fix issues with paged_vecvec and vecvec

include/cista/containers/paged.h

@@ -97,8 +97,12 @@ struct paged {
     std::memcpy(&data_[offset], &x, sizeof(T));
   }
 
-  value_type* data(page_t const& p) { return &data_[p.start_]; }
-  value_type const* data(page_t const& p) const { return &data_[p.start_]; }
+  value_type* data(page_t const& p) {
+    return data_.empty() ? nullptr : &data_[p.start_];
+  }
+  value_type const* data(page_t const& p) const {
+    return data_.empty() ? nullptr : &data_[p.start_];
+  }
 
   value_type* begin(page_t const& p) { return data(p); }
   value_type const* begin(page_t const& p) const { return data(p); }

include/cista/containers/paged_vecvec.h

@@ -65,7 +65,7 @@ struct paged_vecvec {
       return (*this)[size() - 1U];
     }
 
-    reference operator*() const { return *this; }
+    const_bucket operator*() const { return *this; }
 
     size_type size() const { return pv_->page(i_).size_; }
     bool empty() const { return size() == 0U; }
@@ -161,6 +161,14 @@ struct paged_vecvec {
       (*this)[size() - 1U] = x;
     }
 
+    template <typename Arg>
+    iterator insert(iterator const it, Arg&& el) {
+      auto const old_offset = std::distance(begin(), it);
+      auto const old_size = size();
+      push_back(data_value_type{el});
+      return std::rotate(begin() + old_offset, begin() + old_size, end());
+    }
+
     template <typename T = std::decay_t<data_value_type>,
               typename = std::enable_if_t<std::is_same_v<T, char>>>
     std::string_view view() const {
@@ -196,7 +204,7 @@ struct paged_vecvec {
       return *(begin() + i);
     }
 
-    reference operator*() const { return *this; }
+    bucket operator*() const { return *this; }
 
     operator const_bucket() const { return {pv_, i_}; }
 
@@ -286,7 +294,7 @@ struct paged_vecvec {
   const_bucket front() const { return at(Key{0}); }
   const_bucket back() const { return at(Key{size() - 1}); }
 
-  size_type size() const { return idx_.size(); }
+  base_t<Key> size() const { return idx_.size(); }
   bool empty() const { return idx_.empty(); }
 
   bucket begin() { return front(); }

include/cista/containers/vecvec.h

@@ -159,10 +159,12 @@ struct basic_vecvec {
 
   private:
     index_value_type bucket_begin_idx() const {
-      return to_idx(map_->bucket_starts_[i_]);
+      return map_->empty() ? index_value_type{}
+                           : to_idx(map_->bucket_starts_[i_]);
     }
     index_value_type bucket_end_idx() const {
-      return to_idx(map_->bucket_starts_[i_ + 1U]);
+      return map_->empty() ? index_value_type{}
+                           : to_idx(map_->bucket_starts_[i_ + 1U]);
     }
     bool is_inside_bucket(std::size_t const i) const {
       return bucket_begin_idx() + i < bucket_end_idx();
@@ -335,11 +337,10 @@ struct basic_vecvec {
     if (bucket_starts_.empty()) {
       bucket_starts_.emplace_back(index_value_type{0U});
     }
-    bucket_starts_.emplace_back(
-        static_cast<index_value_type>(data_.size() + bucket.size()));
     data_.insert(std::end(data_),  //
                  std::make_move_iterator(std::begin(bucket)),
                  std::make_move_iterator(std::end(bucket)));
+    bucket_starts_.emplace_back(data_.size());
   }
 
   bucket add_back_sized(std::size_t const bucket_size) {