Merge pull request #207 from openvanilla/rebased-user-override-model

Implements an exponential decay-based user candidate override model, rebased from #135

McBopomofo.xcodeproj/project.pbxproj

@@ -49,6 +49,7 @@
 		6AFF97F3253B299E007F1C49 /* OVNonModalAlertWindowController.m in Sources */ = {isa = PBXBuildFile; fileRef = 6AFF97F1253B299E007F1C49 /* OVNonModalAlertWindowController.m */; };
 		D427A9C125ED28CC005D43E0 /* OpenCCBridge.swift in Sources */ = {isa = PBXBuildFile; fileRef = D427A9C025ED28CC005D43E0 /* OpenCCBridge.swift */; };
 		D48550A325EBE689006A204C /* OpenCC in Frameworks */ = {isa = PBXBuildFile; productRef = D48550A225EBE689006A204C /* OpenCC */; };
+		6AE30A491F7F40B7008735BD /* UserOverrideModel.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 6AE30A471F7F40B7008735BD /* UserOverrideModel.cpp */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -211,6 +212,8 @@
 		6AFF97F1253B299E007F1C49 /* OVNonModalAlertWindowController.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = OVNonModalAlertWindowController.m; sourceTree = "<group>"; };
 		D427A9BF25ED28CC005D43E0 /* McBopomofo-Bridging-Header.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "McBopomofo-Bridging-Header.h"; sourceTree = "<group>"; };
 		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/Engine/Gramambular/Bigram.h

@@ -28,6 +28,8 @@
 #ifndef Bigram_h
 #define Bigram_h
 
+#include <vector>
+
 #include "KeyValuePair.h"
 
 namespace Formosa {

Source/Engine/Gramambular/BlockReadingBuilder.h

@@ -199,7 +199,7 @@ namespace Formosa {
             }
         }
         
-        const string BlockReadingBuilder::Join(vector<string>::const_iterator begin, vector<string>::const_iterator end, const string& separator)
+        inline const string BlockReadingBuilder::Join(vector<string>::const_iterator begin, vector<string>::const_iterator end, const string& separator)
         {
             string result;
             for (vector<string>::const_iterator iter = begin ; iter != end ; ) {

Source/Engine/Gramambular/Grid.h

@@ -47,8 +47,19 @@ namespace Formosa {
             size_t width() const;
             vector<NodeAnchor> nodesEndingAt(size_t inLocation);
             vector<NodeAnchor> nodesCrossingOrEndingAt(size_t inLocation);
+
+            // "Freeze" the node with the unigram that represents the selected canditate value.
+            // After this, the node that contains the unigram will always be evaluated to that
+            // unigram, while all other overlapping nodes will be reset to their initial state
+            // (that is, if any of those nodes were "frozen" or fixed, they will be unfrozen.)
             void fixNodeSelectedCandidate(size_t location, const string& value);
 
+            // Similar to fixNodeSelectedCandidate, but instead of "freezing" the node, only
+            // boost the unigram that represents the value with an overriding score. This
+            // has the same side effect as fixNodeSelectedCandidate, which is that all other
+            // overlapping nodes will be reset to their initial state.
+            void overrideNodeScoreForSelectedCandidate(size_t location, const string& value, float overridingScore);
+            
             const string dumpDOT();
             
         protected:
@@ -195,6 +206,24 @@ namespace Formosa {
             }
         }
 
+        inline void Grid::overrideNodeScoreForSelectedCandidate(size_t location, const string& value, float overridingScore)
+        {
+            vector<NodeAnchor> nodes = nodesCrossingOrEndingAt(location);
+            for (auto nodeAnchor : nodes) {
+                auto candidates = nodeAnchor.node->candidates();
+
+                // Reset the candidate-fixed state of every node at the location.
+                const_cast<Node*>(nodeAnchor.node)->resetCandidate();
+
+                for (size_t i = 0, c = candidates.size(); i < c; ++i) {
+                    if (candidates[i].value == value) {
+                        const_cast<Node*>(nodeAnchor.node)->selectFloatingCandidateAtIndex(i, overridingScore);
+                        break;
+                    }
+                }
+            }
+        }
+        
         inline const string Grid::dumpDOT()
         {
             stringstream sst;

