package main

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/go-redis/redis/v8"
	"github.com/gorilla/mux"
)

const (
	ItemChannelBuffer = 100000
	ItemWrapSize      = 100000
)

type ProjectRedisConfig struct {
	Host string `json:"host"`
	Pass string `json:"pass"`
	Port int    `json:"port"`
}

type ProjectConfig struct {
	RedisConfig *ProjectRedisConfig `json:"redis,omitempty"`
}

type BackfeedItem struct {
	PrimaryShard   byte
	SecondaryShard string
	Item           []byte
}

type ProjectBackfeedManager struct {
	Context       context.Context
	Cancel        context.CancelFunc
	Done          chan bool
	C             chan *BackfeedItem
	Name          string
	BackfeedRedis *redis.ClusterClient
	ProjectRedis  *redis.Client
	LegacyRedis   *redis.Client
	Lock          sync.RWMutex
	ProjectConfig ProjectConfig
}

func (that *ProjectBackfeedManager) RedisConfigDiffers(new *ProjectRedisConfig) bool {
	if that.ProjectConfig.RedisConfig == nil && new == nil {
		return false
	}
	if that.ProjectConfig.RedisConfig == nil || new == nil || that.ProjectConfig.RedisConfig.Host != new.Host || that.ProjectConfig.RedisConfig.Port != new.Port || that.ProjectConfig.RedisConfig.Pass != new.Pass {
		return true
	}
	return false
}

func (that *ProjectBackfeedManager) PushItem(ctx context.Context, item *BackfeedItem) bool {
	that.Lock.RLock()
	defer that.Lock.RUnlock()
	if that.C == nil {
		return false
	}
	select {
	case <-ctx.Done():
		return false
	case <-that.Context.Done():
		return false
	case that.C <- item:
		return true
	}
}

func (that *ProjectBackfeedManager) PopItem(blocking bool) (*BackfeedItem, bool) {
	if blocking {
		select {
		case <-that.Context.Done():
			return nil, false
		case item := <-that.C:
			return item, true
		}
	} else {
		select {
		case <-that.Context.Done():
			return nil, false
		case item := <-that.C:
			return item, true
		default:
			return nil, false
		}
	}
}

func (that *ProjectBackfeedManager) CloseItemChannel() {
	that.Lock.Lock()
	defer that.Lock.Unlock()
	if that.C == nil {
		return
	}
	close(that.C)
	that.C = nil
}

func (that *ProjectBackfeedManager) Do() {
	defer close(that.Done)
	defer that.CloseItemChannel()
	defer that.Cancel()

	for {
		select {
		case <-that.Context.Done():
			break
		case <-that.Done:
			break
		default:
		}
		item, ok := that.PopItem(true)
		if !ok {
			break
		}
		keyMap := map[string][][]byte{}
		key := fmt.Sprintf("%s:%02x:%s", that.Name, item.PrimaryShard, item.SecondaryShard)
		keyMap[key] = append(keyMap[key], item.Item)
		wrapped := 1
		for wrapped < ItemWrapSize {
			item, ok := that.PopItem(false)
			if !ok {
				break
			}
			key := fmt.Sprintf("%s:%02x:%s", that.Name, item.PrimaryShard, item.SecondaryShard)
			keyMap[key] = append(keyMap[key], item.Item)
			wrapped++
		}
		select {
		case <-that.Context.Done():
			break
		case <-that.Done:
			break
		default:
		}
		resultMap := map[string]*redis.Cmd{}
		pipe := that.BackfeedRedis.Pipeline()
		for key, items := range keyMap {
			args := []interface{}{
				"bf.madd",
				key,
			}
			for _, item := range items {
				args = append(args, item)
			}
			resultMap[key] = pipe.Do(context.Background(), args...)
		}
		_, err := pipe.Exec(context.Background())
		if err != nil {
			log.Printf("%s", err)
			continue
		}
		var sAddItems []interface{}
		for key, items := range keyMap {
			rawRes, err := resultMap[key].Result()
			if err != nil {
				log.Printf("%s", err)
				continue
			}
			rawResArray, ok := rawRes.([]interface{})
			if !ok || len(keyMap[key]) != len(rawResArray) {
				continue
			}
			for i, vi := range rawResArray {
				v, ok := vi.(int64)
				if !ok || v != 1 {
					continue
				}
				sAddItems = append(sAddItems, items[i])
			}
		}
		dupes := wrapped - len(sAddItems)
		if len(sAddItems) != 0 {
			args := []interface{}{
				"bf.mexists",
				that.Name,
			}
			args = append(args, sAddItems...)

