Started work on multi file hooks loading

hook/hook.go

@@ -273,7 +273,7 @@ func (h *ResponseHeaders) String() string {
 		result[idx] = fmt.Sprintf("%s=%s", responseHeader.Name, responseHeader.Value)
 	}
 
-	return fmt.Sprint(strings.Join(result, ", "))
+	return strings.Join(result, ", ")
 }
 
 // Set method appends new Header object from header=value notation
@@ -288,6 +288,23 @@ func (h *ResponseHeaders) Set(value string) error {
 	return nil
 }
 
+// HooksFiles is a slice of String
+type HooksFiles []string
+
+func (h *HooksFiles) String() string {
+	if len(*h) == 0 {
+		return "hooks.json"
+	}
+
+	return strings.Join(*h, ", ")
+}
+
+// Set method appends new string
+func (h *HooksFiles) Set(value string) error {
+	*h = append(*h, value)
+	return nil
+}
+
 // Hook type is a structure containing details for a single hook
 type Hook struct {
 	ID                       string          `json:"id,omitempty"`
@@ -426,6 +443,19 @@ func (h *Hooks) LoadFromFile(path string) error {
 	return e
 }
 
+// Append appends hooks unless the new hooks contain a hook with an ID that already exists
+func (h *Hooks) Append(other *Hooks) error {
+	for _, hook := range *other {
+		if h.Match(hook.ID) != nil {
+			return fmt.Errorf("hook with ID %s is already defined", hook.ID)
+		}
+
+		*h = append(*h, hook)
+	}
+
+	return nil
+}
+
 // Match iterates through Hooks and returns first one that matches the given ID,
 // if no hook matches the given ID, nil is returned
 func (h *Hooks) Match(id string) *Hook {