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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.
*/
#include "mongo/db/pipeline/window_function/window_function_exec_linear_fill.h"
namespace {
mongo::Value interpolate(
mongo::Value x1, mongo::Value y1, mongo::Value x2, mongo::Value y2, mongo::Value xCoord) {
// Given two known points (x1, y1) and (x2, y2) and a value x that lies between those two
// points, we solve (or fill) for y with the following formula: y = y1 + (x - x1) * ((y2 -
// y1)/(x2 - x1))
return uassertStatusOK(mongo::ExpressionSubtract::apply(y2, y1).andThen([&](auto&& numerator) {
return mongo::ExpressionSubtract::apply(x2, x1).andThen([&](auto&& denominator) {
return mongo::ExpressionDivide::apply(numerator, denominator)
.andThen([&](auto&& quotient) {
return mongo::ExpressionSubtract::apply(xCoord, x1)
.andThen([&](auto&& difference) {
return mongo::ExpressionMultiply::apply(quotient, difference)
.andThen([&](auto&& product) {
return mongo::ExpressionAdd::apply(y1, product);
});
});
});
});
}));
}
} // namespace
namespace mongo {
boost::optional<Value> WindowFunctionExecLinearFill::evaluateInput(const Document& doc) {
Value fillFieldValue = _input->evaluate(doc, &_input->getExpressionContext()->variables);
if (!fillFieldValue.nullish()) {
return boost::optional<Value>(fillFieldValue);
}
return boost::none;
}
boost::optional<std::pair<Value, Value>> WindowFunctionExecLinearFill::findX2Y2() {
auto index = 1;
while (const auto doc = _iter[index]) {
if (const auto fillFieldValue = evaluateInput(*doc)) {
Value sortFieldValue =
_sortBy->evaluate(*doc, &_sortBy->getExpressionContext()->variables);
if (!sortFieldValue.nullish()) {
_prevX2Y2 = boost::optional<std::pair<Value, Value>>(
std::make_pair(sortFieldValue, *fillFieldValue));
return _prevX2Y2;
}
}
index++;
}
return boost::none;
}
Value WindowFunctionExecLinearFill::getNext() {
const auto currentDoc = *_iter[0];
Value fillFieldValue = _input->evaluate(currentDoc, &_input->getExpressionContext()->variables);
uassert(ErrorCodes::TypeMismatch,
str::stream() << "Value to be filled must be numeric or nullish, but found "
<< fillFieldValue.getType(),
fillFieldValue.numeric() || fillFieldValue.nullish());
Value sortFieldValue =
_sortBy->evaluate(currentDoc, &_sortBy->getExpressionContext()->variables);
uassert(ErrorCodes::TypeMismatch,
str::stream() << "Value of the sortBy field must be numeric or a date, but found "
<< sortFieldValue.getType(),
sortFieldValue.numeric() || sortFieldValue.coercibleToDate());
// We do not allow repeated sort field values. This is because if we have the following
// collection that has a repeated sort value and different fill values, eg [(10, 100), (10,
// -100), (20, null), (30, 50)], it is unclear if the left value, (X1, Y1), should be (10, 100)
// or (10, -100) when we interpolate on the third document.
uassert(6050106,
"There can be no repeated values in the sort field",
ValueComparator{}.evaluate(sortFieldValue != _lastSeenElement));
if (!_lastSeenElement.missing())
// Throw an error If the sort value was previously of type numeric, but we've just found a
// date (or vice versa).
uassert(ErrorCodes::TypeMismatch,
str::stream() << "Conflicting sort value types, previously received type "
<< _lastSeenElement.getType() << ", but found "
<< sortFieldValue.getType(),
(sortFieldValue.coercibleToDate() && _lastSeenElement.coercibleToDate()) ||
(sortFieldValue.numeric() && _lastSeenElement.numeric()));
_lastSeenElement = sortFieldValue;
// We have found either (x1, y1) or (x2, y2).
if (!fillFieldValue.nullish()) {
// We can expire all documents before the current document in the cache. We don't want to
// expire the current document, because it may become our *first* non-null, ie (x1, x2), for
// the next set of null documents.
_iter.manualExpireUpTo(-1);
// If (x2, y2) is known, it becomes our (x1, y1) for the next sequence of null documents.
// Otherwise the current document becomes (x1, y1).
_prevX1Y1 = _prevX2Y2 ? _prevX2Y2
: boost::optional<std::pair<Value, Value>>(
std::make_pair(sortFieldValue, fillFieldValue));
_prevX2Y2 = boost::none;
return fillFieldValue;
}
// Interpolation requires that the documents with null values for the field we are filling,
// be bookended with documents with non-null sort and input field numeric values.
// To do this, we store the previous known coordinates so that we don't scan the same null
// documents multiple times as we search for a non-null value.
auto firstCoord = _prevX1Y1;
if (!firstCoord) {
return kDefault;
}
auto secondCoord = _prevX2Y2 ? _prevX2Y2 : findX2Y2();
if (!secondCoord) {
return kDefault;
}
return interpolate(firstCoord->first,
firstCoord->second,
secondCoord->first,
secondCoord->second,
sortFieldValue);
}
} // namespace mongo
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