[io] add helpers for std::chrono

dumux/io/chrono.hh

+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+//
+// SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+// SPDX-License-Identifier: GPL-3.0-or-later
+//
+/*!
+ * \file
+ * \ingroup InputOutput
+ * \brief Helper functions for working with std::chrono.
+ */
+#ifndef DUMUX_IO_CHRONO_HH
+#define DUMUX_IO_CHRONO_HH
+
+#include <cctype>
+#include <chrono>
+#include <string>
+#include <unordered_map>
+#include <algorithm>
+
+namespace Dumux::Chrono {
+
+//! Try to construct a std::chrono::duration from a string
+template<typename Rep, typename Period>
+void toDuration(std::chrono::duration<Rep, Period>& duration, const std::string& s)
+{
+    using std::chrono::duration_cast;
+    using namespace std::chrono_literals;
+    using S = std::chrono::duration<Rep>;
+    static const std::unordered_map<std::string, S> unitMap{
+        {"", S(1)}, // assume seconds if no unit is given
+        {"s", S(1)},
+        {"ns", duration_cast<S>(std::chrono::nanoseconds(1))},
+        {"us", duration_cast<S>(std::chrono::microseconds(1))},
+        {"ms", duration_cast<S>(std::chrono::milliseconds(1))},
+        {"min", duration_cast<S>(std::chrono::minutes(1))},
+        {"h", duration_cast<S>(std::chrono::hours(1))},
+        // After requiring cpp20, we can use the aliases in std::chrono
+        {"d", duration_cast<S>(std::chrono::hours(24))},
+        {"y", duration_cast<S>(std::chrono::seconds(31556952))}  // to match cpp20, see https://en.cppreference.com/w/cpp/chrono/duration
+    };
+
+    const auto unitIt = std::find_if(s.rbegin(), s.rend(), [] (const auto& c) { return !std::isalpha(c); });
+    const auto unitPos = s.size() - std::distance(s.rbegin(), unitIt);
+    const auto number = std::stod(s.substr(0, unitPos));
+    const auto unit = s.substr(unitPos);
+    duration = duration_cast<std::chrono::duration<Rep, Period>>(number*unitMap.at(unit));
+}
+
+//! Try to construct an instance of std::chrono::seconds from a string including a unit suffix
+template<typename Rep = double>
+std::chrono::duration<Rep> toSeconds(const std::string& s)
+{
+    std::chrono::duration<Rep> result;
+    toDuration(result, s);
+    return result;
+}
+
+} // end namespace Dumux::Chrono
+
+#endif