package safew

import (
	"context"
	"errors"
	"log/slog"
	"strings"
	"sync"
	"time"

	"aiaa-notification-service/internal/adapter"
)

type Poller func(token string, offset int64, timeout int) ([]adapter.SafewChat, int64, error)

const pollLockTTL = 60 * time.Second

type runner struct {
	cancel    context.CancelFunc
	firstDone chan struct{}
	mu        sync.Mutex
	firstErr  error
}

func (r *runner) setFirst(err error) {
	r.mu.Lock()
	r.firstErr = err
	r.mu.Unlock()
	select {
	case <-r.firstDone:
	default:
		close(r.firstDone)
	}
}

func (r *runner) waitFirst(ctx context.Context) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-r.firstDone:
		r.mu.Lock()
		defer r.mu.Unlock()
		return r.firstErr
	}
}

type Watcher struct {
	store  ChatStore
	poll   Poller
	bgIdle time.Duration

	mu      sync.Mutex
	running map[string]*runner
	stopped bool
}

func NewWatcher(store ChatStore, poll Poller) *Watcher {
	return &Watcher{
		store:   store,
		poll:    poll,
		bgIdle:  time.Second,
		running: map[string]*runner{},
	}
}

func (w *Watcher) Ensure(token string) {
	w.ensure(token)
}

func (w *Watcher) ensure(token string) *runner {
	if token == "" || w == nil {
		return nil
	}
	w.mu.Lock()
	defer w.mu.Unlock()
	if w.stopped {
		return nil
	}
	if r, ok := w.running[token]; ok {
		return r
	}
	ctx, cancel := context.WithCancel(context.Background())
	r := &runner{cancel: cancel, firstDone: make(chan struct{})}
	w.running[token] = r
	go w.loop(ctx, token, r)
	return r
}

func (w *Watcher) Stop() {
	w.mu.Lock()
	w.stopped = true
	for _, r := range w.running {
		r.cancel()
	}
	w.running = map[string]*runner{}
	w.mu.Unlock()
}

func (w *Watcher) Refresh(ctx context.Context, token string) error {
	r := w.ensure(token)
	if r == nil {
		return nil
	}
	return r.waitFirst(ctx)
}

func (w *Watcher) List(ctx context.Context, token, q string) ([]adapter.SafewChat, error) {
	chats, err := w.store.ListSafewChats(ctx, token)
	if err != nil {
		return nil, err
	}
	return adapter.FilterSafewChats(chats, q), nil
}

func (w *Watcher) loop(ctx context.Context, token string, r *runner) {
	for {
		err := w.pollOnce(ctx, token, 0)
		if ctx.Err() != nil {
			r.setFirst(ctx.Err())
			return
		}
		if isSafewAuth(err) {
			r.setFirst(err)
			return
		}
		if isGetUpdatesConflict(err) {
			if !w.sleep(ctx, conflictBackoff(w.bgIdle)) {
				r.setFirst(ctx.Err())
				return
			}
			continue
		}
		r.setFirst(err)
		break
	}

	for {
		if err := w.pollOnce(ctx, token, 30); err != nil {
			if ctx.Err() != nil {
				return
			}
			if isSafewAuth(err) {
				slog.Warn("safew watcher poll", "error", err)
				return
			}
			if isGetUpdatesConflict(err) {
				slog.Debug("safew watcher poll conflict", "error", err)
				if !w.sleep(ctx, conflictBackoff(w.bgIdle)) {
					return
				}
				continue
			}
			slog.Warn("safew watcher poll", "error", err)
		}
		if !w.sleep(ctx, w.bgIdle) {
			return
		}
	}
}

func (w *Watcher) sleep(ctx context.Context, d time.Duration) bool {
	if d <= 0 {
		d = time.Second
	}
	select {
	case <-ctx.Done():
		return false
	case <-time.After(d):
		return true
	}
}

func (w *Watcher) pollOnce(ctx context.Context, token string, timeout int) error {
	ok, err := w.store.TrySafewPollLock(ctx, token, pollLockTTL)
	if err != nil {
		return err
	}
	if !ok {
		return nil
	}
	defer func() { _ = w.store.UnlockSafewPoll(ctx, token) }()

	offset, err := w.store.GetSafewOffset(ctx, token)
	if err != nil {
		return err
	}
	chats, next, err := w.poll(token, offset, timeout)
	if err != nil {
		return err
	}
	if err := w.store.MergeSafewChats(ctx, token, chats); err != nil {
		return err
	}
	if next != offset {
		return w.store.SetSafewOffset(ctx, token, next)
	}
	return nil
}

func isSafewAuth(err error) bool {
	var e *adapter.SafewAuthError
	return errors.As(err, &e)
}

func isGetUpdatesConflict(err error) bool {
	if err == nil {
		return false
	}
	s := strings.ToLower(err.Error())
	return strings.Contains(s, "conflict") && strings.Contains(s, "getupdates")
}

func conflictBackoff(idle time.Duration) time.Duration {
	if idle <= 0 {
		return 3 * time.Second
	}
	d := idle * 3
	if d < 3*time.Second {
		return 3 * time.Second
	}
	return d
}