package repository

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/prabhupadasays/spsays-bff/internal/model"
)

var (
	// ErrNotParticipant is the authorization failure for every chat read and
	// write: if you are not in the thread, it does not exist for you.
	ErrNotParticipant   = errors.New("not a participant in this conversation")
	ErrConversationGone = errors.New("conversation not found")
	// ErrReplyTargetNotHere guards against replying to a message from another
	// thread. The foreign key only proves the target exists somewhere, so
	// without this check a client could quote a conversation it was never in.
	ErrReplyTargetNotHere = errors.New("cannot reply to a message from another conversation")
	ErrAttachmentGone     = errors.New("attachment not found")
	ErrMessageNotHere     = errors.New("message is not in this conversation")
	ErrUserGone           = errors.New("user not found")
)

type ChatRepo struct{ pg *Postgres }

func NewChatRepo(pg *Postgres) *ChatRepo { return &ChatRepo{pg: pg} }

// dmKey builds the sorted pair key that makes "one DM thread per pair" a
// database guarantee rather than a service-layer race.
func dmKey(a, b string) string {
	if a < b {
		return a + ":" + b
	}
	return b + ":" + a
}

// EnsureDM returns the DM between two users, creating it if absent.
//
// Idempotent under concurrency: two people tapping "message" simultaneously
// race on the partial unique index, and the loser falls through to the SELECT
// rather than erroring or creating a second thread.
func (r *ChatRepo) EnsureDM(ctx context.Context, userA, userB string) (*model.Conversation, error) {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return nil, fmt.Errorf("begin dm tx: %w", err)
	}
	defer tx.Rollback(ctx) //nolint:errcheck // no-op once committed

	key := dmKey(userA, userB)
	var c model.Conversation
	err = tx.QueryRow(ctx, `
		INSERT INTO conversations (kind, dm_key, created_by)
		VALUES ('dm', $1, $2)
		ON CONFLICT (dm_key) WHERE kind = 'dm' DO NOTHING
		RETURNING id, kind, title, avatar_key, send_policy, last_seq, last_message_at, created_at`,
		key, userA,
	).Scan(&c.ID, &c.Kind, &c.Title, &c.AvatarKey, &c.SendPolicy, &c.LastSeq, &c.LastMessageAt, &c.CreatedAt)

	if errors.Is(err, pgx.ErrNoRows) {
		// Already existed — read it back.
		err = tx.QueryRow(ctx, `
			SELECT id, kind, title, avatar_key, send_policy, last_seq, last_message_at, created_at
			FROM conversations WHERE dm_key = $1 AND kind = 'dm'`, key,
		).Scan(&c.ID, &c.Kind, &c.Title, &c.AvatarKey, &c.SendPolicy, &c.LastSeq, &c.LastMessageAt, &c.CreatedAt)
	}
	if err != nil {
		return nil, fmt.Errorf("ensure dm: %w", err)
	}

	// Participants are inserted unconditionally: a thread created moments ago
	// by the other party may not list us yet.
	if _, err := tx.Exec(ctx, `
		INSERT INTO conversation_participants (conversation_id, user_id)
		VALUES ($1, $2), ($1, $3)
		ON CONFLICT (conversation_id, user_id) DO NOTHING`,
		c.ID, userA, userB,
	); err != nil {
		return nil, fmt.Errorf("ensure dm participants: %w", err)
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, fmt.Errorf("commit dm: %w", err)
	}
	return &c, nil
}

// CreateGroup opens a group thread with creator as owner and members joined.
func (r *ChatRepo) CreateGroup(ctx context.Context, creatorID, title string, memberIDs []string) (*model.Conversation, error) {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return nil, fmt.Errorf("begin group tx: %w", err)
	}
	defer tx.Rollback(ctx) //nolint:errcheck

	var c model.Conversation
	if err := tx.QueryRow(ctx, `
		INSERT INTO conversations (kind, title, created_by)
		VALUES ('group', $1, $2)
		RETURNING id, kind, title, avatar_key, send_policy, last_seq, last_message_at, created_at`,
		title, creatorID,
	).Scan(&c.ID, &c.Kind, &c.Title, &c.AvatarKey, &c.SendPolicy, &c.LastSeq, &c.LastMessageAt, &c.CreatedAt); err != nil {
		return nil, fmt.Errorf("create group: %w", err)
	}

	if _, err := tx.Exec(ctx, `
		INSERT INTO conversation_participants (conversation_id, user_id, role)
		VALUES ($1, $2, 'owner') ON CONFLICT DO NOTHING`, c.ID, creatorID,
	); err != nil {
		return nil, fmt.Errorf("add group owner: %w", err)
	}
	for _, m := range memberIDs {
		if m == creatorID {
			continue
		}
		if _, err := tx.Exec(ctx, `
			INSERT INTO conversation_participants (conversation_id, user_id)
			VALUES ($1, $2) ON CONFLICT DO NOTHING`, c.ID, m,
		); err != nil {
			return nil, fmt.Errorf("add group member: %w", err)
		}
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, fmt.Errorf("commit group: %w", err)
	}
	return &c, nil
}

// EnsureAIThread returns the caller's Kautilya thread, creating it on first
// use. One participant; the assistant has no user row.
func (r *ChatRepo) EnsureAIThread(ctx context.Context, userID string) (*model.Conversation, error) {
	var c model.Conversation
	err := r.pg.Pool.QueryRow(ctx, `
		SELECT c.id, c.kind, c.title, c.avatar_key, c.send_policy, c.last_seq, c.last_message_at, c.created_at
		FROM conversations c
		JOIN conversation_participants p ON p.conversation_id = c.id AND p.user_id = $1
		WHERE c.kind = 'ai' ORDER BY c.created_at LIMIT 1`, userID,
	).Scan(&c.ID, &c.Kind, &c.Title, &c.AvatarKey, &c.SendPolicy, &c.LastSeq, &c.LastMessageAt, &c.CreatedAt)
	if err == nil {
		return &c, nil
	}
	if !errors.Is(err, pgx.ErrNoRows) {
		return nil, fmt.Errorf("find ai thread: %w", err)
	}

