package api

import (
	"context"
	"fmt"
	"strconv"
	"time"

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

// Telling somebody the thing they asked for has arrived.
//
// This is the one part of the request feature that cannot be answered by looking: every
// other state on a card is derived per read from the *arrs and the library, but "it has just
// become ready" is a *difference between two observations*, and a viewer has to be told about
// it exactly once. media_requests.last_status is the memory that makes the difference
// visible; this sweep is what looks.
//
// It is a personal notification rather than a service alert, and that is the same distinction
// the watch-time digest makes: a service alert is the house being told something, and one
// person's request arriving is news for one person. It therefore lands in My Alerts and
// follows them to whichever television they sign into, rather than dropping a bar across
// somebody else's film.

const (
	// requestReadyKind is what the television files the notification under. An app that
	// predates it draws the fallback icon, which is why the wording has to stand on its own.
	requestReadyKind = "request-ready"
	// notifySourceRequestReady names this producer in the notification log, so an operator
	// answering "did Memby tell them?" has one thing to filter on.
	notifySourceRequestReady = "request-ready"
)

// RegisterRequestTasks declares the arrival sweep.
//
// Registered as an ordinary scheduler job for the reason the digest is: an operator can see
// when it last ran and can run one by hand. For a job whose whole output is silence on a
// quiet day, that is the difference between "nothing has arrived" and "it has not run".
func (s *Server) RegisterRequestTasks(sched *scheduler.Scheduler) {
	if sched == nil {
		return
	}
	sched.Register(scheduler.Task{
		ID:    "request-ready-scan",
		Name:  "Requested content arrivals",
		Group: "Notifications",
		Description: "Notices when something a viewer requested has become watchable and tells " +
			"the person who asked for it. Needs Radarr or Sonarr.",
		// Five minutes is chosen against what it is watching rather than against cost. An
		// import is the last few seconds of a wait measured in tens of minutes, so being up
		// to five minutes late with the news is invisible; being an hour late is the
		// difference between a notification and a thing somebody had already found for
		// themselves.
		Interval: 5 * time.Minute,
		Timeout:  2 * time.Minute,
		Run:      s.runRequestReadyScan,
	})
}

func (s *Server) runRequestReadyScan(ctx context.Context) (string, error) {
	if s.store == nil {
		return "", nil
	}
	// Nothing to compare against with both catalogues gone: every card would read
	// "requested", which is not a transition and must not be recorded as one.
	if !s.radarrEnabled(ctx) && !s.sonarrEnabled(ctx) {
		return "", nil
	}

	// Retire pins nobody has acted on in a fortnight before looking at anything else, so a
	// stale REQUEST READY tag is gone from Home within a sweep of its deadline rather than
	// leaning on SurfacedReadyRequests' own window clause to keep hiding it.
	if expired, err := s.store.ExpireStaleReadyRequests(ctx); err != nil {
		s.loggerFor(ctx).Warn("stale request pins not expired", "error", err)
	} else {
		s.invalidateHomeFor(ctx, expired...)
	}

	owned, err := s.store.AllMediaRequests(ctx, store.MediaRequestSweepLimit)
	if err != nil {
		return "", fmt.Errorf("request arrivals: read requests: %w", err)
	}
	if len(owned) == 0 {
		return "", nil
	}

	stored := make([]store.MediaRequest, 0, len(owned))
	for _, req := range owned {
		stored = append(stored, req.MediaRequest)
	}
	// progressAware is true because nothing here is drawn: the sweep wants the truth, and
	// collapsing it would make a download and a search indistinguishable in the memory this
	// writes back.
	cards := s.decorateRequests(ctx, stored, true)
	if len(cards) != len(owned) {
		// decorateRequests answers one card per stored ask, in order. If that ever stopped
		// being true the zip below would attribute one person's arrival to another, which is
		// the one mistake here that reaches somebody as a notification about a title they
		// never asked for.
		return "", fmt.Errorf("request arrivals: %d cards for %d requests", len(cards), len(owned))
	}

