package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"os/user"
	"path/filepath"
	"strings"
	"syscall"
	"time"

	"github.com/sirupsen/logrus"
	"golang.org/x/net/context"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/calendar/v3"
)

var (
	nowTime          = time.Now()
	oneYearString    = fmt.Sprintf("%dh", 365*24)
	oneYear, _       = time.ParseDuration(oneYearString)
	clientSecretFlag = flag.String(
		"s", getEnvDefault("CLIENT_SECRET", "client_secret.json"), "client secret json file")
	calendarIDFlag = flag.String(
		"i", getEnvDefault("CALENDAR", "primary"), "calendar ID to search")
	endTimeFlag = flag.String(
		"e", getEnvDefault("END_TIME", nowTime.Format(dateFmt)), "end time for search")
	timeWindowFlag = flag.Duration(
		"t", func() time.Duration {
			stringVal := getEnvDefault("DURATION", oneYearString)
			val, _ := time.ParseDuration(stringVal)
			return val
		}(), "time window duration from before end time")
	defaultLocationFlag = flag.String(
		"l", getEnvDefault("DEFAULT_LOCATION", "notset"), "default location for where")

	locationAliases = map[string]string{
		"pittsburgh": "dan",
		"kennywood":  "dan",
		"akron":      "sarah",
	}
)

const (
	dateFmt = "2006-01-02"
)

func getEnvDefault(key, defVal string) string {
	for _, k := range []string{"WHEREWHEN_" + key, key} {
		if v, ok := syscall.Getenv(k); ok {
			return v
		}
	}
	return defVal
}

func main() {
	flag.Parse()

	ctx := context.Background()

	b, err := ioutil.ReadFile(*clientSecretFlag)
	if err != nil {
		logrus.Fatalf("Unable to read client secret file: %v", err)
	}

	config, err := google.ConfigFromJSON(b, calendar.CalendarReadonlyScope)
	if err != nil {
		logrus.Fatalf("Unable to parse client secret file to config: %v", err)
	}
	client := getClient(ctx, config)

	srv, err := calendar.New(client)
	if err != nil {
		logrus.Fatalf("Unable to retrieve calendar Client %v", err)
	}

	endT, err := time.Parse(dateFmt, *endTimeFlag)
	if err != nil {
		logrus.Fatalf("Unable to parse end time %q: %v", *endTimeFlag, err)
	}

	maxResults := int64(2500)
	startT := endT.Add(-*timeWindowFlag)
	t := startT.Format(time.RFC3339)
	events, err := srv.Events.List(*calendarIDFlag).ShowDeleted(false).
		SingleEvents(true).TimeMin(t).TimeMax(endT.Format(time.RFC3339)).
		MaxResults(maxResults).OrderBy("startTime").Do()
	if err != nil {
		logrus.Fatalf("Unable to retrieve next %d events. %v", maxResults, err)
	}

	logrus.WithField("count", len(events.Items)).Infof("found events")
	logrus.Debugf("generating days between %v and %v", startT, endT)

	days := generateDays(startT, endT)
	foundEvents := []*lilEvent{}
	defaultLocation := *defaultLocationFlag

	logrus.Debugf("generated %d days between %v and %v", len(days), startT, endT)

	if len(events.Items) > 0 {
		for _, i := range events.Items {
			var (
				startDate string
				endDate   string
			)

			if i.Start.DateTime != "" {
				startT, err := time.Parse(time.RFC3339, i.Start.DateTime)
				if err != nil {
					logrus.Errorf("error parsing start date: %v", err)
					continue
				}

				endT, err := time.Parse(time.RFC3339, i.End.DateTime)
				if err != nil {
					logrus.Errorf("error parsing end date: %v", err)
					continue
				}
				startDate = startT.Format(dateFmt)
				endDate = endT.Format(dateFmt)
			} else {
				startDate = i.Start.Date
				endDate = i.End.Date
			}

			evt := &lilEvent{
				Start:    startDate,
				End:      endDate,
				Location: defaultLocation,
				Summary:  strings.ToLower(strings.TrimSpace(i.Summary)),
			}

			summ := strings.ToLower(i.Summary)
			if strings.Contains(summ, "possible") {
				continue
			}

