Android project initiated

AndroidManifest.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<manifest xmlns:a="http://schemas.android.com/apk/res/android"
+	  package="org.solovyev.android.calculator"
+      versionCode="1"
+      versionName="1.0">
+    <a:uses-sdk a:minSdkVersion="8"/>
+
+    <a:application a:icon="@drawable/icon" a:label="@string/app_name_caption">
+        <a:activity a:name=".Calculator" a:label="@string/app_name_caption">
+            <a:intent-filter>
+                <a:action a:name="android.intent.action.MAIN" />
+                <a:category a:name="android.intent.category.LAUNCHER" />
+            </a:intent-filter>
+        </a:activity>
+
+    </a:application>
+</manifest>

default.properties

@@ -0,0 +1,11 @@
+# This file is automatically generated by Android Tools.
+# Do not modify this file -- YOUR CHANGES WILL BE ERASED!
+#
+# This file must be checked in Version Control Systems.
+#
+# To customize properties used by the Ant build system use,
+# "build.properties", and override values to adapt the script to your
+# project structure.
+
+# Project target.
+target=android-8

find_bugs_excluded_filter.xml

@@ -0,0 +1,5 @@
+ <FindBugsFilter>
+	<Match>
+		<Class name="org.solovyev.android.calculator.R" />
+	</Match>
+</FindBugsFilter>

gen/org/solovyev/android/calculator/R.java

@@ -0,0 +1,116 @@
+/* AUTO-GENERATED FILE.  DO NOT MODIFY.
+ *
+ * This class was automatically generated by the
+ * aapt tool from the resource data it found.  It
+ * should not be modified by hand.
+ */
+
+package org.solovyev.android.calculator;
+
+public final class R {
+    public static final class attr {
+        /** <p>Must be a string value, using '\\;' to escape characters such as '\\n' or '\\uxxxx' for a unicode character.
+<p>This may also be a reference to a resource (in the form
+"<code>@[<i>package</i>:]<i>type</i>:<i>name</i></code>") or
+theme attribute (in the form
+"<code>?[<i>package</i>:][<i>type</i>:]<i>name</i></code>")
+containing a value of this type.
+         */
+        public static final int textDown=0x7f010001;
+        /** <p>Must be a string value, using '\\;' to escape characters such as '\\n' or '\\uxxxx' for a unicode character.
+<p>This may also be a reference to a resource (in the form
+"<code>@[<i>package</i>:]<i>type</i>:<i>name</i></code>") or
+theme attribute (in the form
+"<code>?[<i>package</i>:][<i>type</i>:]<i>name</i></code>")
+containing a value of this type.
+         */
+        public static final int textUp=0x7f010000;
+    }
+    public static final class drawable {
+        public static final int icon=0x7f020000;
+    }
+    public static final class id {
+        public static final int curlyBracketsButton=0x7f060013;
+        public static final int editText=0x7f060000;
+        public static final int eigthDigitButton=0x7f06000f;
+        public static final int equalsButton=0x7f060011;
+        public static final int fiveDigitButton=0x7f060009;
+        public static final int fourDigitButton=0x7f060008;
+        public static final int historyButton=0x7f060018;
+        public static final int minusButton=0x7f06000c;
+        public static final int muliplicationButton=0x7f060005;
+        public static final int nineDigitButton=0x7f060010;
+        public static final int numericButton=0x7f060016;
+        public static final int oneDigitButton=0x7f060002;
+        public static final int piButton=0x7f060019;
+        public static final int plusButton=0x7f060006;
+        public static final int pointDigitButton=0x7f060015;
+        public static final int resultEditText=0x7f060001;
+        public static final int roundBracketsButton=0x7f060007;
+        public static final int sevenDigitButton=0x7f06000e;
+        public static final int simplifyButton=0x7f060017;
+        public static final int sixDigitButton=0x7f06000a;
+        public static final int sqrtButton=0x7f060012;
+        public static final int squareBracketsButton=0x7f06000d;
+        public static final int subtractionButton=0x7f06000b;
+        public static final int threeDigitButton=0x7f060004;
+        public static final int twoDigitButton=0x7f060003;
+        public static final int zeroDigitButton=0x7f060014;
+    }
+    public static final class layout {
+        public static final int main=0x7f030000;
+    }
+    public static final class string {
+        public static final int app_name_caption=0x7f040000;
+        public static final int syntax_error=0x7f040001;
+    }
+    public static final class style {
+        public static final int digitButtonStyle=0x7f050001;
+        public static final int editTextInputStyle=0x7f050000;
+    }
+    public static final class styleable {
+        /** Attributes that can be used with a DragButton.
+           <p>Includes the following attributes:</p>
+           <table>
+           <colgroup align="left" />
+           <colgroup align="left" />
+           <tr><th>Attribute</th><th>Description</th></tr>
+           <tr><td><code>{@link #DragButton_textDown org.solovyev.android.calculator:textDown}</code></td><td></td></tr>
+           <tr><td><code>{@link #DragButton_textUp org.solovyev.android.calculator:textUp}</code></td><td></td></tr>
+           </table>
+           @see #DragButton_textDown
+           @see #DragButton_textUp
+         */
+        public static final int[] DragButton = {
+            0x7f010000, 0x7f010001
+        };
+        /**
+          <p>This symbol is the offset where the {@link org.solovyev.android.calculator.R.attr#textDown}
+          attribute's value can be found in the {@link #DragButton} array.
+
+
+          <p>Must be a string value, using '\\;' to escape characters such as '\\n' or '\\uxxxx' for a unicode character.
+<p>This may also be a reference to a resource (in the form
+"<code>@[<i>package</i>:]<i>type</i>:<i>name</i></code>") or
+theme attribute (in the form
+"<code>?[<i>package</i>:][<i>type</i>:]<i>name</i></code>")
+containing a value of this type.
+          @attr name android:textDown
+        */
+        public static final int DragButton_textDown = 1;
+        /**
+          <p>This symbol is the offset where the {@link org.solovyev.android.calculator.R.attr#textUp}
+          attribute's value can be found in the {@link #DragButton} array.
+
+
+          <p>Must be a string value, using '\\;' to escape characters such as '\\n' or '\\uxxxx' for a unicode character.
+<p>This may also be a reference to a resource (in the form
+"<code>@[<i>package</i>:]<i>type</i>:<i>name</i></code>") or
+theme attribute (in the form
+"<code>?[<i>package</i>:][<i>type</i>:]<i>name</i></code>")
+containing a value of this type.
+          @attr name android:textUp
+        */
+        public static final int DragButton_textUp = 0;
+    };
+}

