Restore union of terms in buildNgramsLists

src/Gargantext/Core/Text/List.hs

@@ -30,7 +30,7 @@ import Data.Text qualified as T
 import Data.Tuple.Extra (both)
 import Gargantext.API.Ngrams (NgramsRepoElement)
 import Gargantext.API.Ngrams.Tools (getNodeStory)
-import Gargantext.API.Ngrams.Types (NgramsElement, NgramsTerm(..), ngramsElementFromRepo, ne_ngrams, ne_list)
+import Gargantext.API.Ngrams.Types (NgramsElement(..), ngramsElementFromRepo, NgramsTerm(..), ne_ngrams, ne_list)
 import Gargantext.Core.NodeStory
 import Gargantext.Core.Text (size)
 import Gargantext.Core.Text.List.Group ( toGroupedTree, setScoresWithMap, toGroupedTreeInstitutes )
@@ -105,9 +105,7 @@ buildNgramsLists env user (nodeId, listId) mCid pref gp = do
   -- such that if we run multiple searches the maplist will evolve organically.
   $(txLogLocM) DEBUG "Trying to fetch existing terms..."
   let buildStrategy = toNgramsBuildStrategy pref
-  existingTerms <- case buildStrategy of
-    MergeWithExistingNgrams -> pure mempty
-    OverrideExistingNgrams  -> do
+  existingTerms <- do
       archiveState <- getNodeStory env listId
       let (ngramsState  :: Map NgramsType (Map NgramsTerm NgramsRepoElement))  = archiveState ^. a_state
       let (ngramsState' :: Map.Map NgramsType (Map NgramsTerm NgramsElement)) =
@@ -120,7 +118,7 @@ buildNgramsLists env user (nodeId, listId) mCid pref gp = do
   -- Combine the maplist just computed with the existing one (see #517).
   let freshTerms = Map.unions $ ngTerms : instTerms : othersTerms
   case buildStrategy of
-    MergeWithExistingNgrams -> pure freshTerms
+    MergeWithExistingNgrams -> pure $ Map.unionWith      merge freshTerms existingTerms
     OverrideExistingNgrams  -> pure $ Map.differenceWith diffy freshTerms existingTerms
 
 newtype IndexedNgramsElement = IndexedNgramsElement { _IndexedNgramsElement :: NgramsElement }
@@ -138,6 +136,12 @@ diffy fresh existing = Just $ unwrap $ Set.toList $ Set.difference (wrap fresh)
     wrap   = Set.fromList . map IndexedNgramsElement
     unwrap = map _IndexedNgramsElement
 
+merge :: [NgramsElement] -> [NgramsElement] -> [NgramsElement]
+merge fresh existing = unwrap $ Set.toList $ Set.union (wrap fresh) (wrap existing)
+  where
+    wrap   = Set.fromList . map IndexedNgramsElement
+    unwrap = map _IndexedNgramsElement
+
 _debugDumpExisting :: Map NgramsType [NgramsElement] -> Text
 _debugDumpExisting mp = T.unlines $ map processIt $ Map.toList mp
   where