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/*
* Copyright 2018 Google
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_COMPARISON_H_
#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_COMPARISON_H_
#if __OBJC__
#import <Foundation/Foundation.h>
#endif
#include <sys/types.h>
#include <cstdint>
#include <functional>
#include <string>
#include <vector>
#include "Firestore/core/src/firebase/firestore/util/string_apple.h"
#include "absl/strings/string_view.h"
namespace firebase {
namespace firestore {
namespace util {
/**
* An enumeration describing the result of a three-way comparison among
* strongly-ordered values (i.e. where comparison between values always yields
* less-than, equal-to, or greater-than).
*
* This is equivalent to:
*
* * NSComparisonResult from the iOS/macOS Foundation framework.
* * std::strong_ordering from C++20
*
* The values of the constants are specifically chosen so as to make casting
* between this type and NSComparisonResult possible.
*/
enum class ComparisonResult {
/** The left hand side was less than the right. */
Ascending = -1,
/** The left hand side was equal to the right. */
Same = 0,
/** The left hand side was greater than the right. */
Descending = 1
};
/**
* Returns the reverse order (i.e. Ascending => Descending) etc.
*/
constexpr ComparisonResult ReverseOrder(ComparisonResult result) {
return static_cast<ComparisonResult>(-static_cast<int>(result));
}
/**
* A generalized comparator for types in Firestore, with ordering defined
* according to Firestore's semantics. This is useful as argument to e.g.
* std::sort.
*
* Comparators are only defined for the limited set of types for which
* Firestore defines an ordering.
*/
template <typename T>
struct Comparator {
// By default comparison is not defined
};
/** Compares two strings. */
template <>
struct Comparator<absl::string_view> {
bool operator()(const absl::string_view& left,
const absl::string_view& right) const;
};
/** Compares two bools: false < true. */
template <>
struct Comparator<bool> : public std::less<bool> {};
/** Compares two int32_t. */
template <>
struct Comparator<int32_t> : public std::less<int32_t> {};
/** Compares two int64_t. */
template <>
struct Comparator<int64_t> : public std::less<int64_t> {};
/** Compares two doubles (using Firestore semantics for NaN). */
template <>
struct Comparator<double> {
bool operator()(double left, double right) const;
};
/** Compare two byte sequences. */
// TODO(wilhuff): perhaps absl::Span<uint8_t> would be better?
template <>
struct Comparator<std::vector<uint8_t>>
: public std::less<std::vector<uint8_t>> {};
/**
* Perform a three-way comparison between the left and right values using
* the appropriate Comparator for the values based on their type.
*/
template <typename T, typename C = Comparator<T>>
ComparisonResult Compare(const T& left,
const T& right,
const C& less_than = C()) {
if (less_than(left, right)) {
return ComparisonResult::Ascending;
} else if (less_than(right, left)) {
return ComparisonResult::Descending;
} else {
return ComparisonResult::Same;
}
}
#if __OBJC__
/**
* Returns true if the given ComparisonResult and NSComparisonResult have the
* same integer values (at compile time).
*/
constexpr bool EqualValue(ComparisonResult lhs, NSComparisonResult rhs) {
return static_cast<int>(lhs) == static_cast<int>(rhs);
}
/**
* Performs a three-way comparison, identically to Compare, but converts the
* result to an NSComparisonResult.
*
* This function exists for interoperation with Objective-C++ and should
* eventually be removed.
*/
template <typename T>
inline NSComparisonResult WrapCompare(const T& left, const T& right) {
static_assert(EqualValue(ComparisonResult::Ascending, NSOrderedAscending),
"Ascending invalid");
static_assert(EqualValue(ComparisonResult::Same, NSOrderedSame),
"Same invalid");
static_assert(EqualValue(ComparisonResult::Descending, NSOrderedDescending),
"Descending invalid");
return static_cast<NSComparisonResult>(Compare<T>(left, right));
}
#endif
/** Compares a double and an int64_t. */
ComparisonResult CompareMixedNumber(double doubleValue, int64_t longValue);
/** Normalizes a double and then return the raw bits as a uint64_t. */
uint64_t DoubleBits(double d);
/**
* Compares the bitwise representation of two doubles, but normalizes NaN
* values. This is similar to what the backend and android clients do, including
* comparing -0.0 as not equal to 0.0.
*/
bool DoubleBitwiseEquals(double left, double right);
/**
* Computes a bitwise hash of a double, but normalizes NaN values, suitable for
* use when using FSTDoublesAreBitwiseEqual for equality.
*/
size_t DoubleBitwiseHash(double d);
} // namespace util
} // namespace firestore
} // namespace firebase
#endif // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_COMPARISON_H_
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