Implement descending criticality thresholds

JSON can't represent infinity (at least not portably) so we need to use
a finite value. I certainly won't be worried if a disk will fill up in
32 years.

dashboard.py

@@ -77,7 +77,29 @@ class Widget:
                 return f"hsl(0, 100%, {brightness}%)"
         else:
             log.debug("the other side")
-            return "#CCC"
+            if self.lastvalue > self.stops[0]:
+                log.debug("definitely ok")
+                return f"hsl(120, 100%, {brightness}%)"
+            elif self.lastvalue > self.stops[1]:
+                log.debug("mostly ok")
+                hue = 120 - round(
+                                (self.lastvalue - self.stops[0])
+                              / (self.stops[1] - self.stops[0])
+                              * 60
+                            )
+                return f"hsl({hue}, 100%, {brightness}%)"
+            elif self.lastvalue > self.stops[2]:
+                log.debug("maybe fail")
+                hue =  60 - round(
+                                (self.lastvalue - self.stops[1])
+                              / (self.stops[2] - self.stops[1])
+                              * 60
+                            )
+                return f"hsl({hue}, 100%, {brightness}%)"
+            else:
+                log.debug("definitely fail")
+                return f"hsl(0, 100%, {brightness}%)"
+
 
 class TimeSeries(Widget):
     def __init__(self, d):
@@ -94,6 +116,7 @@ class Gauge(Widget):
     @property
     def gaugepos(self):
         max_value = max([d[1] for d in self.lts.data])
+        max_value = max(max_value, 1) # ensure positive
         log.debug("max_value = %s", max_value)
         return self.lastvalue / max_value * self.gaugesize
 

process_queue

@@ -35,7 +35,7 @@ class DiskFullPredictor:
             return
         current_used_bytes = lts.data[-1][1]
         current_usable_bytes = usable_lts.data[-1][1]
-        tuf = float('inf')
+        tuf = 1E9
         for d in reversed(lts.data):
             if d[1] < current_usable_bytes * 0.1:
                 continue # for sanity