Add custom handler helper (#3)

Author: alexarchambault

directive-handler/src/main/scala/scala/cli/directivehandler/DirectiveHandlers.scala

@@ -2,7 +2,10 @@ package scala.cli.directivehandler
 
 import scala.cli.directivehandler.EitherSequence._
 
-final case class DirectiveHandlers[T](handlers: Seq[DirectiveHandler[T]]) {
+final case class DirectiveHandlers[T](
+  handlers: Seq[DirectiveHandler[T]],
+  customHandler: String => Option[DirectiveHandler[T]] = (key: String) => None
+) {
 
   private lazy val handlersMap = handlers.flatMap(h => h.keys.map(_ -> h)).toMap
 
@@ -19,7 +22,8 @@ final case class DirectiveHandlers[T](handlers: Seq[DirectiveHandler[T]]) {
 
     directives
       .map { dir =>
-        handlersMap.get(dir.directive.key) match {
+        val key = dir.directive.key
+        handlersMap.get(key).orElse(customHandler(key)) match {
           case Some(h) =>
             h.handleValues(dir)
           case None =>
@@ -31,14 +35,25 @@ final case class DirectiveHandlers[T](handlers: Seq[DirectiveHandler[T]]) {
   }
 
   def map[U](f: T => U): DirectiveHandlers[U] =
-    copy(handlers = handlers.map(_.map(f)))
+    copy(
+      handlers = handlers.map(_.map(f)),
+      customHandler = key => customHandler(key).map(_.map(f))
+    )
 
   def mapDirectives[U](f: DirectiveHandler[T] => DirectiveHandler[U]): DirectiveHandlers[U] =
-    copy(handlers = handlers.map(f))
+    copy(
+      handlers = handlers.map(f),
+      customHandler = key => customHandler(key).map(f)
+    )
 
   def ++(other: DirectiveHandlers[T]): DirectiveHandlers[T] =
     if (other.handlers.isEmpty) this
     else if (handlers.isEmpty) other
     else DirectiveHandlers(handlers ++ other.handlers)
 
+  def addCustomHandler(f: String => Option[DirectiveHandler[T]]): DirectiveHandlers[T] =
+    copy(
+      customHandler = key => customHandler(key).orElse(f(key))
+    )
+
 }