Add string-to-string time conversion.

src/time.cpp

@@ -16,16 +16,25 @@
 
 #include "time.hpp"
 
+#include <chrono>
 #include <cstdint>
 #include <ctime>
+#include <iomanip>
+#include <sstream>
+#include <string>
 #include <string_view>
 
 namespace FediBlock::time
 {
 
+using std::get_time;
+using std::strftime;
+using std::string;
 using std::string_view;
+using std::stringstream;
 using std::time_t;
 using std::uint16_t;
+using std::chrono::system_clock;
 
 string to_string(const system_clock::time_point &timepoint,
                  const string_view format)
@@ -35,9 +44,20 @@ string to_string(const system_clock::time_point &timepoint,
     std::tm *tm{nullptr};
     tm = std::gmtime(&time);
     char buffer[bufsize];
-    std::strftime(buffer, bufsize, format.data(), tm);
+    strftime(buffer, bufsize, format.data(), tm);
 
     return buffer;
 }
 
+string to_string(const string_view timestring, const string_view format)
+{
+    std::tm tm{};
+    tm.tm_isdst = -1; // Detect daylight saving time.
+    stringstream ss(timestring.data());
+    ss >> get_time(&tm,
+                   "%Y-%m-%dT%T"); // Assume time is UTC (%F doesn't work).
+
+    return to_string(system_clock::from_time_t(timegm(&tm)), format);
+}
+
 } // namespace FediBlock::time

src/time.hpp

@@ -34,11 +34,26 @@ using std::chrono::system_clock;
  *  @param  timepoint The point in time to convert.
  *  @param  format    Format of the string (optional, defaults to %FT%T).
  *
+ *  See strftime(3) for information on how to construct a valid format string.
+ *
  *  @since  0.2.0
  */
 [[nodiscard]] string to_string(const system_clock::time_point &timepoint,
                                string_view format = "%FT%T");
 
+/*!
+ *  @brief  Return date and time as string.
+
+ *  @param  timestring The time string to convert. Must be %FT%T.
+ *  @param  format     Format of the string (optional, defaults to %FT%T).
+ *
+ *  See strftime(3) for information on how to construct a valid format string.
+ *
+ *  @since  0.2.0
+ */
+[[nodiscard]] string to_string(string_view timestring,
+                               string_view format = "%FT%T");
+
 } // namespace FediBlock::time
 
 #endif // FEDIBLOCK_BACKEND_TIME_HPP