package library

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

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgtype"
	"github.com/jackc/pgx/v5/pgxpool"

	"git.fabledsword.com/bvandeusen/minstrel/internal/acoustid"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
)

// AcoustID lookup worker (M401 #3921).
//
// A track whose tags carry no recording MBID is invisible to the ListenBrainz
// similarity arm: it is never a seed and never comes back as a result. This
// worker fingerprints such tracks and asks AcoustID which recording they are,
// writing an id only when the answer is unambiguous (D5). The file's own tag
// always outranks it (D4).
//
// It never gates anything else (rule 164). With no key, switched off or
// AcoustID unreachable, it idles and says why through Status; scans and
// playback do not notice.

// acoustIDLookupTick is how often the worker looks for work. A settings save
// starts a pass at once, so this only paces new tracks and retries after an
// outage.
const acoustIDLookupTick = 15 * time.Minute

// acoustIDLookupBatch is how many tracks one query hands the worker.
const acoustIDLookupBatch = 50

// acoustIDLookupConcurrency is how many files are fingerprinted at once. The
// client serialises the requests themselves to AcoustID's rate, so this only
// overlaps fpcalc's decodes; low for the reason the loudness backfill's is.
const acoustIDLookupConcurrency = 2

// acoustIDDurationToleranceSec is how far a recording's MusicBrainz length may
// be from the file's and still count as the same take when telling candidates
// apart. A release's length and a rip's differ by a second or two of
// silence; a radio edit or a live take differs by far more.
const acoustIDDurationToleranceSec = 3

// Lookup states, as migration 0069's CHECK has them.
const (
	lookupMatched   = "matched"
	lookupAmbiguous = "ambiguous"
	lookupNoMatch   = "no_match"
	lookupFailed    = "failed"
)

// recordingLookup is the AcoustID client as the worker uses it.
type recordingLookup interface {
	Lookup(ctx context.Context, apiKey, fingerprint string, durationSec int) ([]acoustid.Candidate, error)
}

// AcoustIDLookupStatus is what the admin card shows about the worker.
type AcoustIDLookupStatus struct {
	Running    bool
	LastPassAt time.Time
	// Problem says why the last pass stopped short, in words for the card:
	// the key was refused, or AcoustID could not be reached. Empty when the
	// last pass ran to the end.
	Problem string
}

// AcoustIDLookupResult tallies one pass.
type AcoustIDLookupResult struct {
	Processed    int
	Matched      int
	Ambiguous    int
	NoMatch      int
	Failed       int
	Inconclusive int // nothing stored; tried again on a later pass
}

func (r *AcoustIDLookupResult) add(state string) {
	r.Processed++
	switch state {
	case lookupMatched:
		r.Matched++
	case lookupAmbiguous:
		r.Ambiguous++
	case lookupNoMatch:
		r.NoMatch++
	case lookupFailed:
		r.Failed++
	default:
		r.Inconclusive++
	}
}

// errPassStopped ends a pass early: every further lookup would fail the same
// way, so asking again would only spend the rate limit.
type errPassStopped struct{ reason string }

func (e errPassStopped) Error() string { return e.reason }

// AcoustIDLookupWorker fills recording MBIDs through AcoustID.
type AcoustIDLookupWorker struct {
	pool     *pgxpool.Pool
	logger   *slog.Logger
	settings *AcoustIDSettingsService
	client   recordingLookup
	tick     time.Duration
	batch    int32
	// fingerprint is a field so an integration test pins which tracks a pass
	// touches, not what fpcalc prints.
	fingerprint func(ctx context.Context, path string) (lookupFingerprint, error)
	kick        chan struct{}

	mu     sync.Mutex
	status AcoustIDLookupStatus
}

// NewAcoustIDLookupWorker builds a worker with the production cadence.
func NewAcoustIDLookupWorker(
	pool *pgxpool.Pool, logger *slog.Logger, settings *AcoustIDSettingsService, client recordingLookup,
) *AcoustIDLookupWorker {
	return &AcoustIDLookupWorker{
		pool:        pool,
		logger:      logger,
		settings:    settings,
		client:      client,
		tick:        acoustIDLookupTick,
		batch:       acoustIDLookupBatch,
		fingerprint: computeLookupFingerprint,
		kick:        make(chan struct{}, 1),
	}
}

