redshift: Only print period information when it changes

This change adds functions to determine what the current period is
so we can keep track and only print the period when it changes.

src/redshift.c

@@ -294,6 +294,20 @@ typedef enum {
 	PROGRAM_MODE_MANUAL
 } program_mode_t;
 
+/* Periods of day. */
+typedef enum {
+	PERIOD_DAYTIME = 0,
+	PERIOD_NIGHT,
+	PERIOD_TRANSITION
+} period_t;
+
+/* Names of periods of day */
+static const char *period_names[] = {
+	"Daytime",
+	"Night",
+	"Transition"
+};
+
 #if defined(HAVE_SIGNAL_H) && !defined(__WIN32__)
 
 static volatile sig_atomic_t exiting = 0;
@@ -325,18 +339,46 @@ static float transition_low = TRANSITION_LOW;
 static float transition_high = TRANSITION_HIGH;
 
 
-/* Print which period (night, day or transition) we're currently in. */
-static void
-print_period(double elevation)
+/* Determine which period we are currently in. */
+static period_t
+get_period(double elevation)
 {
 	if (elevation < transition_low) {
-		printf(_("Period: Night\n"));
+		return PERIOD_NIGHT;
 	} else if (elevation < transition_high) {
-		float a = (transition_low - elevation) /
-			(transition_low - transition_high);
-		printf(_("Period: Transition (%.2f%% day)\n"), a*100);
+		return PERIOD_TRANSITION;
 	} else {
-		printf(_("Period: Daytime\n"));
+		return PERIOD_DAYTIME;
+	}
+}
+
+/* Determine how far through the transition we are. */
+static double
+get_transition_progress(double elevation)
+{
+	if (elevation < transition_low) {
+		return 0.0;
+	} else if (elevation < transition_high) {
+		return (transition_low - elevation) /
+			(transition_low - transition_high);
+	} else {
+		return 1.0;
+	}
+}
+
+/* Print verbose description of the given period. */
+static void
+print_period(period_t period, double transition)
+{
+	switch (period) {
+	case PERIOD_NIGHT:
+	case PERIOD_DAYTIME:
+		printf(_("Period: %s\n"), period_names[period]);
+		break;
+	case PERIOD_TRANSITION:
+		printf(_("Period: %s (%.2f%% day)\n"),
+		       period_names[period], transition*100);
+		break;
 	}
 }
 
@@ -1289,7 +1331,9 @@ main(int argc, char *argv[])
 		interpolate_color_settings(elevation, &day, &night, &interp);
 
 		if (verbose || mode == PROGRAM_MODE_PRINT) {
-			print_period(elevation);
+			period_t period = get_period(elevation);
+			double transition = get_transition_progress(elevation);
+			print_period(period, transition);
 			printf(_("Color temperature: %uK\n"), interp.temperature);
 			printf(_("Brightness: %.2f\n"), interp.brightness);
 		}
@@ -1373,6 +1417,7 @@ main(int argc, char *argv[])
 		/* Save previous colors so we can avoid
 		   printing status updates if the values
 		   did not change. */
+		period_t prev_period = -1;
 		color_setting_t prev_interp =
 			{ -1, { NAN, NAN, NAN }, NAN };
 
@@ -1446,7 +1491,17 @@ main(int argc, char *argv[])
 			color_setting_t interp;
 			interpolate_color_settings(elevation, &day, &night, &interp);
 
-			if (verbose) print_period(elevation);
+			/* Print period if it changed during this update,
+			   or if we are in transition. In transition we
+			   print the progress, so we always print it in
+			   that case. */
+			period_t period = get_period(elevation);
+			if (verbose && (period != prev_period ||
+					period == PERIOD_TRANSITION)) {
+				double transition =
+					get_transition_progress(elevation);
+				print_period(period, transition);
+			}
 
 			/* Ongoing short transition */
 			if (short_trans_delta) {
@@ -1501,6 +1556,7 @@ main(int argc, char *argv[])
 			}
 
 			/* Save temperature as previous */
+			prev_period = period;
 			memcpy(&prev_interp, &interp,
 			       sizeof(color_setting_t));