// Package library imports Emby's catalogue into Postgres so the gateway can answer from
// its own copy instead of asking Emby on every request.
//
// Two shapes of import:
//
//   - **full** — page through everything, then delete whatever the pass did not touch.
//     Run once to seed, and again whenever the library has been reorganised.
//   - **incremental** — ask Emby only for items changed since the last successful run.
//     Cheap enough to run hourly, which is what new episodes need; films appearing
//     weekly are picked up by the same pass.
//
// Only shared metadata is imported (EnableUserData=false). Watched state, favourites and
// resume positions are per-user and stay live.
package library

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/ponzischeme89/memby/server/internal/emby"
	"github.com/ponzischeme89/memby/server/internal/store"
)

const (
	// pageSize balances round trips against Emby's response size. 500 items of metadata
	// is roughly a megabyte of JSON.
	pageSize = 500

	// syncFields is everything the gateway serves or filters on. Images are requested as
	// tags only — the artwork itself is proxied on demand.
	//
	// ProviderIds is here for external ratings: it is what a title is called at MDBList,
	// and reading it from the import means a home row resolves forty cards from one
	// indexed query instead of asking Emby about each of them.
	syncFields = "Genres,Studios,Overview,Taglines,ProductionYear,CommunityRating,OfficialRating," +
		"RunTimeTicks,SeriesName,PrimaryImageAspectRatio,DateCreated,PremiereDate,People," +
		"CollectionName,MediaStreams,RecursiveItemCount,ProviderIds"

	syncImageTypes = "Backdrop,Primary,Logo,Thumb"
	syncItemTypes  = "Movie,Series,Episode"
)

// ErrNoCredentials means nothing has ever signed in and no service account is set, so
// there is no way to talk to Emby on the library's behalf.
var ErrNoCredentials = errors.New("library: no emby credentials available for sync")

type Syncer struct {
	emby  *emby.Client
	store *store.Store
	log   *slog.Logger

	// serviceCred is the optional configured account. When empty, the newest TV session
	// is borrowed instead.
	serviceCred emby.Credentials

	mu        sync.Mutex
	running   bool
	afterSync func(Result)
}

func NewSyncer(embyClient *emby.Client, st *store.Store, serviceCred emby.Credentials, log *slog.Logger) *Syncer {
	return &Syncer{emby: embyClient, store: st, serviceCred: serviceCred, log: log}
}

// SetAfterSync installs the inexpensive invalidation callback used by derived data.
func (s *Syncer) SetAfterSync(callback func(Result)) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.afterSync = callback
}

// Result summarises one import.
type Result struct {
	Kind       string        `json:"kind"`
	Seen       int           `json:"seen"`
	Upserted   int           `json:"upserted"`
	Changed    int           `json:"changed"`
	Removed    int           `json:"removed"`
	Duration   time.Duration `json:"-"`
	DurationMs int64         `json:"durationMs"`
}

// Running reports whether an import is in flight, so the admin page can disable its
// buttons and the scheduler can skip a tick.
func (s *Syncer) Running() bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.running
}

// Sync runs an import. kind is "full" or "incremental"; an incremental run with no prior
// successful sync silently upgrades itself to a full one, because there is no watermark
// to work from.
func (s *Syncer) Sync(ctx context.Context, kind, trigger string) (Result, error) {
	s.mu.Lock()
	if s.running {
		s.mu.Unlock()
		return Result{}, errors.New("library: a sync is already running")
	}
	s.running = true
	s.mu.Unlock()
	defer func() {
		s.mu.Lock()
		s.running = false
		s.mu.Unlock()
	}()

	cred, err := s.credentials(ctx)
	if err != nil {
		return Result{}, err
	}

	var since *time.Time
	if kind == "incremental" {
		since, err = s.store.LastSuccessfulSyncAt(ctx)
		if err != nil {
			return Result{}, err
		}
		if since == nil {
			s.log.Info("no previous sync; upgrading to a full import")
			kind = "full"
		}
	}

