Add some additional API for context words and only keep words based on max lm order

src/libime/core/languagemodel.cpp

@@ -148,6 +148,8 @@ LanguageModel::LanguageModel(
 
 LanguageModel::~LanguageModel() {}
 
+size_t LanguageModel::maxOrder() { return KENLM_MAX_ORDER; }
+
 std::shared_ptr<const StaticLanguageModelFile>
 LanguageModel::languageModelFile() const {
     FCITX_D();

src/libime/core/languagemodel.h

@@ -73,6 +73,8 @@ class LIBIMECORE_EXPORT LanguageModel : public LanguageModelBase {
         std::shared_ptr<const StaticLanguageModelFile> file = nullptr);
     virtual ~LanguageModel();
 
+    static size_t maxOrder();
+
     std::shared_ptr<const StaticLanguageModelFile> languageModelFile() const;
 
     WordIndex beginSentence() const override;

src/libime/pinyin/pinyincontext.cpp

@@ -10,6 +10,7 @@
 #include <functional>
 #include <iterator>
 #include <limits>
+#include <list>
 #include <memory>
 #include <span>
 #include <stdexcept>
@@ -81,7 +82,7 @@ class PinyinContextPrivate : public fcitx::QPtrHolder<PinyinContext> {
     mutable std::vector<SentenceResult> candidatesToCursor_;
     mutable std::unordered_set<std::string> candidatesToCursorSet_;
     std::vector<fcitx::ScopedConnection> conn_;
-    std::vector<WordNode> contextWords_;
+    std::list<WordNode> contextWords_;
 
     size_t alignCursorToNextSegment() const {
         FCITX_Q();
@@ -988,10 +989,38 @@ void PinyinContext::setContextWords(
     const std::vector<std::string> &contextWords) {
     FCITX_D();
     d->contextWords_.clear();
-    for (const auto &word : contextWords) {
+    appendContextWords(contextWords);
+}
+
+void PinyinContext::clearContextWords() {
+    FCITX_D();
+    d->contextWords_.clear();
+}
+
+void PinyinContext::appendContextWords(
+    const std::vector<std::string> &contextWords) {
+    FCITX_D();
+
+    size_t needed = LanguageModel::maxOrder() - 1;
+
+    for (const auto &word :
+         std::span{contextWords}.last(std::min(contextWords.size(), needed))) {
         d->contextWords_.push_back(
             WordNode(word, d->ime_->model()->index(word)));
     }
+    while (d->contextWords_.size() > needed) {
+        d->contextWords_.pop_front();
+    }
+}
+
+std::vector<std::string> PinyinContext::contextWords() const {
+    FCITX_D();
+    std::vector<std::string> words;
+    words.reserve(d->contextWords_.size());
+    for (const auto &word : d->contextWords_) {
+        words.push_back(word.word());
+    }
+    return words;
 }
 
 bool PinyinContext::learnWord() { return false; }

src/libime/pinyin/pinyincontext.h

@@ -144,6 +144,26 @@ class LIBIMEPINYIN_EXPORT PinyinContext : public InputBuffer {
      */
     void setContextWords(const std::vector<std::string> &contextWords);
 
+    /**
+     * Clear context words.
+     * @since 1.1.13
+     */
+    void clearContextWords();
+
+    /**
+     * Append context words for better prediction.
+     * @param contextWords The context words.
+     * @since 1.1.13
+     */
+    void appendContextWords(const std::vector<std::string> &contextWords);
+
+    /**
+     * Get context words for better prediction.
+     * @return current context words
+     * @since 1.1.13
+     */
+    std::vector<std::string> contextWords() const;
+
 protected:
     bool typeImpl(const char *s, size_t length) override;
 

test/testpinyincontext.cpp

@@ -10,7 +10,9 @@
 #include <memory>
 #include <ostream>
 #include <sstream>
+#include <string>
 #include <string_view>
+#include <vector>
 #include <fcitx-utils/log.h>
 #include "libime/core/historybigram.h"
 #include "libime/core/lattice.h"
@@ -262,7 +264,15 @@ int main() {
         }
         {
             c.clear();
-            c.setContextWords({"他", "爱"});
+            c.setContextWords({"我", "不", "知道"});
+            FCITX_ASSERT(c.contextWords() ==
+                         std::vector<std::string>{"不", "知道"});
+            c.setContextWords({"谁", "他"});
+            FCITX_ASSERT(c.contextWords() ==
+                         std::vector<std::string>{"谁", "他"});
+            c.appendContextWords({"爱"});
+            FCITX_ASSERT(c.contextWords() ==
+                         std::vector<std::string>{"他", "爱"});
             c.type("ta");
             size_t i = 0;
             for (const auto &candidate : c.candidatesToCursor()) {