res/layout/main.xml

@@ -0,0 +1,65 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout 
+	xmlns:a="http://schemas.android.com/apk/res/android"
+	xmlns:calc="http://schemas.android.com/apk/res/org.solovyev.android.calculator"
+	
+    a:orientation="vertical"
+    a:layout_width="fill_parent"
+    a:layout_height="fill_parent">
+    
+    <EditText 
+    		a:id="@+id/editText"
+    		style="@style/editTextInputStyle" 
+    		a:maxLines="5"
+    		a:minLines="5"
+    		a:gravity="top|left"
+        	a:textAppearance="?android:attr/textAppearanceMedium"
+        	a:typeface="monospace"
+    		a:singleLine="false" />
+    		
+	<EditText 
+    		a:id="@+id/resultEditText"
+    		style="@style/editTextInputStyle" 
+    		a:gravity="top|left"
+        	a:textAppearance="?android:attr/textAppearanceMedium"
+        	a:typeface="monospace"
+        	a:editable="false"
+        	a:focusable="false"/>
+    		
+    <TableLayout 
+    	a:layout_width="fill_parent"
+    	a:layout_height="fill_parent">
+    	<TableRow>
+    		<org.solovyev.android.view.DragButton a:id="@+id/oneDigitButton" a:text="1" calc:textUp="sin" calc:textDown="asin" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/twoDigitButton" a:text="2" calc:textUp="cos" calc:textDown="acos"  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/threeDigitButton" a:text="3" calc:textUp="tg" calc:textDown="atg"  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+			<org.solovyev.android.view.DragButton a:id="@+id/muliplicationButton" a:text="*" calc:textUp="^" calc:textDown="^2" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+   			<org.solovyev.android.view.DragButton a:id="@+id/plusButton" a:text="+" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+   			<org.solovyev.android.view.DragButton a:id="@+id/roundBracketsButton" a:text="()" calc:textUp="(" calc:textDown=")" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	</TableRow>
+    	<TableRow>
+    		<org.solovyev.android.view.DragButton a:id="@+id/fourDigitButton" a:text="4" calc:textUp="exp" calc:textDown="mod"  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/fiveDigitButton" a:text="5" calc:textUp="log" calc:textDown="ln"  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/sixDigitButton" a:text="6" calc:textUp="!" calc:textDown=""  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/subtractionButton" a:text="/" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+   			<org.solovyev.android.view.DragButton a:id="@+id/minusButton" a:text="-" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	    <org.solovyev.android.view.DragButton a:id="@+id/squareBracketsButton" a:text="[]" calc:textUp="[" calc:textDown="]" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	</TableRow>
+    	<TableRow>
+    		<org.solovyev.android.view.DragButton a:id="@+id/sevenDigitButton" a:text="7" calc:textUp="" calc:textDown=""  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/eigthDigitButton" a:text="8" calc:textUp="" calc:textDown=""  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/nineDigitButton" a:text="9" calc:textUp="" calc:textDown=""  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    		<org.solovyev.android.view.DragButton a:id="@+id/equalsButton" a:text="=" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	    <org.solovyev.android.view.DragButton a:id="@+id/sqrtButton" a:text="sqrt" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	    <org.solovyev.android.view.DragButton a:id="@+id/curlyBracketsButton" a:text="{}" calc:textUp="{" calc:textDown="}" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	</TableRow>
+    	<TableRow>
+    		<org.solovyev.android.view.DragButton a:id="@+id/zeroDigitButton" a:text="0" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	    <org.solovyev.android.view.DragButton a:id="@+id/pointDigitButton" a:text="." calc:textDown=","  style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	    <org.solovyev.android.view.DragButton a:id="@+id/numericButton" a:text="numeric" style="@style/digitButtonStyle" a:onClick="numericButtonClickHandler"/>
+    	    <org.solovyev.android.view.DragButton a:id="@+id/simplifyButton" a:text="simplify" style="@style/digitButtonStyle" a:onClick="simplifyButtonClickHandler"/>
+       	    <org.solovyev.android.view.DragButton a:id="@+id/historyButton" calc:textUp="undo" calc:textDown="redo" style="@style/digitButtonStyle"/>
+       	    <org.solovyev.android.view.DragButton a:id="@+id/piButton" a:text="pi" calc:textUp="e" style="@style/digitButtonStyle" a:onClick="digitButtonClickHandler"/>
+    	</TableRow>
+    </TableLayout>
+</LinearLayout>

