fix(coderd): truncate task prompt to 160 characters in notifications (#20147)

Truncates the task prompt used in notifications to a maximum of 160
characters. The length of 160 characters was chosen arbitrarily.

coderd/util/strings/strings.go

@@ -23,15 +23,64 @@ func JoinWithConjunction(s []string) string {
 	)
 }
 
-// Truncate returns the first n characters of s.
-func Truncate(s string, n int) string {
+type TruncateOption int
+
+func (o TruncateOption) String() string {
+	switch o {
+	case TruncateWithEllipsis:
+		return "TruncateWithEllipsis"
+	case TruncateWithFullWords:
+		return "TruncateWithFullWords"
+	default:
+		return fmt.Sprintf("TruncateOption(%d)", o)
+	}
+}
+
+const (
+	// TruncateWithEllipsis adds a Unicode ellipsis character to the end of the string.
+	TruncateWithEllipsis TruncateOption = 1 << 0
+	// TruncateWithFullWords ensures that words are not split in the middle.
+	// As a special case, if there is no word boundary, the string is truncated.
+	TruncateWithFullWords TruncateOption = 1 << 1
+)
+
+// Truncate truncates s to n characters.
+// Additional behaviors can be specified using TruncateOptions.
+func Truncate(s string, n int, opts ...TruncateOption) string {
+	var options TruncateOption
+	for _, opt := range opts {
+		options |= opt
+	}
 	if n < 1 {
 		return ""
 	}
 	if len(s) <= n {
 		return s
 	}
-	return s[:n]
+
+	maxLen := n
+	if options&TruncateWithEllipsis != 0 {
+		maxLen--
+	}
+	var sb strings.Builder
+	// If we need to truncate to full words, find the last word boundary before n.
+	if options&TruncateWithFullWords != 0 {
+		lastWordBoundary := strings.LastIndexFunc(s[:maxLen], unicode.IsSpace)
+		if lastWordBoundary < 0 {
+			// We cannot find a word boundary. At this point, we'll truncate the string.
+			// It's better than nothing.
+			_, _ = sb.WriteString(s[:maxLen])
+		} else { // lastWordBoundary <= maxLen
+			_, _ = sb.WriteString(s[:lastWordBoundary])
+		}
+	} else {
+		_, _ = sb.WriteString(s[:maxLen])
+	}
+
+	if options&TruncateWithEllipsis != 0 {
+		_, _ = sb.WriteString("…")
+	}
+	return sb.String()
 }
 
 var bmPolicy = bluemonday.StrictPolicy()