實作簡單的用戶選字記憶模型

這個模型基本上只是根據游標前的兩個 unigram 記憶當前的用戶選字。當有超過
一個以上的用戶選字時，則要給每個選字評分。評分標準是選字頻率乘上一個透過
半衰期遞減的最近選字經歷時間。如此一來我們在「少用但最近選過」及「常用但
最近少選」之間取得一個平衡。半衰期透過經驗法則決定。

目前這個簡易模型並不存入磁碟，因此下一次重開機後就會洗掉重來。目前這樣選
擇純粹是因為模型有半衰期，因此長時間存放後還是會遺忘。

這個模型的好處是對既有詞庫提供詞的影響很小，對於連續單字詞的 override 有
還不錯的幫助。如此對於人名、地名、公司名等專有名詞，應該可以減少選字的頻
率。這個模型應用起來的缺點是，如果用戶修改的字詞原來是個雙字詞，例如先前
的兩個 unigram 分別是 A, BB ，而用戶想改的是 BB 的第二個字，使選完後的三
個字分別是 A, B', C，這個 C 往往是記不起來的，但如果一開始用戶逐字選取，
亦即在 BB 只出現 B 時就選取 B' 然後再打 C ，則 A, B', C 這個組合往往能被
正確記憶。實際發生原因在此不討論，但跟底層所用的組字網架的架構有關。確實
要改進的話得要從底層重新架構來下手，但至少目前這個模型給的建議偏保守，不
至干擾原有的預設選字。衡諸得失，這個模型提供一些邊際上的改善，應該還是值
得採用的。

McBopomofo.xcodeproj/project.pbxproj

@@ -49,6 +49,7 @@
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 		D48550A325EBE689006A204C /* OpenCC in Frameworks */ = {isa = PBXBuildFile; productRef = D48550A225EBE689006A204C /* OpenCC */; };
+		6AE30A491F7F40B7008735BD /* UserOverrideModel.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 6AE30A471F7F40B7008735BD /* UserOverrideModel.cpp */; };
 /* End PBXBuildFile section */
 
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@@ -211,6 +212,8 @@
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 		D427A9C025ED28CC005D43E0 /* OpenCCBridge.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OpenCCBridge.swift; sourceTree = "<group>"; };
+		6AE30A471F7F40B7008735BD /* UserOverrideModel.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = UserOverrideModel.cpp; sourceTree = "<group>"; };
+		6AE30A481F7F40B7008735BD /* UserOverrideModel.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = UserOverrideModel.h; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -286,6 +289,10 @@
 				6A0D4ECC15FC0D6400ABF4B3 /* PreferencesWindowController.m */,
 				D427A9C025ED28CC005D43E0 /* OpenCCBridge.swift */,
 				D427A9BF25ED28CC005D43E0 /* McBopomofo-Bridging-Header.h */,
+				6A0D4ECD15FC0D6400ABF4B3 /* UpdateNotificationController.h */,
+				6A0D4ECE15FC0D6400ABF4B3 /* UpdateNotificationController.m */,
+				6AE30A471F7F40B7008735BD /* UserOverrideModel.cpp */,
+				6AE30A481F7F40B7008735BD /* UserOverrideModel.h */,
 			);
 			path = Source;
 			sourceTree = "<group>";
@@ -647,6 +654,7 @@
 				6A0D4F0015FC0DA600ABF4B3 /* VTHorizontalCandidateView.m in Sources */,
 				6AFF97F3253B299E007F1C49 /* OVNonModalAlertWindowController.m in Sources */,
 				6A0D4F0115FC0DA600ABF4B3 /* VTVerticalCandidateController.m in Sources */,
+				6AE30A491F7F40B7008735BD /* UserOverrideModel.cpp in Sources */,
 				6A0D4F0215FC0DA600ABF4B3 /* VTVerticalCandidateTableView.m in Sources */,
 				6A0D4F0315FC0DA600ABF4B3 /* VTVerticalKeyLabelStripView.m in Sources */,
 				D427A9C125ED28CC005D43E0 /* OpenCCBridge.swift in Sources */,

