package storage

import (
	"context"
	"errors"
	"os"
)

type DatabaseStats struct {
	AllocatedBytes int64
	WALBytes       int64
	Connections    int
	InUse          int
	Waits          int64
}

// Read allocation metadata, not global row counts, so that scrapes remain independent of index size.
func (s *SQLite) DatabaseStats(ctx context.Context) (DatabaseStats, error) {
	var pages, size int64
	if err := s.conn.QueryRowContext(ctx, "PRAGMA page_count").Scan(&pages); err != nil {
		return DatabaseStats{}, err
	}
	if err := s.conn.QueryRowContext(ctx, "PRAGMA page_size").Scan(&size); err != nil {
		return DatabaseStats{}, err
	}
	pool := s.conn.Stats()
	stats := DatabaseStats{AllocatedBytes: pages * size, Connections: pool.OpenConnections, InUse: pool.InUse, Waits: pool.WaitCount}
	file, err := os.Stat(s.path + "-wal")
	if err != nil && !errors.Is(err, os.ErrNotExist) {
		return DatabaseStats{}, err
	}
	if err == nil {
		stats.WALBytes = file.Size()
	}
	return stats, nil
}