res/values-ru/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name_caption">Калькулятор</string>
+</resources>

res/values/attrs.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <declare-styleable name="DragButton">
+        <attr name="textUp" format="string" />
+        <attr name="textDown" format="string" />
+    </declare-styleable>
+</resources>

res/values/strings.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name_caption">Calculator</string>
+    <string name="syntax_error">Syntax error</string>
+</resources>

res/values/styles.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <style name="editTextInputStyle">
+        <item name="android:layout_width">fill_parent</item>
+        <item name="android:layout_height">wrap_content</item>
+        <item name="android:typeface">monospace</item>
+    </style>
+    
+   <style name="digitButtonStyle">
+        <item name="android:width">50dp</item>
+        <item name="android:height">50dp</item>
+        <item name="android:typeface">monospace</item>
+    </style> 
+</resources>

src/org/solovyev/android/calculator/Calculator.java

@@ -0,0 +1,196 @@
+package org.solovyev.android.calculator;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.solovyev.android.calculator.R;
+import org.solovyev.android.view.DragButton;
+import org.solovyev.android.view.DragEvent;
+import org.solovyev.android.view.OnDragListener;
+import org.solovyev.android.view.SimpleOnDragListener;
+import org.solovyev.util.StringUtils;
+import org.solovyev.util.math.MathEntityType;
+
+import bsh.EvalError;
+import bsh.Interpreter;
+
+import android.app.Activity;
+import android.os.Bundle;
+import android.util.Log;
+import android.view.View;
+import android.widget.EditText;
+
+public class Calculator extends Activity {
+
+	@NotNull
+	private EditText editText;
+	
+	@NotNull
+	private EditText resultEditText;
+
+	@NotNull
+	private Interpreter interpreter;
+
+	@NotNull
+	private HistoryHelper<EditorHistoryState> historyHelper;
+	
+	/** Called when the activity is first created. */
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.main);
+
+		this.editText = (EditText) findViewById(R.id.editText);
+		
+		this.resultEditText = (EditText) findViewById(R.id.resultEditText);
+
+		final SimpleOnDragListener onDragListener = new SimpleOnDragListener();
+
+		// todo serso: check if there is more convenient method for doing this
+		final R.id ids = new R.id();
+		for (Field field : R.id.class.getDeclaredFields()) {
+			int modifiers = field.getModifiers();
+			if (Modifier.isFinal(modifiers) && Modifier.isStatic(modifiers)) {
+				try {
+					final View view = findViewById(field.getInt(ids));
+					if (view instanceof DragButton) {
+						((DragButton) view).setOnDragListener(onDragListener);
+					}
+				} catch (IllegalArgumentException e) {
+					Log.e(Calculator.class.getName(), e.getMessage());
+				} catch (IllegalAccessException e) {
+					Log.e(Calculator.class.getName(), e.getMessage());
+				}
+			}
+		}
+
+		((DragButton) findViewById(R.id.historyButton)).setOnDragListener(new HistoryOnDragListener());
+		
+		this.interpreter = new Interpreter();
+
+		try {
+			interpreter.eval(Preprocessor.wrap(JsclOperation.importCommands, "/jscl/editorengine/commands"));
+		} catch (EvalError e) {
+			Log.e(Calculator.class.getName(), e.getMessage());
+		}
+		
+		this.historyHelper = new SimpleHistoryHelper<EditorHistoryState>();
+		this.historyHelper.addState(getCurrentHistoryState());
+	}
+	
+	public void elementaryButtonClickHandler(@NotNull View v) {
+		eval(JsclOperation.elementary);
+	}
+	
+	public void numericButtonClickHandler(@NotNull View v) {
+		eval(JsclOperation.numeric);
+	}
+
+	public void simplifyButtonClickHandler(@NotNull View v) {
+		eval(JsclOperation.simplify);
+	}
+
+	private void eval(@NotNull JsclOperation operation) {
+		try {
+			final String preprocessedString = Preprocessor.process(String.valueOf(editText.getText()));
+			resultEditText.setText(String.valueOf(interpreter.eval(Preprocessor.wrap(operation, preprocessedString))));
+		} catch (EvalError e) {
+			Log.e(Calculator.class.getName(), e.getMessage());
+			resultEditText.setText(R.string.syntax_error);
+		}
+	}
+	
+	public void digitButtonClickHandler(@NotNull View v) {
