package library

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"sort"
	"strings"
	"time"

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

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

// Duplicate sweep (M400 #3910).
//
// Reads fingerprints, runs them through the matcher and records what it proposes
// in duplicate_groups. It never merges or deletes anything the operator has not
// asked for: a group is a proposal, reviewed in the admin report (#3912).
//
// Blocked on duration, deliberately not on title: the #3885 pair are titled
// "WWW" and "WWW (instrumental)", so a title block would have missed the case
// that started the milestone. Candidates stream in (duration_ms, id) order and
// the grouper holds only a few seconds of durations at a time.

// duplicateCandidatePage is how many candidates one query returns. Each row
// carries a ~4 KB fingerprint, so a page is about 2 MB.
const duplicateCandidatePage = 500

// duplicateSweepTick is how often the worker checks for anything new to sweep.
// With nothing new, a tick is two cheap aggregate queries.
const duplicateSweepTick = time.Hour

// staleDuplicateSweepThreshold is the age past which an in-flight sweep is
// assumed dead — a crash mid-sweep leaves finished_at NULL for ever — and another
// may start. Twice the library scan's threshold, because a sweep compares
// fingerprints across the whole library and can legitimately run long on a big
// one.
const staleDuplicateSweepThreshold = 2 * time.Hour

// duplicateSweepFinishTimeout bounds recording that a sweep ended. It runs on a
// context detached from the sweep's own, so a sweep cancelled at shutdown still
// closes its row rather than leaving it in flight until the reaper.
const duplicateSweepFinishTimeout = 10 * time.Second

// DuplicateSweepResult tallies one sweep.
type DuplicateSweepResult struct {
	Candidates int // tracks with a chromaprint that were streamed
	Groups     int // groups the matcher found
	Proposed   int // written as pending, new or refreshed
	Suppressed int // not proposed: already dismissed or resolved by the operator
	Retired    int // pending proposals this sweep did not find again, removed
	Oversize   int // acoustic clusters too large to propose
}

// RunDuplicateSweep runs one sweep and records it in duplicate_sweeps.
func RunDuplicateSweep(ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger) (DuplicateSweepResult, error) {
	return runDuplicateSweep(ctx, pool, logger, duplicateCandidatePage)
}

func runDuplicateSweep(
	ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger, pageSize int32,
) (DuplicateSweepResult, error) {
	q := dbq.New(pool)
	sweep, err := q.StartDuplicateSweep(ctx)
	if err != nil {
		return DuplicateSweepResult{}, fmt.Errorf("start duplicate sweep: %w", err)
	}

	res, runErr := sweepDuplicates(ctx, q, sweep.ID, pageSize)

	finishCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), duplicateSweepFinishTimeout)
	defer cancel()
	errMsg := ""
	if runErr != nil {
		errMsg = runErr.Error()
	}
	candidates, groups, oversize := int32(res.Candidates), int32(res.Groups), int32(res.Oversize)
	if ferr := q.FinishDuplicateSweep(finishCtx, dbq.FinishDuplicateSweepParams{
		ID: sweep.ID, Candidates: &candidates, GroupsFound: &groups, OversizeClusters: &oversize,
		ErrorMessage: errMsg,
	}); ferr != nil {
		logger.Error("duplicate sweep: recording the end of the sweep failed", "err", ferr)
		if runErr == nil {
			runErr = fmt.Errorf("finish duplicate sweep: %w", ferr)
		}
	}

	logger.Info("duplicate sweep complete",
		"candidates", res.Candidates, "groups", res.Groups, "proposed", res.Proposed,
		"suppressed", res.Suppressed, "retired", res.Retired, "oversize", res.Oversize, "err", runErr)
	return res, runErr
}

func sweepDuplicates(
	ctx context.Context, q *dbq.Queries, sweepID pgtype.UUID, pageSize int32,
) (DuplicateSweepResult, error) {
	var res DuplicateSweepResult

	// Exact tier, library-wide, in one query.
	exactRows, err := q.ListExactDuplicateHashes(ctx, fingerprintVersion)
	if err != nil {
		return res, fmt.Errorf("list exact duplicates: %w", err)
	}
	exactMembers := make([][]string, len(exactRows))
	exactOf := map[string]int{}
	for i, row := range exactRows {
		exactMembers[i] = formatUUIDs(row.TrackIds)
		for _, id := range exactMembers[i] {
			exactOf[id] = i
		}
	}
	exactSeen := make([]bool, len(exactRows))

