Add interactivity

Rectangles are good, but we need to handle card clicks.
To separate model from view, we add Card structure with
basic fields - color and some boolean flag behaviours.
At any point we can check behaviour value and draw either
face or back of the card.
Clicking the card would toggle the opened value.

game.flow

@@ -1,24 +1,37 @@
 import lib/tropic/tropic_ui;
 
+Card(
+	face: TColor,
+	opened: DynamicBehaviour<bool>,
+	solved: DynamicBehaviour<bool>,
+);
 
-drawCard() -> Tropic {
-	TRectangle([Fill(darkGray)], TFixed(150.0, 150.0));
+drawCard(color: TColor) -> Tropic {
+	size = TFixed(150.0, 150.0);
+
+	card = Card(color, make(false), make(false));
+	toggleCard = \ -> reverseBehaviour(card.opened);
+
+	TSelect(card.opened, \opened -> {
+		faceColor = if (opened) card.face else TDarkGrey();
+		TTextButton("", "", [faceColor, TForeground(size)], [TOnClicked(toggleCard)]);
+	});
 }
 
 main() {
 	header = TText("Memory game", [FontSize(20.0)]);
 
 	cards = TCols([
-		drawCard(),
-		drawCard(),
-		drawCard(),
-		drawCard(),
+		drawCard(TGreen()),
+		drawCard(TRed()),
+		drawCard(TGreen()),
+		drawCard(TRed()),
 	]);
 
-	view = TLines([
-		header |> TCenterX,
-		cards  |> TCenterX,
-	]);
+	view = TLinesXCenter([
+		header,
+		cards,
+	]) |> TCenterX;
 
 	trender(view, []);
 }