package download

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"strconv"

	"github.com/wailsapp/wails/v3/pkg/application"

	"yellowjacket/backend/events"
)

// ErrNoLibrary means the caller did not name a library to attach the
// download to.  Letting it through would hit the download_downloads /
// download_requests foreign key on library_id and surface as a raw
// SQLite error, so it is rejected here with a message the UI can show.
var ErrNoLibrary = errors.New("no library selected")

// Service is the frontend-facing surface of the download subsystem.
// Its methods are bound into Wails and called from TypeScript, so
// signatures use plain types and return errors the UI can render.
type Service struct {
	logger  *slog.Logger
	manager *Manager
	store   *Store
	secrets SecretStore

	// reconciler works the wanted list.  Optional; nil means wants are
	// stored but never acted on.
	reconciler *Reconciler

	ctx context.Context
}

// NewService builds the bound service.
func NewService(
	logger *slog.Logger,
	manager *Manager,
	store *Store,
	secrets SecretStore,
) *Service {
	return &Service{
		logger:  logger,
		manager: manager,
		store:   store,
		secrets: secrets,
	}
}

// ServiceStartup is v3's service lifecycle hook: it runs once the
// runtime exists, and ctx is cancelled when the app shuts down.  It
// replaces v2's SetContext, which had to be called by hand from
// OnStartup and was exported, so it was also bound to the frontend.
func (s *Service) ServiceStartup(
	ctx context.Context,
	_ application.ServiceOptions,
) error {
	s.ctx = ctx

	return nil
}

// emit publishes an event, tolerating a service that has no runtime
// context yet.
func (s *Service) emit(name string, data ...any) {
	events.Emit(s.ctx, name, data...)
}

// ---------------------------------------------------------------------------
// Provider configuration
// ---------------------------------------------------------------------------

// ProviderKinds returns every provider type that can be added, with the
// settings each one needs.  The settings page renders its forms from
// this, so a new adapter needs no frontend change.
func (s *Service) ProviderKinds() []Descriptor {
	return Descriptors()
}

// ListProviders returns the user's configured download clients.
func (s *Service) ListProviders() ([]Config, error) {
	cfgs, err := s.store.ListProviders(context.Background())
	if err != nil {
		return nil, err
	}

	for i := range cfgs {
		cfgs[i].SetSecrets = s.setSecretFlags(cfgs[i])
	}

	return cfgs, nil
}

// setSecretFlags reports, for each secret field the provider's kind
// declares, whether a value is already stored — so the settings form
// can distinguish an unset secret from one it simply isn't shown.
func (s *Service) setSecretFlags(cfg Config) map[string]bool {
	desc, ok := DescriptorFor(cfg.Kind)
	if !ok {
		return nil
	}

	flags := map[string]bool{}

	for _, field := range desc.Fields {
		if !field.Secret {
			continue
		}

		v, err := s.secrets.Get(cfg.ID, field.Key)
		flags[field.Key] = err == nil && v != ""
	}

	return flags
}

// AddProvider creates a provider and stores any secret settings
// separately.  Secrets arrive in the same map as ordinary settings
// because that is what the form submits; they are split out here and
// never written to the provider row.
func (s *Service) AddProvider(
	kind string,
	name string,
	settings map[string]string,
) (int64, error) {
	desc, ok := DescriptorFor(Kind(kind))
	if !ok {
		return 0, fmt.Errorf("%w: %s", ErrUnknownKind, kind)
	}

	plain, secret := splitSecrets(desc, settings)

	id, err := s.store.CreateProvider(context.Background(), Config{
		Kind:     Kind(kind),
		Name:     name,
		Enabled:  true,
		Priority: 50,
		Settings: plain,
	})
	if err != nil {
		return 0, err
	}

	for k, v := range secret {
		if err := s.secrets.Set(id, k, v); err != nil {
			return 0, err
		}
	}

	if err := s.manager.Reload(context.Background()); err != nil {
		return 0, err
	}

	s.emit(events.DownloadProvidersChanged)

	return id, nil
}

// UpdateProvider saves changes to a provider.  A secret field left
// blank keeps its stored value rather than clearing it — the form does
// not echo secrets back, so an empty box means "unchanged", not
// "delete".
func (s *Service) UpdateProvider(
	id int64,
	name string,
	enabled bool,
	priority int,
	settings map[string]string,
) error {
	ctx := context.Background()

	existing, err := s.store.GetProvider(ctx, id)
	if err != nil {
		return err
	}

	desc, ok := DescriptorFor(existing.Kind)
	if !ok {
		return fmt.Errorf("%w: %s", ErrUnknownKind, existing.Kind)
	}

	plain, secret := splitSecrets(desc, settings)