	// Acoustic tier, streamed in duration order. The first member of an exact
	// group the stream meets stands in for the whole group; the rest are skipped.
	grouper := newStreamGrouper(defaultAcousticMaxBitErrorRate)
	params := dbq.ListDuplicateCandidatesParams{
		CurrentVersion: fingerprintVersion,
		// Durations are never negative, and the all-zero uuid sorts first: every
		// row is after this cursor. Valid must be true, or "> NULL" matches nothing.
		AfterDurationMs: -1,
		AfterID:         pgtype.UUID{Valid: true},
		PageLimit:       pageSize,
	}
	for {
		if err := ctx.Err(); err != nil {
			return res, err
		}
		rows, err := q.ListDuplicateCandidates(ctx, params)
		if err != nil {
			return res, fmt.Errorf("list duplicate candidates: %w", err)
		}
		for _, row := range rows {
			res.Candidates++
			id := syncpkg.FormatUUID(row.ID)
			unit := &groupUnit{ids: []string{id}, durationMs: row.DurationMs, sortKey: id}
			if gi, ok := exactOf[id]; ok {
				if exactSeen[gi] {
					continue
				}
				exactSeen[gi] = true
				unit.ids, unit.exact = exactMembers[gi], true
			}
			unit.print = preparePrint(row.Chromaprint)
			grouper.push(unit)
		}
		if int32(len(rows)) < pageSize {
			break
		}
		last := rows[len(rows)-1]
		params.AfterDurationMs, params.AfterID = last.DurationMs, last.ID
	}

	found := grouper.finish()
	// Exact groups none of whose members has a chromaprint never reached the
	// stream. Identical bytes need no acoustic evidence.
	for gi, seen := range exactSeen {
		if !seen {
			found.Groups = append(found.Groups, duplicateGroup{Tier: tierExact, Members: exactMembers[gi]})
		}
	}
	sortGroups(found.Groups)
	res.Groups, res.Oversize = len(found.Groups), found.OversizeClusters

	dismissed, err := q.ListDismissedDuplicateMemberSets(ctx)
	if err != nil {
		return res, fmt.Errorf("list dismissed duplicate groups: %w", err)
	}
	dismissedSets := make([]map[string]struct{}, 0, len(dismissed))
	for _, d := range dismissed {
		set := map[string]struct{}{}
		for _, id := range formatUUIDs(d.TrackIds) {
			set[id] = struct{}{}
		}
		dismissedSets = append(dismissedSets, set)
	}

	for _, group := range found.Groups {
		if coveredByDismissal(group.Members, dismissedSets) {
			res.Suppressed++
			continue
		}
		up := dbq.UpsertDuplicateGroupParams{
			MemberKey: strings.Join(group.Members, ","),
			Tier:      string(group.Tier),
			SweepID:   sweepID,
		}
		if group.Tier == tierAcoustic {
			worst := float32(group.WorstBitErrorRate)
			up.WorstBitErrorRate = &worst
		}
		groupID, err := q.UpsertDuplicateGroup(ctx, up)
		if errors.Is(err, pgx.ErrNoRows) {
			// This exact member set was already dismissed or merged.
			res.Suppressed++
			continue
		}
		if err != nil {
			return res, fmt.Errorf("upsert duplicate group: %w", err)
		}
		for _, id := range group.Members {
			var trackID pgtype.UUID
			if err := trackID.Scan(id); err != nil {
				return res, fmt.Errorf("parse track id %q: %w", id, err)
			}
			if err := q.AddDuplicateGroupMember(ctx, dbq.AddDuplicateGroupMemberParams{
				GroupID: groupID, TrackID: trackID,
			}); err != nil {
				return res, fmt.Errorf("add duplicate group member: %w", err)
			}
		}
		res.Proposed++
	}

	// Only after a complete sweep: a sweep that failed partway has no basis for
	// concluding that anything it did not reach has gone.
	retired, err := q.DeleteStalePendingDuplicateGroups(ctx, sweepID)
	if err != nil {
		return res, fmt.Errorf("retire stale duplicate groups: %w", err)
	}
	res.Retired = int(retired)
	return res, nil
}