	announced, moved := 0, 0
	for index, card := range cards {
		req := owned[index]
		if card.Status == req.LastStatus {
			continue
		}
		// A state that could not be established is not a transition. With Radarr restarting,
		// every card falls back to "requested", and recording that would throw away the
		// memory of what each request was actually doing — so the next sweep, once Radarr is
		// back, would read an arrival as a move from "requested" and announce titles that had
		// been on the shelf for a week.
		if card.Status == RequestStatusRequested {
			continue
		}
		if card.Status == RequestStatusAvailable && req.LastStatus != RequestStatusAvailable {
			if s.announceRequestReady(ctx, req, card) {
				announced++
			}
			// Pin it to the front of the requester's Continue Watching row until they play
			// it. Only possible once the library has an item id — a title the *arr reports a
			// file for but Emby has not imported yet is still worth the notification above,
			// but there is nothing for a card to open. MarkRequestReadySurfaced's own guard
			// makes the repeat a no-op, so this is safe to call on every observed transition.
			if card.EmbyItemID != "" {
				if err := s.store.MarkRequestReadySurfaced(
					ctx, req.UserID, req.MediaType, req.ForeignID, card.EmbyItemID,
				); err != nil {
					s.loggerFor(ctx).Warn("request ready pin not recorded",
						"user_id", req.UserID, "type", req.MediaType,
						"foreign_id", req.ForeignID, "error", err)
				} else {
					s.invalidateHomeFor(ctx, req.UserID)
				}
			}
		}
		if err := s.store.SetMediaRequestStatus(
			ctx, req.UserID, req.MediaType, req.ForeignID, card.Status,
		); err != nil {
			s.loggerFor(ctx).Warn("request status not recorded",
				"user_id", req.UserID, "type", req.MediaType,
				"foreign_id", req.ForeignID, "error", err)
			continue
		}
		moved++
	}

	// An empty detail keeps a job that runs every five minutes out of the operator's feed
	// every five minutes; see scheduler.announce. Movement without an arrival is real work
	// and worth reporting, because it is the evidence that the sweep is watching anything
	// at all on a household where nothing has finished downloading yet.
	switch {
	case announced == 1:
		return "1 request ready", nil
	case announced > 1:
		return fmt.Sprintf("%d requests ready", announced), nil
	case moved > 0:
		return fmt.Sprintf("%d requests moved on", moved), nil
	default:
		return "", nil
	}
}

// announceRequestReady tells one viewer their title has landed.
//
// It carries the Emby item id whenever the library has one, which is what lets pressing the
// notification open the title's own detail page rather than a page about nothing. A title the
// *arr reports a file for but Emby has not imported yet legitimately has none — the news is
// still true and still worth sending, and the notification simply is not a link.
//
// There is deliberately no preference check. The other personal notifications are things
// Memby decided to send somebody; this one is the answer to a question they asked by pressing
// a button, and a viewer who has requested a film has said as clearly as they can that they
// want to know when it arrives.
func (s *Server) announceRequestReady(
	ctx context.Context, req store.OwnedMediaRequest, card myRequest,
) bool {
	title := card.Title
	if title == "" {
		title = req.Title
	}
	thing := "film"
	if req.MediaType == "series" {
		thing = "series"
	}
	eventAt := time.Now()
	sent := s.notifyUser(ctx, notify.Notification{
		Kind:   requestReadyKind,
		Source: notifySourceRequestReady,
		UserID: req.UserID,
		Title:  "Your " + thing + " is ready",
		Body:   title + " is now available to watch.",
		ItemID: card.EmbyItemID,
		// The key names the request rather than the moment, so the arrival is announced once
		// however many times the sweep runs — and a viewer who deletes the request, asks
		// again and waits through a second download is a second key only if the title left
		// the library in between, which is the case where the news is genuinely new.
		SourceKey: "request-ready:" + req.MediaType + ":" + strconv.Itoa(req.ForeignID) +
			":" + req.UserID,
		EventAt: &eventAt,
		Metadata: map[string]any{
			"mediaType": req.MediaType,
			"foreignId": req.ForeignID,
		},
	})
	if sent {
		s.loggerFor(ctx).Info("requested title is ready",
			"user_id", req.UserID, "type", req.MediaType,
			"title", clientLogValue(title), "foreign_id", req.ForeignID,
			"item_id", card.EmbyItemID)
	}
	return sent
}