package dataset

import (
	"bytes"
	"io"
	"net/http"
	"net/url"
	"os"
	"sync"
	"time"

	"git.maze.io/maze/styx/logger"
)

type Updater struct {
	storage  Storage
	lists    sync.Map // map[int64]List
	updaters sync.Map // map[int64]*updaterJob
	done     chan struct{}
}

func NewUpdater(storage Storage) *Updater {
	u := &Updater{
		storage: storage,
		done:    make(chan struct{}, 1),
	}
	go u.refresh()
	return u
}

func (u *Updater) Close() error {
	select {
	case <-u.done:
		return nil
	default:
		close(u.done)
		return nil
	}
}

func (u *Updater) refresh() {
	check := time.NewTicker(time.Second)
	defer check.Stop()

	var (
		log = logger.StandardLog
	)
	for {
		select {
		case <-u.done:
			log.Debug("Updater closing, stopping updaters...")
			u.updaters.Range(func(key, value any) bool {
				if value != nil {
					close(value.(*updaterJob).done)
				}
				return true
			})
			return

		case now := <-check.C:
			u.check(now, log)
		}
	}
}

func (u *Updater) check(now time.Time, log logger.Structured) (wait time.Duration) {
	log.Trace("Checking lists")
	lists, err := u.storage.Lists()
	if err != nil {
		log.Err(err).Error("Updater can't retrieve lists")
		return -1
	}

	var missing = make(map[int64]bool)
	u.lists.Range(func(key, _ any) bool {
		log.Tracef("List %d has updater running", key)
		missing[key.(int64)] = true
		return true
	})
	for _, list := range lists {
		log.Tracef("List %d is active: %t", list.ID, list.IsEnabled)
		if !list.IsEnabled {
			continue
		}
		delete(missing, list.ID)
		if _, exists := u.lists.Load(list.ID); !exists {
			u.lists.Store(list.ID, list)
			updater := newUpdaterJob(u.storage, &list)
			u.updaters.Store(list.ID, updater)
		}
	}

	for id := range missing {
		log.Tracef("List %d has updater running, but is no longer active, reaping...", id)
		if updater, ok := u.updaters.Load(id); ok {
			close(updater.(*updaterJob).done)
			u.updaters.Delete(id)
		}
	}

	return
}

type updaterJob struct {
	storage Storage
	list    *List
	done    chan struct{}
}

func newUpdaterJob(storage Storage, list *List) *updaterJob {
	job := &updaterJob{
		storage: storage,
		list:    list,
		done:    make(chan struct{}, 1),
	}
	go job.loop()
	return job
}

func (job *updaterJob) loop() {
	var (
		ticker = time.NewTicker(job.list.Refresh)
		first  = time.After(0)
		now    time.Time
		log    = logger.StandardLog.Values(logger.Values{
			"list": job.list.ID,
			"type": job.list.Type,
		})
	)
	defer ticker.Stop()
	for {
		select {
		case <-job.done:
			log.Debug("List updater stopping")
			return

		case now = <-ticker.C:
		case now = <-first:
		}

		log.Debug("List updater running")
		if update, err := job.run(now); err != nil {
			log.Err(err).Error("List updater failed")
		} else if update {
			if err = job.storage.SaveList(job.list); err != nil {
				log.Err(err).Error("List updater save failed")
			}
		}
	}
}

// run this updater
func (job *updaterJob) run(now time.Time) (update bool, err error) {
	u, err := url.Parse(job.list.Source)
	if err != nil {
		return false, err
	}

	log := logger.StandardLog.Values(logger.Values{
		"list":   job.list.ID,
		"source": job.list.Source,
	})
	if u.Scheme == "" || u.Scheme == "file" {
		log.Debug("Updating list from file")
		return job.updateFile(u.Path)
	}
	log.Debug("Updating list from URL")
	return job.updateHTTP(u)
}

func (job *updaterJob) updateFile(name string) (update bool, err error) {
	var b []byte
	if b, err = os.ReadFile(name); err != nil {
		return
	}
	if update = !bytes.Equal(b, job.list.Cache); update {
		job.list.Cache = b
	}
	return
}

func (job *updaterJob) updateHTTP(location *url.URL) (update bool, err error) {
	if update, err = job.shouldUpdateHTTP(location); err != nil || !update {
		return
	}
	var (
		req *http.Request
		res *http.Response
	)
	if req, err = http.NewRequest(http.MethodGet, location.String(), nil); err != nil {
		return
	}
	if res, err = http.DefaultClient.Do(req); err != nil {
		return
	}
	defer res.Body.Close()

	if job.list.Cache, err = io.ReadAll(res.Body); err != nil {
		return
	}
	return true, nil
}

func (job *updaterJob) shouldUpdateHTTP(location *url.URL) (update bool, err error) {
	if len(job.list.Cache) == 0 {
		// Nothing cached, please update.
		return true, nil
	}

	var (
		req *http.Request
		res *http.Response
	)
	if req, err = http.NewRequest(http.MethodHead, location.String(), nil); err != nil {
		return
	}
	if res, err = http.DefaultClient.Do(req); err != nil {
		return
	}
	defer res.Body.Close()

	if lastModified, err := time.Parse(http.TimeFormat, res.Header.Get("Last-Modified")); err == nil {
		return lastModified.After(job.list.UpdatedAt), nil
	}
	return true, nil // not sure, no Last-Modified, so let's update?
}