From 6693339bc0832c5c79c0f422166c36659b7c7496 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20B=C3=BCrgmann?= <martin.buergmann@gmail.com>
Date: Sat, 4 Apr 2020 12:58:51 +0200
Subject: [PATCH] Now you can insert form elements add a position

---
 cppcms/form.h | 38 +++++++++++++++++++++++++++++++++++
 src/form.cpp  | 55 +++++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 83 insertions(+), 10 deletions(-)

diff --git a/cppcms/form.h b/cppcms/form.h
index 33e5a6b9..b183458d 100644
--- a/cppcms/form.h
+++ b/cppcms/form.h
@@ -242,12 +242,31 @@ namespace cppcms {
 		///
 		virtual void clear();
 
+		///
+		/// Add \a subform at specific position to form. The ownership is not
+		/// transferred to the parent.
+		/// When \a index is negative it is interpreted from the back, if index
+		/// is greater than the number of already added elemenets, the element
+		/// will simply add at the end (or beginning if negative).
+		///
+		void add(int index, form &subform);
+
 		///
 		/// Add \a subform to form. The ownership is not transferred to
 		/// the parent.
 		///
 		void add(form &subform);
 
+		///
+		/// Add \a subform at specific position to form. The ownership is
+		/// transferred to the parent and the subform will be destroyed together
+		/// with the parent.
+		/// When \a index is negative it is interpreted from the back, if index
+		/// is greater than the number of already added elemenets, the element
+		/// will simply add at the end (or beginning if negative).
+		///
+		void attach(int index, form *subform);
+
 		///
 		/// Add \a subform to form. The ownership is transferred to
 		/// the parent and the subform will be destroyed together with
@@ -255,12 +274,31 @@ namespace cppcms {
 		///
 		void attach(form *subform);
 
+		///
+		/// Add \a widget at specific position to form. The ownership is not
+		/// transferred to to the parent.
+		/// When \a index is negative it is interpreted from the back, if index
+		/// is greater than the number of already added elemenets, the element
+		/// will simply add at the end (or beginning if negative).
+		///
+		void add(int index, widgets::base_widget &widget);
+
 		///
 		/// Add \a widget to form. The ownership is not transferred to
 		/// to the parent.
 		///
 		void add(widgets::base_widget &widget);
 
+		///
+		/// Add \a widget at specific position to form. The ownership is
+		/// transferred to the parent and the widget will be destroyed together
+		/// with the parent.
+		/// When \a index is negative it is interpreted from the back, if index
+		/// is greater than the number of already added elemenets, the element
+		/// will simply add at the end (or beginning if negative).
+		///
+		void attach(int index, widgets::base_widget *widget);
+
 		///
 		/// Add \a widget to form. The ownership is transferred to
 		/// the parent and the widget will be destroyed together with
diff --git a/src/form.cpp b/src/form.cpp
index 2ccc0be7..508fb889 100644
--- a/src/form.cpp
+++ b/src/form.cpp
@@ -150,27 +150,62 @@ void form::clear()
 	}
 }
 
+namespace {
+
+// std::advance is not applicable because UB when n > size
+template<class Iter>
+Iter advance(Iter it, const Iter& end, int n) {
+	while (n--)
+		if (it == end)
+			break;
+		else
+			++it;
+	return it;
+}
+template<class V, class T>
+void add_impl(form* self, V& elements_, T* form, bool owning, int position) {
+	if (position < 0) {
+		auto it = advance(elements_.rend(), elements_.rbegin(), position * -1);
+		elements_.emplace(it.base() -1, form, owning);
+	} else {
+		auto it = advance(elements_.begin(), elements_.end(), position);
+		elements_.emplace(it, form, owning);
+	}
+	form->parent(self);
+}
+}
+void form::add(int index, widgets::base_widget &form)
+{
+	add_impl(this, elements_, &form, false, index);
+}
+void form::add(int index, form &subform)
+{
+	add_impl(this, elements_, &subform, false, index);
+}
 void form::add(widgets::base_widget &form)
 {
-	elements_.push_back(widget_type(&form,false));
-	form.parent(this);
+	add_impl(this, elements_, &form, false, elements_.size());
 }
 void form::add(form &subform)
 {
-	elements_.push_back(widget_type(&subform,false));
-	subform.parent(this);
+	add_impl(this, elements_, &subform, false, elements_.size());
 }
 
+void form::attach(int index, form *subform)
+{
+	add_impl(this, elements_, subform, true, index);
+}
+void form::attach(int index, widgets::base_widget *form)
+{
+	add_impl(this, elements_, form, true, index);
+}
 void form::attach(form *subform)
 {
-	elements_.push_back(widget_type(subform,true));
-	subform->parent(this);
+	add_impl(this, elements_, subform, true, elements_.size());
 }
-
-void form::attach(widgets::base_widget *subform)
+void form::attach(widgets::base_widget *form)
 {
-	elements_.push_back(widget_type(subform,true));
-	subform->parent(this);
+	add_impl(this, elements_, form, true, elements_.size());
 }
 
 struct form::iterator::_data {};