	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return nil, fmt.Errorf("begin ai tx: %w", err)
	}
	defer tx.Rollback(ctx) //nolint:errcheck
	if err := tx.QueryRow(ctx, `
		INSERT INTO conversations (kind, created_by) VALUES ('ai', $1)
		RETURNING id, kind, title, avatar_key, send_policy, last_seq, last_message_at, created_at`, userID,
	).Scan(&c.ID, &c.Kind, &c.Title, &c.AvatarKey, &c.SendPolicy, &c.LastSeq, &c.LastMessageAt, &c.CreatedAt); err != nil {
		return nil, fmt.Errorf("create ai thread: %w", err)
	}
	if _, err := tx.Exec(ctx, `
		INSERT INTO conversation_participants (conversation_id, user_id) VALUES ($1, $2)`, c.ID, userID,
	); err != nil {
		return nil, fmt.Errorf("add ai participant: %w", err)
	}
	if err := tx.Commit(ctx); err != nil {
		return nil, fmt.Errorf("commit ai thread: %w", err)
	}
	return &c, nil
}

// Conversation loads a thread by id, without any membership check — callers
// pair it with Participant when the caller's access matters.
func (r *ChatRepo) Conversation(ctx context.Context, id string) (*model.Conversation, error) {
	var c model.Conversation
	err := r.pg.Pool.QueryRow(ctx, `
		SELECT id, kind, title, avatar_key, send_policy, last_seq, last_message_at, created_at
		FROM conversations WHERE id = $1`, id,
	).Scan(&c.ID, &c.Kind, &c.Title, &c.AvatarKey, &c.SendPolicy, &c.LastSeq, &c.LastMessageAt, &c.CreatedAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrConversationGone
	}
	if err != nil {
		return nil, fmt.Errorf("load conversation: %w", err)
	}
	return &c, nil
}

// Participant loads the caller's membership row — the authorization primitive
// behind every other chat call and the realtime channel rule.
func (r *ChatRepo) Participant(ctx context.Context, conversationID, userID string) (*model.Participant, error) {
	var p model.Participant
	err := r.pg.Pool.QueryRow(ctx, `
		SELECT conversation_id, user_id, role, last_read_seq, last_delivered_seq,
		       muted_until, joined_at, left_at
		FROM conversation_participants
		WHERE conversation_id = $1 AND user_id = $2 AND left_at IS NULL`,
		conversationID, userID,
	).Scan(&p.ConversationID, &p.UserID, &p.Role, &p.LastReadSeq, &p.LastDeliveredSeq,
		&p.MutedUntil, &p.JoinedAt, &p.LeftAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotParticipant
	}
	if err != nil {
		return nil, fmt.Errorf("load participant: %w", err)
	}
	return &p, nil
}

// Participants lists everyone still in the thread with the details needed to
// render a name and avatar beside their messages.
func (r *ChatRepo) Participants(ctx context.Context, conversationID string) ([]model.ChatPeer, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT u.id, u.handle, u.name, u.avatar_url, p.role, p.joined_at
		FROM conversation_participants p
		JOIN users u ON u.id = p.user_id
		WHERE p.conversation_id = $1 AND p.left_at IS NULL
		-- Owner first, then admins, then members by seniority: the order the
		-- member list is read in.
		ORDER BY CASE p.role WHEN 'owner' THEN 0 WHEN 'admin' THEN 1 ELSE 2 END,
		         p.joined_at`, conversationID)
	if err != nil {
		return nil, fmt.Errorf("query participants: %w", err)
	}
	defer rows.Close()

	people := []model.ChatPeer{}
	for rows.Next() {
		var c model.ChatPeer
		if err := rows.Scan(&c.ID, &c.Handle, &c.Name, &c.AvatarURL, &c.Role, &c.JoinedAt); err != nil {
			return nil, fmt.Errorf("scan participant: %w", err)
		}
		people = append(people, c)
	}
	return people, rows.Err()
}

// ParticipantIDs lists everyone still in the thread — the fan-out list for
// realtime publishes and push.
func (r *ChatRepo) ParticipantIDs(ctx context.Context, conversationID string) ([]string, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT user_id FROM conversation_participants
		WHERE conversation_id = $1 AND left_at IS NULL`, conversationID)
	if err != nil {
		return nil, fmt.Errorf("participant ids: %w", err)
	}
	defer rows.Close()
	var ids []string
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, fmt.Errorf("scan participant id: %w", err)
		}
		ids = append(ids, id)
	}
	return ids, rows.Err()
}

// Inbox lists the caller's threads of the given kinds, most recent first.
//
// The last-message line comes from a LATERAL on (conversation_id, seq DESC)
// rather than a denormalized column, so an edit or delete is reflected without
// a second write path that could drift. Messages the caller deleted for
// themselves are skipped, so their inbox preview matches their thread.
func (r *ChatRepo) Inbox(ctx context.Context, userID string, kinds []string, limit int) ([]model.InboxItem, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT c.id, c.kind, c.title, c.avatar_key, c.send_policy, c.last_seq, c.last_message_at, c.created_at,
		       GREATEST(c.last_seq - p.last_read_seq, 0) AS unread,
		       p.muted_until,
		       m.seq, m.sender_id, m.kind, m.body, m.deleted_at,
		       COALESCE(su.name, ''),
		       peer.id, peer.handle, peer.name, peer.avatar_url
		FROM conversation_participants p
		JOIN conversations c ON c.id = p.conversation_id
		LEFT JOIN LATERAL (
		    SELECT msg.seq, msg.sender_id, msg.kind, msg.body, msg.deleted_at
		    FROM messages msg
		    WHERE msg.conversation_id = c.id
		      AND NOT EXISTS (SELECT 1 FROM message_hides h
		                      WHERE h.message_id = msg.id AND h.user_id = $1)
		    ORDER BY msg.seq DESC LIMIT 1
		) m ON TRUE
		LEFT JOIN users su ON su.id = m.sender_id
		LEFT JOIN LATERAL (
		    SELECT u2.id, u2.handle, u2.name, u2.avatar_url
		    FROM conversation_participants p2
		    JOIN users u2 ON u2.id = p2.user_id
		    WHERE p2.conversation_id = c.id AND p2.user_id <> $1
		    LIMIT 1
		) peer ON c.kind = 'dm'
		WHERE p.user_id = $1 AND p.left_at IS NULL AND c.kind = ANY($2)
		ORDER BY c.last_message_at DESC NULLS LAST, c.created_at DESC
		LIMIT $3`, userID, kinds, limit)
	if err != nil {
		return nil, fmt.Errorf("query inbox: %w", err)
	}
	defer rows.Close()