	if err := s.store.UpdateProvider(ctx, Config{
		ID:       id,
		Kind:     existing.Kind,
		Name:     name,
		Enabled:  enabled,
		Priority: priority,
		Settings: plain,
	}); err != nil {
		return err
	}

	for k, v := range secret {
		if v == "" {
			continue
		}

		if err := s.secrets.Set(id, k, v); err != nil {
			return err
		}
	}

	if err := s.manager.Reload(ctx); err != nil {
		return err
	}

	s.emit(events.DownloadProvidersChanged)

	return nil
}

// DeleteProvider removes a provider and its credentials.
func (s *Service) DeleteProvider(id int64) error {
	ctx := context.Background()

	if err := s.store.DeleteProvider(ctx, id); err != nil {
		return err
	}

	if err := s.secrets.DeleteProvider(id); err != nil {
		s.logger.Warn(
			"could not delete provider secrets", "provider", id, "error", err,
		)
	}

	if err := s.manager.Reload(ctx); err != nil {
		return err
	}

	s.emit(events.DownloadProvidersChanged)

	return nil
}

// TestProvider backs the "test connection" button.  It builds the
// provider from its stored config and asks it to check itself, so the
// result reflects exactly what a real search would use.
func (s *Service) TestProvider(id int64) error {
	ctx := context.Background()

	cfg, err := s.store.GetProvider(ctx, id)
	if err != nil {
		return err
	}

	p, err := New(cfg, lookupFor(s.secrets, id), s.logger)
	if err != nil {
		return err
	}

	defer func() { _ = p.Close() }()

	if err := p.Check(ctx); err != nil {
		return fmt.Errorf("%s: %w", cfg.Name, err)
	}

	return nil
}

// SetPreferences pushes the auto-download guardrails straight into the
// running Manager, without persisting them.  Persistence is
// config.Config's job (GetDownloadPreferences/SetDownloadPreferences);
// this package cannot depend on config, since config already depends on
// download for UserConfig.  The frontend settings save is expected to
// call the config setter and this method in the same action, the way
// UpdateProvider already achieves "live without a restart" by touching
// storage and the running Manager together.
func (s *Service) SetPreferences(prefs AutoDownloadPrefs) {
	s.manager.SetPreferences(prefs)
}

// ---------------------------------------------------------------------------
// Downloads
// ---------------------------------------------------------------------------

// SearchRequest is what the frontend submits to start a download.
type SearchRequest struct {
	LibraryID        int64           `json:"libraryId"`
	ReleaseMBID      string          `json:"releaseMbid"`
	ReleaseGroupMBID string          `json:"releaseGroupMbid"`
	Artist           string          `json:"artist"`
	Album            string          `json:"album"`
	Query            string          `json:"query"`
	Expected         []ExpectedTrack `json:"expected"`
}

// StartResult is what the picker needs after a search.
type StartResult struct {
	DownloadID string      `json:"downloadId"`
	Candidates []Candidate `json:"candidates"`

	// AutoPicked reports that the pipeline already chose and is
	// downloading, so the picker should show progress rather than a
	// list of choices.
	AutoPicked bool `json:"autoPicked"`
}

// StartDownload searches for a release and either auto-picks a clear
// winner or returns ranked candidates for the user to choose from.
//
// When the search carries a MusicBrainz anchor, it also resolves or
// creates the durable Request the anchor names and attaches it, via
// ensureRequest — so a manual download that fails or finds nothing
// right now leaves a durable record behind instead of just vanishing,
// and the reconciler picks it up on its normal schedule exactly as if
// the user had explicitly added it to the request list.
func (s *Service) StartDownload(req SearchRequest) (StartResult, error) {
	if req.LibraryID <= 0 {
		return StartResult{}, ErrNoLibrary
	}

	dl := Download{
		ID:               newID(),
		LibraryID:        req.LibraryID,
		ReleaseMBID:      req.ReleaseMBID,
		ReleaseGroupMBID: req.ReleaseGroupMBID,
		Artist:           req.Artist,
		Album:            req.Album,
		Query:            req.Query,
		Expected:         req.Expected,
	}

	if id, ok := s.ensureRequest(dl); ok {
		dl.RequestID = id
	}

	candidates, err := s.manager.Start(context.Background(), dl)
	if err != nil {
		return StartResult{}, err
	}

	result := StartResult{
		DownloadID: dl.ID,
		Candidates: candidates,
		AutoPicked: s.manager.AutoPickable(dl, candidates),
	}

	s.emit(events.DownloadsChanged)

	return result, nil
}

// ensureRequest resolves or creates the durable Request an anchored
// manual download should be attached to.  Free-text downloads (no
// MBID) have nothing stable to attach to and are left alone.
//
// AddRequest already treats "asking twice" as one request and never
// resets backoff or un-pauses a paused request on conflict, so a
// manual download on something already paused still runs its one
// interactive attempt now without disturbing the request's state.
func (s *Service) ensureRequest(d Download) (int64, bool) {
	var (
		entity Entity
		mbid   string
	)