Source/Engine/Gramambular/KeyValuePair.h

@@ -28,6 +28,7 @@
 #ifndef KeyValuePair_h
 #define KeyValuePair_h
 
+#include <ostream>
 #include <string>
 
 namespace Formosa {

Source/Engine/Gramambular/Node.h

@@ -47,10 +47,12 @@ namespace Formosa {
             const vector<KeyValuePair>& candidates() const;
             void selectCandidateAtIndex(size_t inIndex = 0, bool inFix = true);
             void resetCandidate();
+            void selectFloatingCandidateAtIndex(size_t index, double score);
             
             const string& key() const;
             double score() const;
             const KeyValuePair currentKeyValue() const;
+            double highestUnigramScore() const;
             
         protected:
             const LanguageModel* m_LM;
@@ -176,6 +178,16 @@ namespace Formosa {
             }
         }
 
+        inline void Node::selectFloatingCandidateAtIndex(size_t index, double score) {
+            if (index >= m_unigrams.size()) {
+                m_selectedUnigramIndex = 0;
+            } else {
+                m_selectedUnigramIndex = index;
+            }
+            m_candidateFixed = false;
+            m_score = score;
+        }
+        
         inline const string& Node::key() const
         {
             return m_key;
@@ -186,6 +198,13 @@ namespace Formosa {
             return m_score;
         }
 
+        inline double Node::highestUnigramScore() const {
+            if (m_unigrams.empty()) {
+                return 0.0;
+            }
+            return m_unigrams[0].score;
+        }
+        
         inline const KeyValuePair Node::currentKeyValue() const
         {
             if(m_selectedUnigramIndex >= m_unigrams.size()) {

Source/InputMethodController.h

@@ -37,6 +37,7 @@
 #import "Mandarin.h"
 #import "Gramambular.h"
 #import "FastLM.h"
+#import "UserOverrideModel.h"
 
 @interface McBopomofoInputMethodController : IMKInputController
 {
@@ -53,6 +54,9 @@
     // latest walked path (trellis) using the Viterbi algorithm
     std::vector<Formosa::Gramambular::NodeAnchor> _walkedNodes;
 
+    // user override model
+    McBopomofo::UserOverrideModel *_uom;
+
     // the latest composing buffer that is updated to the foreground app
     NSMutableString *_composingBuffer;
     NSInteger _latestReadingCursor;

Source/InputMethodController.mm

@@ -76,7 +76,6 @@ static NSString *const kCandidateListTextSizeKey = @"CandidateListTextSize";
 static NSString *const kSelectPhraseAfterCursorAsCandidatePreferenceKey = @"SelectPhraseAfterCursorAsCandidate";
 static NSString *const kUseHorizontalCandidateListPreferenceKey = @"UseHorizontalCandidateList";
 static NSString *const kComposingBufferSizePreferenceKey = @"ComposingBufferSize";
-static NSString *const kDisableUserCandidateSelectionLearning = @"DisableUserCandidateSelectionLearning";
 static NSString *const kChooseCandidateUsingSpaceKey = @"ChooseCandidateUsingSpaceKey";
 static NSString *const kChineseConversionEnabledKey = @"ChineseConversionEnabledKey";
 static NSString *const kEscToCleanInputBufferKey = @"EscToCleanInputBufferKey";
@@ -104,9 +103,6 @@ enum {
     kDeleteKeyCode = 117
 };
 
-// a global object for saving the "learned" user candidate selections
-NSMutableDictionary *gCandidateLearningDictionary = nil;
-NSString *gUserCandidatesDictionaryPath = nil;
 VTCandidateController *gCurrentCandidateController = nil;
 
 // if DEBUG is defined, a DOT file (GraphViz format) will be written to the
@@ -119,6 +115,10 @@ static NSString *const kGraphVizOutputfile = @"/tmp/McBopomofo-visualization.dot
 FastLM gLanguageModel;
 FastLM gLanguageModelPlainBopomofo;
 
+static const int kUserOverrideModelCapacity = 500;
+static const double kObservedOverrideHalflife = 5400.0;  // 1.5 hr.
+McBopomofo::UserOverrideModel gUserOverrideModel(kUserOverrideModelCapacity, kObservedOverrideHalflife);
+
 // https://clang-analyzer.llvm.org/faq.html
 __attribute__((annotate("returns_localized_nsstring")))
 static inline NSString *LocalizationNotNeeded(NSString *s) {
@@ -133,10 +133,7 @@ static inline NSString *LocalizationNotNeeded(NSString *s) {
 - (void)collectCandidates;
 
 - (size_t)actualCandidateCursorIndex;
-- (NSString *)neighborTrigramString;
 
-- (void)_performDeferredSaveUserCandidatesDictionary;
-- (void)saveUserCandidatesDictionary;
 - (void)_showCandidateWindowUsingVerticalMode:(BOOL)useVerticalMode client:(id)client;
 
 - (void)beep;
@@ -153,6 +150,19 @@ public:
     }
 };
 
