// Package playevents owns the four write paths into play_events / skip_events:
// RecordPlayStarted, RecordPlayEnded, RecordPlaySkipped, and
// RecordSyntheticCompletedPlay (used by the Subsonic /rest/scrobble shim).
//
// All paths run inside a single transaction. The auto-close-prior step on
// RecordPlayStarted bounds each user to at most one open play_event at any
// time (per spec data-flow section).
package playevents

import (
	"context"
	"encoding/json"
	"errors"
	"log/slog"
	"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"
	"git.fabledsword.com/bvandeusen/minstrel/internal/playsessions"
	"git.fabledsword.com/bvandeusen/minstrel/internal/recommendation"
	"git.fabledsword.com/bvandeusen/minstrel/internal/scrobble"
)

type Writer struct {
	pool                    *pgxpool.Pool
	logger                  *slog.Logger
	sessionTimeout          time.Duration
	skipMaxCompletionRatio  float64
	skipMaxDurationPlayedMs int32
}

// NewWriter constructs a writer. timeout is the play-session window; the two
// remaining args are the skip rule thresholds from spec §6.
func NewWriter(
	pool *pgxpool.Pool,
	logger *slog.Logger,
	sessionTimeout time.Duration,
	skipMaxCompletionRatio float64,
	skipMaxDurationPlayedMs int,
) *Writer {
	return &Writer{
		pool:                    pool,
		logger:                  logger,
		sessionTimeout:          sessionTimeout,
		skipMaxCompletionRatio:  skipMaxCompletionRatio,
		skipMaxDurationPlayedMs: int32(skipMaxDurationPlayedMs),
	}
}

type StartedResult struct {
	PlayEventID pgtype.UUID
	SessionID   pgtype.UUID
}

// RecordPlayStarted: in one transaction, auto-close any prior open row for
// the user, FindOrCreate the play_session, insert the new play_event,
// return its id and session id.
func (w *Writer) RecordPlayStarted(
	ctx context.Context,
	userID, trackID pgtype.UUID,
	clientID string,
	at time.Time,
) (StartedResult, error) {
	var out StartedResult
	err := pgx.BeginFunc(ctx, w.pool, func(tx pgx.Tx) error {
		q := dbq.New(tx)
		if err := w.autoClosePriorOpen(ctx, q, userID, at); err != nil {
			return err
		}
		sessionID, err := playsessions.FindOrCreate(ctx, q, userID, at, clientID, w.sessionTimeout)
		if err != nil {
			return err
		}
		var clientIDPtr *string
		if clientID != "" {
			clientIDPtr = &clientID
		}
		ev, err := q.InsertPlayEvent(ctx, dbq.InsertPlayEventParams{
			UserID:    userID,
			TrackID:   trackID,
			SessionID: sessionID,
			StartedAt: pgtype.Timestamptz{Time: at, Valid: true},
			ClientID:  clientIDPtr,
		})
		if err != nil {
			return err
		}
		out.PlayEventID = ev.ID
		out.SessionID = sessionID

		// Capture session vector for the just-inserted row.
		if err := w.captureSessionVector(ctx, q, ev.ID, sessionID, at); err != nil {
			return err
		}
		return nil
	})
	return out, err
}

