fix(plot): single-rounding clock labels, log-axis fits that refuse non-positive data

tests/test_ticks.cpp

@@ -1,11 +1,42 @@
 #include "harness.hpp"
 #include <plot/plot/ticks.hpp>
 #include <cmath>
+#include <cstdlib>
 #include <cstring>
 #include <limits>
 #include <string>
 #include <vector>
 
+namespace {
+
+/// Fails if any colon-separated field of a clock label reaches its radix: minutes
+/// and seconds must stay below 60 and hours below 24 (a value that rounds up to
+/// 24 h takes the day shape instead), so "1:60" or "24:00:00" cannot slip through.
+void check_no_field_reaches_its_radix(const std::string& label) {
+  const std::size_t colons = static_cast<std::size_t>(std::count(label.begin(), label.end(), ':'));
+  if (colons == 0) return;                    // decimal shapes have no fields
+  // Two colons mean h:mm:ss, one means m:ss: only the former starts with hours.
+  const int first_radix = colons >= 2 ? 24 : 60;
+  std::string clock = label;
+  if (!clock.empty() && (clock[0] == '-' || clock[0] == '+')) clock.erase(0, 1);
+  std::size_t start = 0;
+  std::size_t field = 0;
+  while (start <= clock.size()) {
+    const std::size_t colon = clock.find(':', start);
+    const std::string part =
+        clock.substr(start, colon == std::string::npos ? std::string::npos : colon - start);
+    if (!part.empty()) {
+      const int value = std::atoi(part.c_str());
+      PLOT_CHECK(value >= 0 && value < (field == 0 ? first_radix : 60));
+    }
+    if (colon == std::string::npos) break;
+    start = colon + 1;
+    ++field;
+  }
+}
+
+}  // namespace
+
 PLOT_TEST(nice_ticks_are_powers_of_ten_times_125) {
   std::vector<plot::Tick> t;
   plot::generate_ticks({0.0, 1.0}, /*px=*/500.0f, /*min_px=*/60.0f, t);
@@ -107,3 +138,29 @@ PLOT_TEST(format_time_shapes) {
   plot::format_time(86400.0, b, sizeof b);  PLOT_CHECK(std::string(b) == "1d");
   plot::format_time(std::nan(""), b, sizeof b); PLOT_CHECK(std::string(b) == "nan");
 }
+
+PLOT_TEST(format_time_never_lets_a_field_reach_its_radix) {
+  char b[32];
+  // Rounding the seconds leftover on its own used to print 119.5 s as "1:60";
+  // every field now comes from one rounded whole-second count.
+  plot::format_time(119.5, b, sizeof b);    PLOT_CHECK(std::string(b) == "2:00");
+  plot::format_time(3599.5, b, sizeof b);   PLOT_CHECK(std::string(b) == "1:00:00");
+  plot::format_time(59.4999, b, sizeof b);  PLOT_CHECK(std::string(b) == "59.5s");
+  plot::format_time(59.5, b, sizeof b);     PLOT_CHECK(std::string(b) == "1:00");
+  plot::format_time(60.0, b, sizeof b);     PLOT_CHECK(std::string(b) == "1:00");
+  // At 24 h the day field appears, so the hour field never reaches 24.
+  plot::format_time(86399.4, b, sizeof b);  PLOT_CHECK(std::string(b) == "23:59:59");
+  plot::format_time(86399.5, b, sizeof b);  PLOT_CHECK(std::string(b) == "1d");
+  plot::format_time(86400.0, b, sizeof b);  PLOT_CHECK(std::string(b) == "1d");
+
+  // Sweep the boundary neighbourhoods and check every emitted field.
+  const double values[] = {0.4, 0.9995, 1.0, 59.4, 59.4999, 59.5, 59.9, 60.0, 90.0, 119.5, 3599.4,
+                           3599.5, 3599.9, 86399.4, 86399.5, 86399.9, 86400.0, 172800.0, -119.5,
+                           -3599.5, -86399.5};
+  for (const double v : values) {
+    plot::format_time(v, b, sizeof b);
+    const std::string label(b);
+    PLOT_CHECK(!label.empty());
+    check_no_field_reaches_its_radix(label);
+  }
+}