+		processButtonAction(v, ((DragButton) v).getTextMiddle());
+	}
+	
+	private final class HistoryOnDragListener implements OnDragListener {
+		@Override
+		public void onDrag(@NotNull DragButton dragButton, @NotNull DragEvent event) {
+			Log.d(String.valueOf(dragButton.getId()), "History on drag event start: " + event.getDirection());
+
+			String actionText = getActionText(dragButton, event);
+			if (!StringUtils.isEmpty(actionText)) {
+				try {
+					final HistoryAction historyAction = HistoryAction.valueOf(actionText);
+					if ( historyHelper.isActionAvailable(historyAction) ){
+						final EditorHistoryState newState = historyHelper.doAction(historyAction, getCurrentHistoryState());
+						if (newState != null) {
+							setCurrentHistoryState(newState);
+						}
+					}
+				} catch (IllegalArgumentException e) {
+					Log.e(String.valueOf(dragButton.getId()), "Unsupported history action: " + actionText);
+				}
+			}
+		}
+	}
+
+	@Nullable
+	private static String getActionText(@NotNull DragButton dragButton, @NotNull DragEvent event) {
+		final String result;
+		
+		switch(event.getDirection()) {
+			case up:
+				result = dragButton.getTextUp();
+				break;
+			
+			case down:
+				result = dragButton.getTextDown();
+				break;
+				
+			default:
+				result = null;
+				break;
+		}
+		
+		return result;
+	}
+	
+	public void setCurrentHistoryState(@Nullable EditorHistoryState editorHistoryState) {
+		this.editText.setText(editorHistoryState.getText());
+		this.editText.setSelection(editorHistoryState.getCursorPosition(), editorHistoryState.getCursorPosition());
+	}
+	
+	@NotNull
+	public EditorHistoryState getCurrentHistoryState() {
+		final EditorHistoryState result = new EditorHistoryState();
+		
+		result.setText(String.valueOf(this.editText.getText()));
+		result.setCursorPosition(this.editText.getSelectionStart());
+		
+		return result;
+	}
+
+	private void processButtonAction(@NotNull View v, @Nullable String text) {
+		//Toast.makeText(Calculator.this, text, Toast.LENGTH_SHORT).show();
+
+		if (!StringUtils.isEmpty(text)) {
+			final MathEntityType type = MathEntityType.getType(text);
+			
+			int cursorPositionOffset = 0;
+
+			if (type != null) {
+				switch (type) {
+					case function:
+						text += "()";
+						cursorPositionOffset = -1;
+						break;
+					case group_symbols:
+						cursorPositionOffset = -1;
+						break;
+
+					default:
+						break;
+				}
+
+			}
+			
+			this.editText.getText().insert(this.editText.getSelectionStart(), text);
+			this.editText.setSelection(this.editText.getSelectionStart() + cursorPositionOffset, this.editText.getSelectionEnd() + cursorPositionOffset);
+			this.historyHelper.addState(getCurrentHistoryState());			
+		}
+	}
+}

src/org/solovyev/android/calculator/EditorHistoryState.java

@@ -0,0 +1,37 @@
+package org.solovyev.android.calculator;
+
+import org.jetbrains.annotations.Nullable;
+
+public class EditorHistoryState {
+	
+	private int cursorPosition;
+	
+	@Nullable
+	private String text;
+	
+	public EditorHistoryState() {
+	}
+	
+	public EditorHistoryState( int cursorPosition, @Nullable String text ) {
+		this.cursorPosition = cursorPosition;
+		this.text = text;
+	}
+
+	public void setText(String text) {
+		this.text = text;
+	}
+
+	public String getText() {
+		return text;
+	}
+
+	public void setCursorPosition(int cursorPosition) {
+		this.cursorPosition = cursorPosition;
+	}
+
+	public int getCursorPosition() {
+		return cursorPosition;
+	}
+
+
+}

src/org/solovyev/android/calculator/HistoryAction.java

@@ -0,0 +1,8 @@
+package org.solovyev.android.calculator;
+
+public enum HistoryAction {
+	
+	redo,
+	undo;
+
+}

src/org/solovyev/android/calculator/HistoryHelper.java

@@ -0,0 +1,24 @@
+package org.solovyev.android.calculator;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public interface HistoryHelper<T> {
+
+	boolean isUndoAvailable();
+	
+	@Nullable
+	T undo (@Nullable T currentState);
+	
+	boolean isRedoAvailable();
+	
+	@Nullable
+	T redo (@Nullable T currentState);
+	
+	boolean isActionAvailable(@NotNull HistoryAction historyAction);
+	
+	@Nullable
+	T doAction(@NotNull HistoryAction historyAction, @Nullable T currentState);
+	
+	void addState(@Nullable T currentState);
+}

