Add new APIs, peek selection and change page

Context:Peek

src/rime/context.cc

@@ -110,17 +110,33 @@ void Context::Clear() {
 }
 
 bool Context::Select(size_t index) {
-  if (composition_.empty())
+  bool result = Peek(index);
+  if (result)
+    select_notifier_(this);
+  return result;
+}
+
+bool Context::Peek(size_t index) {
+  if (composition_.empty() || !composition_.back().menu)
     return false;
   Segment& seg(composition_.back());
-  if (auto cand = seg.GetCandidateAt(index)) {
-    seg.selected_index = index;
-    seg.status = Segment::kSelected;
-    DLOG(INFO) << "Selected: '" << cand->text() << "', index = " << index;
-    select_notifier_(this);
-    return true;
+  size_t new_index = index;
+  if (index < 0) {
+    DLOG(INFO) << "selection index < 0, fallback to 0";
+    new_index = 0;
+  } else {
+    size_t candidate_count = seg.menu->Prepare(index + 1);
+    if (index >= candidate_count) {
+      DLOG(INFO) << "selection index exceed candidate pool, fallback to last";
+      new_index = candidate_count - 1;
+    }
   }
-  return false;
+  size_t previous_index = seg.selected_index;
+  seg.selected_index = new_index;
+  update_notifier_(this);
+
+  DLOG(INFO) << "Selection changed from: " << previous_index << " to: " << new_index;
+  return true;
 }
 
 bool Context::DeleteCandidate(

src/rime/context.h

@@ -45,6 +45,7 @@ class Context {
 
   // return false if there is no candidate at index
   bool Select(size_t index);
+  bool Peek(size_t index);
   bool DeleteCandidate(size_t index);
   // return false if there's no candidate for current segment
   bool ConfirmCurrentSelection();

src/rime_api.cc

@@ -970,11 +970,43 @@ static bool do_with_candidate_on_current_page(
     return (ctx->*verb)(page_start + index);
 }
 
+Bool RimeChangePage(RimeSessionId session_id, Bool previous) {
+  an<Session> session(Service::instance().GetSession(session_id));
+  if (!session)
+    return False;
+  Context *ctx = session->context();
+  if (!ctx || !ctx->HasMenu())
+    return False;
+  Schema *schema = session->schema();
+  if (!schema)
+    return False;
+  size_t page_size = (size_t)schema->page_size();
+  const auto& seg(ctx->composition().back());
+  size_t selected_index = seg.selected_index;
+  ctx->composition().back().tags.insert("paging");
+  if (previous) {
+    size_t index = selected_index <= page_size ? 0 : selected_index - page_size;
+    DLOG(INFO) << "Current selection: " << selected_index << ", Previous page, Peek at " << index;
+    return ctx->Peek(index);
+  } else {
+    size_t index = selected_index + page_size;
+    DLOG(INFO) << "Current selection: " << selected_index << ", Next page, Peek at " << index;
+    return ctx->Peek(index);
+  }
+}
+
+Bool RimePeekCandidate(RimeSessionId session_id, size_t index) {
+  return do_with_candidate(session_id, index, &Context::Peek);
+}
 
 Bool RimeSelectCandidate(RimeSessionId session_id, size_t index) {
   return do_with_candidate(session_id, index, &Context::Select);
 }
 
+Bool RimePeekCandidateOnCurrentPage(RimeSessionId session_id, size_t index) {
+  return do_with_candidate_on_current_page(session_id, index, &Context::Peek);
+}
+
 Bool RimeSelectCandidateOnCurrentPage(RimeSessionId session_id, size_t index) {
   return do_with_candidate_on_current_page(session_id, index, &Context::Select);
 }
@@ -1116,6 +1148,9 @@ RIME_API RimeApi* rime_get_api() {
     s_api.get_state_label = &RimeGetStateLabel;
     s_api.delete_candidate = &RimeDeleteCandidate;
     s_api.delete_candidate_on_current_page = &RimeDeleteCandidateOnCurrentPage;
+    s_api.peek_candidate = &RimePeekCandidate;
+    s_api.peek_candidate_on_current_page = &RimePeekCandidateOnCurrentPage;
+    s_api.change_page = &RimeChangePage;
     s_api.get_state_label_abbreviated = &RimeGetStateLabelAbbreviated;
   }
   return &s_api;

src/rime_api.h

@@ -524,6 +524,8 @@ typedef struct rime_api_t {
 
   //! select a candidate at the given index in candidate list.
   Bool (*select_candidate)(RimeSessionId session_id, size_t index);
+  //! peek a selection without commiting to it
+  Bool (*peek_candidate)(RimeSessionId session_id, size_t index);
 
   //! get the version of librime
   const char* (*get_version)(void);
@@ -533,6 +535,10 @@ typedef struct rime_api_t {
 
   //! select a candidate from current page.
   Bool (*select_candidate_on_current_page)(RimeSessionId session_id, size_t index);
+  //! peek a selection without commiting to it
+  Bool (*peek_candidate_on_current_page)(RimeSessionId session_id, size_t index);
+
+  Bool (*change_page)(RimeSessionId session_id, Bool previous);
 
   //! access candidate list.
   Bool (*candidate_list_begin)(RimeSessionId session_id, RimeCandidateListIterator* iterator);