+static const double kEpsilon = 0.000001;
+
+static double FindHighestScore(const vector<NodeAnchor>& nodes, double epsilon) {
+    double highestScore = 0.0;
+    for (auto ni = nodes.begin(), ne = nodes.end(); ni != ne; ++ni) {
+        double score = ni->node->highestUnigramScore();
+        if (score > highestScore) {
+            highestScore = score;
+        }
+    }
+    return highestScore + epsilon;
+}
+
 @implementation McBopomofoInputMethodController
 - (void)dealloc
 {
@@ -183,6 +193,7 @@ public:
         // create the lattice builder
         _languageModel = &gLanguageModel;
         _builder = new BlockReadingBuilder(_languageModel);
+        _uom = &gUserOverrideModel;
 
         // each Mandarin syllable is separated by a hyphen
         _builder->setJoinSeparator("-");
@@ -190,11 +201,6 @@ public:
         // create the composing buffer
         _composingBuffer = [[NSMutableString alloc] init];
 
-        // populate the settings, by default, DISABLE user candidate learning
-        if (![[NSUserDefaults standardUserDefaults] objectForKey:kDisableUserCandidateSelectionLearning]) {
-            [[NSUserDefaults standardUserDefaults] setObject:(id)kCFBooleanTrue forKey:kDisableUserCandidateSelectionLearning];
-        }
-
         _inputMode = kBopomofoModeIdentifier;
         _chineseConversionEnabled = [[NSUserDefaults standardUserDefaults] boolForKey:kChineseConversionEnabledKey];
     }
@@ -209,30 +215,6 @@ public:
     NSMenuItem *preferenceMenuItem = [[NSMenuItem alloc] initWithTitle:NSLocalizedString(@"McBopomofo Preferences", @"") action:@selector(showPreferences:) keyEquivalent:@""];
     [menu addItem:preferenceMenuItem];
 
-    // If Option key is pressed, show the learning-related menu
-
-    #if DEBUG
-    //I think the following line is 10.6+ specific
-    if ([[NSEvent class] respondsToSelector:@selector(modifierFlags)] && ([NSEvent modifierFlags] & NSAlternateKeyMask)) {
-
-        BOOL learningEnabled = ![[NSUserDefaults standardUserDefaults] boolForKey:kDisableUserCandidateSelectionLearning];
-
-        NSMenuItem *learnMenuItem = [[NSMenuItem alloc] initWithTitle:NSLocalizedString(@"Enable Selection Learning", @"") action:@selector(toggleLearning:) keyEquivalent:@""];
-        learnMenuItem.state = learningEnabled ? NSControlStateValueOn : NSControlStateValueOff;
-        [menu addItem:learnMenuItem];
-
-        if (learningEnabled) {
-            NSString *clearMenuItemTitle = [NSString stringWithFormat:NSLocalizedString(@"Clear Learning Dictionary (%ju Items)", @""), (uintmax_t)[gCandidateLearningDictionary count]];
-            NSMenuItem *clearMenuItem = [[NSMenuItem alloc] initWithTitle:clearMenuItemTitle action:@selector(clearLearningDictionary:) keyEquivalent:@""];
-            [menu addItem:clearMenuItem];
-
-
-            NSMenuItem *dumpMenuItem = [[NSMenuItem alloc] initWithTitle:NSLocalizedString(@"Dump Learning Data to Console", @"") action:@selector(dumpLearningDictionary:) keyEquivalent:@""];
-            [menu addItem:dumpMenuItem];
-        }
-    }
-    #endif //DEBUG
-
     NSMenuItem *chineseConversionMenuItem = [[NSMenuItem alloc] initWithTitle:NSLocalizedString(@"Chinese Conversion", @"") action:@selector(toggleChineseConverter:) keyEquivalent:@"G"];
     chineseConversionMenuItem.keyEquivalentModifierMask = NSEventModifierFlagCommand | NSEventModifierFlagControl;
     chineseConversionMenuItem.state = _chineseConversionEnabled ? NSControlStateValueOn : NSControlStateValueOff;
@@ -695,15 +677,15 @@ public:
         // then walk the lattice
         [self popOverflowComposingTextAndWalk:client];
 