src/org/solovyev/android/calculator/JsclOperation.java

@@ -0,0 +1,10 @@
+package org.solovyev.android.calculator;
+
+public enum JsclOperation {
+
+	simplify,
+	elementary,
+	importCommands,
+	numeric;
+	
+}

src/org/solovyev/android/calculator/Preprocessor.java

@@ -0,0 +1,31 @@
+package org.solovyev.android.calculator;
+
+import org.jetbrains.annotations.NotNull;
+
+public class Preprocessor {
+
+	@NotNull
+	public static String process(@NotNull String s) {
+		final StringBuilder sb = new StringBuilder();
+
+		for (int i = 0; i < s.length(); i++) {
+			char ch = s.charAt(i);
+
+			if (ch == '[' || ch == '{') {
+				sb.append('(');
+			} else if (ch == ']' || ch == '}') {
+				sb.append(')');
+			} else if ( ch == ',' ) {
+				sb.append('.');
+			} else {
+				sb.append(ch);
+			}
+		}
+
+		return sb.toString();
+	}
+	
+	public static String wrap (@NotNull JsclOperation operation, @NotNull String s) {
+		return operation.name() + "(\"" + s + "\");"; 
+	}
+}

src/org/solovyev/android/calculator/SimpleHistoryHelper.java

@@ -0,0 +1,91 @@
+package org.solovyev.android.calculator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class SimpleHistoryHelper<T> implements HistoryHelper<T> {
+
+	private List<T> history = new ArrayList<T>();
+	
+	private int currentStateIndex = -1;
+	
+	@Override
+	public T undo(@Nullable T currentState) {
+		if ( !isUndoAvailable() ) { 
+			throw new IndexOutOfBoundsException();
+		}
+		
+		currentStateIndex--;
+		
+		return history.get(currentStateIndex);
+	}
+
+	@Override
+	public T redo(@Nullable T currentState) {
+		if (!isRedoAvailable()) {
+			throw new IndexOutOfBoundsException();
+		}
+		currentStateIndex++;
+		return history.get(currentStateIndex);
+	}
+
+	@Override
+	public void addState(@Nullable T currentState) {
+		if (currentStateIndex == history.size() - 1) {
+			currentStateIndex++;
+			history.add(currentState);
+		} else {
+			assert currentStateIndex < history.size() - 1 : "Invalid history state index!";
+			currentStateIndex++;
+			history.set(currentStateIndex, currentState);
+			while( history.size() > currentStateIndex + 1 ) {
+				history.remove(history.size() - 1);
+			}
+		}
+	}
+
+	@Override
+	public boolean isUndoAvailable() {
+		return currentStateIndex > 0;
+	}
+
+	@Override
+	public boolean isRedoAvailable() {
+		return currentStateIndex < history.size() - 1;
+	}
+
+	@Override
+	public boolean isActionAvailable(@NotNull HistoryAction historyAction) {
+		boolean result = false;
+		
+		switch (historyAction) {
+			case undo:
+				result = isUndoAvailable();
+				break;
+			case redo:
+				result = isRedoAvailable();
+				break;
+		}
+		
+		return result;
+	}
+
+	@Override
+	public T doAction(@NotNull HistoryAction historyAction, @Nullable T currentState) {
+		T result = null;
+		
+		switch (historyAction) {
+			case undo:
+				result = undo(currentState);
+				break;
+			case redo:
+				result = redo(currentState);
+				break;
+		}
+		
+		return result;
+	}
+}

