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/**
* Copyright (C) 2021-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/db/pipeline/accumulator.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/expression.h"
namespace mongo {
/**
* A WindowFunctionState is a mutable, removable accumulator.
*
* Implementations must ensure that 'remove()' undoes 'add()' when called in FIFO order.
* For example:
* 'add(x); add(y); remove(x)' == 'add(y)'
* 'add(a); add(b); add(z); remove(a); remove(b)' == 'add(z)'
*/
class WindowFunctionState {
public:
virtual ~WindowFunctionState() = default;
virtual void add(Value) = 0;
virtual void remove(Value) = 0;
virtual Value getValue() const = 0;
virtual void reset() = 0;
};
template <AccumulatorMinMax::Sense sense>
class WindowFunctionMinMax : public WindowFunctionState {
public:
static Value getDefault() {
return Value{BSONNULL};
};
/**
* The comparator must outlive the constructed WindowFunctionMinMax.
*/
explicit WindowFunctionMinMax(const ValueComparator& cmp)
: _values(cmp.makeOrderedValueMultiset()) {}
void add(Value value) final {
_values.insert(std::move(value));
}
void remove(Value value) final {
// std::multiset::insert is guaranteed to put the element after any equal elements
// already in the container. So find() / erase() will remove the oldest equal element,
// which is what we want, to satisfy "remove() undoes add() when called in FIFO order".
auto iter = _values.find(std::move(value));
tassert(5371400, "Can't remove from an empty WindowFunctionMinMax", iter != _values.end());
_values.erase(iter);
}
void reset() final {
_values.clear();
}
Value getValue() const final {
if (_values.empty())
return getDefault();
switch (sense) {
case AccumulatorMinMax::Sense::kMin:
return *_values.begin();
case AccumulatorMinMax::Sense::kMax:
return *_values.rbegin();
}
MONGO_UNREACHABLE_TASSERT(5371401);
}
protected:
// Holds all the values in the window, in order, with constant-time access to both ends.
ValueMultiset _values;
};
using WindowFunctionMin = WindowFunctionMinMax<AccumulatorMinMax::Sense::kMin>;
using WindowFunctionMax = WindowFunctionMinMax<AccumulatorMinMax::Sense::kMax>;
} // namespace mongo
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