	switch {
	case d.ReleaseMBID != "":
		entity, mbid = EntityRelease, d.ReleaseMBID
	case d.ReleaseGroupMBID != "":
		entity, mbid = EntityReleaseGroup, d.ReleaseGroupMBID
	case d.RecordingMBID != "":
		entity, mbid = EntityRecording, d.RecordingMBID
	default:
		return 0, false
	}

	id, err := s.store.AddRequest(context.Background(), Request{
		MBID:      mbid,
		Entity:    entity,
		LibraryID: d.LibraryID,
		Artist:    d.Artist,
		Title:     d.Album,
	})
	if err != nil {
		s.logger.Warn("could not attach request to manual download", "error", err)

		return 0, false
	}

	return id, true
}

// Pick starts the transfer for the candidate the user chose.
func (s *Service) Pick(downloadID, candidateID string) error {
	if err := s.manager.Pick(
		context.Background(), downloadID, candidateID,
	); err != nil {
		return err
	}

	s.emit(events.DownloadsChanged)

	return nil
}

// Cancel aborts a live download.
func (s *Service) Cancel(downloadID string) error {
	if err := s.manager.Cancel(context.Background(), downloadID); err != nil {
		return err
	}

	s.emit(events.DownloadsChanged)

	return nil
}

// Candidates returns the ranked candidates of a live download, so the
// picker can be reopened without searching again.
func (s *Service) Candidates(downloadID string) []Candidate {
	return s.manager.Candidates(downloadID)
}

// DownloadView is one row of the downloads list.
//
// would stop reading as "one row of the Downloads list" the moment this
// package also has a Requests list — see RequestInput/Request nearby.
//
//nolint:revive // stutters as download.DownloadView, but a bare "View"
type DownloadView struct {
	Download

	State State          `json:"state"`
	Error string         `json:"error,omitempty"`
	Items []DownloadItem `json:"items"`
}

// ListDownloads returns recent downloads, newest first.
func (s *Service) ListDownloads(limit int) ([]DownloadView, error) {
	const defaultLimit = 50

	if limit <= 0 {
		limit = defaultLimit
	}

	ctx := context.Background()

	downloads, err := s.store.ListDownloads(ctx, limit)
	if err != nil {
		return nil, err
	}

	out := make([]DownloadView, 0, len(downloads))

	for _, d := range downloads {
		state, errText, err := s.store.GetDownloadState(ctx, d.ID)
		if err != nil {
			return nil, err
		}

		items, err := s.store.ListItemsForDownload(ctx, d.ID)
		if err != nil {
			return nil, err
		}

		out = append(out, DownloadView{
			Download: d,
			State:    state,
			Error:    errText,
			Items:    items,
		})
	}

	return out, nil
}

// ClearFinished removes terminal downloads from the list.
func (s *Service) ClearFinished() error {
	if err := s.store.ClearFinished(context.Background()); err != nil {
		return err
	}

	s.emit(events.DownloadsChanged)

	return nil
}

// ---------------------------------------------------------------------------
// Request list
// ---------------------------------------------------------------------------

// SetReconciler wires the request-list loop.  Optional: without it the
// request list still stores and lists requests, it just never acts on
// them.
//
//wails:ignore // internal wiring, not part of the app's IPC surface.
func (s *Service) SetReconciler(r *Reconciler) {
	s.reconciler = r
}

// RequestInput is what the frontend submits to request something.  It
// is one MBID and the type of thing it names, because that is
// genuinely all a durable request is.
type RequestInput struct {
	MBID      string `json:"mbid"`
	Entity    string `json:"entity"`
	LibraryID int64  `json:"libraryId"`

	// Artist and Title are display text only, and optional: the
	// reconciler fills them in from the catalog when the caller has
	// nothing but an MBID.
	Artist string `json:"artist"`
	Title  string `json:"title"`

	// Scope and Secondary apply to artist requests.
	Scope     string `json:"scope"`
	Secondary bool   `json:"secondary"`
}