-        // see if we need to override the selection if a learned one exists
+        // get user override model suggestion
-        if (![[NSUserDefaults standardUserDefaults] boolForKey:kDisableUserCandidateSelectionLearning]) {
+        string overrideValue =
-            NSString *trigram = [self neighborTrigramString];
+            (_inputMode == kPlainBopomofoModeIdentifier) ? "" :
-
+                _uom->suggest(_walkedNodes, _builder->cursorIndex(), [[NSDate date] timeIntervalSince1970]);
-            // Lookup from the user dict to see if the trigram fit or not
+        if (!overrideValue.empty()) {
-            NSString *overrideCandidateString = [gCandidateLearningDictionary objectForKey:trigram];
+            size_t cursorIndex = [self actualCandidateCursorIndex];
-            if (overrideCandidateString) {
+            vector<NodeAnchor> nodes = _builder->grid().nodesCrossingOrEndingAt(cursorIndex);
-                [self candidateSelected:(NSAttributedString *)overrideCandidateString];
+            double highestScore = FindHighestScore(nodes, kEpsilon);
-            }
+            _builder->grid().overrideNodeScoreForSelectedCandidate(cursorIndex, overrideValue, highestScore);
         }
 
         // then update the text
@@ -1292,78 +1274,6 @@ public:
     return cursorIndex;
 }
 
-- (NSString *)neighborTrigramString
-{
-    // gather the "trigram" for user candidate selection learning
-
-    NSMutableArray *termArray = [NSMutableArray array];
-
-    size_t cursorIndex = [self actualCandidateCursorIndex];
-    vector<NodeAnchor> nodes = _builder->grid().nodesCrossingOrEndingAt(cursorIndex);
-
-    const Node* prev = 0;
-    const Node* current = 0;
-    const Node* next = 0;
-
-    size_t wni = 0;
-    size_t wnc = _walkedNodes.size();
-    size_t accuSpanningLength = 0;
-    for (wni = 0; wni < wnc; wni++) {
-        NodeAnchor& anchor = _walkedNodes[wni];
-        if (!anchor.node) {
-            continue;
-        }
-
-        accuSpanningLength += anchor.spanningLength;
-        if (accuSpanningLength >= cursorIndex) {
-            prev = current;
-            current = anchor.node;
-            break;
-        }
-
-        current = anchor.node;
-    }
-
-    if (wni + 1 < wnc) {
-        next = _walkedNodes[wni + 1].node;
-    }
-
-    string term;
-    if (prev) {
-        term = prev->currentKeyValue().key;
-        [termArray addObject:[NSString stringWithUTF8String:term.c_str()]];
-    }
-
-    if (current) {
-        term = current->currentKeyValue().key;
-        [termArray addObject:[NSString stringWithUTF8String:term.c_str()]];
-    }
-
-    if (next) {
-        term = next->currentKeyValue().key;
-        [termArray addObject:[NSString stringWithUTF8String:term.c_str()]];
-    }
-
-    return [termArray componentsJoinedByString:@"-"];
-}
-
-- (void)_performDeferredSaveUserCandidatesDictionary
-{
-    BOOL __unused success = [gCandidateLearningDictionary writeToFile:gUserCandidatesDictionaryPath atomically:YES];
-}
-
-- (void)saveUserCandidatesDictionary
-{
-    if (!gUserCandidatesDictionaryPath) {
-        return;
-    }
-
-    [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(_performDeferredSaveUserCandidatesDictionary) object:nil];
-
-    // TODO: Const-ize the delay
-    [self performSelector:@selector(_performDeferredSaveUserCandidatesDictionary) withObject:nil afterDelay:5.0];
-}
-
 - (void)_showCandidateWindowUsingVerticalMode:(BOOL)useVerticalMode client:(id)client
 {
     // set the candidate panel style
@@ -1467,30 +1377,12 @@ public:
     [[NSApplication sharedApplication] activateIgnoringOtherApps:YES];
 }
 
-- (void)toggleLearning:(id)sender
-{
-    BOOL toggle = ![[NSUserDefaults standardUserDefaults] boolForKey:kDisableUserCandidateSelectionLearning];
-
-    [[NSUserDefaults standardUserDefaults] setBool:toggle forKey:kDisableUserCandidateSelectionLearning];
-}
-
 - (void)toggleChineseConverter:(id)sender
 {
     _chineseConversionEnabled = !_chineseConversionEnabled;
     [[NSUserDefaults standardUserDefaults] setBool:_chineseConversionEnabled forKey:kChineseConversionEnabledKey];
 }
 
-- (void)clearLearningDictionary:(id)sender
-{
-    [gCandidateLearningDictionary removeAllObjects];
-    [self _performDeferredSaveUserCandidatesDictionary];
-}
-
-- (void)dumpLearningDictionary:(id)sender
-{
-    NSLog(@"%@", gCandidateLearningDictionary);
-}
-
 - (NSUInteger)candidateCountForController:(VTCandidateController *)controller
 {
     return [_candidates count];
@@ -1508,15 +1400,11 @@ public:
     // candidate selected, override the node with selection
     string selectedValue = [[_candidates objectAtIndex:index] UTF8String];
 