// Kick asks for a pass now, for the admin card's "look up now". A pass
// already running absorbs it.
func (w *AcoustIDLookupWorker) Kick() {
	if w == nil {
		return
	}
	select {
	case w.kick <- struct{}{}:
	default:
	}
}

// Settings is the settings service the worker reads, for the admin API. A
// nil worker has none, which serves the defaults.
func (w *AcoustIDLookupWorker) Settings() *AcoustIDSettingsService {
	if w == nil {
		return nil
	}
	return w.settings
}

// Status reports the worker's state for the admin card.
func (w *AcoustIDLookupWorker) Status() AcoustIDLookupStatus {
	if w == nil {
		return AcoustIDLookupStatus{}
	}
	w.mu.Lock()
	defer w.mu.Unlock()
	return w.status
}

// Run blocks until ctx is cancelled: one pass at start, then one per tick, on
// a kick, and after every settings save.
func (w *AcoustIDLookupWorker) Run(ctx context.Context) {
	w.runOnce(ctx)
	t := time.NewTicker(w.tick)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
		case <-w.kick:
		case <-w.settings.Changed():
		}
		w.runOnce(ctx)
	}
}

// runOnce contains a pass so that nothing it does (an error, a panic) can stop
// the next one from starting (rule 157).
func (w *AcoustIDLookupWorker) runOnce(ctx context.Context) {
	w.setStatus(func(s *AcoustIDLookupStatus) { s.Running = true })
	problem := ""
	defer func() {
		if r := recover(); r != nil {
			w.logger.Error("acoustid lookup: pass panicked", "panic", r)
			problem = "The last lookup pass stopped on an internal error; see the server log."
		}
		w.setStatus(func(s *AcoustIDLookupStatus) {
			s.Running, s.LastPassAt, s.Problem = false, time.Now(), problem
		})
	}()
	res, err := w.pass(ctx)
	var stopped errPassStopped
	switch {
	case errors.As(err, &stopped):
		problem = stopped.reason
		w.logger.Warn("acoustid lookup: pass stopped", "reason", stopped.reason, "processed", res.Processed)
	case err != nil && ctx.Err() == nil:
		problem = "The last lookup pass failed; see the server log."
		w.logger.Warn("acoustid lookup: pass failed", "err", err, "processed", res.Processed)
	}
	if res.Processed > 0 {
		w.logger.Info("acoustid lookup: pass complete",
			"processed", res.Processed, "matched", res.Matched, "ambiguous", res.Ambiguous,
			"no_match", res.NoMatch, "failed", res.Failed, "inconclusive", res.Inconclusive)
	}
}

func (w *AcoustIDLookupWorker) setStatus(f func(*AcoustIDLookupStatus)) {
	w.mu.Lock()
	f(&w.status)
	w.mu.Unlock()
}

// pass walks the queue once, keyset-paged on id so it ends even when every
// attempt is inconclusive. Settings are read before every batch, so switching
// the lookup off or changing the threshold applies at the next batch.
func (w *AcoustIDLookupWorker) pass(ctx context.Context) (AcoustIDLookupResult, error) {
	q := dbq.New(w.pool)
	var res AcoustIDLookupResult
	after := pgtype.UUID{Valid: true}
	for {
		if err := ctx.Err(); err != nil {
			return res, err
		}
		cfg := w.settings.Get()
		if !cfg.Ready() {
			return res, nil
		}
		rows, err := q.ListTracksNeedingAcoustIDLookup(ctx, dbq.ListTracksNeedingAcoustIDLookupParams{
			AfterID:    after,
			BatchLimit: w.batch,
		})
		if err != nil {
			return res, fmt.Errorf("list tracks needing a lookup: %w", err)
		}
		if len(rows) == 0 {
			return res, nil
		}
		if err := w.lookupBatch(ctx, cfg, rows, &res); err != nil {
			return res, err
		}
		after = rows[len(rows)-1].ID
	}
}