// AddRequest puts something on the request list and asks for a
// reconcile pass, so the user sees something happen rather than
// waiting six hours for the next scheduled one.
func (s *Service) AddRequest(req RequestInput) (int64, error) {
	if req.LibraryID <= 0 {
		return 0, ErrNoLibrary
	}

	entity := Entity(req.Entity)
	if !entity.Valid() {
		return 0, fmt.Errorf("%w: entity %q", ErrUnsupported, req.Entity)
	}

	scope := RequestScope(req.Scope)
	if scope != ScopeAll {
		scope = ScopeFuture
	}

	id, err := s.store.AddRequest(context.Background(), Request{
		MBID:      req.MBID,
		Entity:    entity,
		LibraryID: req.LibraryID,
		Artist:    req.Artist,
		Title:     req.Title,
		Scope:     scope,
		Secondary: req.Secondary,
	})
	if err != nil {
		return 0, err
	}

	s.emit(events.RequestsChanged)

	if s.reconciler != nil {
		s.reconciler.Trigger()
	}

	return id, nil
}

// ListRequests returns the whole durable request list.
func (s *Service) ListRequests() ([]Request, error) {
	return s.store.ListRequests(context.Background())
}

// IsRequested answers the Explore pages' question — should this album
// show "want" or "wanted?" — without making them load the whole list.
func (s *Service) IsRequested(mbid string, libraryID int64) (bool, error) {
	_, found, err := s.store.FindRequest(context.Background(), mbid, libraryID)

	return found, err
}

// RemoveRequest takes something off the list.  Removing an artist takes
// its derived albums with it, by cascade; an album the user pinned
// themselves has no parent and survives.
func (s *Service) RemoveRequest(id int64) error {
	ctx := context.Background()

	// Tell any external list first, while the row is still readable.
	s.withdrawExternal(ctx, id)

	if err := s.store.DeleteRequest(ctx, id); err != nil {
		return err
	}

	s.emit(events.RequestsChanged)

	return nil
}

// PauseRequest stops attempts without forgetting the request.
func (s *Service) PauseRequest(id int64, paused bool) error {
	state := RequestStateWanted
	if paused {
		state = RequestStatePaused
	}

	if err := s.store.SetRequestState(
		context.Background(), id, state, "",
	); err != nil {
		return err
	}

	s.emit(events.RequestsChanged)

	return nil
}

// ClearSatisfiedRequests drops everything already owned.
func (s *Service) ClearSatisfiedRequests() error {
	if err := s.store.ClearSatisfiedRequests(context.Background()); err != nil {
		return err
	}

	s.emit(events.RequestsChanged)

	return nil
}

// ReconcileRequests runs a pass now and reports what it did.  This
// backs the "check now" button, so it runs synchronously: the user
// pressed it and is waiting for an answer.
func (s *Service) ReconcileRequests() (Summary, error) {
	if s.reconciler == nil {
		return Summary{}, fmt.Errorf(
			"%w: the request list is not running", ErrUnsupported,
		)
	}

	summary, err := s.reconciler.RunNow(context.Background())
	if err != nil {
		return summary, err
	}

	s.emit(events.RequestsChanged)

	return summary, nil
}

// ImportExternalRequests adopts a provider's own list — "import the
// artists Lidarr is already monitoring".
func (s *Service) ImportExternalRequests(
	providerID int64,
	libraryID int64,
) (int, error) {
	if s.reconciler == nil {
		return 0, fmt.Errorf(
			"%w: the request list is not running", ErrUnsupported,
		)
	}

	n, err := s.reconciler.ImportExternal(
		context.Background(), providerID, libraryID,
	)
	if err != nil {
		return 0, err
	}

	s.emit(events.RequestsChanged)

	return n, nil
}

// withdrawExternal best-effort unmonitors a request in the external
// lists it was pushed to.  Failures are logged and ignored: the user
// asked to remove it from *this* list, and an unreachable Lidarr is not
// a reason to refuse.
func (s *Service) withdrawExternal(ctx context.Context, id int64) {
	r, err := s.store.GetRequest(ctx, id)
	if err != nil || len(r.ExternalIDs) == 0 {
		return
	}

	for key, externalID := range r.ExternalIDs {
		providerID, err := strconv.ParseInt(key, 10, 64)
		if err != nil {
			continue
		}

		l, ok := s.manager.listers()[providerID]
		if !ok {
			continue
		}

		if err := l.RemoveRequest(ctx, externalID); err != nil {
			s.logger.Debug(
				"could not withdraw request from external list",
				"request", id,
				"provider", providerID,
				"error", err,
			)
		}
	}
}

// splitSecrets partitions a submitted settings map into plain values,
// which go in the provider row, and secret values, which go in the
// secret store.  The split is driven by the descriptor so a provider
// declaring a field secret is enough to keep it out of the database.
func splitSecrets(
	desc Descriptor,
	settings map[string]string,
) (plain, secret map[string]string) {
	plain = make(map[string]string, len(settings))
	secret = make(map[string]string)

	secretKeys := make(map[string]bool, len(desc.Fields))

	for _, f := range desc.Fields {
		if f.Secret {
			secretKeys[f.Key] = true
		}
	}

	for k, v := range settings {
		if secretKeys[k] {
			secret[k] = v

			continue
		}

		plain[k] = v
	}

	return plain, secret
}