RescanDelay(folder string, delaySeconds int) error {
	_, err := p.Post(fmt.Sprintf("/rest/db/scan?folder=%s&next=%d", folder, delaySeconds), nil)
	return err
}

func InSync(folder string, ps ...*Process) bool {
	for _, p := range ps {
		p.eventMut.Lock()
	}
	defer func() {
		for _, p := range ps {
			p.eventMut.Unlock()
		}
	}()

	for i := range ps {
		// If our latest FolderSummary didn't report 100%, then we are not done.

		if !ps[i].done[folder] {
			return false
		}

		// Check LocalVersion for each device. The local version seen by remote
		// devices should be the same as what it has locally, or the index
		// hasn't been sent yet.

		sourceID := ps[i].id.String()
		sourceVersion := ps[i].localVersion[folder][sourceID]
		for j := range ps {
			if i != j {
				remoteVersion := ps[j].localVersion[folder][sourceID]
				if remoteVersion != sourceVersion {
					return false
				}
			}
		}
	}

	return true
}

func AwaitSync(folder string, ps ...*Process) {
	for {
		time.Sleep(250 * time.Millisecond)
		if InSync(folder, ps...) {
			return
		}
	}
}

type Model struct {
	GlobalBytes   int
	GlobalDeleted int
	GlobalFiles   int
	InSyncBytes   int
	InSyncFiles   int
	Invalid       string
	LocalBytes    int
	LocalDeleted  int
	LocalFiles    int
	NeedBytes     int
	NeedFiles     int
	State         string
	StateChanged  time.Time
	Version       int
}

func (p *Process) Model(folder string) (Model, error) {
	bs, err := p.Get("/rest/db/status?folder=" + folder)
	if err != nil {
		return Model{}, err
	}

	var res Model
	if err := json.Unmarshal(bs, &res); err != nil {
		return Model{}, err
	}

	if debug {
		l.Debugf("%+v", res)
	}

	return res, nil
}

func (p *Process) readResponse(resp *http.Response) ([]byte, error) {
	bs, err := ioutil.ReadAll(resp.Body)
	resp.Body.Close()
	if err != nil {
		return bs, err
	}
	if resp.StatusCode != 200 {
		return bs, fmt.Errorf("%s", resp.Status)
	}
	return bs, nil
}

func (p *Process) checkForProblems(logfd *os.File) error {
	fd, err := os.Open(logfd.Name())
	if err != nil {
		return err
	}
	defer fd.Close()

	raceConditionStart := []byte("WARNING: DATA RACE")
	raceConditionSep := []byte("==================")
	panicConditionStart := []byte("panic:")
	panicConditionSep := []byte(p.id.String()[:5])
	sc := bufio.NewScanner(fd)
	race := false
	_panic := false

	for sc.Scan() {
		line := sc.Bytes()
		if race || _panic {
			if bytes.Contains(line, panicConditionSep) {
				_panic = false
				continue
			}
			fmt.Printf("%s\n", line)
			if bytes.Contains(line, raceConditionSep) {
				race = false
			}
		} else if bytes.Contains(line, raceConditionStart) {
			fmt.Printf("%s\n", raceConditionSep)
			fmt.Printf("%s\n", raceConditionStart)
			race = true
			if err == nil {
				err = errors.New("Race condition detected")
			}
		} else if bytes.Contains(line, panicConditionStart) {
			_panic = true
			if err == nil {
				err = errors.New("Panic detected")
			}
		}
	}

	return err
}

func (p *Process) eventLoop() {
	since := 0
	notScanned := make(map[string]struct{})
	start := time.Now()
	for {
		p.eventMut.Lock()
		if p.stop {
			p.eventMut.Unlock()
			return
		}
		p.eventMut.Unlock()

		time.Sleep(250 * time.Millisecond)

		events, err := p.Events(since)
		if err != nil {
			if time.Since(start) < 5*time.Second {
				// The API has probably not started yet, lets give it some time.
				continue
			}

			// If we're stopping, no need to print the error.
			p.eventMut.Lock()
			if p.stop {
				p.eventMut.Unlock()
				return
			}
			p.eventMut.Unlock()

			log.Println("eventLoop: events:", err)
			continue
		}
		since = events[len(events)-1].ID

		for _, ev := range events {
			switch ev.Type {
			case "Starting":
				// The Starting event tells us where the configuration is. Load
				// it and populate our list of folders.

				data := ev.Data.(map[string]interface{})
				id, err := protocol.DeviceIDFromString(data["myID"].(string))
				if err != nil {
					log.Println("eventLoop: DeviceIdFromString:", err)
					continue
				}
				p.id = id

				home := data["home"].(string)
				w, err := config.Load(filepath.Join(home, "config.xml"), protocol.LocalDeviceID)
				if err != nil {
					log.Println("eventLoop: Starting:", err)
					continue
				}
				for id := range w.Folders() {
					p.eventMut.Lock()
					p.folders = append(p.folders, id)
					p.eventMut.Unlock()
					notScanned[id] = struct{}{}
				}

			case "StateChanged":
				// When a folder changes to idle, we tick it off by removing
				// it from p.notScanned.

				if !p.startComplete {
					data := ev.Data.(map[string]interface{})
					to := data["to"].(string)
					if to == "idle" {
						folder := data["folder"].(string)
						delete(notScanned, folder)
						if len(notScanned) == 0 {
							p.eventMut.Lock()
							p.startComplete = true
							p.startCompleteCond.Broadcast()
							p.eventMut.Unlock()
						}
					}
				}

			case "LocalIndexUpdated":
				data := ev.Data.(map[string]interface{})
				folder := data["folder"].(string)
				version, _ := data["version"].(json.Number).Int64()
				p.eventMut.Lock()
				m := p.localVersion[folder]
				if m == nil {
					m = make(map[string]int64)
				}
				m[p.id.String()] = version
				p.localVersion[folder] = m
				p.done[folder] = false
				if debug {
					l.Debugf("LocalIndexUpdated %v %v done=false\n\t%+v", p.id, folder, m)
				}
				p.eventMut.Unlock()

			case "RemoteIndexUpdated":
				data := ev.Data.(map[string]interface{})
				device := data["device"].(string)
				folder := data["folder"].(string)
				version, _ := data["version"].(json.Number).Int64()
				p.eventMut.Lock()
				m := p.localVersion[folder]
				if m == nil {
					m = make(map[string]int64)
				}
				m[device] = version
				p.localVersion[folder] = m
				p.done[folder] = false
				if debug {
					l.Debugf("RemoteIndexUpdated %v %v done=false\n\t%+v", p.id, folder, m)
				}
				p.eventMut.Unlock()

			case "FolderSummary":
				data := ev.Data.(map[string]interface{})
				folder := data["folder"].(string)
				summary := data["summary"].(map[string]interface{})
				need, _ := summary["needBytes"].(json.Number).Int64()
				done := need == 0
				p.eventMut.Lock()
				p.done[folder] = done
				if debug {
					l.Debugf("Foldersummary %v %v\n\t%+v", p.id, folder, p.done)
				}
				p.eventMut.Unlock()
			}
		}
	}
}