	items := []model.InboxItem{}
	for rows.Next() {
		var it model.InboxItem
		var seq *int64
		var senderID, msgKind, body *string
		var deletedAt *time.Time
		var senderName string
		var peerID, peerHandle, peerName, peerAvatar *string

		if err := rows.Scan(
			&it.ID, &it.Kind, &it.Title, &it.AvatarKey, &it.SendPolicy, &it.LastSeq, &it.LastMessageAt, &it.CreatedAt,
			&it.Unread, &it.MutedUntil,
			&seq, &senderID, &msgKind, &body, &deletedAt,
			&senderName,
			&peerID, &peerHandle, &peerName, &peerAvatar,
		); err != nil {
			return nil, fmt.Errorf("scan inbox row: %w", err)
		}

		if seq != nil {
			it.LastMessage = &model.MessagePreview{
				Seq: *seq, SenderID: senderID, SenderName: senderName,
				Kind: derefOr(msgKind, model.MessageText), Body: derefOr(body, ""),
				DeletedAt: deletedAt,
			}
		}
		if peerID != nil {
			it.Peer = &model.ChatPeer{
				ID: *peerID, Handle: derefOr(peerHandle, ""),
				Name: derefOr(peerName, ""), AvatarURL: peerAvatar,
			}
		}
		items = append(items, it)
	}
	return items, rows.Err()
}

// Messages returns one page of history, newest first. beforeSeq == 0 starts at
// the newest message; otherwise it is an exclusive upper bound, which makes
// paging stable even as new messages arrive at the top.
func (r *ChatRepo) Messages(ctx context.Context, conversationID, userID string, beforeSeq int64, limit int) ([]model.Message, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT m.id, m.conversation_id, m.seq, m.sender_id, m.kind, m.body, m.entities,
		       m.client_msg_id, m.reply_to_id, m.forwarded_from_id, m.edited_at, m.deleted_at, m.created_at,
		       rep.id, rep.seq, rep.sender_id, rep.body, rep.deleted_at, COALESCE(rep.sender_name, '')
		FROM messages m
		LEFT JOIN LATERAL (
		    SELECT r.id, r.seq, r.sender_id, r.body, r.deleted_at, ru.name AS sender_name
		    FROM messages r
		    LEFT JOIN users ru ON ru.id = r.sender_id
		    -- The conversation guard is repeated here on purpose: even a row
		    -- written before the write-side check existed cannot leak another
		    -- thread's text through a quote.
		    WHERE r.id = m.reply_to_id AND r.conversation_id = m.conversation_id
		) rep ON TRUE
		WHERE m.conversation_id = $1
		  AND ($2 = 0 OR m.seq < $2)
		  AND NOT EXISTS (SELECT 1 FROM message_hides h
		                  WHERE h.message_id = m.id AND h.user_id = $3)
		ORDER BY m.seq DESC
		LIMIT $4`, conversationID, beforeSeq, userID, limit)
	if err != nil {
		return nil, fmt.Errorf("query messages: %w", err)
	}
	defer rows.Close()

	msgs := []model.Message{}
	for rows.Next() {
		var m model.Message
		var entities []byte
		var repID *string
		var repSeq *int64
		var repSender *string
		var repBody *string
		var repDeleted *time.Time
		var repSenderName string

		if err := rows.Scan(&m.ID, &m.ConversationID, &m.Seq, &m.SenderID, &m.Kind, &m.Body,
			&entities, &m.ClientMsgID, &m.ReplyToID, &m.ForwardedFromID,
			&m.EditedAt, &m.DeletedAt, &m.CreatedAt,
			&repID, &repSeq, &repSender, &repBody, &repDeleted, &repSenderName); err != nil {
			return nil, fmt.Errorf("scan message: %w", err)
		}
		m.Entities = json.RawMessage(entities)
		if repID != nil {
			m.ReplyTo = &model.ReplyPreview{
				ID: *repID, Seq: derefInt64(repSeq), SenderID: repSender,
				SenderName: repSenderName, Body: derefOr(repBody, ""),
				Deleted: repDeleted != nil,
			}
		}
		msgs = append(msgs, m)
	}
	return msgs, rows.Err()
}

// AppendParams carries everything needed to persist one outgoing message.
type AppendParams struct {
	ConversationID  string
	SenderID        *string
	Kind            string
	Body            string
	Entities        json.RawMessage
	ClientMsgID     *string
	ReplyToID       *string
	ForwardedFromID *string
}

// Append persists a message and assigns its sequence number.
//
// The conversation row is locked FOR UPDATE first. That serialises sends within
// a thread — which is what makes `seq` gapless — and it also means the
// duplicate check below runs under the lock, so a retried send returns the
// original message instead of consuming a sequence number and leaving a hole.
func (r *ChatRepo) Append(ctx context.Context, p AppendParams) (*model.Message, bool, error) {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return nil, false, fmt.Errorf("begin append tx: %w", err)
	}
	defer tx.Rollback(ctx) //nolint:errcheck

	var lastSeq int64
	if err := tx.QueryRow(ctx,
		`SELECT last_seq FROM conversations WHERE id = $1 FOR UPDATE`, p.ConversationID,
	).Scan(&lastSeq); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, false, ErrConversationGone
		}
		return nil, false, fmt.Errorf("lock conversation: %w", err)
	}

	if p.ClientMsgID != nil {
		existing, err := scanMessage(tx.QueryRow(ctx, `
			SELECT id, conversation_id, seq, sender_id, kind, body, entities,
			       client_msg_id, reply_to_id, forwarded_from_id, edited_at, deleted_at, created_at
			FROM messages WHERE conversation_id = $1 AND client_msg_id = $2`,
			p.ConversationID, *p.ClientMsgID))
		if err == nil {
			return existing, false, tx.Commit(ctx)
		}
		if !errors.Is(err, pgx.ErrNoRows) {
			return nil, false, fmt.Errorf("dedup lookup: %w", err)
		}
	}