src/org/solovyev/android/view/DragButton.java

@@ -0,0 +1,168 @@
+package org.solovyev.android.view;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.solovyev.android.calculator.R;
+import org.solovyev.util.StringUtils;
+import org.solovyev.util.math.MathUtils;
+import org.solovyev.util.math.Point2d;
+
+import android.content.Context;
+import android.content.res.TypedArray;
+import android.text.Html;
+import android.util.AttributeSet;
+import android.util.Log;
+import android.view.MotionEvent;
+import android.view.View;
+import android.widget.Button;
+
+public class DragButton extends Button {
+
+	// max time in ms to register drag event
+	private long maxTime = 700;
+
+	@Nullable
+	private Point2d startPoint = null;
+
+	@Nullable
+	private OnDragListener onDragListener;
+
+	private final OnTouchListener onTouchListener = new OnTouchListenerImpl();
+
+	@Nullable
+	private String textUp;
+
+	@Nullable
+	private String textDown;
+
+	@Nullable
+	private String textMiddle;
+
+	public DragButton(Context context, @NotNull AttributeSet attrs) {
+		super(context, attrs);
+		init(context, attrs);
+	}
+
+	public DragButton(Context context, AttributeSet attrs, int defStyle) {
+		super(context, attrs, defStyle);
+		init(context, attrs);
+	}
+
+	private void init(@NotNull Context context, @NotNull AttributeSet attrs) {
+		TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.DragButton);
+
+		final int N = a.getIndexCount();
+		for (int i = 0; i < N; i++) {
+			int attr = a.getIndex(i);
+			switch (attr) {
+				case R.styleable.DragButton_textUp:
+					this.textUp = a.getString(attr);
+					break;
+				case R.styleable.DragButton_textDown:
+					this.textDown = a.getString(attr);
+					break;
+			}
+		}
+
+		// backup text
+		this.textMiddle = String.valueOf(getText());
+
+		setText(Html.fromHtml(getStyledUpDownText(this.textUp) + "<br><b>" + StringUtils.getNotEmpty(this.textMiddle, "&nbsp;") + "</b><br>" + getStyledUpDownText(this.textDown)));
+
+		// change top padding in order to show all text
+		setPadding(getPaddingLeft(), -7, getPaddingRight(), getPaddingBottom());
+
+		setOnTouchListener(this.onTouchListener);
+	}
+
+	private String getStyledUpDownText(@Nullable String text) {
+		final StringBuilder sb = new StringBuilder();
+
+		sb.append("<font color='#585858'><small><small>");
+		sb.append(StringUtils.getNotEmpty(text, "&nbsp;"));
+		sb.append("</small></small></font>");
+		return sb.toString();
+	}
+
+	public void setOnDragListener(@Nullable OnDragListener onDragListener) {
+		this.onDragListener = onDragListener;
+	}
+
+	@Nullable
+	public OnDragListener getOnDragListener() {
+		return onDragListener;
+	}
+
+	public void setTextUp(String textUp) {
+		this.textUp = textUp;
+	}
+
+	public String getTextUp() {
+		return textUp;
+	}
+
+	public void setTextDown(String textDown) {
+		this.textDown = textDown;
+	}
+
+	public String getTextDown() {
+		return textDown;
+	}
+
+	public void setTextMiddle(String textMiddle) {
+		this.textMiddle = textMiddle;
+	}
+
+	public String getTextMiddle() {
+		return textMiddle;
+	}
+
+	/**
+	 * OnTouchListener implementation that fires onDrag()
+	 * 
+	 * @author serso
+	 * 
+	 */
+	private final class OnTouchListenerImpl implements OnTouchListener {
+
+		@Override
+		public boolean onTouch(@NotNull View v, @NotNull MotionEvent event) {
+			// processing on touch event
+
+			if (onDragListener != null) {
+				// only if onDrag() listener specified
+
+				Log.d(String.valueOf(getId()), "onTouch() for: " + getId() + " . Motion event: " + event);
+
+				switch (event.getAction()) {
+					case MotionEvent.ACTION_DOWN:
+						// start tracking: set start point
+						startPoint = new Point2d(event.getX(), event.getY());
+						break;
+
+					case MotionEvent.ACTION_MOVE:
+						if (event.getEventTime() - event.getDownTime() > maxTime) {
+							// do not allow very long touch movements
+							startPoint = null;
+						}
+						break;
+
+					case MotionEvent.ACTION_UP:
+						// stop tracking
+							
+						if (onDragListener.onDrag(DragButton.this, new DragEvent(startPoint, event))) {
+							if (onDragListener.isSuppressOnClickEvent()) {
+								// prevent on click action
+								setPressed(false);
+							}
+						}
+
+						startPoint = null;
+						break;
+				}
+			}
+
+			return false;
+		}
+	}
+}

src/org/solovyev/android/view/DragDirection.java

@@ -0,0 +1,7 @@
+package org.solovyev.android.view;
+
+public enum DragDirection {
+
+	up, 
+	down;
+}

src/org/solovyev/android/view/DragEvent.java

@@ -0,0 +1,33 @@
+package org.solovyev.android.view;
+
+import org.jetbrains.annotations.NotNull;
+import org.solovyev.util.math.Point2d;
+
+import android.view.MotionEvent;
+
+public class DragEvent {
+	
+	@NotNull
+	private final Point2d startPoint;
+	
+	@NotNull
+	private final MotionEvent motionEvent;
+
+	public DragEvent(@NotNull Point2d startPoint, @NotNull MotionEvent motionEvent) {
+		this.startPoint = startPoint;
+		this.motionEvent = motionEvent;
+	}
+
+	@NotNull
+	public MotionEvent getMotionEvent() {
+		return motionEvent;
+	}
+
+	@NotNull
+	public Point2d getStartPoint() {
+		return startPoint;
+	}
+	
+	
+	
+}

