package cmd

import (
	"context"
	"encoding/json"
	"fmt"
	"strconv"
	"time"

	"github.com/DataDog/datadog-go/statsd"
	"github.com/adjust/rmq/v4"
	"github.com/christianselig/apollo-backend/internal/cmdutil"
	"github.com/go-co-op/gocron"
	"github.com/go-redis/redis/v8"
	"github.com/jackc/pgx/v4"
	"github.com/jackc/pgx/v4/pgxpool"
	"github.com/sirupsen/logrus"
	"github.com/spf13/cobra"
)

const (
	batchSize      = 200
	checkTimeout   = 60 // how long until we force a check
	enqueueTimeout = 5  // how long until we try to re-enqueue
)

func SchedulerCmd(ctx context.Context) *cobra.Command {
	cmd := &cobra.Command{
		Use:   "scheduler",
		Args:  cobra.ExactArgs(0),
		Short: "Schedules jobs and runs several maintenance tasks periodically.",
		RunE: func(cmd *cobra.Command, args []string) error {
			logger := cmdutil.NewLogrusLogger(false)

			statsd, err := cmdutil.NewStatsdClient()
			if err != nil {
				return err
			}
			defer statsd.Close()

			db, err := cmdutil.NewDatabasePool(ctx, 1)
			if err != nil {
				return err
			}
			defer db.Close()

			redis, err := cmdutil.NewRedisClient(ctx)
			if err != nil {
				return err
			}
			defer redis.Close()

			queue, err := cmdutil.NewQueueClient(logger, redis, "worker")
			if err != nil {
				return err
			}

			// Eval lua so that we don't keep parsing it
			luaSha, err := evalScript(ctx, redis)
			if err != nil {
				return err
			}

			notifQueue, err := queue.OpenQueue("notifications")
			if err != nil {
				return err
			}

			s := gocron.NewScheduler(time.UTC)
			s.Every(1).Second().SingletonMode().Do(func() { enqueueAccounts(ctx, logger, statsd, db, redis, luaSha, notifQueue) })
			s.Every(1).Second().Do(func() { cleanQueues(ctx, logger, queue) })
			s.Every(1).Minute().Do(func() { reportStats(ctx, logger, statsd, db, redis) })
			s.Every(1).Minute().Do(func() { cleanAccounts(ctx, logger, db) })
			s.StartAsync()

			<-ctx.Done()

			s.Stop()

			return nil
		},
	}

	return cmd
}

func evalScript(ctx context.Context, redis *redis.Client) (string, error) {
	lua := fmt.Sprintf(`
		local retv={}
		local ids=cjson.decode(ARGV[1])

		for i=1, #ids do
			local key = KEYS[1] .. ":" .. ids[i]
			if redis.call("exists", key) == 0 then
				redis.call("setex", key, %d, 1)
				retv[#retv + 1] = ids[i]
			end
		end

		return retv
	`, checkTimeout)

	return redis.ScriptLoad(ctx, lua).Result()
}

func cleanAccounts(ctx context.Context, logger *logrus.Logger, pool *pgxpool.Pool) {
	now := time.Now().Unix() - 7200
	count := 0
	ids := []int64{}

	err := pool.BeginFunc(ctx, func(tx pgx.Tx) error {
		stmt := `
			WITH account AS (
			  SELECT id
				FROM accounts
				WHERE
					expires_at < $1
			)
			DELETE FROM accounts
			WHERE accounts.id IN(SELECT id FROM account)
			RETURNING accounts.id`
		rows, err := tx.Query(ctx, stmt, now)
		if err != nil {
			return err
		}
		defer rows.Close()

		for rows.Next() {
			var id int64
			rows.Scan(&id)
			ids = append(ids, id)
			count++
		}
		return nil
	})

	if err != nil {
		logger.WithFields(logrus.Fields{
			"err": err,
		}).Error("failed cleaning stale accounts")
		return
	}

	logger.WithFields(logrus.Fields{
		"count": count,
	}).Info("cleaned stale accounts")
}

func cleanQueues(ctx context.Context, logger *logrus.Logger, jobsConn rmq.Connection) {
	cleaner := rmq.NewCleaner(jobsConn)
	count, err := cleaner.Clean()
	if err != nil {
		logger.WithFields(logrus.Fields{
			"err": err,
		}).Error("failed cleaning jobs from queues")
		return
	}