// lookupBatch looks up one batch, acoustIDLookupConcurrency at a time. The
// first track that stops the pass stops the batch: the tracks already started
// finish, no new ones start.
func (w *AcoustIDLookupWorker) lookupBatch(
	ctx context.Context, cfg AcoustIDSettings, rows []dbq.ListTracksNeedingAcoustIDLookupRow, res *AcoustIDLookupResult,
) error {
	ctx, cancel := context.WithCancelCause(ctx)
	defer cancel(nil)
	var (
		mu  sync.Mutex
		wg  sync.WaitGroup
		sem = make(chan struct{}, acoustIDLookupConcurrency)
	)
	for _, row := range rows {
		if ctx.Err() != nil {
			break
		}
		sem <- struct{}{}
		// The slot may have come free because a lookup just stopped the pass.
		if ctx.Err() != nil {
			<-sem
			break
		}
		wg.Add(1)
		go func(row dbq.ListTracksNeedingAcoustIDLookupRow) {
			defer wg.Done()
			defer func() { <-sem }()
			defer func() {
				if r := recover(); r != nil {
					w.logger.Error("acoustid lookup: track panicked", "path", row.FilePath, "panic", r)
				}
			}()
			state, err := w.lookupTrack(ctx, cfg, row)
			if err != nil {
				cancel(err)
			}
			mu.Lock()
			res.add(state)
			mu.Unlock()
		}(row)
	}
	wg.Wait()
	if cause := context.Cause(ctx); cause != nil && !errors.Is(cause, context.Canceled) {
		return cause
	}
	return nil
}

// lookupTrack fingerprints one file, asks AcoustID and stores the answer. It
// returns the state stored ("" when nothing was), and an errPassStopped when
// no further lookup can succeed this pass.
func (w *AcoustIDLookupWorker) lookupTrack(
	ctx context.Context, cfg AcoustIDSettings, row dbq.ListTracksNeedingAcoustIDLookupRow,
) (string, error) {
	fp, err := w.fingerprint(ctx, row.FilePath)
	if err != nil {
		if isInconclusive(err) {
			return "", nil
		}
		// fpcalc ran and rejected the file: a verdict, settled until it changes.
		return w.store(ctx, row, lookupDecision{state: lookupFailed, detail: err.Error()}), nil
	}
	cands, err := w.client.Lookup(ctx, cfg.APIKey, fp.fingerprint, fp.durationSec)
	switch {
	case err == nil:
	case errors.Is(err, acoustid.ErrInvalidKey):
		return "", errPassStopped{"AcoustID refused the API key. Check it in Settings."}
	case errors.Is(err, acoustid.ErrUnavailable):
		return "", errPassStopped{"AcoustID could not be reached; lookups resume on the next pass."}
	case errors.Is(err, acoustid.ErrInvalidFingerprint):
		return w.store(ctx, row, lookupDecision{state: lookupFailed, detail: err.Error()}), nil
	default:
		// The caller's cancellation, or a request this client built wrongly.
		// Neither is a verdict on the track.
		if ctx.Err() == nil {
			w.logger.Warn("acoustid lookup: lookup failed", "path", row.FilePath, "err", err)
		}
		return "", nil
	}
	return w.store(ctx, row, chooseRecording(cands, cfg.MinScore, row.Title, row.DurationMs)), nil
}

