Implement negate_search

rslib/backend.proto

@@ -87,6 +87,7 @@ service BackendService {
     rpc NormalizeSearch (String) returns (String);
     rpc SearchCards (SearchCardsIn) returns (SearchCardsOut);
     rpc SearchNotes (SearchNotesIn) returns (SearchNotesOut);
+    rpc NegateSearch (String) returns (String);
     rpc FindAndReplace (FindAndReplaceIn) returns (UInt32);
 
     // scheduling

rslib/src/backend/mod.rs

@@ -32,7 +32,9 @@ use crate::{
     },
     sched::cutoff::local_minutes_west_for_stamp,
     sched::timespan::{answer_button_time, time_span},
-    search::{normalize_search, SortMode},
+    search::{
+        concatenate_searches, negate_search, normalize_search, replace_search_term, SortMode,
+    },
     stats::studied_today,
     sync::{
         get_remote_sync_meta, sync_abort, sync_login, FullSyncProgress, NormalSyncProgress,
@@ -430,6 +432,9 @@ impl BackendService for Backend {
         })
     }
 
+    fn negate_search(&self, input: pb::String) -> Result<pb::String> {
+        Ok(negate_search(&input.val)?.into())
+    }
     fn find_and_replace(&self, input: pb::FindAndReplaceIn) -> BackendResult<pb::UInt32> {
         let mut search = if input.regex {
             input.search

rslib/src/search/mod.rs

@@ -5,4 +5,4 @@ mod sqlwriter;
 mod writer;
 
 pub use cards::SortMode;
-pub use writer::normalize_search;
+pub use writer::{concatenate_searches, negate_search, normalize_search, replace_search_term};

rslib/src/search/writer.rs

@@ -14,8 +14,32 @@ pub fn normalize_search(input: &str) -> Result<String> {
     Ok(write_nodes(&parse(input)?))
 }
 
-fn write_nodes(nodes: &[Node]) -> String {
-    nodes.iter().map(|node| write_node(node)).collect()
+/// Take an Anki-style search string and return the negated counterpart.
+/// Empty searches (whole collection) remain unchanged.
+pub fn negate_search(input: &str) -> Result<String> {
+    let mut nodes = parse(input)?;
+    use Node::*;
+    Ok(if nodes.len() == 1 {
+        let node = nodes.remove(0);
+        match node {
+            Not(n) => write_node(&n),
+            Search(SearchNode::WholeCollection) => "".to_string(),
+            Group(_) | Search(_) => write_node(&Not(Box::new(node))),
+            _ => unreachable!(),
+        }
+    } else {
+        write_node(&Not(Box::new(Group(nodes))))
+    })
+}
+}
+
+}
+
+fn write_nodes<'a, I>(nodes: I) -> String
+where
+    I: IntoIterator<Item = &'a Node<'a>>,
+{
+    nodes.into_iter().map(|node| write_node(node)).collect()
 }
 
 fn write_node(node: &Node) -> String {