	logger.WithFields(logrus.Fields{
		"count": count,
	}).Debug("returned jobs to queues")
}

func reportStats(ctx context.Context, logger *logrus.Logger, statsd *statsd.Client, pool *pgxpool.Pool, redisConn *redis.Client) {
	var (
		count int64

		metrics = []struct {
			query string
			name  string
		}{
			{"SELECT COUNT(*) FROM accounts", "apollo.registrations.accounts"},
			{"SELECT COUNT(*) FROM devices", "apollo.registrations.devices"},
		}
	)

	for _, metric := range metrics {
		pool.QueryRow(ctx, metric.query).Scan(&count)
		statsd.Gauge(metric.name, float64(count), []string{}, 1)

		logger.WithFields(logrus.Fields{
			"count":  count,
			"metric": metric.name,
		}).Debug("fetched metrics")
	}
}

func enqueueAccounts(ctx context.Context, logger *logrus.Logger, statsd *statsd.Client, pool *pgxpool.Pool, redisConn *redis.Client, luaSha string, queue rmq.Queue) {
	start := time.Now()

	now := float64(time.Now().UnixNano()/int64(time.Millisecond)) / 1000

	// Start looking for accounts that were last checked at least 5 seconds ago
	// and at most 6 seconds ago. Also look for accounts that haven't been checked
	// in over a minute.
	ts := start.Unix()
	ready := ts - enqueueTimeout
	expired := ts - checkTimeout

	ids := []int64{}

	err := pool.BeginFunc(ctx, func(tx pgx.Tx) error {
		stmt := `
			WITH account AS (
			  SELECT id
				FROM accounts
				WHERE
					last_enqueued_at < $1
					OR last_checked_at < $2
				ORDER BY last_checked_at
				LIMIT 2000
				FOR UPDATE SKIP LOCKED
			)
			UPDATE accounts
			SET last_enqueued_at = $3
			WHERE accounts.id IN(SELECT id FROM account)
			RETURNING accounts.id`
		rows, err := tx.Query(ctx, stmt, ready, expired, now)
		if err != nil {
			return err
		}
		defer rows.Close()
		for rows.Next() {
			var id int64
			rows.Scan(&id)
			ids = append(ids, id)
		}
		return nil
	})

	if err != nil {
		logger.WithFields(logrus.Fields{
			"err": err,
		}).Error("failed to fetch batch of accounts")
		return
	}

	logger.WithFields(logrus.Fields{
		"count": len(ids),
		"start": ready,
	}).Debug("enqueueing account batch")

	enqueued := 0
	skipped := 0

	// Split ids in batches
	for i := 0; i < len(ids); i += batchSize {
		j := i + batchSize
		if j > len(ids) {
			j = len(ids)
		}
		batch := Int64Slice(ids[i:j])

		logger.WithFields(logrus.Fields{
			"len": len(batch),
		}).Debug("enqueueing batch")

		res, err := redisConn.EvalSha(ctx, luaSha, []string{"locks:accounts"}, batch).Result()
		if err != nil {
			logger.WithFields(logrus.Fields{
				"err": err,
			}).Error("failed to check for locked accounts")

		}

		vals := res.([]interface{})
		skipped += len(batch) - len(vals)
		enqueued += len(vals)

		if len(vals) == 0 {
			continue
		}

		batchIds := make([]string, len(vals))
		for k, v := range vals {
			batchIds[k] = strconv.FormatInt(v.(int64), 10)
		}

		if err = queue.Publish(batchIds...); err != nil {
			logger.WithFields(logrus.Fields{
				"err": err,
			}).Error("failed to enqueue account")
		}
	}

	statsd.Histogram("apollo.queue.enqueued", float64(enqueued), []string{}, 1)
	statsd.Histogram("apollo.queue.skipped", float64(skipped), []string{}, 1)
	statsd.Histogram("apollo.queue.runtime", float64(time.Now().Sub(start).Milliseconds()), []string{}, 1)

	logger.WithFields(logrus.Fields{
		"count":   enqueued,
		"skipped": skipped,
		"start":   ready,
	}).Debug("done enqueueing account batch")
}

type Int64Slice []int64

func (ii Int64Slice) MarshalBinary() (data []byte, err error) {
	bytes, err := json.Marshal(ii)
	return bytes, err
}