// store records a decision and applies it to tracks.mbid in one transaction,
// so the gauge never shows a match whose id was not written. A failed write
// stores nothing and the track is tried again.
func (w *AcoustIDLookupWorker) store(ctx context.Context, row dbq.ListTracksNeedingAcoustIDLookupRow, d lookupDecision) string {
	err := pgx.BeginFunc(ctx, w.pool, func(tx pgx.Tx) error {
		q := dbq.New(tx)
		params := dbq.RecordAcoustIDLookupParams{
			TrackID: row.ID, State: d.state, Candidates: int32(d.candidates),
		}
		if d.candidates > 0 {
			params.BestScore = &d.bestScore
		}
		if d.recording != "" {
			params.RecordingMbid = &d.recording
		}
		if d.detail != "" {
			params.Detail = &d.detail
		}
		if err := q.RecordAcoustIDLookup(ctx, params); err != nil {
			return err
		}
		if d.state == lookupMatched {
			_, err := q.SetTrackMbidFromAcoustID(ctx, dbq.SetTrackMbidFromAcoustIDParams{ID: row.ID, Mbid: &d.recording})
			return err
		}
		// A re-lookup of changed bytes that no longer matches takes back the
		// id the earlier lookup wrote.
		return q.ClearTrackAcoustIDMbid(ctx, row.ID)
	})
	if err != nil {
		if ctx.Err() == nil {
			w.logger.Warn("acoustid lookup: storing the result failed", "path", row.FilePath, "err", err)
		}
		return ""
	}
	return d.state
}

// lookupDecision is what one lookup settles on.
type lookupDecision struct {
	state      string
	recording  string // set only when matched
	bestScore  float32
	candidates int
	detail     string
}

// chooseRecording applies D5 to AcoustID's candidates (best score first):
// only recordings at or above minScore count, one of them is a match, and
// several are told apart by the track's title and length or not at all. A
// wrong MBID would feed similarity the wrong neighbours, which is worse than
// none, so anything left unresolved is ambiguous and writes nothing.
func chooseRecording(cands []acoustid.Candidate, minScore float32, title string, durationMs int32) lookupDecision {
	d := lookupDecision{candidates: len(cands)}
	if len(cands) > 0 {
		d.bestScore = float32(cands[0].Score)
	}
	var above []acoustid.Candidate
	for _, c := range cands {
		if float32(c.Score) >= minScore {
			above = append(above, c)
		}
	}
	switch len(above) {
	case 0:
		d.state = lookupNoMatch
		return d
	case 1:
		d.state, d.recording = lookupMatched, above[0].ID
		return d
	}
	want := normalizeTitle(title)
	var same []acoustid.Candidate
	for _, c := range above {
		if normalizeTitle(c.Title) == want && sameLength(c.DurationSec, durationMs) {
			same = append(same, c)
		}
	}
	if len(same) == 1 {
		d.state, d.recording = lookupMatched, same[0].ID
		return d
	}
	d.state = lookupAmbiguous
	return d
}

// sameLength reports whether a recording's length (0 when MusicBrainz has
// none) fits the file's. An unknown length on either side tells nothing, so
// it does not rule a candidate out.
func sameLength(recordingSec int, fileMs int32) bool {
	if recordingSec <= 0 || fileMs <= 0 {
		return true
	}
	diff := recordingSec*1000 - int(fileMs)
	return diff <= acoustIDDurationToleranceSec*1000 && diff >= -acoustIDDurationToleranceSec*1000
}

// normalizeTitle compares titles by their letters and digits alone, case
// folded, so "Don't Stop" and "Dont stop" match while "Song (Radio Edit)"
// and "Song" do not.
func normalizeTitle(s string) string {
	var b strings.Builder
	for _, r := range strings.ToLower(s) {
		if unicode.IsLetter(r) || unicode.IsDigit(r) {
			b.WriteRune(r)
		}
	}
	return b.String()
}

// AcoustIDCoverage reports where the library's recording MBIDs came from and
// what the lookups found, for the admin gauge.
func AcoustIDCoverage(ctx context.Context, pool *pgxpool.Pool) (dbq.GetMbidCoverageRow, error) {
	return dbq.New(pool).GetMbidCoverage(ctx)
}