// RecordPlayEnded closes a play_event with duration + computed completion
// ratio. Applies the spec §6 skip rule (AND of completion < threshold AND
// duration_played < threshold) — both conditions must hold for the row to
// be marked was_skipped=true. If skipped, also writes a skip_events row.
func (w *Writer) RecordPlayEnded(
	ctx context.Context,
	playEventID pgtype.UUID,
	durationPlayedMs int32,
	at time.Time,
) error {
	if err := pgx.BeginFunc(ctx, w.pool, func(tx pgx.Tx) error {
		q := dbq.New(tx)
		ev, err := q.GetPlayEventByID(ctx, playEventID)
		if err != nil {
			return err
		}
		track, err := q.GetTrackByID(ctx, ev.TrackID)
		if err != nil {
			return err
		}
		ratio := 0.0
		if track.DurationMs > 0 {
			ratio = float64(durationPlayedMs) / float64(track.DurationMs)
		}
		isSkip := ratio < w.skipMaxCompletionRatio && durationPlayedMs < w.skipMaxDurationPlayedMs
		ratioPtr := ratio
		durPtr := durationPlayedMs
		if _, err := q.UpdatePlayEventEnded(ctx, dbq.UpdatePlayEventEndedParams{
			ID:               playEventID,
			EndedAt:          pgtype.Timestamptz{Time: at, Valid: true},
			DurationPlayedMs: &durPtr,
			CompletionRatio:  &ratioPtr,
			WasSkipped:       isSkip,
		}); err != nil {
			return err
		}
		if isSkip {
			if _, err := q.InsertSkipEvent(ctx, dbq.InsertSkipEventParams{
				UserID:     ev.UserID,
				TrackID:    ev.TrackID,
				SessionID:  ev.SessionID,
				SkippedAt:  pgtype.Timestamptz{Time: at, Valid: true},
				PositionMs: durationPlayedMs,
			}); err != nil {
				return err
			}
		}
		return nil
	}); err != nil {
		return err
	}
	// Post-commit best-effort scrobble enqueue. Errors logged + swallowed:
	// scrobble delivery is enrichment, not a precondition for canonical play
	// history.
	if err := scrobble.MaybeEnqueue(ctx, dbq.New(w.pool), playEventID); err != nil {
		w.logger.Warn("playevents: scrobble enqueue failed", "play_event_id", playEventID, "err", err)
	}
	return nil
}

// RecordPlaySkipped is the user-initiated-skip variant: was_skipped is forced
// true regardless of the rule, and a skip_events row is always written.
func (w *Writer) RecordPlaySkipped(
	ctx context.Context,
	playEventID pgtype.UUID,
	positionMs int32,
	at time.Time,
) error {
	return pgx.BeginFunc(ctx, w.pool, func(tx pgx.Tx) error {
		q := dbq.New(tx)
		ev, err := q.GetPlayEventByID(ctx, playEventID)
		if err != nil {
			return err
		}
		track, err := q.GetTrackByID(ctx, ev.TrackID)
		if err != nil {
			return err
		}
		ratio := 0.0
		if track.DurationMs > 0 {
			ratio = float64(positionMs) / float64(track.DurationMs)
		}
		ratioPtr := ratio
		durPtr := positionMs
		if _, err := q.UpdatePlayEventEnded(ctx, dbq.UpdatePlayEventEndedParams{
			ID:               playEventID,
			EndedAt:          pgtype.Timestamptz{Time: at, Valid: true},
			DurationPlayedMs: &durPtr,
			CompletionRatio:  &ratioPtr,
			WasSkipped:       true,
		}); err != nil {
			return err
		}
		_, err = q.InsertSkipEvent(ctx, dbq.InsertSkipEventParams{
			UserID:     ev.UserID,
			TrackID:    ev.TrackID,
			SessionID:  ev.SessionID,
			SkippedAt:  pgtype.Timestamptz{Time: at, Valid: true},
			PositionMs: positionMs,
		})
		return err
	})
}

