LibSQL: Add a helper to convert a SQL::Value to a UnixDateTime

Support for constructing a Value from a UnixDateTime was added in commit
effcd08.

That constructor just stores the value as the number of milliseconds
since epoch. There's no way for outside users to know this, so this adds
a helper to retrieve the value as a UnixDateTime and let SQL::Value be
the source of truth for how the value is encoded/decoded.

Author: trflynn89

Tests/LibSQL/TestSqlValueAndTuple.cpp

@@ -7,6 +7,7 @@
 
 #include <unistd.h>
 
+#include <AK/Time.h>
 #include <LibSQL/Meta.h>
 #include <LibSQL/Row.h>
 #include <LibSQL/Tuple.h>
@@ -471,6 +472,39 @@ TEST_CASE(serialize_boolean_value)
     EXPECT_EQ(v, v2);
 }
 
+TEST_CASE(unix_date_time_value)
+{
+    auto now = UnixDateTime::now();
+    {
+        SQL::Value value(now);
+        EXPECT_EQ(value.type(), SQL::SQLType::Integer);
+
+        auto result = value.to_unix_date_time();
+        VERIFY(result.has_value());
+        EXPECT_EQ(result->milliseconds_since_epoch(), now.milliseconds_since_epoch());
+    }
+    {
+        auto now_plus_10s = now + Duration::from_seconds(10);
+
+        SQL::Value value(now_plus_10s);
+        EXPECT_EQ(value.type(), SQL::SQLType::Integer);
+
+        auto result = value.to_unix_date_time();
+        VERIFY(result.has_value());
+        EXPECT_EQ(result->milliseconds_since_epoch(), now_plus_10s.milliseconds_since_epoch());
+    }
+    {
+        auto now_minus_10s = now - Duration::from_seconds(10);
+
+        SQL::Value value(now_minus_10s);
+        EXPECT_EQ(value.type(), SQL::SQLType::Integer);
+
+        auto result = value.to_unix_date_time();
+        VERIFY(result.has_value());
+        EXPECT_EQ(result->milliseconds_since_epoch(), now_minus_10s.milliseconds_since_epoch());
+    }
+}
+
 TEST_CASE(tuple_value)
 {
     NonnullRefPtr<SQL::TupleDescriptor> descriptor = adopt_ref(*new SQL::TupleDescriptor);

Userland/Libraries/LibSQL/Value.cpp

@@ -277,6 +277,15 @@ Optional<bool> Value::to_bool() const
         });
 }
 
+Optional<UnixDateTime> Value::to_unix_date_time() const
+{
+    auto time = to_int<i64>();
+    if (!time.has_value())
+        return {};
+
+    return UnixDateTime::from_milliseconds_since_epoch(*time);
+}
+
 Optional<Vector<Value>> Value::to_vector() const
 {
     if (is_null() || (type() != SQLType::Tuple))

Userland/Libraries/LibSQL/Value.h

@@ -77,6 +77,7 @@ class Value {
     [[nodiscard]] ByteString to_byte_string() const;
     [[nodiscard]] Optional<double> to_double() const;
     [[nodiscard]] Optional<bool> to_bool() const;
+    [[nodiscard]] Optional<UnixDateTime> to_unix_date_time() const;
     [[nodiscard]] Optional<Vector<Value>> to_vector() const;
 
     template<Integer T>