Add functionality to remove categories

lib/entry/libimagentrycategory/src/entry.rs

@@ -41,6 +41,8 @@ pub trait EntryCategory {
 
     fn has_category(&self) -> Result<bool>;
 
+    fn remove_category(&mut self) -> Result<()>;
+
 }
 
 impl EntryCategory for Entry {
@@ -82,4 +84,20 @@ impl EntryCategory for Entry {
             .map(|x| x.is_some())
     }
 
+    /// Remove the category setting
+    ///
+    /// # Warning
+    ///
+    /// This does _only_ remove the category setting in the header. This does _not_ remove the
+    /// internal link to the category entry, nor does it remove the category from the store.
+    fn remove_category(&mut self) -> Result<()> {
+        use toml_query::delete::TomlValueDeleteExt;
+
+        self.get_header_mut()
+            .delete("category.value")
+            .chain_err(|| CEK::HeaderWriteError)
+            .map(|_| ())
+    }
+
+
 }

lib/entry/libimagentrycategory/src/store.rs

@@ -82,9 +82,26 @@ impl CategoryStore for Store {
     }
 
     /// Delete a category
+    ///
+    /// Automatically removes all category settings from entries which are linked to this category.
     fn delete_category(&self, name: &str) -> Result<()> {
+        use libimagentrylink::internal::InternalLinker;
+        use category::Category;
+
         trace!("Deleting category: '{}'", name);
         let sid = mk_category_storeid(self.path().clone(), name)?;
+
+        {
+            let mut category = self.get(sid.clone())?
+                .ok_or_else(|| CEK::CategoryDoesNotExist)
+                .map_err(CE::from_kind)?;
+
+            for entry in category.get_entries(self)? {
+                let mut entry = entry?;
+                let _         = category.remove_internal_link(&mut entry)?;
+            }
+        }
+
         self.delete(sid).map_err(CE::from)
     }