	// Checked under the conversation lock we already hold.
	if p.ReplyToID != nil {
		var sameThread bool
		if err := tx.QueryRow(ctx,
			`SELECT EXISTS(SELECT 1 FROM messages WHERE id = $1 AND conversation_id = $2)`,
			*p.ReplyToID, p.ConversationID,
		).Scan(&sameThread); err != nil {
			return nil, false, fmt.Errorf("validate reply target: %w", err)
		}
		if !sameThread {
			return nil, false, ErrReplyTargetNotHere
		}
	}

	entities := p.Entities
	if len(entities) == 0 {
		entities = json.RawMessage(`[]`)
	}

	seq := lastSeq + 1
	m, err := scanMessage(tx.QueryRow(ctx, `
		INSERT INTO messages (conversation_id, seq, sender_id, kind, body, entities,
		                      client_msg_id, reply_to_id, forwarded_from_id)
		VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9)
		RETURNING id, conversation_id, seq, sender_id, kind, body, entities,
		          client_msg_id, reply_to_id, forwarded_from_id, edited_at, deleted_at, created_at`,
		p.ConversationID, seq, p.SenderID, p.Kind, p.Body, entities,
		p.ClientMsgID, p.ReplyToID, p.ForwardedFromID))
	if err != nil {
		return nil, false, fmt.Errorf("insert message: %w", err)
	}

	if _, err := tx.Exec(ctx, `
		UPDATE conversations SET last_seq = $2, last_message_at = now(), updated_at = now()
		WHERE id = $1`, p.ConversationID, seq); err != nil {
		return nil, false, fmt.Errorf("bump conversation: %w", err)
	}

	// The sender has trivially seen their own message; advancing their cursors
	// here keeps their unread count at zero without a follow-up write.
	if p.SenderID != nil {
		if _, err := tx.Exec(ctx, `
			UPDATE conversation_participants
			SET last_read_seq = GREATEST(last_read_seq, $3),
			    last_delivered_seq = GREATEST(last_delivered_seq, $3)
			WHERE conversation_id = $1 AND user_id = $2`,
			p.ConversationID, *p.SenderID, seq); err != nil {
			return nil, false, fmt.Errorf("advance sender cursor: %w", err)
		}
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, false, fmt.Errorf("commit append: %w", err)
	}
	return m, true, nil
}

// MarkRead advances the caller's read cursor. GREATEST means an out-of-order
// or replayed request can never move a cursor backwards and resurrect unreads.
// Reading implies delivery, so both cursors move together.
func (r *ChatRepo) MarkRead(ctx context.Context, conversationID, userID string, seq int64) error {
	_, err := r.pg.Pool.Exec(ctx, `
		UPDATE conversation_participants
		SET last_read_seq = GREATEST(last_read_seq, $3),
		    last_delivered_seq = GREATEST(last_delivered_seq, $3)
		WHERE conversation_id = $1 AND user_id = $2`, conversationID, userID, seq)
	if err != nil {
		return fmt.Errorf("mark read: %w", err)
	}
	return nil
}

// MarkDelivered advances only the delivery cursor — the client received the
// message but the user has not opened the thread.
func (r *ChatRepo) MarkDelivered(ctx context.Context, conversationID, userID string, seq int64) error {
	_, err := r.pg.Pool.Exec(ctx, `
		UPDATE conversation_participants
		SET last_delivered_seq = GREATEST(last_delivered_seq, $3)
		WHERE conversation_id = $1 AND user_id = $2`, conversationID, userID, seq)
	if err != nil {
		return fmt.Errorf("mark delivered: %w", err)
	}
	return nil
}

// AddAttachmentParams describes one attachment to persist.
type AddAttachmentParams struct {
	MessageID      string
	ConversationID string
	Ord            int
	Kind           string

	R2Key      *string
	Mime       *string
	SizeBytes  *int64
	Width      *int
	Height     *int
	DurationMs *int
	Blurhash   *string
	FileName   *string

	URL         *string
	Title       *string
	Description *string
	SiteName    *string
	ImageURL    *string

	// Shared entity: the durable reference plus a snapshot used only as a
	// fallback. Live data is re-resolved per viewer at read time.
	EntityType *string
	EntityID   *string
	Snapshot   []byte
}

// AddAttachment persists one attachment. conversation_id is denormalized here
// so the chat profile's media and links tabs are a single index scan.
func (r *ChatRepo) AddAttachment(ctx context.Context, p AddAttachmentParams) (*model.Attachment, error) {
	var a model.Attachment
	err := r.pg.Pool.QueryRow(ctx, `
		INSERT INTO message_attachments
		    (message_id, conversation_id, ord, kind, r2_key, mime, size_bytes,
		     width, height, duration_ms, blurhash, file_name,
		     url, title, description, site_name, image_url,
		     entity_type, entity_id, snapshot)
		VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$20)
		RETURNING id, message_id, ord, kind, mime, size_bytes, width, height,
		          duration_ms, blurhash, file_name, url, title, description,
		          site_name, image_url, entity_type, entity_id, snapshot, created_at`,
		p.MessageID, p.ConversationID, p.Ord, p.Kind, p.R2Key, p.Mime, p.SizeBytes,
		p.Width, p.Height, p.DurationMs, p.Blurhash, p.FileName,
		p.URL, p.Title, p.Description, p.SiteName, p.ImageURL,
		p.EntityType, p.EntityID, p.Snapshot,
	).Scan(&a.ID, &a.MessageID, &a.Ord, &a.Kind, &a.Mime, &a.SizeBytes, &a.Width,
		&a.Height, &a.DurationMs, &a.Blurhash, &a.FileName, &a.URL, &a.Title,
		&a.Description, &a.SiteName, &a.ImageURL,
		&a.EntityType, &a.EntityID, &a.Entity, &a.CreatedAt)
	if err != nil {
		return nil, fmt.Errorf("add attachment: %w", err)
	}
	return &a, nil
}