// RecordSyntheticCompletedPlay writes a start+end pair for a Subsonic
// scrobble?submission=true call. ended_at = at + track.duration_ms,
// duration_played_ms = track.duration_ms, was_skipped = false.
func (w *Writer) RecordSyntheticCompletedPlay(
	ctx context.Context,
	userID, trackID pgtype.UUID,
	clientID string,
	at time.Time,
) error {
	var playEventID pgtype.UUID
	if err := pgx.BeginFunc(ctx, w.pool, func(tx pgx.Tx) error {
		q := dbq.New(tx)
		track, err := q.GetTrackByID(ctx, trackID)
		if err != nil {
			return err
		}
		if err := w.autoClosePriorOpen(ctx, q, userID, at); err != nil {
			return err
		}
		sessionID, err := playsessions.FindOrCreate(ctx, q, userID, at, clientID, w.sessionTimeout)
		if err != nil {
			return err
		}
		var clientIDPtr *string
		if clientID != "" {
			clientIDPtr = &clientID
		}
		ev, err := q.InsertPlayEvent(ctx, dbq.InsertPlayEventParams{
			UserID:    userID,
			TrackID:   trackID,
			SessionID: sessionID,
			StartedAt: pgtype.Timestamptz{Time: at, Valid: true},
			ClientID:  clientIDPtr,
		})
		if err != nil {
			return err
		}
		playEventID = ev.ID
		if err := w.captureSessionVector(ctx, q, ev.ID, sessionID, at); err != nil {
			return err
		}
		ratio := 1.0
		dur := track.DurationMs
		_, err = q.UpdatePlayEventEnded(ctx, dbq.UpdatePlayEventEndedParams{
			ID:               ev.ID,
			EndedAt:          pgtype.Timestamptz{Time: at.Add(time.Duration(track.DurationMs) * time.Millisecond), Valid: true},
			DurationPlayedMs: &dur,
			CompletionRatio:  &ratio,
			WasSkipped:       false,
		})
		return err
	}); err != nil {
		return err
	}
	// Post-commit best-effort scrobble enqueue. Errors logged + swallowed:
	// scrobble delivery is enrichment, not a precondition for canonical play
	// history.
	if err := scrobble.MaybeEnqueue(ctx, dbq.New(w.pool), playEventID); err != nil {
		w.logger.Warn("playevents: scrobble enqueue failed", "play_event_id", playEventID, "err", err)
	}
	return nil
}

// captureSessionVector queries the user's prior plays in the given session
// (before `at`), builds the session vector, and UPDATEs the just-inserted
// play_event with it. Runs inside the caller's transaction (q is the
// transaction-bound *dbq.Queries). Errors here propagate — vector capture
// is best-effort, but DB errors should fail the transaction.
func (w *Writer) captureSessionVector(
	ctx context.Context,
	q *dbq.Queries,
	playEventID, sessionID pgtype.UUID,
	at time.Time,
) error {
	priorTracks, err := q.ListRecentSessionTracks(ctx, dbq.ListRecentSessionTracksParams{
		SessionID: sessionID,
		StartedAt: pgtype.Timestamptz{Time: at, Valid: true},
		Limit:     5,
	})
	if err != nil {
		return err
	}
	vec := recommendation.BuildSessionVector(priorTracks)
	vecJSON, err := json.Marshal(vec)
	if err != nil {
		return err
	}
	return q.UpdatePlayEventVector(ctx, dbq.UpdatePlayEventVectorParams{
		ID:                  playEventID,
		SessionVectorAtPlay: vecJSON,
	})
}

// autoClosePriorOpen closes any open (ended_at IS NULL) play_event for the
// user. Sets ended_at = at, duration_played_ms = min(at - started_at, track
// duration), was_skipped = true. Skip rule is NOT applied — auto-closed
// rows are flagged skipped regardless because we don't know what the user
// actually heard.
func (w *Writer) autoClosePriorOpen(
	ctx context.Context,
	q *dbq.Queries,
	userID pgtype.UUID,
	at time.Time,
) error {
	prior, err := q.GetOpenPlayEventForUser(ctx, userID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil
		}
		return err
	}
	track, err := q.GetTrackByID(ctx, prior.TrackID)
	if err != nil {
		return err
	}
	elapsedMs := int32(at.Sub(prior.StartedAt.Time) / time.Millisecond)
	if elapsedMs < 0 {
		elapsedMs = 0
	}
	if elapsedMs > track.DurationMs && track.DurationMs > 0 {
		elapsedMs = track.DurationMs
	}
	ratio := 0.0
	if track.DurationMs > 0 {
		ratio = float64(elapsedMs) / float64(track.DurationMs)
	}
	ratioPtr := ratio
	durPtr := elapsedMs
	if _, err := q.UpdatePlayEventEnded(ctx, dbq.UpdatePlayEventEndedParams{
		ID:               prior.ID,
		EndedAt:          pgtype.Timestamptz{Time: at, Valid: true},
		DurationPlayedMs: &durPtr,
		CompletionRatio:  &ratioPtr,
		WasSkipped:       true,
	}); err != nil {
		return err
	}
	w.logger.Info("playevents: auto-closed prior open row",
		"play_event_id", prior.ID, "elapsed_ms", elapsedMs)
	return nil
}