feat: added described.As matcher

described/as.go

@@ -0,0 +1,45 @@
+package described
+
+import (
+	"github.com/maurofran/hamcrest4go/matcher"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+var argPattern = regexp.MustCompile("%([0-9]+)")
+
+// As gets a description decorator matcher.
+func As[T any](template string, matcher matcher.Matcher[T], args ...interface{}) matcher.Matcher[T] {
+	return as[T]{
+		matcher:  matcher,
+		template: template,
+		args:     args,
+	}
+}
+
+type as[T any] struct {
+	matcher  matcher.Matcher[T]
+	template string
+	args     []interface{}
+}
+
+func (a as[T]) Matches(value T) bool {
+	return a.matcher.Matches(value)
+}
+
+func (a as[T]) DescribeTo(description matcher.Description) {
+	parts := argPattern.Split(a.template, -1)
+	for _, part := range parts {
+		if strings.HasPrefix(part, "%") {
+			idx, _ := strconv.Atoi(part[1:])
+			description.AppendValue(a.args[idx])
+		} else {
+			description.AppendText(part)
+		}
+	}
+}
+
+func (a as[T]) DescribeMismatch(actual T, description matcher.Description) {
+	a.matcher.DescribeMismatch(actual, description)
+}