Improve update interval calculation

src/timer_base.cpp

@@ -28,7 +28,20 @@ namespace duck {
 namespace {
 	[[gnu::pure]]
 	unsigned long time_interval (const oro::Header& header, double min_wait, double extra) {
-		return std::max(header.retry_after / header.rate_limit + extra, min_wait);
+		//The way I understand retry_after as returned by the origins server is
+		//that it's just how long you need to wait before all your retries
+		//reset to the max. When you get for example to 5/8 retries, even if you
+		//wait some time that number will never go back to 6. At some point it
+		//will just resent to 8. You can do as many as 8 calls one after the
+		//other too, it simply means that until the counter resets back to 8 you
+		//just won't be able to do anything else.
+		const double rem = static_cast<double>(header.rate_limit_remaining);
+		const auto& retry_after = header.retry_after;
+		const double ra = static_cast<double>(retry_after);
+
+		const auto wait = static_cast<unsigned long>(ra / (rem + 1.0) + 0.5);
+		const auto extra_sec = (wait == retry_after ? 1UL : 0UL);
+		return std::max(wait + extra_sec + extra, min_wait);
 	}
 
 	oro::Timestamp calc_next_update (const oro::Header& header, double min_wait, double extra) {