Port over Icing c++ code from upstream

Change-Id: Ia3981fed7e0e70589efc027d4123f306cdfbe990

1 files changed, 49 insertions, 0 deletions

diff --git a/icing/util/clock.h b/icing/util/clock.h
new file mode 100644
index 0000000..09cb375
--- /dev/null
+++ b/icing/util/clock.h
@@ -0,0 +1,49 @@
+// Copyright (C) 2019 Google LLC
+//
+// 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 ICING_UTIL_CLOCK_H_
+#define ICING_UTIL_CLOCK_H_
+
+#include <ctime>
+
+namespace icing {
+namespace lib {
+
+// Wrapper around real-time clock functions. This is separated primarily so
+// tests can override this clock and inject it into the class under test.
+//
+// A few things to note about std::time_t :
+// From cppreference:
+//   "Although not defined, this is almost always an integral value holding the
+//   number of seconds (not counting leap seconds) since 00:00, Jan 1 1970 UTC,
+//   corresponding to POSIX time"
+//
+// From Wikipedia:
+//   "ISO C defines time_t as an arithmetic type, but does not specify any
+//   particular type, range, resolution, or encoding for it. Also unspecified
+//   are the meanings of arithmetic operations applied to time values."
+class Clock {
+ public:
+  virtual ~Clock() {}
+
+  // Returns:
+  //   The current time defined by the clock on success
+  //   std::time_t(-1) on error
+  virtual std::time_t GetCurrentSeconds() const { return std::time(nullptr); }
+};
+
+}  // namespace lib
+}  // namespace icing
+
+#endif  // ICING_UTIL_CLOCK_H_