Improved Model

Added Keyboard Selection Support
Added Mouse Selection Support
Added Keyboard Editing Support
Corrected Some Bugs
Abstracted the Layout System further
Added Functions Button (test)

MathPad/MPExpression.m

@@ -20,13 +20,10 @@
 @interface MPExpression (MPExpressionPrivate)
 
 - (NSUInteger)lengthOfElements:(NSArray *)elements;
-- (NSUInteger)indexOfElementAtLocation:(NSUInteger)location;
 
 - (void)validateElements:(NSArray *)elements;
 - (BOOL)splitElementsAtLocation:(NSUInteger)location
                  insertionIndex:(out NSUInteger *)insertionIndex;
-- (NSUInteger)calculateSplitOffsetForSplitLocation:(NSUInteger)location
-                                  inElementAtIndex:(out NSUInteger *)elementIndex;
 
 @end
 
@@ -41,13 +38,6 @@
     return length;
 }
 
-- (NSUInteger)indexOfElementAtLocation:(NSUInteger)location
-{
-    NSUInteger index = 0;
-    [self calculateSplitOffsetForSplitLocation:location inElementAtIndex:&index];
-    return index;
-}
-
 - (void)validateElements:(NSArray *)elements
 {
     for (id element in elements) {
@@ -66,18 +56,14 @@
         *insertionIndex = 0;
         return NO;
     }
-    NSUInteger splitElementIndex;
-    NSUInteger splitOffset = [self calculateSplitOffsetForSplitLocation:location
-                                                       inElementAtIndex:&splitElementIndex];
-    id<MPExpressionElement> splitElement = self.elements[splitElementIndex];
-    if (splitOffset == splitElement.length) {
-        splitOffset = 0;
-        splitElementIndex++;
-    }
+    
+    NSUInteger splitOffset;
+    NSUInteger splitElementIndex = [self indexOfElementAtSymbolLocation:location
+                                                                 offset:&splitOffset];
     if (splitOffset != 0) {
-        NSString *stringElement = (NSString *)splitElement;
-        NSString *leftPart = [stringElement substringToIndex:splitOffset];
-        NSString *rightPart = [stringElement substringFromIndex:splitOffset];
+        NSString *splitElement = (NSString *)self.elements[splitElementIndex];
+        NSString *leftPart = [splitElement substringToIndex:splitOffset];
+        NSString *rightPart = [splitElement substringFromIndex:splitOffset];
         [self.elements replaceObjectsInRange:NSMakeRange(splitElementIndex, 1)
                         withObjectsFromArray:@[leftPart, rightPart]];
         ++splitElementIndex;
@@ -86,24 +72,6 @@
     return splitOffset != 0;
 }
 
-- (NSUInteger)calculateSplitOffsetForSplitLocation:(NSUInteger)location
-                                  inElementAtIndex:(out NSUInteger *)elementIndex
-{
-    NSUInteger length = 0;
-    NSUInteger index = 0;
-    NSUInteger elementLength = 0;
-    for (id<MPExpressionElement> element in self.elements) {
-        elementLength = element.length;
-        length += elementLength;
-        if (length >= location) {
-            break;
-        }
-        ++index;
-    }
-    *elementIndex = index;
-    return elementLength - (length - location);
-}
-
 @end
 
 @implementation MPExpression {
@@ -215,6 +183,41 @@
     return [self.elements indexOfObject:element];
 }
 
+- (NSUInteger)indexOfElementAtSymbolLocation:(NSUInteger)location
+                                      offset:(out NSUInteger *)offset
+{
+    if (location == 0) {
+        if (offset != NULL) {
+            *offset = 0;
+        }
+        return 0;
+    }
+    
+    // Calculating elementIndex and splitOffset
+    NSUInteger totalLength = 0;
+    NSUInteger elementIndex = 0;
+    NSUInteger elementLength = 0;
+    for (id<MPExpressionElement> element in self.elements) {
+        elementLength = element.length;
+        totalLength += elementLength;
+        if (totalLength >= location) {
+            break;
+        }
+        ++elementIndex;
+    }
+    NSUInteger splitOffset = elementLength - (totalLength - location);
+
+    id<MPExpressionElement> element = self.elements[elementIndex];
+    if (splitOffset == element.length) {
+        splitOffset = 0;
+        elementIndex++;
+    }
+    if (offset != NULL) {
+        *offset = splitOffset;
+    }
+    return elementIndex;
+}
+
 - (void)replaceSymbolsInRange:(NSRange)range
                   withElements:(NSArray *)elements
 {
@@ -276,7 +279,7 @@
 }
 
 #pragma mark Basic NSObject Methods
-
+/*
 - (BOOL)isEqual:(id)object
 {
     if (self == object) {
@@ -295,7 +298,7 @@
 {
     return [self.elements isEqualToArray:anExpression.elements];
 }
-
+*/
 - (NSString *)description
 {
 #warning Bad Implementation
@@ -359,6 +362,14 @@
 @implementation MPExpression (MPExpressionExtension)
 
 #pragma mark Working With the Expression Tree
+- (MPExpression *)rootExpression
+{
+    if (self.parent == nil) {
+        return self;
+    }
+    return [self.parent rootExpression];
+}
+
 - (id)elementAtIndexPath:(NSIndexPath *)indexPath
 {
     if (indexPath.length == 0) {
@@ -369,7 +380,7 @@
         return element;
     }
     if ([element isFunction]) {
-        return [(MPFunction *)element elementAtIndexPath:[indexPath indexPathByRemovingLastIndex]];
+        return [(MPFunction *)element elementAtIndexPath:[indexPath indexPathByRemovingFirstIndex]];
     }
     return nil;
 }