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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_multi.h"
#include "mongo/db/pipeline/window_function/window_function.h"
namespace mongo {
using FirstLastSense = AccumulatorFirstLastN::Sense;
template <FirstLastSense S>
class WindowFunctionFirstLastN : public WindowFunctionState {
public:
static std::unique_ptr<WindowFunctionState> create(ExpressionContext* const expCtx,
long long n) {
return std::make_unique<WindowFunctionFirstLastN<S>>(expCtx, n);
}
static AccumulationExpression parse(ExpressionContext* const expCtx,
BSONElement elem,
VariablesParseState vps) {
return AccumulatorFirstLastN::parseFirstLastN<S>(expCtx, elem, vps);
}
static const char* getName() {
if constexpr (S == FirstLastSense::kFirst) {
return AccumulatorFirstN::getName();
} else {
return AccumulatorLastN::getName();
}
}
WindowFunctionFirstLastN(ExpressionContext* const expCtx, long long n)
: WindowFunctionState(expCtx), _n(n) {
_memUsageBytes = sizeof(*this);
}
void add(Value value) final {
auto valToInsert = value.missing() ? Value(BSONNULL) : value;
_memUsageBytes += valToInsert.getApproximateSize();
_values.emplace_back(std::move(valToInsert));
}
void remove(Value value) final {
auto valToRemove = value.missing() ? Value(BSONNULL) : value;
tassert(5788400, "Can't remove from an empty WindowFunctionFirstLastN", !_values.empty());
auto iter = _values.begin();
tassert(5788402,
str::stream() << "Attempted to remove an element other than the first element from "
"window function "
<< getName(),
_expCtx->getValueComparator().compare(*iter, valToRemove) == 0);
_memUsageBytes -= iter->getApproximateSize();
_values.erase(iter);
}
Value getValue() const final {
if (_values.empty())
return Value(std::vector<Value>{});
auto n = static_cast<size_t>(_n);
if (n >= _values.size()) {
return Value(std::vector<Value>(_values.begin(), _values.end()));
}
if constexpr (S == FirstLastSense::kFirst) {
return Value(std::vector<Value>(_values.begin(), _values.begin() + n));
} else {
return Value(std::vector<Value>(_values.end() - n, _values.end()));
}
}
void reset() final {
_values.clear();
_memUsageBytes = sizeof(*this);
}
private:
std::vector<Value> _values;
long long _n;
};
using WindowFunctionFirstN = WindowFunctionFirstLastN<FirstLastSense::kFirst>;
using WindowFunctionLastN = WindowFunctionFirstLastN<FirstLastSense::kLast>;
}; // namespace mongo
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