// coveredByDismissal reports whether every member of a proposal sat together in
// one group the operator dismissed. A subset counts: dismissing {A, B, C} said
// none of them are copies of each other, so proposing {A, B} again would be
// asking the same question twice. A superset does not count: a new copy joining
// is new evidence, and worth asking about.
func coveredByDismissal(members []string, dismissed []map[string]struct{}) bool {
	for _, set := range dismissed {
		covered := true
		for _, id := range members {
			if _, ok := set[id]; !ok {
				covered = false
				break
			}
		}
		if covered {
			return true
		}
	}
	return false
}

func formatUUIDs(ids []pgtype.UUID) []string {
	out := make([]string, len(ids))
	for i, id := range ids {
		out[i] = syncpkg.FormatUUID(id)
	}
	sort.Strings(out)
	return out
}

// TryStartDuplicateSweep starts a sweep in the background unless one is already
// running, reaping a sweep that has been in flight past
// staleDuplicateSweepThreshold. Mirrors TryStartScan. The sweep runs on ctx, so
// a caller answering an HTTP request must pass a context that outlives it.
func TryStartDuplicateSweep(ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger) (bool, error) {
	q := dbq.New(pool)
	row, err := q.GetInFlightDuplicateSweep(ctx)
	switch {
	case err == nil:
		age := time.Since(row.StartedAt.Time)
		if age <= staleDuplicateSweepThreshold {
			return false, nil
		}
		logger.Warn("reaping stale duplicate sweep", "id", syncpkg.FormatUUID(row.ID), "age", age)
		if ferr := q.FinishDuplicateSweep(ctx, dbq.FinishDuplicateSweepParams{
			ID: row.ID, ErrorMessage: "reaped (stale)",
		}); ferr != nil {
			return false, fmt.Errorf("reap stale duplicate sweep: %w", ferr)
		}
	case !errors.Is(err, pgx.ErrNoRows):
		return false, fmt.Errorf("duplicate sweep in-flight check: %w", err)
	}

	go func() {
		if _, err := RunDuplicateSweep(ctx, pool, logger); err != nil {
			logger.Warn("duplicate sweep failed", "err", err)
		}
	}()
	return true, nil
}

// DuplicateSweepWorker sweeps whenever fingerprints have changed.
type DuplicateSweepWorker struct {
	pool   *pgxpool.Pool
	logger *slog.Logger
	tick   time.Duration
}

// NewDuplicateSweepWorker builds a worker with the production cadence.
func NewDuplicateSweepWorker(pool *pgxpool.Pool, logger *slog.Logger) *DuplicateSweepWorker {
	return &DuplicateSweepWorker{pool: pool, logger: logger, tick: duplicateSweepTick}
}

// Run blocks until ctx is cancelled, checking once at start and then each tick.
func (w *DuplicateSweepWorker) Run(ctx context.Context) {
	w.tickOnce(ctx)
	t := time.NewTicker(w.tick)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			w.tickOnce(ctx)
		}
	}
}

// tickOnce contains one check so nothing it does can stop the next tick (rule 157).
func (w *DuplicateSweepWorker) tickOnce(ctx context.Context) {
	defer func() {
		if r := recover(); r != nil {
			w.logger.Error("duplicate sweep: tick panicked", "panic", r)
		}
	}()
	due, err := duplicateSweepDue(ctx, dbq.New(w.pool))
	if err != nil {
		if ctx.Err() == nil {
			w.logger.Warn("duplicate sweep: due check failed", "err", err)
		}
		return
	}
	if !due {
		return
	}
	if _, err := TryStartDuplicateSweep(ctx, w.pool, w.logger); err != nil {
		w.logger.Warn("duplicate sweep: start failed", "err", err)
	}
}

// duplicateSweepDue reports whether any fingerprint was written after the latest
// sweep started. Fingerprints are the sweep's only input, so nothing else can
// change its answer; while the backfill is running this is true every tick.
func duplicateSweepDue(ctx context.Context, q *dbq.Queries) (bool, error) {
	latest, err := q.GetLatestFingerprintComputedAt(ctx)
	if err != nil {
		return false, fmt.Errorf("latest fingerprint: %w", err)
	}
	if !latest.Valid {
		return false, nil // nothing fingerprinted yet
	}
	last, err := q.GetLatestDuplicateSweep(ctx)
	if errors.Is(err, pgx.ErrNoRows) {
		return true, nil
	}
	if err != nil {
		return false, fmt.Errorf("latest duplicate sweep: %w", err)
	}
	return latest.Time.After(last.StartedAt.Time), nil
}