			parts := strings.Split(summ, " ")
			locIdx := 0
			for i, part := range parts {
				if part == "in" || part == "with" {
					locIdx = i + 1
				}
			}
			loc := strings.TrimSpace(parts[locIdx])
			if locAlias, ok := locationAliases[loc]; ok {
				loc = locAlias
			}
			evt.Location = loc

			if evt.Start == evt.End {
				logrus.Debugf("skipping same-day event on %s (%s)", evt.Start, evt.Summary)
				continue
			}
			foundEvents = append(foundEvents, evt)
		}
	} else {
		logrus.Info("No events found")
	}

	for _, day := range days {
		logrus.Debugf("working on date %v", day)

		for _, evt := range foundEvents {
			logrus.Debugf("checking if %s is in range %s %s", day.Date, evt.Start, evt.End)

			if evt.HasDate(day.Date) {
				logrus.Debugf("match found for %s in range %s %s, setting location to %s", day.Date, evt.Start, evt.End, evt.Location)
				day.Location = evt.Location
			}
		}
	}

	for _, day := range days {
		asJson, err := json.Marshal(day)
		if err != nil {
			logrus.Error(err)
			continue
		}

		fmt.Println(string(asJson))
	}
}

func getClient(ctx context.Context, config *oauth2.Config) *http.Client {
	cacheFile, err := tokenCacheFile()
	if err != nil {
		logrus.Fatalf("Unable to get path to cached credential file. %v", err)
	}
	tok, err := tokenFromFile(cacheFile)
	if err != nil {
		tok = getTokenFromWeb(config)
		saveToken(cacheFile, tok)
	}
	return config.Client(ctx, tok)
}

func getTokenFromWeb(config *oauth2.Config) *oauth2.Token {
	authURL := config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
	fmt.Printf("Go to the following link in your browser then type the "+
		"authorization code: \n%v\n", authURL)

	var code string
	if _, err := fmt.Scan(&code); err != nil {
		logrus.Fatalf("Unable to read authorization code %v", err)
	}

	tok, err := config.Exchange(oauth2.NoContext, code)
	if err != nil {
		logrus.Fatalf("Unable to retrieve token from web %v", err)
	}
	return tok
}

func tokenCacheFile() (string, error) {
	usr, err := user.Current()
	if err != nil {
		return "", err
	}
	tokenCacheDir := filepath.Join(usr.HomeDir, ".credentials")
	os.MkdirAll(tokenCacheDir, 0700)
	return filepath.Join(tokenCacheDir,
		url.QueryEscape("wherewhen.json")), err
}

func tokenFromFile(file string) (*oauth2.Token, error) {
	f, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	t := &oauth2.Token{}
	err = json.NewDecoder(f).Decode(t)
	defer f.Close()
	return t, err
}

func saveToken(file string, token *oauth2.Token) {
	fmt.Printf("Saving credential file to: %s\n", file)
	f, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		logrus.Fatalf("Unable to cache oauth token: %v", err)
	}
	defer f.Close()
	json.NewEncoder(f).Encode(token)
}

type lilEvent struct {
	Start    string `json:"start"`
	End      string `json:"end"`
	Location string `json:"loc"`
	Summary  string `json:"summ"`
}

func (e *lilEvent) HasDate(d string) bool {
	if e.Start == d {
		logrus.Debugf("match for %s at %s", d, e.Start)
		return true
	}

	dT, err := time.Parse(dateFmt, d)
	if err != nil {
		logrus.Error(err)
		return false
	}

	dr := e.dateRange()
	return dr[0].Before(dT) && dr[1].After(dT)
}

func (e *lilEvent) dateRange() []time.Time {
	ret := []time.Time{}
	for _, t := range []string{e.Start, e.End} {
		parsedDate, err := time.Parse(dateFmt, t)
		if err != nil {
			logrus.Error(err)
			ret = append(ret, time.Time{})
			continue
		}
		ret = append(ret, parsedDate)
	}

	return ret
}

type lilDay struct {
	Date     string `json:"date"`
	Location string `json:"loc"`
}

func generateDays(startT, endT time.Time) []*lilDay {
	defaultLocation := *defaultLocationFlag
	days := []*lilDay{}

	curT := startT
	for {
		if curT.After(endT) {
			return days
		}

		days = append(days, &lilDay{
			Date:     curT.Format(dateFmt),
			Location: defaultLocation,
		})

		curT = curT.Add(24 * time.Hour)
	}
}