			rawRes, err := that.LegacyRedis.Do(context.Background(), args...).Result()
			if err != nil {
				log.Printf("unable to dedupe against %s legacy backfeed: %s", that.Name, err)
			} else {
				rawResArray, ok := rawRes.([]interface{})
				if ok && len(sAddItems) != len(rawResArray) {
					var filteredSAddItems []interface{}
					for i, vi := range rawResArray {
						v, ok := vi.(int64)
						if !ok || v != 0 {
							continue
						}
						filteredSAddItems = append(filteredSAddItems, sAddItems[i])
					}
					sAddItems = filteredSAddItems
				}
			}
		}
		if len(sAddItems) != 0 {
			err := that.ProjectRedis.SAdd(context.Background(), fmt.Sprintf("%s:todo:backfeed", that.Name), sAddItems...).Err()
			if err != nil {
				log.Printf("failed to sadd items for %s: %s", that.Name, err)
			}
		}
		if dupes > 0 {
			that.BackfeedRedis.HIncrBy(context.Background(), ":", that.Name, int64(dupes))
		}
	}
}

type GlobalBackfeedManager struct {
	Context       context.Context
	Cancel        context.CancelFunc
	ActiveFeeds   map[string]*ProjectBackfeedManager
	ActiveSlugs   map[string]string
	TrackerRedis  *redis.Client
	BackfeedRedis *redis.ClusterClient
	LegacyRedis   *redis.Client
	Lock          sync.RWMutex
}

func (that *GlobalBackfeedManager) RefreshFeeds() error {
	slugProjectMap, err := that.TrackerRedis.HGetAll(that.Context, "backfeed").Result()
	if err != nil {
		return err
	}
	var projects []string
	projectSlugMap := map[string][]string{}
	for slug, project := range slugProjectMap {
		projectSlugMap[project] = append(projectSlugMap[project], slug)
	}
	for project := range projectSlugMap {
		projects = append(projects, project)
	}
	projectConfigs := map[string]ProjectConfig{}
	if len(projects) != 0 {
		cfgi, err := that.TrackerRedis.HMGet(that.Context, "trackers", projects...).Result()
		if err != nil {
			return err
		}
		if len(projects) != len(cfgi) {
			return fmt.Errorf("hmget result had unexpected length")
		}
		for i, project := range projects {
			configString, ok := cfgi[i].(string)
			if !ok {
				continue
			}
			config := ProjectConfig{}
			err := json.Unmarshal([]byte(configString), &config)
			if err != nil {
				continue
			}
			projectConfigs[project] = config
		}
	}
	projects = nil
	for project := range projectSlugMap {
		if _, has := projectConfigs[project]; !has {
			delete(projectSlugMap, project)
			continue
		}
		projects = append(projects, project)
	}
	for slug, project := range slugProjectMap {
		if _, has := projectConfigs[project]; !has {
			delete(slugProjectMap, slug)
		}
	}
	// add feeds for new projects
	for _, project := range projects {
		projectConfig := projectConfigs[project]
		var outdatedProjectBackfeedManager *ProjectBackfeedManager
		if projectBackfeedManager, has := that.ActiveFeeds[project]; has {
			if that.ActiveFeeds[project].RedisConfigDiffers(projectConfig.RedisConfig) {
				outdatedProjectBackfeedManager = projectBackfeedManager
			} else {
				continue
			}
		}
		ctx, cancel := context.WithCancel(that.Context)
		projectBackfeedManager := &ProjectBackfeedManager{
			Context:       ctx,
			Cancel:        cancel,
			Done:          make(chan bool),
			C:             make(chan *BackfeedItem, ItemChannelBuffer),
			BackfeedRedis: that.BackfeedRedis,
			Name:          project,
			ProjectConfig: projectConfig,
			LegacyRedis:   that.LegacyRedis,
		}
		if projectConfig.RedisConfig != nil {
			projectBackfeedManager.ProjectRedis = redis.NewClient(&redis.Options{
				Addr:        fmt.Sprintf("%s:%d", projectConfig.RedisConfig.Host, projectConfig.RedisConfig.Port),
				Username:    "default",
				Password:    projectConfig.RedisConfig.Pass,
				ReadTimeout: 15 * time.Minute,
			})
		} else {
			projectBackfeedManager.ProjectRedis = that.TrackerRedis
		}
		go projectBackfeedManager.Do()
		that.Lock.Lock()
		that.ActiveFeeds[project] = projectBackfeedManager
		that.Lock.Unlock()
		if outdatedProjectBackfeedManager != nil {
			outdatedProjectBackfeedManager.Cancel()
			<-outdatedProjectBackfeedManager.Done
			log.Printf("updated project: %s", project)
		} else {
			log.Printf("added project: %s", project)
		}
	}
	that.Lock.Lock()
	that.ActiveSlugs = slugProjectMap
	that.Lock.Unlock()
	// remove feeds for old projects
	for project, projectBackfeedManager := range that.ActiveFeeds {
		if _, has := projectSlugMap[project]; has {
			continue
		}
		log.Printf("removing project: %s", project)
		that.Lock.Lock()
		delete(that.ActiveFeeds, project)
		that.Lock.Unlock()
		projectBackfeedManager.Cancel()
		<-projectBackfeedManager.Done
		log.Printf("removed project: %s", project)
	}
	return nil
}