Source/UserOverrideModel.cpp

@@ -0,0 +1,202 @@
+//
+// UserOverrideModel.cpp
+//
+// Copyright (c) 2017 The McBopomofo Project.
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+//
+
+#include "UserOverrideModel.h"
+
+#include <cassert>
+#include <cmath>
+#include <sstream>
+
+using namespace McBopomofo;
+
+// About 20 generations.
+static const double DecayThreshould = 1.0 / 1048576.0;
+
+static double Score(size_t eventCount,
+                    size_t totalCount,
+                    double eventTimestamp,
+                    double timestamp,
+                    double lambda);
+static string WalkedNodesToKey(const std::vector<NodeAnchor>& walkedNodes,
+                               size_t cursorIndex);
+
+UserOverrideModel::UserOverrideModel(size_t capacity, double decayConstant)
+    : m_capacity(capacity) {
+    assert(m_capacity > 0);
+    m_decayExponent = log(0.5) / decayConstant;
+}
+
+void UserOverrideModel::observe(const std::vector<NodeAnchor>& walkedNodes,
+                                size_t cursorIndex,
+                                const string& candidate,
+                                double timestamp) {
+    string key = WalkedNodesToKey(walkedNodes, cursorIndex);
+    auto mapIter = m_lruMap.find(key);
+    if (mapIter == m_lruMap.end()) {
+        auto keyValuePair = KeyObservationPair(key, Observation());
+        Observation& observation = keyValuePair.second;
+        observation.update(candidate, timestamp);
+
+        m_lruList.push_front(keyValuePair);
+        auto listIter = m_lruList.begin();
+        auto lruKeyValue = std::pair<std::string,
+                std::list<KeyObservationPair>::iterator>(key, listIter);
+        m_lruMap.insert(lruKeyValue);
+
+        if (m_lruList.size() > m_capacity) {
+            auto lastKeyValuePair = m_lruList.end();
+            --lastKeyValuePair;
+            m_lruMap.erase(lastKeyValuePair->first);
+            m_lruList.pop_back();
+        }
+    } else {
+        auto listIter = mapIter->second;
+        m_lruList.splice(m_lruList.begin(), m_lruList, listIter);
+
+        auto& keyValuePair = *listIter;
+        Observation& observation = keyValuePair.second;
+        observation.update(candidate, timestamp);
+    }
+}
+
+string UserOverrideModel::suggest(const std::vector<NodeAnchor>& walkedNodes,
+                                  size_t cursorIndex,
+                                  double timestamp) {
+    string key = WalkedNodesToKey(walkedNodes, cursorIndex);
+    auto mapIter = m_lruMap.find(key);
+    if (mapIter == m_lruMap.end()) {
+        return string();
+    }
+
+    auto listIter = mapIter->second;
+    auto& keyValuePair = *listIter;
+    const Observation& observation = keyValuePair.second;
+
+    string candidate;
+    double score = 0.0;
+    for (auto i = observation.overrides.begin();
+         i != observation.overrides.end();
+         ++i) {
+        const Override& o = i->second;
+        double overrideScore = Score(o.count,
+                                     observation.count,
+                                     o.timestamp,
+                                     timestamp,
+                                     m_decayExponent);
+        if (overrideScore == 0.0) {
+            continue;
+        }
+
+        if (overrideScore > score) {
+            candidate = i->first;
+            score = overrideScore;
+        }
+    }
+    return candidate;
+}
+
+void UserOverrideModel::Observation::update(const string& candidate,
+                                            double timestamp) {
+    count++;
+    auto& o = overrides[candidate];
+    o.timestamp = timestamp;
+    o.count++;
+}
+
+static double Score(size_t eventCount,
+                    size_t totalCount,
+                    double eventTimestamp,
+                    double timestamp,
+                    double lambda) {
+    double decay = exp((timestamp - eventTimestamp) * lambda);
+    if (decay < DecayThreshould) {
+        return 0.0;
+    }
+
+    double prob = (double)eventCount / (double)totalCount;
+    return prob * decay;
+}
+
+static string WalkedNodesToKey(const std::vector<NodeAnchor>& walkedNodes,
+                               size_t cursorIndex) {
+    std::stringstream s;
+    std::vector<NodeAnchor> n;
+    size_t ll = 0;
+    for (std::vector<NodeAnchor>::const_iterator i = walkedNodes.begin();
+         i != walkedNodes.end();
+         ++i) {
+        const auto& nn = *i;
+        n.push_back(nn);
+        ll += nn.spanningLength;
+        if (ll >= cursorIndex) {
+            break;
+        }
+    }
+
+    std::vector<NodeAnchor>::const_reverse_iterator r = n.rbegin();
+
+    if (r == n.rend()) {
+        return "";
+    }
+
+    string current = (*r).node->currentKeyValue().key;
+    ++r;
+
+    s.clear();
+    s.str(std::string());
+    if (r != n.rend()) {
+        s << "("
+                << (*r).node->currentKeyValue().key
+                << ","
+                << (*r).node->currentKeyValue().value
+                << ")";
+        ++r;
+    } else {
+        s << "()";
+    }
+    string prev = s.str();
+
+    s.clear();
+    s.str(std::string());
+    if (r != n.rend()) {
+        s << "("
+                << (*r).node->currentKeyValue().key
+                << ","
+                << (*r).node->currentKeyValue().value
+                << ")";
+        ++r;
+    } else {
+        s << "()";
+    }
+    string anterior = s.str();
+
+    s.clear();
+    s.str(std::string());
+    s << "(" << anterior << "," << prev << "," << current << ")";
+
+    return s.str();
+}

Source/UserOverrideModel.h

@@ -0,0 +1,81 @@
+//
+// UserOverrideModel.h
+//
+// Copyright (c) 2017 The McBopomofo Project.
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+//
+
+#ifndef USEROVERRIDEMODEL_H
+#define USEROVERRIDEMODEL_H
+
+#include <list>
+#include <map>
+#include <string>
+
+#include "Gramambular.h"
+
+namespace McBopomofo {
+
+using namespace Formosa::Gramambular;
+
+class UserOverrideModel {
+public:
+    UserOverrideModel(size_t capacity, double decayConstant);
+
+    void observe(const std::vector<NodeAnchor>& walkedNodes,
+                 size_t cursorIndex,
+                 const string& candidate,
+                 double timestamp);
+
+    string suggest(const std::vector<NodeAnchor>& walkedNodes,
+                   size_t cursorIndex,
+                   double timestamp);
+
+private:
+    struct Override {
+        size_t count;
+        double timestamp;
+
+        Override() : count(0), timestamp(0.0) {}
+    };
+
+    struct Observation {
+        size_t count;
+        std::map<std::string, Override> overrides;
+
+        Observation() : count(0) {}
+        void update(const string& candidate, double timestamp);
+    };
+
+    typedef std::pair<std::string, Observation> KeyObservationPair;
+
+    size_t m_capacity;
+    double m_decayExponent;
+    std::list<KeyObservationPair> m_lruList;
+    std::map<std::string, std::list<KeyObservationPair>::iterator> m_lruMap;
+};
+
+};   // namespace McBopomofo
+
+#endif
+