// AttachmentsFor loads the attachments of the given messages, keyed by message.
func (r *ChatRepo) AttachmentsFor(ctx context.Context, messageIDs []string) (map[string][]model.Attachment, error) {
	out := map[string][]model.Attachment{}
	if len(messageIDs) == 0 {
		return out, nil
	}
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT id, message_id, ord, kind, mime, size_bytes, width, height,
		       duration_ms, blurhash, file_name, url, title, description,
		       site_name, image_url, entity_type, entity_id, snapshot, created_at
		FROM message_attachments
		WHERE message_id = ANY($1)
		ORDER BY message_id, ord`, messageIDs)
	if err != nil {
		return nil, fmt.Errorf("query attachments: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var a model.Attachment
		if err := rows.Scan(&a.ID, &a.MessageID, &a.Ord, &a.Kind, &a.Mime, &a.SizeBytes,
			&a.Width, &a.Height, &a.DurationMs, &a.Blurhash, &a.FileName, &a.URL,
			&a.Title, &a.Description, &a.SiteName, &a.ImageURL,
			&a.EntityType, &a.EntityID, &a.Entity, &a.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan attachment: %w", err)
		}
		out[a.MessageID] = append(out[a.MessageID], a)
	}
	return out, rows.Err()
}

// AttachmentLocation returns an attachment's storage key and the conversation
// it belongs to, so a download can be authorized before a URL is minted.
func (r *ChatRepo) AttachmentLocation(ctx context.Context, attachmentID string) (conversationID, r2Key string, err error) {
	var key *string
	err = r.pg.Pool.QueryRow(ctx, `
		SELECT conversation_id, r2_key FROM message_attachments WHERE id = $1`,
		attachmentID).Scan(&conversationID, &key)
	if errors.Is(err, pgx.ErrNoRows) {
		return "", "", ErrAttachmentGone
	}
	if err != nil {
		return "", "", fmt.Errorf("attachment location: %w", err)
	}
	if key == nil || *key == "" {
		return "", "", ErrAttachmentGone
	}
	return conversationID, *key, nil
}

// GalleryKindsMedia / GalleryKindsLink name the two chat-profile tabs.
var (
	GalleryKindsMedia = []string{model.AttachmentImage, model.AttachmentVideo, model.AttachmentAudio, model.AttachmentFile}
	GalleryKindsLink  = []string{model.AttachmentLink}
)

// Gallery lists a thread's attachments of the given kinds, newest first.
//
// Served by message_attachments_gallery_idx, which is why conversation_id is
// denormalized onto attachments: this is one index range scan rather than a
// join back through messages.
//
// Attachments of messages the caller deleted for themselves are excluded, so
// the gallery matches the thread they actually see.
func (r *ChatRepo) Gallery(ctx context.Context, conversationID, userID string, kinds []string, before *time.Time, limit int) ([]model.Attachment, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT a.id, a.message_id, a.ord, a.kind, a.mime, a.size_bytes, a.width,
		       a.height, a.duration_ms, a.blurhash, a.file_name, a.url, a.title,
		       a.description, a.site_name, a.image_url,
		       a.entity_type, a.entity_id, a.snapshot, a.created_at
		FROM message_attachments a
		JOIN messages m ON m.id = a.message_id
		WHERE a.conversation_id = $1
		  AND a.kind = ANY($2)
		  AND m.deleted_at IS NULL
		  AND ($3::timestamptz IS NULL OR a.created_at < $3)
		  AND NOT EXISTS (SELECT 1 FROM message_hides h
		                  WHERE h.message_id = a.message_id AND h.user_id = $4)
		ORDER BY a.created_at DESC
		LIMIT $5`, conversationID, kinds, before, userID, limit)
	if err != nil {
		return nil, fmt.Errorf("query gallery: %w", err)
	}
	defer rows.Close()

	out := []model.Attachment{}
	for rows.Next() {
		var a model.Attachment
		if err := rows.Scan(&a.ID, &a.MessageID, &a.Ord, &a.Kind, &a.Mime, &a.SizeBytes,
			&a.Width, &a.Height, &a.DurationMs, &a.Blurhash, &a.FileName, &a.URL,
			&a.Title, &a.Description, &a.SiteName, &a.ImageURL,
			&a.EntityType, &a.EntityID, &a.Entity, &a.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan gallery row: %w", err)
		}
		out = append(out, a)
	}
	return out, rows.Err()
}

// SetStar stars or unstars a message for one user.
//
// The message must belong to the conversation: the caller's membership is
// checked against the thread, so accepting a message id from elsewhere would
// let them star something they cannot see.
func (r *ChatRepo) SetStar(ctx context.Context, conversationID, messageID, userID string, starred bool) error {
	if !starred {
		_, err := r.pg.Pool.Exec(ctx,
			`DELETE FROM message_stars WHERE message_id = $1 AND user_id = $2`, messageID, userID)
		if err != nil {
			return fmt.Errorf("unstar: %w", err)
		}
		return nil
	}

	tag, err := r.pg.Pool.Exec(ctx, `
		INSERT INTO message_stars (message_id, user_id, conversation_id)
		SELECT $1, $2, $3
		WHERE EXISTS (SELECT 1 FROM messages WHERE id = $1 AND conversation_id = $3)
		ON CONFLICT (message_id, user_id) DO NOTHING`, messageID, userID, conversationID)
	if err != nil {
		return fmt.Errorf("star: %w", err)
	}
	// No row inserted and no conflict means the message isn't in this thread.
	if tag.RowsAffected() == 0 {
		var exists bool
		if err := r.pg.Pool.QueryRow(ctx,
			`SELECT EXISTS(SELECT 1 FROM message_stars WHERE message_id=$1 AND user_id=$2)`,
			messageID, userID).Scan(&exists); err != nil {
			return fmt.Errorf("star check: %w", err)
		}
		if !exists {
			return ErrMessageNotHere
		}
	}
	return nil
}