type Splitter struct {
	Delimiter []byte
	IgnoreEOF bool
}

func (that *Splitter) Split(data []byte, atEOF bool) (int, []byte, error) {
	for i := 0; i < len(data); i++ {
		if bytes.Equal(data[i:i+len(that.Delimiter)], that.Delimiter) {
			return i + len(that.Delimiter), data[:i], nil
		}
	}
	if len(data) == 0 || !atEOF {
		return 0, nil, nil
	}
	if atEOF && that.IgnoreEOF {
		return len(data), data, nil
	}
	return 0, data, io.ErrUnexpectedEOF
}

func GenShardHash(b []byte) (final byte) {
	for i, b := range b {
		final = (b ^ final ^ byte(i)) + final + byte(i) + final*byte(i)
	}
	return final
}

func WriteResponse(res http.ResponseWriter, statusCode int, v interface{}) {
	res.Header().Set("Content-Type", "application/json")
	res.WriteHeader(statusCode)
	if statusCode == http.StatusNoContent {
		return
	}
	if err, isError := v.(error); isError {
		v = map[string]interface{}{
			"error":       fmt.Sprintf("%v", err),
			"status_code": statusCode,
		}
	} else {
		log.Printf("%#v", v)
		v = map[string]interface{}{
			"data":        v,
			"status_code": statusCode,
		}
	}
	json.NewEncoder(res).Encode(v)
}

func (that *GlobalBackfeedManager) GetFeed(slug string) *ProjectBackfeedManager {
	that.Lock.RLock()
	defer that.Lock.RUnlock()
	project, has := that.ActiveSlugs[slug]
	if !has {
		return nil
	}
	projectBackfeedManager, has := that.ActiveFeeds[project]
	if !has {
		return nil
	}
	return projectBackfeedManager
}

func (that *GlobalBackfeedManager) Handle(res http.ResponseWriter, req *http.Request) {
	defer req.Body.Close()

	vars := mux.Vars(req)
	slug := vars["slug"]
	secondaryShard := req.URL.Query().Get("shard")

	projectBackfeedManager := that.GetFeed(slug)
	if projectBackfeedManager == nil {
		WriteResponse(res, http.StatusNotFound, fmt.Errorf("%s", "no such backfeed channel"))
		return
	}

	splitter := &Splitter{
		Delimiter: []byte(req.URL.Query().Get("delimiter")),
		IgnoreEOF: req.URL.Query().Get("ignoreeof") != "",
	}
	if len(splitter.Delimiter) == 0 {
		splitter.Delimiter = []byte{0x00}
	}
	scanner := bufio.NewScanner(req.Body)
	scanner.Split(splitter.Split)

