package api

import (
	"context"
	"fmt"
	"time"

	"github.com/ponzischeme89/memby/server/internal/notify"
	"github.com/ponzischeme89/memby/server/internal/scheduler"
	"github.com/ponzischeme89/memby/server/internal/store"
)

// The weekly viewing summary, delivered as a personal notification rather than as a service
// alert: a service alert is the house being told something, and how long somebody watched is
// nobody else's news. It therefore lands in My Alerts, follows the person to whichever
// television they sign into, and is dismissed the way every other notification there is.
//
// Two things make this safe to run hourly. The *source key* is the only thing preventing a
// repeat — `watch-time:weekly:2026-W33` is written ON CONFLICT DO NOTHING, so a container
// restarted three times on a Sunday evening delivers one summary, and a gateway that was
// switched off all evening still delivers it the next hour it is up. And every window it
// reports is computed from a household-local calendar rather than by subtracting hours, so a
// daylight-saving change cannot move a week boundary underneath it.

const (
	watchTimeWeeklyKind  = "watch-time-week"
	watchTimeMonthlyKind = "watch-time-month"
)

// RegisterWatchTimeTasks declares the digest. Registered beside the housekeeping jobs so the
// console lists it, an operator can run it by hand, and its last run is visible — which for a
// job that fires once a week is the difference between "it has not sent anything" and "it has
// not run".
func (s *Server) RegisterWatchTimeTasks(sched *scheduler.Scheduler) {
	if sched == nil {
		return
	}
	sched.Register(scheduler.Task{
		ID:    "watch-time-digest",
		Name:  "Weekly watch-time summary",
		Group: "Notifications",
		Description: fmt.Sprintf(
			"Sends each viewer their week-to-date and month-to-date viewing on %s evening, "+
				"and a summary of the month just gone once it ends. Needs Tracearr.",
			digestWeekday),
		// Hourly rather than daily: the send window is an evening in the household's own
		// time, and a daily task would have to be lucky to land inside it.
		Interval: time.Hour,
		Timeout:  5 * time.Minute,
		Run:      s.runWatchTimeDigest,
	})
}

func (s *Server) runWatchTimeDigest(ctx context.Context) (string, error) {
	// Three refusals before any work, in the order that costs least. A household with no
	// Tracearr has nothing to report; an operator who has switched the feature off has said
	// so for the whole house; and outside the send window there is nothing due.
	if !s.tracearrEnabled() {
		return "", nil
	}
	if !s.featureEnabled(ctx, featureWatchTimeDigest) {
		return "", nil
	}
	location := s.householdLocation()
	now := time.Now()
	weekly := weeklyDigestDue(now, location)
	monthly := monthlyDigestDue(now, location)
	if !weekly && !monthly {
		return "", nil
	}

	accounts, err := s.store.KnownUsers(ctx)
	if err != nil {
		return "", fmt.Errorf("watch-time digest: read viewers: %w", err)
	}
	if len(accounts) == 0 {
		return "", nil
	}
	identities, err := s.store.TracearrIdentities(ctx)
	if err != nil {
		// Same trade the console makes: the username join still works, so only a viewer
		// renamed in one system loses their summary rather than everybody losing theirs.
		s.log.Warn("Tracearr identity map unavailable for watch-time digest", "error", err)
		identities = map[string]store.RecommendationIdentity{}
	}

	sent := 0
	if weekly {
		count, err := s.sendWeeklyWatchTime(ctx, now, location, accounts, identities)
		if err != nil {
			return "", err
		}
		sent += count
	}
	if monthly {
		count, err := s.sendMonthlyWatchTime(ctx, now, location, accounts, identities)
		if err != nil {
			return "", err
		}
		sent += count
	}
	// An empty detail keeps a job that runs every hour out of the operator's notification
	// feed every hour; see scheduler.announce.
	if sent == 0 {
		return "", nil
	}
	if sent == 1 {
		return "1 viewing summary sent", nil
	}
	return fmt.Sprintf("%d viewing summaries sent", sent), nil
}

func (s *Server) sendWeeklyWatchTime(
	ctx context.Context,
	now time.Time,
	location *time.Location,
	accounts []store.KnownUser,
	identities map[string]store.RecommendationIdentity,
) (int, error) {
	weekStart := weekStartIn(now, location)
	week, err := s.store.TracearrWatchTimeRange(ctx, weekStart, now)
	if err != nil {
		return 0, fmt.Errorf("watch-time digest: week: %w", err)
	}
	month, err := s.store.TracearrWatchTimeRange(ctx, monthStartIn(now, location), now)
	if err != nil {
		return 0, fmt.Errorf("watch-time digest: month: %w", err)
	}
	weekByID, weekByName := indexWatchTimeRanges(week)
	monthByID, monthByName := indexWatchTimeRanges(month)

