export function query(sql, ...args) {
  validateQuery(sql, ...args);
  return buildQuery(sql, ...args);
}

// Allow for slightly more complex parameter substitution.
// Instances of "???" will be replaced by the same number of comma-separated
// question marks as items in the corresponding nested parateter array
// eg. buildQuery("SELECT (???) FROM ?", [["col1", "col2"], "table1"])
// would output: ["SELECT (?, ?) FROM ?", ["col1", "col2", "table1"]]
export function buildQuery(sql, ...args) {
  const parts = sql.split("???");
  const subParamLengths = args
    .filter(Array.isArray)
    .map((a) => a.length);
  if (parts.length !== subParamLengths.length + 1) {
    throw new PawSQLiteError("Unable to build query: sub-" +
      "paramters do not match sub-paramters in query");
  }

  const newQuery = parts.reduce((p1, p2, i) => {
    const length = subParamLengths[i - 1];
    return p1 + new Array(length).fill("?").join(", ") + p2;
  });

  const flatParams = args.reduce((acc, v) => {
    if (Array.isArray(v)) {
      Array.prototype.push.apply(acc, v);
    } else {
      acc.push(v);
    }
    return acc;
  }, []);

  return [newQuery, ...flatParams];
}

export function validateQuery(sql, ...args) {
  const reg = /^\s*(BEGIN|END|COMMIT|ROLLBACK)(?:[^A-Z]|$)/i;
  const match = reg.exec(sql);
  if (match) {
    const statement = match[1].toUpperCase();
    throw new PawSQLiteError("Manually managing transactions is " +
      "forbidden. Found: \"" + statement + "\" statement.");
  }
}