[Dialogs] Consider all actions alignments for horizontal layout (#9805)

Adding center, leading, trailing and justified alignment to alert actions in horizontal layout.

Co-authored-by: Bryan Oltman <bryanoltman@gmail.com>
PiperOrigin-RevId: 297555954

components/Dialogs/src/private/MDCAlertControllerView+Private.m

@@ -762,7 +762,7 @@ - (void)layoutSubviews {
   if (self.isVerticalActionsLayout) {
     [self layoutVerticalButtons:buttons];
   } else {
-    [self layoutHorizontalButtons:buttons];
+    [self layoutHorizontalButtons:buttons actionSize:actionSize];
   }
 
   // Place scrollviews
@@ -813,22 +813,52 @@ - (void)setHitAreaForButtons:(NSArray<MDCButton *> *)buttons {
   }
 }
 
-- (void)layoutHorizontalButtons:(NSArray<MDCButton *> *)buttons {
+- (void)layoutHorizontalButtons:(NSArray<MDCButton *> *)buttons actionSize:(CGSize)actionSize {
   UIEdgeInsets actionsInsets =
       self.enableAdjustableInsets ? self.actionsInsets : MDCDialogActionsInsets;
+  CGFloat horizontalMargin = (self.enableAdjustableInsets ? self.actionsHorizontalMargin
+                                                          : MDCDialogActionsHorizontalPadding);
+  CGFloat maxButtonWidth =
+      self.actionsScrollView.contentSize.width - (actionsInsets.left + actionsInsets.right);
   CGPoint buttonOrigin = CGPointZero;
-  buttonOrigin.x = self.actionsScrollView.contentSize.width - actionsInsets.right;
+  CGFloat buttonWidth = 0.f;
+  CGFloat multiplier = 1.f;
+  if (self.actionsHorizontalAlignment == MDCContentHorizontalAlignmentTrailing) {
+    buttonOrigin.x = self.actionsScrollView.contentSize.width - actionsInsets.right;
+    multiplier = -1.f;
+  } else if (self.actionsHorizontalAlignment == MDCContentHorizontalAlignmentCenter) {
+    CGFloat actionWidthNoInsets = actionSize.width - actionsInsets.left - actionsInsets.right;
+    buttonOrigin.x = (self.actionsScrollView.contentSize.width - actionWidthNoInsets) / 2.f;
+  } else {  // leading or fill
+    buttonOrigin.x = actionsInsets.left;
+  }
   buttonOrigin.y = actionsInsets.top;
   for (UIButton *button in buttons) {
     CGRect buttonRect = button.frame;
 
-    buttonOrigin.x -= buttonRect.size.width;
+    buttonWidth = buttonRect.size.width;
+
+    if (self.actionsHorizontalAlignment == MDCContentHorizontalAlignmentTrailing) {
+      buttonOrigin.x -= buttonRect.size.width;
+    } else if (self.actionsHorizontalAlignment == MDCContentHorizontalAlignmentJustified) {
+      if (buttons.count > 1) {
+        CGFloat totalMargin = horizontalMargin * (buttons.count - 1);
+        buttonWidth = (maxButtonWidth - totalMargin) / buttons.count;
+      } else {
+        buttonWidth = maxButtonWidth;
+      }
+    }
     buttonRect.origin = buttonOrigin;
+    buttonRect.size.width = buttonWidth;
 
     button.frame = buttonRect;
 
     if (button != buttons.lastObject) {
-      buttonOrigin.x -= MDCDialogActionsHorizontalPadding;
+      if (self.actionsHorizontalAlignment != MDCContentHorizontalAlignmentTrailing) {
+        buttonOrigin.x += buttonRect.size.width + horizontalMargin;
+      } else {
+        buttonOrigin.x -= horizontalMargin;
+      }
     }
   }
   // Handle RTL