src/org/solovyev/android/view/OnDragListener.java

@@ -0,0 +1,22 @@
+package org.solovyev.android.view;
+
+import org.jetbrains.annotations.NotNull;
+
+
+public interface OnDragListener {
+	
+	/**
+	 * 
+	 * @return 'true': if drag event has taken place (i.e. onDrag() method returned true) then click action will be suppresed
+	 */
+	boolean isSuppressOnClickEvent();
+	
+	/**
+	 * @param dragButton drag button object for which onDrag listener was set
+	 * @param event drag event
+	 *
+	 * @return 'true' if drag event occurred, 'false' otherwise
+	 */
+	boolean onDrag(@NotNull DragButton dragButton, @NotNull DragEvent event);
+
+}

src/org/solovyev/android/view/SimpleOnDragListener.java

@@ -0,0 +1,93 @@
+package org.solovyev.android.view;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.solovyev.util.StringUtils;
+import org.solovyev.util.math.MathUtils;
+import org.solovyev.util.math.Point2d;
+
+import android.util.Log;
+import android.view.MotionEvent;
+
+public class SimpleOnDragListener implements OnDragListener {
+
+	@NotNull
+	private final Point2d axis = new Point2d(0, 1);
+	
+	private float minDragDist = 20f;
+
+	private float maxDragDist = 80f;
+
+	// max angle (in degrees!) between start and end point vector and axis
+	// vector to register drag event
+	private double maxAngle = 30;
+
+	@Override
+	public boolean onDrag(@NotNull DragButton dragButton, @NotNull DragEvent event) {
+		logDragEvent(dragButton, event);
+		
+		processButtonAction(dragButton, getActionText(dragButton, event));
+	}
+
+	@Override
+	public boolean isSuppressOnClickEvent() {
+		return true;
+	}
+	
+	/**
+	 * Method creates drag event in case if all conditions are satisfied
+	 * 
+	 * @param event
+	 *            motion event
+	 * 
+	 * @return filled drag event object only if drag event is possible, null
+	 *         otherwise
+	 */
+	@Nullable
+	protected DragEvent getDragEvent(@NotNull MotionEvent event) {
+		DragEvent result = null;
+
+		if (startPoint != null) {
+			final Point2d endPoint = new Point2d(event.getX(), event.getY());
+			float distance = MathUtils.getDistance(startPoint, endPoint);
+
+			if (minDragDist < distance && distance < maxDragDist) {
+				double angle = Math.toDegrees(MathUtils.getAngle(startPoint, MathUtils.sum(startPoint, axis), endPoint));
+				
+				final DragDirection direction;
+				if (angle < maxAngle) {
+					direction = DragDirection.down;
+				} else if (180 - angle < maxAngle) {
+					direction = DragDirection.up;
+				} else {
+					direction = null;
+				}
+				
+				if (direction != null) {
+					if ( direction == DragDirection.up && StringUtils.isEmpty(textUp) ) {
+						// no action if text is empty
+					} else if  (direction == DragDirection.down && StringUtils.isEmpty(textDown)) {
+						// no action if text is empty
+					} else {
+						result = new DragEvent(direction);
+					}
+					
+				}
+			}
+		}
+
+		return result;
+	}
+	
+	private void logDragEvent(@NotNull DragButton dragButton, @NotNull DragEvent event) {
+			final Point2d startPoint = event.getStartPoint();
+			final MotionEvent motionEvent = event.getMotionEvent();
+			final Point2d endPoint = new Point2d(motionEvent.getX(), motionEvent.getY());
+			
+			Log.d(String.valueOf(dragButton.getId()), "Start point: " + startPoint + ", End point: " + endPoint);
+			Log.d(String.valueOf(dragButton.getId()), "Distance: " + MathUtils.getDistance(startPoint, endPoint));
+			Log.d(String.valueOf(dragButton.getId()), "Angle: " + Math.toDegrees(MathUtils.getAngle(startPoint, MathUtils.sum(startPoint, axis), endPoint)));
+			Log.d(String.valueOf(dragButton.getId()), "Axis: " + axis + " Vector: " + MathUtils.subtract(endPoint, startPoint));
+			Log.d(String.valueOf(dragButton.getId()), "Total time: " + (motionEvent.getEventTime() - motionEvent.getDownTime()) + " ms");
+	}
+}

src/org/solovyev/util/StringUtils.java

@@ -0,0 +1,17 @@
+package org.solovyev.util;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class StringUtils {
+
+	public static boolean isEmpty ( @Nullable String s ){
+		return s == null || s.length() == 0;
+	}
+	
+	@NotNull
+	public static String getNotEmpty ( @Nullable String s, @NotNull String defaultValue ){
+		return isEmpty(s) ? defaultValue : s;
+	}
+}
+

src/org/solovyev/util/date/DateUtils.java

@@ -0,0 +1,11 @@
+package org.solovyev.util.date;
+
+public class DateUtils {
+	
+	public static long MS_IN_SECONDS = 1000l;
+	
+	public static long msToSeconds (long ms) {
+		return ms / 1000l;
+	}
+
+}

