package async

import (
	"context"
	"fmt"
	"time"

	"github.com/WatchBeam/clock"
	"github.com/fleetdm/fleet/v4/server/config"
	"github.com/fleetdm/fleet/v4/server/contexts/ctxerr"
	"github.com/fleetdm/fleet/v4/server/datastore/redis"
	"github.com/fleetdm/fleet/v4/server/fleet"
	kitlog "github.com/go-kit/log"
	"github.com/go-kit/log/level"
	redigo "github.com/gomodule/redigo/redis"
)

const collectorLockKey = "locks:async_collector:{%s}"

type Task struct {
	datastore   fleet.Datastore
	pool        fleet.RedisPool
	clock       clock.Clock
	taskConfigs map[config.AsyncTaskName]config.AsyncProcessingConfig
	seenHostSet seenHostSet
	otelEnabled bool
}

// NewTask configures and returns a Task.
func NewTask(ds fleet.Datastore, pool fleet.RedisPool, clck clock.Clock, fleetConfig *config.FleetConfig) *Task {
	taskCfgs := make(map[config.AsyncTaskName]config.AsyncProcessingConfig)

	var osqueryConf config.OsqueryConfig
	otelEnabled := false
	if fleetConfig != nil {
		osqueryConf = fleetConfig.Osquery
		otelEnabled = fleetConfig.OTELEnabled()
	}

	taskCfgs[config.AsyncTaskLabelMembership] = osqueryConf.AsyncConfigForTask(config.AsyncTaskLabelMembership)
	taskCfgs[config.AsyncTaskPolicyMembership] = osqueryConf.AsyncConfigForTask(config.AsyncTaskPolicyMembership)
	taskCfgs[config.AsyncTaskHostLastSeen] = osqueryConf.AsyncConfigForTask(config.AsyncTaskHostLastSeen)
	taskCfgs[config.AsyncTaskScheduledQueryStats] = osqueryConf.AsyncConfigForTask(config.AsyncTaskScheduledQueryStats)

	return &Task{
		datastore:   ds,
		pool:        pool,
		clock:       clck,
		taskConfigs: taskCfgs,
		otelEnabled: otelEnabled,
	}
}

// Collect runs the various collectors as distinct background goroutines if
// async processing is enabled.  Each collector will stop processing when ctx
// is done.
func (t *Task) StartCollectors(ctx context.Context, logger kitlog.Logger) {
	collectorErrHandler := func(name string, err error) {
		level.Error(logger).Log("err", fmt.Sprintf("%s collector", name), "details", err)
		ctxerr.Handle(ctx, err)
	}

	handlers := map[config.AsyncTaskName]collectorHandlerFunc{
		config.AsyncTaskLabelMembership:     t.collectLabelQueryExecutions,
		config.AsyncTaskPolicyMembership:    t.collectPolicyQueryExecutions,
		config.AsyncTaskHostLastSeen:        t.collectHostsLastSeen,
		config.AsyncTaskScheduledQueryStats: t.collectScheduledQueryStats,
	}
	for task, cfg := range t.taskConfigs {
		if !cfg.Enabled {
			level.Debug(logger).Log("task", "async disabled, not starting collector", "name", task)
			continue
		}

		cfg := cfg // shadow as local var to avoid capturing the iteration var
		coll := &collector{
			name:         "collect_" + string(task),
			pool:         t.pool,
			ds:           t.datastore,
			execInterval: cfg.CollectInterval,
			jitterPct:    cfg.CollectMaxJitterPercent,
			lockTimeout:  cfg.CollectLockTimeout,
			handler:      handlers[task],
			errHandler:   collectorErrHandler,
		}
		go coll.Start(ctx)
		level.Debug(logger).Log("task", "async enabled, starting collectors", "name", task, "interval", cfg.CollectInterval, "jitter", cfg.CollectMaxJitterPercent)

		if cfg.CollectLogStatsInterval > 0 {
			go func() {
				tick := time.Tick(cfg.CollectLogStatsInterval)
				for {
					select {
					case <-tick:
						stats := coll.ReadStats()
						level.Debug(logger).Log("stats", fmt.Sprintf("%#v", stats), "name", coll.name)
					case <-ctx.Done():
						return
					}
				}
			}()
		}
	}
}

