Refactor TextRenderer a bit.

src/main/java/ch/fritteli/labyrinth/TextRenderer.java

@@ -11,8 +11,11 @@ public class TextRenderer {
     private final Labyrinth labyrinth;
     private final int width;
     private final int height;
+    // column counter
     private int x = 0;
+    // row counter
     private int y = 0;
+    // line counter (top-, center- or bottom line of a row)
     private int line = 0;
 
     private TextRenderer(@NonNull final Labyrinth labyrinth, final int width, final int height) {
@@ -23,10 +26,10 @@ public class TextRenderer {
 
     public static String render(@NonNull final Labyrinth labyrinth) {
         final int width = labyrinth.getWidth();
-        if (width == 0) {
+        final int height = labyrinth.getHeight();
+        if (width == 0 || height == 0) {
             return "";
         }
-        final int height = labyrinth.getHeight();
         final TextRenderer renderer = new TextRenderer(labyrinth, width, height);
 
         final StringBuilder sb = new StringBuilder();
@@ -40,13 +43,6 @@ public class TextRenderer {
         return this.y < this.height;
     }
 
-    private Tile getTileOrNull(final int x, final int y) {
-        if (x < 0 || y < 0 || x >= this.width || y >= this.height) {
-            return null;
-        }
-        return this.labyrinth.getTileAt(x, y);
-    }
-
     private String next() {
         final Tile currentTile = this.labyrinth.getTileAt(this.x, this.y);
         final Tile leftTile = this.getTileOrNull(this.x - 1, this.y);
@@ -66,21 +62,38 @@ public class TextRenderer {
                 s = "";
                 break;
         }
+        this.prepareNextStep();
+        return s;
+    }
+
+    private void prepareNextStep() {
         // do some magic ...
         this.x++;
         if (this.x == this.width) {
+            // Reached the end of the row?
+            // On to the next line then!
             this.x = 0;
             this.line++;
         }
         if (this.line == 2 && this.y < this.height - 1) {
+            // Finished rendering the center line, and more rows available?
+            // On to the next row then!
             this.line = 0;
             this.y++;
         }
         if (this.line == 3) {
+            // Finished rendering the bottom line (of the last row)?
+            // Increment row counter one more time => this is the exit condition.
             this.line = 0;
             this.y++;
         }
-        return s;
+    }
+
+    private Tile getTileOrNull(final int x, final int y) {
+        if (x < 0 || y < 0 || x >= this.width || y >= this.height) {
+            return null;
+        }
+        return this.labyrinth.getTileAt(x, y);
     }
 
     private String renderTopLine(@NonNull final Tile currentTile, @Nullable final Tile leftTile, @Nullable final Tile topTile) {