package social

import (
	"context"
	"fmt"
	"time"

	"github.com/google/uuid"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
)

// MarkRead clears viewerID's unread bit on every chat entry of the game they have not
// yet read — the acknowledgement the client sends when the player opens the move
// history (or the chat). For each entry that flips to read it records the
// publish-to-read latency. It returns the number of entries marked, and is a harmless
// no-op (zero) when the viewer holds no seat or has nothing unread, so the caller may
// invoke it without first checking participation.
func (svc *Service) MarkRead(ctx context.Context, gameID, viewerID uuid.UUID) (int, error) {
	ctx, span := svc.tracer.Start(ctx, "social.MarkRead",
		trace.WithAttributes(attribute.String("game.id", gameID.String())))
	defer span.End()
	marks, err := svc.store.markRead(ctx, gameID, viewerID)
	if err != nil {
		span.RecordError(err)
		return 0, err
	}
	now := svc.now()
	for _, m := range marks {
		svc.metrics.recordRead(ctx, m.kind, now.Sub(m.createdAt))
	}
	span.SetAttributes(attribute.Int("marked.count", len(marks)))
	return len(marks), nil
}

// ClearNudges marks accountID's pending nudges in the game read once they have acted
// (taken their move): a nudge answered by moving stops counting as unread. It records
// the publish-to-read latency for each nudge it clears. It satisfies game.NudgeClearer
// and is wired into the move path; failures are the caller's to log (the move has
// already committed).
func (svc *Service) ClearNudges(ctx context.Context, gameID, accountID uuid.UUID) error {
	ctx, span := svc.tracer.Start(ctx, "social.ClearNudges",
		trace.WithAttributes(attribute.String("game.id", gameID.String())))
	defer span.End()
	times, err := svc.store.clearNudges(ctx, gameID, accountID)
	if err != nil {
		span.RecordError(err)
		return err
	}
	now := svc.now()
	for _, t := range times {
		svc.metrics.recordRead(ctx, kindNudge, now.Sub(t))
	}
	span.SetAttributes(attribute.Int("marked.count", len(times)))
	return nil
}

// UnreadGames returns the set of games in which viewerID has at least one unread chat
// entry, for seeding the lobby's per-card unread badge in a single query.
func (svc *Service) UnreadGames(ctx context.Context, viewerID uuid.UUID) (map[uuid.UUID]bool, error) {
	return svc.store.unreadGames(ctx, viewerID)
}

// HasUnread reports whether viewerID has any unread chat entry in the game, for the
// per-game unread flag of a single game's state and move-result views.
func (svc *Service) HasUnread(ctx context.Context, gameID, viewerID uuid.UUID) (bool, error) {
	return svc.store.hasUnread(ctx, gameID, viewerID)
}

// readMark is one chat entry that flipped from unread to read, carrying what the
// publish-to-read latency metric needs.
type readMark struct {
	kind      string
	createdAt time.Time
}

// markRead clears the viewer's seat bit on the game's entries still unread by them,
// resolving the seat through the game_players join, and returns the cleared entries.
// The bitwise terms are cast through int4 so the operators resolve unambiguously.
func (s *Store) markRead(ctx context.Context, gameID, viewerID uuid.UUID) ([]readMark, error) {
	const q = `UPDATE backend.chat_messages m
SET unread_seats = (m.unread_seats::int & ~(1 << p.seat::int))::smallint
FROM backend.game_players p
WHERE p.game_id = m.game_id AND p.account_id = $2
  AND m.game_id = $1 AND (m.unread_seats::int & (1 << p.seat::int)) <> 0
RETURNING m.kind, m.created_at`
	rows, err := s.db.QueryContext(ctx, q, gameID, viewerID)
	if err != nil {
		return nil, fmt.Errorf("social: mark read: %w", err)
	}
	defer rows.Close()
	var out []readMark
	for rows.Next() {
		var m readMark
		if err := rows.Scan(&m.kind, &m.createdAt); err != nil {
			return nil, fmt.Errorf("social: scan mark read: %w", err)
		}
		out = append(out, m)
	}
	return out, rows.Err()
}

// clearNudges clears the actor's seat bit on the game's still-unread nudges and returns
// their post times (for the latency metric).
func (s *Store) clearNudges(ctx context.Context, gameID, accountID uuid.UUID) ([]time.Time, error) {
	const q = `UPDATE backend.chat_messages m
SET unread_seats = (m.unread_seats::int & ~(1 << p.seat::int))::smallint
FROM backend.game_players p
WHERE p.game_id = m.game_id AND p.account_id = $2
  AND m.game_id = $1 AND m.kind = 'nudge' AND (m.unread_seats::int & (1 << p.seat::int)) <> 0
RETURNING m.created_at`
	rows, err := s.db.QueryContext(ctx, q, gameID, accountID)
	if err != nil {
		return nil, fmt.Errorf("social: clear nudges: %w", err)
	}
	defer rows.Close()
	var out []time.Time
	for rows.Next() {
		var t time.Time
		if err := rows.Scan(&t); err != nil {
			return nil, fmt.Errorf("social: scan clear nudges: %w", err)
		}
		out = append(out, t)
	}
	return out, rows.Err()
}

// unreadGames returns the games where viewerID has an unread entry, resolving their
// seat per game through the game_players join.
func (s *Store) unreadGames(ctx context.Context, viewerID uuid.UUID) (map[uuid.UUID]bool, error) {
	const q = `SELECT DISTINCT m.game_id
FROM backend.chat_messages m
JOIN backend.game_players p ON p.game_id = m.game_id AND p.account_id = $1
WHERE m.unread_seats <> 0 AND (m.unread_seats::int & (1 << p.seat::int)) <> 0`
	rows, err := s.db.QueryContext(ctx, q, viewerID)
	if err != nil {
		return nil, fmt.Errorf("social: unread games: %w", err)
	}
	defer rows.Close()
	out := make(map[uuid.UUID]bool)
	for rows.Next() {
		var id uuid.UUID
		if err := rows.Scan(&id); err != nil {
			return nil, fmt.Errorf("social: scan unread games: %w", err)
		}
		out[id] = true
	}
	return out, rows.Err()
}

// hasUnread reports whether viewerID has an unread entry in the one game.
func (s *Store) hasUnread(ctx context.Context, gameID, viewerID uuid.UUID) (bool, error) {
	const q = `SELECT EXISTS(
  SELECT 1 FROM backend.chat_messages m
  JOIN backend.game_players p ON p.game_id = m.game_id AND p.account_id = $2
  WHERE m.game_id = $1 AND (m.unread_seats::int & (1 << p.seat::int)) <> 0)`
	var ok bool
	if err := s.db.QueryRowContext(ctx, q, gameID, viewerID).Scan(&ok); err != nil {
		return false, fmt.Errorf("social: has unread: %w", err)
	}
	return ok, nil
}

// countUnread counts the chat entries with at least one recipient seat still unread,
// for the chat_unread_messages gauge.
func (s *Store) countUnread(ctx context.Context) (int64, error) {
	var n int64
	if err := s.db.QueryRowContext(ctx,
		`SELECT count(*) FROM backend.chat_messages WHERE unread_seats <> 0`).Scan(&n); err != nil {
		return 0, fmt.Errorf("social: count unread: %w", err)
	}
	return n, nil
}