feat(api): allow using wildcards with custom colors

Fixes #537

docs/CONFIGURATION.md

@@ -345,7 +345,10 @@ labels:
   to configure a set of labels with custom predefined colors applied to them
   rather than generated. Colors can be defined as RGB or HEX values.
   Value is a mapping with `label name` -> `label value` -> `color`, see examples
-  below.
+  below. Wildcard values (`*`) are allowed to provide a fallback custom color,
+  which can also be used instead of `color:static` option. Wildcard options
+  are evaluated after exact matches, so it's possible to mix explicit and
+  wildcard values.
   Note: this option is not available via environment variables, you can only set
   it via the config file.
 - `keep` - list of allowed labels, if empty all labels are allowed.
@@ -398,6 +401,20 @@ labels:
         critical: "#ff220c"
 ```
 
+Example with a wildcard value, `info`, `warning` and `critical` will get colors
+as below, but any value not matching those 3 values will use the color from `*`:
+
+```YAML
+labels:
+  color:
+    custom:
+      severity:
+        "*": "#736598"
+        info: "#87c4e0"
+        warning: "#ffae42"
+        critical: "#ff220c"
+```
+
 Defaults:
 
 ```YAML

internal/transform/color_test.go

@@ -75,6 +75,15 @@ var colorTests = []colorTest{
 		},
 		colors: map[string]string{},
 	},
+	{
+		customLabels: map[string]map[string]string{
+			"node": map[string]string{"*": "#123"},
+		},
+		labels: map[string]string{
+			"node": "localhost",
+		},
+		colors: map[string]string{"node": "localhost"},
+	},
 }
 
 func TestColorLabel(t *testing.T) {

internal/transform/colors.go

@@ -39,6 +39,29 @@ func rgbToBrightness(r, g, b uint8) int32 {
 	return ((int32(r) * 299) + (int32(g) * 587) + (int32(b) * 114)) / 1000
 }
 
+func parseCustomColor(colorStore models.LabelsColorMap, key, val, customColor string) {
+	color, err := plcolors.Parse(customColor)
+	if err != nil {
+		log.Warningf("Failed to parse custom color for %s=%s: %s", key, val, err)
+		return
+	}
+	rgb := color.ToRGB()
+	bc := models.Color{
+		Red:   rgb.R,
+		Green: rgb.G,
+		Blue:  rgb.B,
+		Alpha: 255,
+	}
+	brightness := rgbToBrightness(bc.Red, bc.Green, bc.Blue)
+	if _, found := colorStore[key]; !found {
+		colorStore[key] = make(map[string]models.LabelColors)
+	}
+	colorStore[key][val] = models.LabelColors{
+		Brightness: brightness,
+		Background: bc,
+	}
+}
+
 // ColorLabel update karmaColorMap object with a color object generated
 // from label key and value passed here
 // It's used to generate unique colors for configured labels
@@ -46,30 +69,19 @@ func ColorLabel(colorStore models.LabelsColorMap, key string, val string) {
 	// first handle custom colors
 	_, ok := config.Config.Labels.Color.Custom[key]
 	if ok {
-		c, ol := config.Config.Labels.Color.Custom[key][val]
-		if ol {
-			color, err := plcolors.Parse(c)
-			if err != nil {
-				log.Warningf("Failed to parse custom color for %s=%s: %s", key, val, err)
-				return
-			}
-			rgb := color.ToRGB()
-			bc := models.Color{
-				Red:   rgb.R,
-				Green: rgb.G,
-				Blue:  rgb.B,
-				Alpha: 255,
-			}
-			brightness := rgbToBrightness(bc.Red, bc.Green, bc.Blue)
-			if _, found := colorStore[key]; !found {
-				colorStore[key] = make(map[string]models.LabelColors)
-			}
-			colorStore[key][val] = models.LabelColors{
-				Brightness: brightness,
-				Background: bc,
-			}
+		// try matching both key and value
+		customColor, found := config.Config.Labels.Color.Custom[key][val]
+		if found {
+			parseCustomColor(colorStore, key, val, customColor)
+			return
+		}
+
+		// if not found try matching key and wildcard (*)
+		customColor, found = config.Config.Labels.Color.Custom[key]["*"]
+		if found {
+			parseCustomColor(colorStore, key, val, customColor)
+			return
 		}
-		return
 	}
 
 	// if no custom color is found then generate unique colors if needed