	startedAt := time.Now().UTC()
	runID, err := s.store.StartSyncRun(ctx, kind, trigger)
	if err != nil {
		return Result{}, err
	}

	s.log.Info("library sync started", "kind", kind, "trigger", trigger)
	result, syncErr := s.run(ctx, cred, kind, since, startedAt)
	result.Kind = kind
	result.Duration = time.Since(startedAt)
	result.DurationMs = result.Duration.Milliseconds()

	record := store.SyncRun{
		Status:        store.SyncStatusSuccess,
		ItemsSeen:     result.Seen,
		ItemsUpserted: result.Upserted,
		ItemsRemoved:  result.Removed,
	}
	if syncErr != nil {
		record.Status = store.SyncStatusFailed
		record.Error = syncErr.Error()
	}
	// Always record the outcome, even when the caller's context died mid-import.
	if err := s.store.FinishSyncRun(context.WithoutCancel(ctx), runID, record); err != nil {
		s.log.Error("could not record sync run", "error", err)
	}

	if syncErr != nil {
		return result, syncErr
	}
	s.log.Info("library sync finished",
		"kind", kind, "trigger", trigger, "seen", result.Seen,
		"upserted", result.Upserted, "changed", result.Changed, "removed", result.Removed,
		"duration", result.Duration.Round(time.Millisecond))
	s.mu.Lock()
	afterSync := s.afterSync
	s.mu.Unlock()
	if afterSync != nil {
		afterSync(result)
	}
	return result, nil
}

func (s *Syncer) run(
	ctx context.Context,
	cred emby.Credentials,
	kind string,
	since *time.Time,
	syncedAt time.Time,
) (Result, error) {
	var result Result

	for startIndex := 0; ; startIndex += pageSize {
		params := url.Values{
			"IncludeItemTypes":       {syncItemTypes},
			"Recursive":              {"true"},
			"SortBy":                 {"DateCreated"},
			"SortOrder":              {"Ascending"},
			"StartIndex":             {strconv.Itoa(startIndex)},
			"Limit":                  {strconv.Itoa(pageSize)},
			"Fields":                 {syncFields},
			"ImageTypeLimit":         {"1"},
			"EnableImages":           {"true"},
			"EnableImageTypes":       {syncImageTypes},
			"EnableTotalRecordCount": {"false"},
			// The imported copy is shared by every user, so it must not carry one
			// user's watched/favourite state.
			"EnableUserData": {"false"},
		}
		if since != nil {
			// Emby returns items created or edited after this instant. Overlap by a
			// minute so an item saved during the previous run is not missed.
			params.Set("MinDateLastSaved", since.Add(-time.Minute).UTC().Format(time.RFC3339))
		}

		page, err := s.emby.Items(ctx, cred, params)
		if err != nil {
			return result, fmt.Errorf("library: fetch page at %d: %w", startIndex, err)
		}
		if len(page.Items) == 0 {
			break
		}

		items := make([]store.LibraryItem, 0, len(page.Items))
		for _, raw := range page.Items {
			if item, ok := toLibraryItem(raw); ok {
				items = append(items, item)
			}
		}
		changed, err := s.store.UpsertLibraryItems(ctx, items, syncedAt)
		if err != nil {
			return result, err
		}

		result.Seen += len(page.Items)
		result.Upserted += len(items)
		result.Changed += int(changed)
		s.log.Info("library sync progress",
			"kind", kind,
			"seen", result.Seen,
			"upserted", result.Upserted,
			"changed", result.Changed,
		)

		if len(page.Items) < pageSize {
			break
		}
	}

	// Only a full pass has seen everything, so only a full pass may delete.
	if kind == "full" {
		removed, err := s.store.DeleteLibraryItemsBefore(ctx, syncedAt)
		if err != nil {
			return result, err
		}
		result.Removed = int(removed)
	}
	return result, nil
}