src/org/solovyev/util/math/MathEntity.java

@@ -0,0 +1,37 @@
+package org.solovyev.util.math;
+
+import org.jetbrains.annotations.NotNull;
+
+public enum MathEntity {
+
+	minus("-"),
+	equals("="),
+	factorial("!"),
+	plus("+"),
+	multiply("*"),
+	divide("/"),
+	power("^"),
+	sin("sin"),
+	asin("asin"),
+	cos("cos"),
+	acos("acos"),
+	tg("tg"),
+	atg("atg"),
+	exp("exp"),
+	log("log"),
+	ln("ln"),
+	mod("mod"),
+	sqrt("sqrt");
+		
+	@NotNull
+	private final String text;
+	
+	private MathEntity (@NotNull String text) {
+		this.text = text;
+	}
+
+	@NotNull
+	public String getText() {
+		return text;
+	}
+}

src/org/solovyev/util/math/MathEntityType.java

@@ -0,0 +1,57 @@
+package org.solovyev.util.math;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public enum MathEntityType {
+
+	digit,
+	function, 
+	unary_operation,
+	binary_operation,
+	group_symbols,
+	group_symbol;
+	
+	private static final List<Character> unaryOperations = Arrays.asList('-', '=', '!');
+	
+	private static final List<Character> binaryOperations = Arrays.asList('-', '+', '*', '/', '^' );
+
+	private static final List<String> functions = Arrays.asList("sin", "asin", "cos", "acos", "tg", "atg", "exp", "log", "ln", "mod", "sqrt");
+	
+	private static final List<String> groupSymbols = Arrays.asList("[]", "()", "{}");
+
+	private static final List<Character> singleGroupSymbols = Arrays.asList('[', ']', '(', ')', '{', '}');
+	
+	@Nullable
+	public static MathEntityType getType( @NotNull String s ) {
+		MathEntityType result = null;
+		
+		if ( s.length() == 1 ) {
+			char ch = s.charAt(0);
+			
+			if ( Character.isDigit(ch) ) {
+				result = MathEntityType.digit;
+			} else if ( unaryOperations.contains(ch) ) {
+				result = MathEntityType.unary_operation; 
+			} else if ( binaryOperations.contains(ch) ) {
+				result = MathEntityType.binary_operation; 
+			} else if ( singleGroupSymbols.contains(ch) ) {
+				result = MathEntityType.group_symbol;
+			}
+		}
+		
+		if ( result == null ) {
+			if ( functions.contains(s) ) {
+				result = MathEntityType.function;
+			} else if ( groupSymbols.contains(s) ) {
+				result = MathEntityType.group_symbols;
+			}
+		}
+		
+		
+		return result;
+	}
+}

src/org/solovyev/util/math/MathUtils.java

@@ -0,0 +1,39 @@
+package org.solovyev.util.math;
+
+import org.jetbrains.annotations.NotNull;
+
+public class MathUtils {
+
+	public static float getDistance(@NotNull Point2d startPoint,
+			@NotNull Point2d endPoint) {
+		return getNorm(subtract(endPoint, startPoint));
+	}
+
+	public static Point2d subtract(@NotNull Point2d p1, @NotNull Point2d p2) {
+		return new Point2d(p1.getX() - p2.getX(), p1.getY() - p2.getY());
+	}
+	
+	public static Point2d sum(@NotNull Point2d p1, @NotNull Point2d p2) {
+		return new Point2d(p1.getX() + p2.getX(), p1.getY() + p2.getY());
+	}
+
+	public static float getNorm(@NotNull Point2d point) {
+		return (float) Math.pow(
+				Math.pow(point.getX(), 2) + Math.pow(point.getY(), 2), 0.5);
+	}
+
+	public static float getAngle(@NotNull Point2d startPoint,
+			@NotNull Point2d axisEndPoint, @NotNull Point2d endPoint) {
+		final Point2d axisVector = subtract(axisEndPoint, startPoint);
+		final Point2d vector = subtract(endPoint, startPoint);
+
+		double a_2 = Math.pow(getDistance(vector, axisVector), 2);
+		double b = getNorm(vector);
+		double b_2 = Math.pow(b, 2);
+		double c = getNorm(axisVector);
+		double c_2 = Math.pow(c, 2);
+
+		return (float) Math.acos((-a_2 + b_2 + c_2) / (2 * b * c));
+	}
+
+}

src/org/solovyev/util/math/Point2d.java

@@ -0,0 +1,37 @@
+package org.solovyev.util.math;
+
+public class Point2d {
+	
+	private float x = 0;
+	
+	private float y = 0;
+	
+	public Point2d() {
+	}
+	
+	public Point2d( float x, float y ) {
+		this.x = x;
+		this.y = y;
+	}
+
+	public float getX() {
+		return x;
+	}
+
+	public void setX(float x) {
+		this.x = x;
+	}
+
+	public float getY() {
+		return y;
+	}
+
+	public void setY(float y) {
+		this.y = y;
+	}
+
+	@Override
+	public String toString() {
+		return "Point2d [x=" + x + ", y=" + y + "]";
+	}
+}