ResearchLogging capture full n-gram data

- Captures complete motion data for all words in an n-gram.
- Also filters n-grams properly; if any word in the n-gram is not
  in the dictionary, it is not included.
- Simplify ResearchLog to not require explicit state
- Added LogBuffer class MainLogBuffer class to allow n-gram-level decisions
  about privacy.
- Moved LogUnit out from ResearchLogger

multi-project change with Id997fb6572daa3ff55591afa1676953bb204f33a

Because of a strange Gerrit interaction, earlier patchsets were recorded
as the following separate changes (to soon be abandoned):

- I59d86ae28123890ddb7aabc7dc9a73a75eecbca4
- I9cc95266fa4500d019e09ec53ec00e5dea7ffd38
- Ie6f23a2035e160f231406df1388a43725380df1d
- Id87909e96fa7fa91174c86395a964404f3490fe1
- I57c5cbde0425c42538d589fa4d1802b3e5688f7c
- Ic1f9d7727e416da1b6c4f1a45b53750cd4088dcf
- I20a72ccc4ba1bc08ed3ee39bff71d2adb376588c
- I417f6f364144b90085f5fef4bd2de1a40b5dfa79

Bug: 6188932
Change-Id: I771e57e3b8c0eb6721c2022e775cb0b528bdff93

1 files changed, 111 insertions, 0 deletions

diff --git a/java/src/com/android/inputmethod/research/LogBuffer.java b/java/src/com/android/inputmethod/research/LogBuffer.java
new file mode 100644
index 000000000..65f5f83ae
--- /dev/null
+++ b/java/src/com/android/inputmethod/research/LogBuffer.java
@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.android.inputmethod.research;
+
+import java.util.LinkedList;
+
+/**
+ * A buffer that holds a fixed number of LogUnits.
+ *
+ * LogUnits are added in and shifted out in temporal order.  Only a subset of the LogUnits are
+ * actual words; the other LogUnits do not count toward the word limit.  Once the buffer reaches
+ * capacity, adding another LogUnit that is a word evicts the oldest LogUnits out one at a time to
+ * stay under the capacity limit.
+ */
+public class LogBuffer {
+    protected final LinkedList<LogUnit> mLogUnits;
+    /* package for test */ int mWordCapacity;
+    // The number of members of mLogUnits that are actual words.
+    protected int mNumActualWords;
+
+    /**
+     * Create a new LogBuffer that can hold a fixed number of LogUnits that are words (and
+     * unlimited number of non-word LogUnits), and that outputs its result to a researchLog.
+     *
+     * @param wordCapacity maximum number of words
+     */
+    LogBuffer(final int wordCapacity) {
+        if (wordCapacity <= 0) {
+            throw new IllegalArgumentException("wordCapacity must be 1 or greater.");
+        }
+        mLogUnits = new LinkedList<LogUnit>();
+        mWordCapacity = wordCapacity;
+        mNumActualWords = 0;
+    }
+
+    /**
+     * Adds a new LogUnit to the front of the LIFO queue, evicting existing LogUnit's
+     * (oldest first) if word capacity is reached.
+     */
+    public void shiftIn(LogUnit newLogUnit) {
+        if (newLogUnit.getWord() == null) {
+            // This LogUnit isn't a word, so it doesn't count toward the word-limit.
+            mLogUnits.add(newLogUnit);
+            return;
+        }
+        if (mNumActualWords == mWordCapacity) {
+            shiftOutThroughFirstWord();
+        }
+        mLogUnits.add(newLogUnit);
+        mNumActualWords++; // Must be a word, or we wouldn't be here.
+    }
+
+    private void shiftOutThroughFirstWord() {
+        while (!mLogUnits.isEmpty()) {
+            final LogUnit logUnit = mLogUnits.removeFirst();
+            onShiftOut(logUnit);
+            if (logUnit.hasWord()) {
+                // Successfully shifted out a word-containing LogUnit and made space for the new
+                // LogUnit.
+                mNumActualWords--;
+                break;
+            }
+        }
+    }
+
+    /**
+     * Removes all LogUnits from the buffer without calling onShiftOut().
+     */
+    public void clear() {
+        mLogUnits.clear();
+        mNumActualWords = 0;
+    }
+
+    /**
+     * Called when a LogUnit is removed from the LogBuffer as a result of a shiftIn.  LogUnits are
+     * removed in the order entered.  This method is not called when shiftOut is called directly.
+     *
+     * Base class does nothing; subclasses may override.
+     */
+    protected void onShiftOut(LogUnit logUnit) {
+    }
+
+    /**
+     * Called to deliberately remove the oldest LogUnit.  Usually called when draining the
+     * LogBuffer.
+     */
+    public LogUnit shiftOut() {
+        if (mLogUnits.isEmpty()) {
+            return null;
+        }
+        final LogUnit logUnit = mLogUnits.removeFirst();
+        if (logUnit.hasWord()) {
+            mNumActualWords--;
+        }
+        return logUnit;
+    }
+}