// credentials prefers the configured service account and otherwise borrows the most
// recent TV session.
func (s *Syncer) credentials(ctx context.Context) (emby.Credentials, error) {
	if s.serviceCred.Token != "" && s.serviceCred.UserID != "" {
		return s.serviceCred, nil
	}
	sess, err := s.store.NewestSession(ctx)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			return emby.Credentials{}, ErrNoCredentials
		}
		return emby.Credentials{}, err
	}
	return emby.Credentials{
		UserID:   sess.EmbyUserID,
		Token:    sess.EmbyToken,
		DeviceID: "memby-gateway-sync",
	}, nil
}

// Schedule runs an incremental import on an interval until ctx is cancelled.
//
// New episodes tend to land through the day and films weekly; an hourly incremental pass
// covers both without ever asking Emby for the whole catalogue again.
func (s *Syncer) Schedule(ctx context.Context, interval time.Duration) {
	if interval <= 0 {
		s.log.Info("library auto-sync disabled")
		return
	}
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	s.log.Info("library auto-sync scheduled", "interval", interval.String())
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			if s.Running() {
				s.log.Info("skipping scheduled sync; one is already running")
				continue
			}
			if _, err := s.Sync(ctx, "incremental", "schedule"); err != nil {
				if errors.Is(err, ErrNoCredentials) {
					// Nobody has signed in yet. Not worth an error-level log every hour.
					s.log.Info("skipping scheduled sync; no credentials yet")
					continue
				}
				s.log.Error("scheduled sync failed", "error", err)
			}
		}
	}
}

// syncItem mirrors the Emby fields promoted to columns.
type syncItem struct {
	ID              string   `json:"Id"`
	Name            string   `json:"Name"`
	Type            string   `json:"Type"`
	SeriesID        string   `json:"SeriesId"`
	SeriesName      string   `json:"SeriesName"`
	ProductionYear  *int     `json:"ProductionYear"`
	CommunityRating *float64 `json:"CommunityRating"`
	Genres          []string `json:"Genres"`
	Studios         []struct {
		Name string `json:"Name"`
	} `json:"Studios"`
	DateCreated *time.Time `json:"DateCreated"`
}

// toLibraryItem flattens the columns Postgres filters on while keeping the payload whole.
func toLibraryItem(raw json.RawMessage) (store.LibraryItem, bool) {
	var parsed syncItem
	if err := json.Unmarshal(raw, &parsed); err != nil || parsed.ID == "" {
		return store.LibraryItem{}, false
	}

	studios := make([]string, 0, len(parsed.Studios))
	for _, studio := range parsed.Studios {
		if name := strings.TrimSpace(studio.Name); name != "" {
			studios = append(studios, name)
		}
	}
	genres := make([]string, 0, len(parsed.Genres))
	for _, genre := range parsed.Genres {
		if g := strings.TrimSpace(genre); g != "" {
			genres = append(genres, g)
		}
	}

	return store.LibraryItem{
		ID:              parsed.ID,
		Type:            parsed.Type,
		Name:            parsed.Name,
		SeriesID:        parsed.SeriesID,
		SeriesName:      parsed.SeriesName,
		ProductionYear:  parsed.ProductionYear,
		CommunityRating: parsed.CommunityRating,
		Genres:          genres,
		Studios:         studios,
		DateCreated:     parsed.DateCreated,
		SearchText:      searchText(parsed),
		Payload:         raw,
	}, true
}

// searchText is what full-text search matches against. Series name is included so
// searching a show finds its episodes.
func searchText(parsed syncItem) string {
	parts := []string{parsed.Name}
	if parsed.SeriesName != "" && !strings.EqualFold(parsed.SeriesName, parsed.Name) {
		parts = append(parts, parsed.SeriesName)
	}
	if parsed.ProductionYear != nil {
		parts = append(parts, strconv.Itoa(*parsed.ProductionYear))
	}
	parts = append(parts, parsed.Genres...)
	// Studios too, so "A24" or "Pixar" finds a shelf's worth of titles. Existing rows
	// keep their old text until the next full import rewrites them.
	for _, studio := range parsed.Studios {
		if studio.Name != "" {
			parts = append(parts, studio.Name)
		}
	}
	return strings.Join(parts, " ")
}