implement lesson07

LESSONS.md

@@ -137,3 +137,24 @@ Our snake seems invincible for now and can't eat. Run into a wall - nothing will
 Once you're ready, you can _git merge lesson07_.
 
 ---
+
+## Lesson 07
+
+#### Prequisites
+None
+
+#### Files
+- _components/Snake.cpp_
+- _components/Snake.h_
+- _main.cpp_
+
+#### Task
+
+The snake just learned to grow by itself! How?
+
+1) See the changes to _components/Snake.*_ and try to understand the new code which allows the snake to grow.
+2) Play around with this in _main.cpp_.
+
+Once you're ready, you can _git merge lesson08_.
+
+---

components/Snake.cpp

@@ -106,3 +106,45 @@ bool Snake::hasCrashedWall() const {
            (head.getX() < GAME_LEFT_WALL_X)   ||
            (head.getX() > GAME_RIGHT_WALL_X);
 }
+
+
+uint32_t Snake::getSize() const {
+    return snake_.size();
+}
+
+void Snake::incSize(){
+    const auto tail = std::prev(snake_.end());
+    const uint32_t tailX = tail->getX();
+    const uint32_t tailY = tail->getY();
+
+    const auto prev = std::prev(tail);
+    const uint32_t prevX = prev->getX();
+    const uint32_t prevY = prev->getY();
+
+    if (prevY == tailY){ 
+        // if the two last parts are on the same 'height' (horizontal tail direction)
+        if (prevX < tailX) {
+            // if the tail continues to the left:
+            // add one part to the right of the tail
+            snake_.push_back(Point{tailY, tailX + 1, SNAKE_BODY_CHAR}); 
+        }
+        else {
+            // if the tail continues to the right:
+            // add one part to the left of the tail
+            snake_.push_back(Point{tailY, tailX - 1, SNAKE_BODY_CHAR});
+        }
+    }
+    else {
+        // if the two last parts are on the same 'width' (vertical tail direction)
+        if (prevY < tailY) {
+            // if the tail continues to the upper side:
+            // add one part facing down
+            snake_.push_back(Point{tailY + 1, tailX, SNAKE_BODY_CHAR});
+        }
+        else {
+            // if the tail continues to the lower side:
+            // add one part facing up
+            snake_.push_back(Point{tailY - 1, tailX, SNAKE_BODY_CHAR});
+        }
+    }
+}

components/Snake.h

@@ -28,4 +28,7 @@ public:
     bool isBitten() const;
     bool hasBitSnack(uint32_t snackY, uint32_t snackX) const;
     bool hasCrashedWall() const;
+
+    uint32_t getSize() const;
+    void incSize();
 };