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<?php
/**
* SPDX-FileCopyrightText: 2023 Nextcloud GmbH and Nextcloud contributors
* SPDX-License-Identifier: AGPL-3.0-or-later
*/
namespace OC\Files\Search\QueryOptimizer;
use OC\Files\Search\SearchBinaryOperator;
use OC\Files\Search\SearchComparison;
use OCP\Files\Search\ISearchBinaryOperator;
use OCP\Files\Search\ISearchOperator;
/**
* Attempt to transform
*
* (A AND B) OR (A AND C) OR (A AND D AND E) into A AND (B OR C OR (D AND E))
*
* This is always valid because logical 'AND' and 'OR' are distributive[1].
*
* [1]: https://en.wikipedia.org/wiki/Distributive_property
*/
class MergeDistributiveOperations extends ReplacingOptimizerStep {
public function processOperator(ISearchOperator &$operator): bool {
if ($operator instanceof SearchBinaryOperator) {
// either 'AND' or 'OR'
$topLevelType = $operator->getType();
// split the arguments into groups that share a first argument
$groups = $this->groupBinaryOperatorsByChild($operator->getArguments(), 0);
$outerOperations = array_map(function (array $operators) use ($topLevelType) {
// no common operations, no need to change anything
if (count($operators) === 1) {
return $operators[0];
}
// for groups with size >1 we know they are binary operators with at least 1 child
/** @var ISearchBinaryOperator $firstArgument */
$firstArgument = $operators[0];
// we already checked that all arguments have the same type, so this type applies for all, either 'AND' or 'OR'
$innerType = $firstArgument->getType();
// the common operation we move out ('A' from the example)
$extractedLeftHand = $firstArgument->getArguments()[0];
// for each argument we remove the extracted operation to get the leftovers ('B', 'C' and '(D AND E)' in the example)
// note that we leave them inside the "inner" binary operation for when the "inner" operation contained more than two parts
// in the (common) case where the "inner" operation only has 1 item left it will be cleaned up in a follow up step
$rightHandArguments = array_map(function (ISearchOperator $inner) {
/** @var ISearchBinaryOperator $inner */
$arguments = $inner->getArguments();
array_shift($arguments);
if (count($arguments) === 1) {
return $arguments[0];
}
return new SearchBinaryOperator($inner->getType(), $arguments);
}, $operators);
// combine the extracted operation ('A') with the remaining bit ('(B OR C OR (D AND E))')
// note that because of how distribution work, we use the "outer" type "inside" and the "inside" type "outside".
$extractedRightHand = new SearchBinaryOperator($topLevelType, $rightHandArguments);
return new SearchBinaryOperator(
$innerType,
[$extractedLeftHand, $extractedRightHand]
);
}, $groups);
// combine all groups again
$operator = new SearchBinaryOperator($topLevelType, $outerOperations);
parent::processOperator($operator);
return true;
}
return parent::processOperator($operator);
}
/**
* Group a list of binary search operators that have a common argument
*
* Non-binary operators, or empty binary operators will each get their own 1-sized group
*
* @param ISearchOperator[] $operators
* @return ISearchOperator[][]
*/
private function groupBinaryOperatorsByChild(array $operators, int $index = 0): array {
$result = [];
foreach ($operators as $operator) {
if ($operator instanceof ISearchBinaryOperator && count($operator->getArguments()) > 0) {
/** @var SearchBinaryOperator|SearchComparison $child */
$child = $operator->getArguments()[$index];
$childKey = (string)$child;
$result[$childKey][] = $operator;
} else {
$result[] = [$operator];
}
}
return array_values($result);
}
}
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