	key := "watch-time:weekly:" + weekKey(now, location)
	eventAt := now
	sent := 0
	for _, account := range accounts {
		identity := identities[account.ID]
		watched := lookupWatchTimeRange(weekByID, weekByName, identity, account.Username)
		total := time.Duration(watched.Ms) * time.Millisecond
		if total < watchTimeDigestFloor {
			continue
		}
		monthWatched := lookupWatchTimeRange(monthByID, monthByName, identity, account.Username)
		message := weeklyDigestMessage(
			total, time.Duration(monthWatched.Ms)*time.Millisecond, watched.TopTitle)
		notification := notify.Notification{
			Kind:      watchTimeWeeklyKind,
			Source:    notifySourceWatchTime,
			UserID:    account.ID,
			Username:  account.Username,
			Title:     "Your week in Memby",
			Body:      message,
			SourceKey: key,
			EventAt:   &eventAt,
			Metadata:  map[string]any{"watchedMs": watched.Ms, "topTitle": watched.TopTitle},
		}
		// The floor above is a judgement about the news; this is a judgement about the
		// person, and only the second one is worth recording. "You have summaries switched
		// off" is the answer to somebody reporting that they never get one, and it is not
		// findable anywhere else.
		if !s.watchTimeDigestWanted(ctx, account.ID) {
			s.declineUser(ctx, notification, "this viewer has watch-time summaries switched off")
			continue
		}
		if s.notifyUser(ctx, notification) {
			sent++
		}
	}
	if sent > 0 {
		s.log.Info("weekly watch-time summaries sent", "viewers", sent, "week", weekKey(now, location))
	}
	return sent, nil
}

func (s *Server) sendMonthlyWatchTime(
	ctx context.Context,
	now time.Time,
	location *time.Location,
	accounts []store.KnownUser,
	identities map[string]store.RecommendationIdentity,
) (int, error) {
	from, to, monthID := previousMonth(now, location)
	windows, err := s.store.TracearrWatchTimeRange(ctx, from, to)
	if err != nil {
		return 0, fmt.Errorf("watch-time digest: previous month: %w", err)
	}
	byID, byName := indexWatchTimeRanges(windows)

	key := "watch-time:monthly:" + monthID
	monthName := from.Format("January")
	eventAt := to
	sent := 0
	for _, account := range accounts {
		identity := identities[account.ID]
		watched := lookupWatchTimeRange(byID, byName, identity, account.Username)
		total := time.Duration(watched.Ms) * time.Millisecond
		if total < watchTimeDigestFloor {
			continue
		}
		message := monthlyDigestMessage(total, monthName, watched.TopTitle)
		notification := notify.Notification{
			Kind:      watchTimeMonthlyKind,
			Source:    notifySourceWatchTime,
			UserID:    account.ID,
			Username:  account.Username,
			Title:     monthName + " in Memby",
			Body:      message,
			SourceKey: key,
			EventAt:   &eventAt,
			Metadata:  map[string]any{"watchedMs": watched.Ms, "topTitle": watched.TopTitle, "month": monthID},
		}
		if !s.watchTimeDigestWanted(ctx, account.ID) {
			s.declineUser(ctx, notification, "this viewer has watch-time summaries switched off")
			continue
		}
		if s.notifyUser(ctx, notification) {
			sent++
		}
	}
	if sent > 0 {
		s.log.Info("monthly watch-time summaries sent", "viewers", sent, "month", monthID)
	}
	return sent, nil
}

// watchTimeDigestWanted reads the viewer's own switches. A preference that will not load is
// read as "not now" rather than as consent: this is a notification about somebody's own
// habits, and sending one to a person who may have declined it is the worse of the two
// mistakes.
func (s *Server) watchTimeDigestWanted(ctx context.Context, userID string) bool {
	prefs, err := s.notificationPreferencesFor(ctx, userID)
	if err != nil {
		s.log.Warn("notification preferences unavailable for watch-time digest",
			"user", userID, "error", err)
		return false
	}
	return prefs.Enabled && prefs.WatchTimeDigest
}