-    if (![[NSUserDefaults standardUserDefaults] boolForKey:kDisableUserCandidateSelectionLearning]) {
-        NSString *trigram = [self neighborTrigramString];
-        NSString *selectedNSString = [NSString stringWithUTF8String:selectedValue.c_str()];
-        [gCandidateLearningDictionary setObject:selectedNSString forKey:trigram];
-        [self saveUserCandidatesDictionary];
-    }
-
     size_t cursorIndex = [self actualCandidateCursorIndex];
     _builder->grid().fixNodeSelectedCandidate(cursorIndex, selectedValue);
+    if (_inputMode != kPlainBopomofoModeIdentifier) {
+        _uom->observe(_walkedNodes, cursorIndex, selectedValue, [[NSDate date] timeIntervalSince1970]);
+    }
 
     [_candidates removeAllObjects];
 
@@ -1545,57 +1433,4 @@ void LTLoadLanguageModel()
 {
     LTLoadLanguageModelFile(@"data", gLanguageModel);
     LTLoadLanguageModelFile(@"data-plain-bpmf", gLanguageModelPlainBopomofo);
-
-
-    // initialize the singleton learning dictionary
-    // putting singleton in @synchronized is the standard way in Objective-C
-    // to avoid race condition
-    gCandidateLearningDictionary = [[NSMutableDictionary alloc] init];
-
-    // the first instance is also responsible for loading the dictionary
-    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSApplicationSupportDirectory, NSUserDirectory, YES);
-    if (![paths count]) {
-        NSLog(@"Fatal error: cannot find Applicaiton Support directory.");
-        return;
-    }
-
-    NSString *appSupportPath = [paths objectAtIndex:0];
-    NSString *userDictPath = [appSupportPath stringByAppendingPathComponent:@"McBopomofo"];
-
-    BOOL isDir = NO;
-    BOOL exists = [[NSFileManager defaultManager] fileExistsAtPath:userDictPath isDirectory:&isDir];
-
-    if (exists) {
-        if (!isDir) {
-            NSLog(@"Fatal error: Path '%@' is not a directory", userDictPath);
-            return;
-        }
-    }
-    else {
-        NSError *error = nil;
-        BOOL success = [[NSFileManager defaultManager] createDirectoryAtPath:userDictPath withIntermediateDirectories:YES attributes:nil error:&error];
-        if (!success) {
-            NSLog(@"Failed to create directory '%@', error: %@", userDictPath, error);
-            return;
-        }
-    }
-
-    // TODO: Change this
-    NSString *userDictFile = [userDictPath stringByAppendingPathComponent:@"UserCandidatesCache.plist"];
-    gUserCandidatesDictionaryPath = userDictFile;
-
-    exists = [[NSFileManager defaultManager] fileExistsAtPath:userDictFile isDirectory:&isDir];
-    if (exists && !isDir) {
-        NSData *data = [NSData dataWithContentsOfFile:userDictFile];
-        if (!data) {
-            return;
-        }
-
-        id plist = [NSPropertyListSerialization propertyListWithData:data options:NSPropertyListImmutable format:NULL error:NULL];
-        if (plist && [plist isKindOfClass:[NSDictionary class]]) {
-            [gCandidateLearningDictionary setDictionary:(NSDictionary *)plist];
-            NSLog(@"User dictionary read, item count: %ju", (uintmax_t)[gCandidateLearningDictionary count]);
-        }
-    }
-
 }

Source/UserOverrideModel.cpp

@@ -0,0 +1,219 @@
+//
+// 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 bool IsEndingPunctuation(const string& value);
+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 bool IsEndingPunctuation(const string& value) {
+    return value == "，" || value == "。" || value== "！" || value == "？" ||
+        value == "」" || value == "』" || value== "”" || value == "”";
+}
+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()) {
+        string value = (*r).node->currentKeyValue().value;
+        if (IsEndingPunctuation(value)) {
+            s << "()";
+            r = n.rend();
+        } else {
+            s << "("
+                    << (*r).node->currentKeyValue().key
+                    << ","
+                    << value
+                    << ")";
+            ++r;
+        }
+    } else {
+        s << "()";
+    }
+    string prev = s.str();
+
+    s.clear();
+    s.str(std::string());
+    if (r != n.rend()) {
+        string value = (*r).node->currentKeyValue().value;
+        if (IsEndingPunctuation(value)) {
+            s << "()";
+            r = n.rend();
+        } else {
+            s << "("
+            << (*r).node->currentKeyValue().key
+            << ","
+            << 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
+