package tldrrepo

import (
	"context"
	"database/sql"
)

type Repo struct {
	db *sql.DB
}

func NewRepo(db *sql.DB) *Repo {
	return &Repo{db: db}
}

// GetCursors returns channel_id -> last_message_id for one user in one guild.
func (r *Repo) GetCursors(ctx context.Context, userID, guildID int64) (map[int64]int64, error) {
	const q = `
		SELECT channel_id, last_message_id
		FROM tldr_cursors
		WHERE user_id = $1 AND guild_id = $2
	`
	rows, err := r.db.QueryContext(ctx, q, userID, guildID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := make(map[int64]int64)
	for rows.Next() {
		var channelID, messageID int64
		if err := rows.Scan(&channelID, &messageID); err != nil {
			return nil, err
		}
		out[channelID] = messageID
	}
	return out, rows.Err()
}

// SetCursors upserts the given channel cursors in one transaction. GREATEST
// means a cursor only ever moves forward, so two overlapping runs can't drag
// it back and re-summarize messages.
func (r *Repo) SetCursors(ctx context.Context, userID, guildID int64, cursors map[int64]int64) error {
	if len(cursors) == 0 {
		return nil
	}

	tx, err := r.db.BeginTx(ctx, nil)
	if err != nil {
		return err
	}
	defer tx.Rollback()

	const q = `
		INSERT INTO tldr_cursors (user_id, channel_id, guild_id, last_message_id)
		VALUES ($1, $2, $3, $4)
		ON CONFLICT (user_id, channel_id)
		DO UPDATE SET
			last_message_id = GREATEST(tldr_cursors.last_message_id, EXCLUDED.last_message_id),
			updated_at = NOW()
	`
	for channelID, messageID := range cursors {
		if _, err := tx.ExecContext(ctx, q, userID, channelID, guildID, messageID); err != nil {
			return err
		}
	}
	return tx.Commit()
}