Add percentChange function

docs/custom-api.md

@@ -445,6 +445,7 @@ The following helper functions provided by Glance are available:
 - `sortByTime(key string, layout string, order string, arr []JSON): []JSON`: Sorts an array of JSON objects by a time key in either ascending or descending order. The format must be provided in Go's [date format](https://pkg.go.dev/time#pkg-constants).
 - `concat(strings ...string) string`: Concatenates multiple strings together.
 - `unique(key string, arr []JSON) []JSON`: Returns a unique array of JSON objects based on the given key.
+- `percentChange(current float, previous float) float`: Calculates the percentage change between two numbers.
 
 The following helper functions provided by Go's `text/template` are available:
 

internal/glance/utils.go

@@ -18,6 +18,13 @@ var sequentialWhitespacePattern = regexp.MustCompile(`\s+`)
 var whitespaceAtBeginningOfLinePattern = regexp.MustCompile(`(?m)^\s+`)
 
 func percentChange(current, previous float64) float64 {
+	if previous == 0 {
+		if current == 0 {
+			return 0 // 0% change if both are 0
+		}
+		return 100 // 100% increase if going from 0 to something
+	}
+
 	return (current/previous - 1) * 100
 }
 

internal/glance/widget-custom-api.go

@@ -546,6 +546,7 @@ var customAPITemplateFuncs = func() template.FuncMap {
 			regex := getCachedRegexp(pattern)
 			return itemAtIndexOrDefault(regex.FindStringSubmatch(s), 1, "")
 		},
+		"percentChange": percentChange,
 		"sortByString": func(key, order string, results []decoratedGJSONResult) []decoratedGJSONResult {
 			sort.Slice(results, func(a, b int) bool {
 				if order == "asc" {