// Starred lists the caller's starred messages in a thread, newest first.
func (r *ChatRepo) Starred(ctx context.Context, conversationID, userID string, limit int) ([]model.Message, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT m.id, m.conversation_id, m.seq, m.sender_id, m.kind, m.body, m.entities,
		       m.client_msg_id, m.reply_to_id, m.forwarded_from_id, m.edited_at,
		       m.deleted_at, m.created_at
		FROM message_stars st
		JOIN messages m ON m.id = st.message_id
		WHERE st.user_id = $1 AND st.conversation_id = $2 AND m.deleted_at IS NULL
		ORDER BY st.created_at DESC
		LIMIT $3`, userID, conversationID, limit)
	if err != nil {
		return nil, fmt.Errorf("query starred: %w", err)
	}
	defer rows.Close()

	msgs := []model.Message{}
	for rows.Next() {
		var m model.Message
		var entities []byte
		if err := rows.Scan(&m.ID, &m.ConversationID, &m.Seq, &m.SenderID, &m.Kind,
			&m.Body, &entities, &m.ClientMsgID, &m.ReplyToID, &m.ForwardedFromID,
			&m.EditedAt, &m.DeletedAt, &m.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan starred: %w", err)
		}
		m.Entities = json.RawMessage(entities)
		m.Attachments = []model.Attachment{}
		msgs = append(msgs, m)
	}
	return msgs, rows.Err()
}

// StarredIDs reports which of the given messages the caller has starred, so a
// thread can show the star on each bubble.
func (r *ChatRepo) StarredIDs(ctx context.Context, userID string, messageIDs []string) (map[string]bool, error) {
	out := map[string]bool{}
	if len(messageIDs) == 0 {
		return out, nil
	}
	rows, err := r.pg.Pool.Query(ctx,
		`SELECT message_id FROM message_stars WHERE user_id = $1 AND message_id = ANY($2)`,
		userID, messageIDs)
	if err != nil {
		return nil, fmt.Errorf("query stars: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, fmt.Errorf("scan star: %w", err)
		}
		out[id] = true
	}
	return out, rows.Err()
}

// FollowEdges returns the accepted-follow state between two users in both
// directions, plus when the first of them was accepted.
func (r *ChatRepo) FollowEdges(ctx context.Context, a, b string) (aFollowsB, bFollowsA bool, since *time.Time, err error) {
	rows, qErr := r.pg.Pool.Query(ctx, `
		SELECT follower_id, status, COALESCE(responded_at, created_at)
		FROM follows
		WHERE (follower_id = $1 AND following_id = $2)
		   OR (follower_id = $2 AND following_id = $1)`, a, b)
	if qErr != nil {
		return false, false, nil, fmt.Errorf("follow edges: %w", qErr)
	}
	defer rows.Close()

	for rows.Next() {
		var follower, status string
		var at time.Time
		if err := rows.Scan(&follower, &status, &at); err != nil {
			return false, false, nil, fmt.Errorf("scan follow edge: %w", err)
		}
		if status != "accepted" {
			continue // a pending request is not a friendship
		}
		if follower == a {
			aFollowsB = true
		} else {
			bFollowsA = true
		}
		// "Friends since" is the earliest accepted edge either way.
		if since == nil || at.Before(*since) {
			at := at
			since = &at
		}
	}
	return aFollowsB, bFollowsA, since, rows.Err()
}

// Settings returns a user's chat preferences, falling back to the defaults
// when they have never changed anything.
func (r *ChatRepo) Settings(ctx context.Context, userID string) (model.ChatSettings, error) {
	out := model.DefaultChatSettings()
	var gender *string
	err := r.pg.Pool.QueryRow(ctx, `
		SELECT COALESCE(s.read_receipts, TRUE),
		       COALESCE(s.who_can_message, 'anyone'),
		       COALESCE(s.min_account_age_months, 3),
		       COALESCE(s.train_kautilya, TRUE),
		       u.gender
		FROM users u
		LEFT JOIN chat_settings s ON s.user_id = u.id
		WHERE u.id = $1`, userID,
	).Scan(&out.ReadReceipts, &out.WhoCanMessage, &out.MinAccountAgeMonths,
		&out.TrainKautilya, &gender)
	if errors.Is(err, pgx.ErrNoRows) {
		return out, ErrUserGone
	}
	if err != nil {
		return out, fmt.Errorf("chat settings: %w", err)
	}
	out.GenderSet = gender != nil && *gender != ""
	return out, nil
}

// SaveSettings upserts a user's chat preferences.
func (r *ChatRepo) SaveSettings(ctx context.Context, userID string, s model.ChatSettings) error {
	_, err := r.pg.Pool.Exec(ctx, `
		INSERT INTO chat_settings
		    (user_id, read_receipts, who_can_message, min_account_age_months, train_kautilya)
		VALUES ($1, $2, $3, $4, $5)
		ON CONFLICT (user_id) DO UPDATE SET
		    read_receipts = EXCLUDED.read_receipts,
		    who_can_message = EXCLUDED.who_can_message,
		    min_account_age_months = EXCLUDED.min_account_age_months,
		    train_kautilya = EXCLUDED.train_kautilya,
		    updated_at = now()`,
		userID, s.ReadReceipts, s.WhoCanMessage, s.MinAccountAgeMonths, s.TrainKautilya)
	if err != nil {
		return fmt.Errorf("save chat settings: %w", err)
	}
	return nil
}

// CanStartConversation applies the recipient's "who can message you" rule.
//
// Only gates STARTING a thread. An existing conversation keeps working, so
// tightening the setting never strands people mid-exchange.
func (r *ChatRepo) CanStartConversation(ctx context.Context, senderID, recipientID string) (bool, error) {
	settings, err := r.Settings(ctx, recipientID)
	if err != nil {
		return false, err
	}

	switch settings.WhoCanMessage {
	case model.WhoAnyone:
		return true, nil

	case model.WhoFriends:
		// An accepted follow in EITHER direction counts as a connection.
		following, followedBy, _, err := r.FollowEdges(ctx, senderID, recipientID)
		if err != nil {
			return false, err
		}
		return following || followedBy, nil

	case model.WhoAccountAge:
		var oldEnough bool
		if err := r.pg.Pool.QueryRow(ctx, `
			SELECT created_at <= now() - make_interval(months => $2)
			FROM users WHERE id = $1`, senderID, settings.MinAccountAgeMonths,
		).Scan(&oldEnough); err != nil {
			return false, fmt.Errorf("account age: %w", err)
		}
		return oldEnough, nil

	case model.WhoSameGender:
		// Unusable without the recipient's own gender; treated as "anyone"
		// rather than locking them out of their own inbox.
		if !settings.GenderSet {
			return true, nil
		}
		var same bool
		if err := r.pg.Pool.QueryRow(ctx, `
			SELECT s.gender IS NOT NULL AND s.gender = r.gender
			FROM users s, users r WHERE s.id = $1 AND r.id = $2`,
			senderID, recipientID).Scan(&same); err != nil {
			return false, fmt.Errorf("gender match: %w", err)
		}
		return same, nil
	}
	return true, nil
}