func storePurgeActiveHostID(pool fleet.RedisPool, zsetKey string, hid uint, reportedAt, purgeOlder time.Time) (int, error) {
	// KEYS[1]: the zsetKey
	// ARGV[1]: the host ID to add
	// ARGV[2]: the added host's reported-at timestamp
	// ARGV[3]: purge any entry with score older than this (purgeOlder timestamp)
	//
	// returns how many hosts were removed
	script := redigo.NewScript(1, `
    redis.call('ZADD', KEYS[1], ARGV[2], ARGV[1])
    return redis.call('ZREMRANGEBYSCORE', KEYS[1], '-inf', ARGV[3])
  `)

	conn := pool.Get()
	defer conn.Close()

	if err := redis.BindConn(pool, conn, zsetKey); err != nil {
		return 0, fmt.Errorf("bind redis connection: %w", err)
	}

	count, err := redigo.Int(script.Do(conn, zsetKey, hid, reportedAt.Unix(), purgeOlder.Unix()))
	if err != nil {
		return 0, fmt.Errorf("run redis script: %w", err)
	}
	return count, nil
}

type hostIDLastReported struct {
	HostID       uint
	LastReported int64 // timestamp in unix epoch
}

func loadActiveHostIDs(pool fleet.RedisPool, zsetKey string, scanCount int) ([]hostIDLastReported, error) {
	conn := redis.ConfigureDoer(pool, pool.Get())
	defer conn.Close()

	// using ZSCAN instead of fetching in one shot, as there may be 100K+ hosts
	// and we don't want to block the redis server too long.
	var hosts []hostIDLastReported
	cursor := 0
	for {
		res, err := redigo.Values(conn.Do("ZSCAN", zsetKey, cursor, "COUNT", scanCount))
		if err != nil {
			return nil, fmt.Errorf("scan active host ids: %w", err)
		}
		var hostVals []uint
		if _, err := redigo.Scan(res, &cursor, &hostVals); err != nil {
			return nil, fmt.Errorf("convert scan results: %w", err)
		}
		for i := 0; i < len(hostVals); i += 2 {
			hosts = append(hosts,
				hostIDLastReported{HostID: hostVals[i], LastReported: int64(hostVals[i+1])}) //nolint:gosec // dismiss G115
		}

		if cursor == 0 {
			// iteration completed
			return hosts, nil
		}
	}
}

func removeProcessedHostIDs(pool fleet.RedisPool, zsetKey string, batch []hostIDLastReported) (int, error) {
	// This script removes from the set of active hosts all those that still have
	// the same score as when the batch was read (via loadActiveHostIDs). This is
	// so that any host that would've reported new data since the call to
	// loadActiveHostIDs would *not* get deleted (as the score would change if
	// that was the case).
	//
	// Note that this approach is correct - in that it is safe and won't delete
	// any host that has unsaved reported data - but it is potentially slow, as
	// it needs to check the score of each member before deleting it. Should that
	// become too slow, we have some options:
	//
	// * split the batch in smaller, capped ones (that would be if the redis
	//   server gets blocked for too long processing a single batch)
	// * use ZREMRANGEBYSCORE to remove in one command all members with a score
	//   (reported-at timestamp) lower than the maximum timestamp in batch.
	//   While this would be almost certainly faster, it might be incorrect as
	//   new data could be reported with timestamps older than the maximum one,
	//   e.g. if the clocks are not exactly in sync between fleet instances, or
	//   if hosts report new data while the ZSCAN is going on and don't get picked
	//   up by the SCAN (this is possible, as part of the guarantees of SCAN).

	// KEYS[1]: zsetKey
	// ARGV...: the list of host ID-last reported timestamp pairs
	// returns the count of hosts removed
	script := redigo.NewScript(1, `
    local count = 0
    for i = 1, #ARGV, 2 do
      local member, ts = ARGV[i], ARGV[i+1]
      if redis.call('ZSCORE', KEYS[1], member) == ts then
        count = count + 1
        redis.call('ZREM', KEYS[1], member)
      end
    end
    return count
  `)

	conn := pool.Get()
	defer conn.Close()

	if err := redis.BindConn(pool, conn, zsetKey); err != nil {
		return 0, fmt.Errorf("bind redis connection: %w", err)
	}

	args := redigo.Args{zsetKey}
	for _, host := range batch {
		args = args.Add(host.HostID, host.LastReported)
	}
	count, err := redigo.Int(script.Do(conn, args...))
	if err != nil {
		return 0, fmt.Errorf("run redis script: %w", err)
	}
	return count, nil
}