	var err error
	statusCode := http.StatusNoContent
	for scanner.Scan() {
		b := scanner.Bytes()
		if len(b) == 0 {
			continue
		}
		item := &BackfeedItem{
			PrimaryShard:   GenShardHash(b),
			SecondaryShard: secondaryShard,
			Item:           b,
		}
		ok := projectBackfeedManager.PushItem(req.Context(), item)
		if !ok {
			err = fmt.Errorf("channel closed")
			statusCode = http.StatusServiceUnavailable
			break
		}
	}
	if err == nil {
		err = scanner.Err()
		if err != nil {
			statusCode = http.StatusBadRequest
		}
	}
	WriteResponse(res, statusCode, err)
	return
}

func (that *GlobalBackfeedManager) CancelAllFeeds() {
	that.Cancel()
	for project, projectBackfeedManager := range that.ActiveFeeds {
		log.Printf("waiting for %s channel to shut down...", project)
		<-projectBackfeedManager.Done
		delete(that.ActiveFeeds, project)
	}
}

func main() {
	log.SetFlags(log.Flags() | log.Lshortfile)

	trackerRedisOptions, err := redis.ParseURL(os.Getenv("REDIS_TRACKER"))
	if err != nil {
		log.Panicf("invalid REDIS_TRACKER url: %s", err)
	}
	trackerRedisOptions.ReadTimeout = 15 * time.Minute
	trackerRedisClient := redis.NewClient(trackerRedisOptions)

	legacyRedisOptions, err := redis.ParseURL(os.Getenv("REDIS_LEGACY"))
	if err != nil {
		log.Panicf("invalid REDIS_LEGACY url: %s", err)
	}
	legacyRedisOptions.ReadTimeout = 15 * time.Minute
	legacyRedisClient := redis.NewClient(legacyRedisOptions)

	backfeedRedisClient := redis.NewClusterClient(&redis.ClusterOptions{
		Addrs:       strings.Split(os.Getenv("REDIS_BACKFEED_ADDRS"), ","),
		Username:    os.Getenv("REDIS_BACKFEED_USERNAME"),
		Password:    os.Getenv("REDIS_BACKFEED_PASSWORD"),
		ReadTimeout: 15 * time.Minute,
	})

	if err := trackerRedisClient.Ping(context.Background()).Err(); err != nil {
		log.Panicf("unable to ping tracker redis: %s", err)
	}
	if err := backfeedRedisClient.Ping(context.Background()).Err(); err != nil {
		log.Panicf("unable to ping backfeed redis: %s", err)
	}
	if err := legacyRedisClient.Ping(context.Background()).Err(); err != nil {
		log.Panicf("unable to ping legacy redis: %s", err)
	}

	globalBackfeedManager := &GlobalBackfeedManager{
		ActiveFeeds:   map[string]*ProjectBackfeedManager{},
		ActiveSlugs:   map[string]string{},
		TrackerRedis:  trackerRedisClient,
		BackfeedRedis: backfeedRedisClient,
		LegacyRedis:   legacyRedisClient,
	}

	globalBackfeedManager.Context, globalBackfeedManager.Cancel = context.WithCancel(context.Background())
	defer globalBackfeedManager.CancelAllFeeds()

	err = globalBackfeedManager.RefreshFeeds()
	if err != nil {
		log.Panicf("unable to set up backfeed projects: %s", err)
	}
	r := mux.NewRouter()
	r.Methods(http.MethodPost).Path("/legacy/{slug}").HandlerFunc(globalBackfeedManager.Handle)
	serveErrChan := make(chan error)
	go func() {
		s := &http.Server{
			Addr:           ":21581",
			IdleTimeout:    1 * time.Hour,
			MaxHeaderBytes: 1 * 1024 * 1024,
			Handler:        r,
		}
		serveErrChan <- s.ListenAndServe()
	}()
	sc := make(chan os.Signal, 1)
	signal.Notify(sc, syscall.SIGINT, syscall.SIGTERM, os.Interrupt, os.Kill)
	ticker := time.NewTicker(1 * time.Second)
	for {
		select {
		case <-sc:
			return
		case <-ticker.C:
		}
		err = globalBackfeedManager.RefreshFeeds()
		if err != nil {
			log.Printf("unable to refresh backfeed projects: %s", err)
		}
	}
}