SERVER-51665 Implement $dateDiff expression in SBE

2 files changed, 31 insertions, 17 deletions

diff --git a/src/mongo/db/query/datetime/date_time_support.cpp b/src/mongo/db/query/datetime/date_time_support.cpp
index dc73c52485f..425a4349abc 100644
--- a/src/mongo/db/query/datetime/date_time_support.cpp
+++ b/src/mongo/db/query/datetime/date_time_support.cpp
@@ -677,6 +677,19 @@ inline long long dateDiffMillisecond(Date_t startDate, Date_t endDate) {
             !overflow::sub(endDate.toMillisSinceEpoch(), startDate.toMillisSinceEpoch(), &result));
     return result;
 }
+
+// A mapping from a string expression of TimeUnit to TimeUnit.
+static const StringMap<TimeUnit> timeUnitNameToTimeUnitMap{
+    {"year", TimeUnit::year},
+    {"quarter", TimeUnit::quarter},
+    {"month", TimeUnit::month},
+    {"week", TimeUnit::week},
+    {"day", TimeUnit::day},
+    {"hour", TimeUnit::hour},
+    {"minute", TimeUnit::minute},
+    {"second", TimeUnit::second},
+    {"millisecond", TimeUnit::millisecond},
+};
 }  // namespace
 
 long long dateDiff(Date_t startDate, Date_t endDate, TimeUnit unit, const TimeZone& timezone) {
@@ -709,25 +722,20 @@ long long dateDiff(Date_t startDate, Date_t endDate, TimeUnit unit, const TimeZo
     }
 }
 
-TimeUnit parseTimeUnit(const std::string& unitName) {
-    static const StringMap<TimeUnit> timeUnitNameToTimeUnitMap{
-        {"year", TimeUnit::year},
-        {"quarter", TimeUnit::quarter},
-        {"month", TimeUnit::month},
-        {"week", TimeUnit::week},
-        {"day", TimeUnit::day},
-        {"hour", TimeUnit::hour},
-        {"minute", TimeUnit::minute},
-        {"second", TimeUnit::second},
-        {"millisecond", TimeUnit::millisecond},
-    };
-    auto iterator = timeUnitNameToTimeUnitMap.find(unitName);
+TimeUnit parseTimeUnit(const std::string_view unitName) {
+    const StringData unitNameAsStringData{unitName.data(), unitName.length()};
+    auto iterator = timeUnitNameToTimeUnitMap.find(unitNameAsStringData);
     uassert(ErrorCodes::FailedToParse,
-            str::stream() << "unknown time unit value: " << unitName,
+            str::stream() << "unknown time unit value: " << unitNameAsStringData,
             iterator != timeUnitNameToTimeUnitMap.end());
     return iterator->second;
 }
 
+bool isValidTimeUnit(const std::string_view unitName) {
+    return timeUnitNameToTimeUnitMap.find(StringData{unitName.data(), unitName.length()}) !=
+        timeUnitNameToTimeUnitMap.end();
+}
+
 void TimelibRelTimeDeleter::operator()(timelib_rel_time* relTime) {
     timelib_rel_time_dtor(relTime);
 }
@@ -894,5 +902,4 @@ Date_t dateAdd(Date_t date, TimeUnit unit, long long amount, const TimeZone& tim
     timelib_time_dtor(newTime);
     return returnDate;
 }
-
 }  // namespace mongo
diff --git a/src/mongo/db/query/datetime/date_time_support.h b/src/mongo/db/query/datetime/date_time_support.h
index dee5bcb56f6..640ba01c5a6 100644
--- a/src/mongo/db/query/datetime/date_time_support.h
+++ b/src/mongo/db/query/datetime/date_time_support.h
@@ -451,7 +451,7 @@ public:
 
     /**
      * Returns a TimeZone object representing the zone given by 'timeZoneId', or throws an exception
-     * if the 'timeZoneId' was not recognized.
+     * if it is not a recognized time zone.
      */
     TimeZone getTimeZone(StringData timeZoneId) const;
 
@@ -496,7 +496,14 @@ private:
  * TimeUnit. Throws an exception with error code ErrorCodes::FailedToParse when passed an invalid
  * name.
  */
-TimeUnit parseTimeUnit(const std::string& unitName);
+TimeUnit parseTimeUnit(const std::string_view unitName);
+
+/**
+ * Returns true if 'unitName' is a valid time unit, meaning that it can be parsed by the
+ * 'parseTimeUnit()' function into one of the units represented by the 'TimeUnit' enum. Otherwise
+ * returns 'false'.
+ */
+bool isValidTimeUnit(const std::string_view unitName);
 
 /**
  * A custom-deleter which destructs a timelib_rel_time* when it goes out of scope.