// ReadReceiptsEnabled reports which of the given users allow read receipts.
func (r *ChatRepo) ReadReceiptsEnabled(ctx context.Context, userIDs []string) (map[string]bool, error) {
	out := map[string]bool{}
	if len(userIDs) == 0 {
		return out, nil
	}
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT u.id, COALESCE(s.read_receipts, TRUE)
		FROM users u LEFT JOIN chat_settings s ON s.user_id = u.id
		WHERE u.id = ANY($1)`, userIDs)
	if err != nil {
		return nil, fmt.Errorf("read receipt settings: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var id string
		var on bool
		if err := rows.Scan(&id, &on); err != nil {
			return nil, fmt.Errorf("scan receipt setting: %w", err)
		}
		out[id] = on
	}
	return out, rows.Err()
}

// UserIDsByHandles resolves handles to ids, skipping any that don't exist.
//
// Member operations take handles because that is what the UI has: search
// results and follow lists identify people by handle, and handles are what the
// rest of the API keys on (/u/{handle}/block, /u/{handle}/followers).
func (r *ChatRepo) UserIDsByHandles(ctx context.Context, handles []string) ([]string, error) {
	if len(handles) == 0 {
		return nil, nil
	}
	rows, err := r.pg.Pool.Query(ctx,
		// Banned users are skipped: they cannot be added to a group.
		`SELECT id FROM users WHERE handle = ANY($1) AND banned_at IS NULL`, handles)
	if err != nil {
		return nil, fmt.Errorf("resolve handles: %w", err)
	}
	defer rows.Close()
	ids := []string{}
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, fmt.Errorf("scan handle id: %w", err)
		}
		ids = append(ids, id)
	}
	return ids, rows.Err()
}

// AddParticipants adds members to a group, reviving anyone who had left.
func (r *ChatRepo) AddParticipants(ctx context.Context, conversationID string, userIDs []string) error {
	for _, id := range userIDs {
		if _, err := r.pg.Pool.Exec(ctx, `
			INSERT INTO conversation_participants (conversation_id, user_id, role, joined_at)
			VALUES ($1, $2, 'member', now())
			ON CONFLICT (conversation_id, user_id)
			-- Re-adding someone who left clears left_at and restarts their
			-- tenure; it must not resurrect an old role.
			DO UPDATE SET left_at = NULL, role = 'member', joined_at = now()
			WHERE conversation_participants.left_at IS NOT NULL`,
			conversationID, id); err != nil {
			return fmt.Errorf("add participant: %w", err)
		}
	}
	return nil
}

// RemoveParticipant marks someone as having left. The row stays so their past
// messages still resolve to a member when history is rendered.
func (r *ChatRepo) RemoveParticipant(ctx context.Context, conversationID, userID string) error {
	_, err := r.pg.Pool.Exec(ctx, `
		UPDATE conversation_participants SET left_at = now()
		WHERE conversation_id = $1 AND user_id = $2 AND left_at IS NULL`,
		conversationID, userID)
	if err != nil {
		return fmt.Errorf("remove participant: %w", err)
	}
	return nil
}

// SetRole changes a participant's role.
func (r *ChatRepo) SetRole(ctx context.Context, conversationID, userID, role string) error {
	_, err := r.pg.Pool.Exec(ctx, `
		UPDATE conversation_participants SET role = $3
		WHERE conversation_id = $1 AND user_id = $2 AND left_at IS NULL`,
		conversationID, userID, role)
	if err != nil {
		return fmt.Errorf("set role: %w", err)
	}
	return nil
}

// UpdateGroup changes a group's title and/or send policy. Nil leaves a field
// untouched.
func (r *ChatRepo) UpdateGroup(ctx context.Context, conversationID string, title, sendPolicy, avatarKey *string) error {
	_, err := r.pg.Pool.Exec(ctx, `
		UPDATE conversations
		SET title = COALESCE($2, title),
		    send_policy = COALESCE($3, send_policy),
		    avatar_key = COALESCE($4, avatar_key),
		    updated_at = now()
		WHERE id = $1`, conversationID, title, sendPolicy, avatarKey)
	if err != nil {
		return fmt.Errorf("update group: %w", err)
	}
	return nil
}

// SuccessorOwner picks who inherits a group when its owner leaves: the
// longest-serving remaining admin, else the longest-serving member. Empty when
// nobody is left.
//
// Without this a group whose owner walks away would have no one able to
// administer it.
func (r *ChatRepo) SuccessorOwner(ctx context.Context, conversationID, leavingUserID string) (string, error) {
	var id string
	err := r.pg.Pool.QueryRow(ctx, `
		SELECT user_id FROM conversation_participants
		WHERE conversation_id = $1 AND user_id <> $2 AND left_at IS NULL
		ORDER BY CASE role WHEN 'admin' THEN 0 ELSE 1 END, joined_at
		LIMIT 1`, conversationID, leavingUserID).Scan(&id)
	if errors.Is(err, pgx.ErrNoRows) {
		return "", nil
	}
	if err != nil {
		return "", fmt.Errorf("successor owner: %w", err)
	}
	return id, nil
}

// MessageConversation returns the thread a message belongs to, plus its
// sender — enough to authorize a delete, a forward or a report.
func (r *ChatRepo) MessageConversation(ctx context.Context, messageID string) (conversationID string, senderID *string, err error) {
	err = r.pg.Pool.QueryRow(ctx,
		`SELECT conversation_id, sender_id FROM messages WHERE id = $1`, messageID,
	).Scan(&conversationID, &senderID)
	if errors.Is(err, pgx.ErrNoRows) {
		return "", nil, ErrMessageNotHere
	}
	if err != nil {
		return "", nil, fmt.Errorf("message conversation: %w", err)
	}
	return conversationID, senderID, nil
}

