package sqlite

import (
	"context"
	"database/sql"
	"strings"

	_ "github.com/mattn/go-sqlite3"
)

// https://github.com/mattn/go-sqlite3#connection-string
var dsnOpts = []string{
	"_foreign_keys=1",
	"_journal_mode=WAL",
	"_synchronous=NORMAL",
	"_busy_timeout=5000",
	"_txlock=immediate",
}

func Open(dbPath string) (*sql.DB, error) {
	if err := initFile(dbPath); err != nil {
		return nil, err
	}
	return sql.Open("sqlite3", dbPath+"?"+strings.Join(dsnOpts, "&"))
}

// auto_vacuum only sticks if it is set before the file's first write, which
// switching to wal is. setting it takes the write lock even when it's already
// set, so it can't live in the dsn, where every new pool connection would wait
// out the busy timeout behind whatever transaction is open, and it's skipped
// for files that already have content
func initFile(dbPath string) error {
	db, err := sql.Open("sqlite3", dbPath+"?_busy_timeout=5000")
	if err != nil {
		return err
	}
	defer db.Close()
	conn, err := db.Conn(context.Background())
	if err != nil {
		return err
	}
	defer conn.Close()

	var pages int
	if err := conn.QueryRowContext(context.Background(), `pragma page_count`).Scan(&pages); err != nil {
		return err
	}
	if pages > 0 {
		return nil
	}
	for _, pragma := range []string{`pragma auto_vacuum = incremental`, `pragma journal_mode = wal`} {
		if _, err := conn.ExecContext(context.Background(), pragma); err != nil {
			return err
		}
	}
	return nil
}