// MessageByID loads a single message. Callers authorize separately — this
// only fetches.
func (r *ChatRepo) MessageByID(ctx context.Context, messageID string) (*model.Message, error) {
	m, err := scanMessage(r.pg.Pool.QueryRow(ctx, `
		SELECT id, conversation_id, seq, sender_id, kind, body, entities,
		       client_msg_id, reply_to_id, forwarded_from_id, edited_at,
		       deleted_at, created_at
		FROM messages WHERE id = $1`, messageID))
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrMessageNotHere
	}
	if err != nil {
		return nil, fmt.Errorf("message by id: %w", err)
	}
	return m, nil
}

// HideMessage removes a message from one user's view only. Others keep seeing
// it — this is "delete for me".
func (r *ChatRepo) HideMessage(ctx context.Context, messageID, userID string) error {
	_, err := r.pg.Pool.Exec(ctx, `
		INSERT INTO message_hides (message_id, user_id) VALUES ($1, $2)
		ON CONFLICT DO NOTHING`, messageID, userID)
	if err != nil {
		return fmt.Errorf("hide message: %w", err)
	}
	return nil
}

// DeleteMessage tombstones a message for everyone.
//
// The row survives on purpose: `seq` must stay gapless for the client's
// catch-up cursor, and other participants need something to replace the bubble
// with rather than a hole. Body and entities are cleared so the text is
// actually gone, and attachments go with it.
func (r *ChatRepo) DeleteMessage(ctx context.Context, messageID, byUserID string) error {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin delete tx: %w", err)
	}
	defer tx.Rollback(ctx) //nolint:errcheck

	if _, err := tx.Exec(ctx, `
		UPDATE messages
		SET deleted_at = now(), deleted_by = $2, body = '', entities = '[]'::jsonb
		WHERE id = $1`, messageID, byUserID); err != nil {
		return fmt.Errorf("delete message: %w", err)
	}
	if _, err := tx.Exec(ctx,
		`DELETE FROM message_attachments WHERE message_id = $1`, messageID); err != nil {
		return fmt.Errorf("delete message attachments: %w", err)
	}
	return tx.Commit(ctx)
}

// MessageWithContext returns a message and the few around it — the snapshot a
// report captures so moderators never need to read the live thread.
func (r *ChatRepo) MessageWithContext(ctx context.Context, messageID string, around int) ([]model.Message, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		WITH target AS (
		    SELECT conversation_id, seq FROM messages WHERE id = $1
		)
		SELECT m.id, m.conversation_id, m.seq, m.sender_id, m.kind, m.body, m.entities,
		       m.client_msg_id, m.reply_to_id, m.forwarded_from_id, m.edited_at,
		       m.deleted_at, m.created_at
		FROM messages m, target t
		WHERE m.conversation_id = t.conversation_id
		  AND m.seq BETWEEN t.seq - $2 AND t.seq + $2
		ORDER BY m.seq`, messageID, around)
	if err != nil {
		return nil, fmt.Errorf("message context: %w", err)
	}
	defer rows.Close()

	msgs := []model.Message{}
	for rows.Next() {
		var m model.Message
		var entities []byte
		if err := rows.Scan(&m.ID, &m.ConversationID, &m.Seq, &m.SenderID, &m.Kind,
			&m.Body, &entities, &m.ClientMsgID, &m.ReplyToID, &m.ForwardedFromID,
			&m.EditedAt, &m.DeletedAt, &m.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan context message: %w", err)
		}
		m.Entities = json.RawMessage(entities)
		msgs = append(msgs, m)
	}
	return msgs, rows.Err()
}

// ReportMessage records a report with its evidence copied in.
func (r *ChatRepo) ReportMessage(ctx context.Context, reporterID, messageID, conversationID string, reportedUserID *string, category, reason string, snapshot []byte) error {
	_, err := r.pg.Pool.Exec(ctx, `
		INSERT INTO message_reports
		    (reporter_id, message_id, conversation_id, reported_user_id,
		     category, reason, snapshot)
		VALUES ($1,$2,$3,$4,$5,$6,$7)`,
		reporterID, messageID, conversationID, reportedUserID, category, reason, snapshot)
	if err != nil {
		return fmt.Errorf("report message: %w", err)
	}
	return nil
}

// SetMute sets or clears the caller's mute on a thread. A nil until unmutes.
//
// Mute is per participant, not per conversation: muting a group silences it for
// you alone.
func (r *ChatRepo) SetMute(ctx context.Context, conversationID, userID string, until *time.Time) error {
	_, err := r.pg.Pool.Exec(ctx, `
		UPDATE conversation_participants SET muted_until = $3
		WHERE conversation_id = $1 AND user_id = $2`, conversationID, userID, until)
	if err != nil {
		return fmt.Errorf("set mute: %w", err)
	}
	return nil
}

// Receipts returns the delivery/read cursors across everyone EXCEPT the
// caller, so the caller can draw ticks on their own messages. MIN is the
// deliberate choice: in a group, blue ticks mean everyone has read it.
func (r *ChatRepo) Receipts(ctx context.Context, conversationID, excludeUserID string) (model.Receipts, error) {
	var rc model.Receipts
	err := r.pg.Pool.QueryRow(ctx, `
		SELECT COALESCE(MIN(last_delivered_seq), 0), COALESCE(MIN(last_read_seq), 0)
		FROM conversation_participants
		WHERE conversation_id = $1 AND user_id <> $2 AND left_at IS NULL`,
		conversationID, excludeUserID).Scan(&rc.DeliveredSeq, &rc.ReadSeq)
	if err != nil {
		return rc, fmt.Errorf("receipts: %w", err)
	}
	return rc, nil
}

func scanMessage(row pgx.Row) (*model.Message, error) {
	var m model.Message
	var entities []byte
	if err := row.Scan(&m.ID, &m.ConversationID, &m.Seq, &m.SenderID, &m.Kind, &m.Body,
		&entities, &m.ClientMsgID, &m.ReplyToID, &m.ForwardedFromID,
		&m.EditedAt, &m.DeletedAt, &m.CreatedAt); err != nil {
		return nil, err
	}
	m.Entities = json.RawMessage(entities)
	return &m, nil
}

func derefInt64(v *int64) int64 {
	if v == nil {
		return 0
	}
	return *v
}

func derefOr(s *string, fallback string) string {
	if s == nil {
		return fallback
	}
	return *s
}