Fix prepend_empty_row

After change of the grid to 1D, we need to update the prepend_empty_row

lib/wave_function_collapse/model.rb

@@ -57,23 +57,18 @@ def iterate
     end
 
     def prepend_empty_row
+      @grid = @grid.drop(@width)
+      @grid.each { |cell| cell.y -= 1 }
       x = 0
       while x < @width
-        @grid[x].shift
-        y = 0
-        while y < @height - 1
-          @grid[x][y].y -= 1
-          y += 1
-        end
         new_cell = Cell.new(x, @height - 1, @tiles)
-        @grid[x] << new_cell
+        @grid << new_cell
         @uncollapsed_cells_grid << new_cell
         x += 1
       end
-
-      @width.times do |x|
-        evaluate_neighbor(@grid[x][@height - 2], :up)
-      end
+      @width.times { |x|
+        evaluate_neighbor(cell_at(x, @height - 2), :up)
+      }
     end
 
     def random_cell

test/test_model.rb

@@ -20,4 +20,37 @@ def test_initialize
     assert model.solve
     assert model.iterate
   end
+
+  def test_prepend_empty_row
+    tiles = [
+      Tile.new(tileid: 0, wangid: [0, 0, 0, 0, 0, 0, 0, 0]),
+      Tile.new(tileid: 1, wangid: [0, 0, 0, 0, 0, 0, 0, 0]),
+      Tile.new(tileid: 2, wangid: [0, 0, 0, 0, 0, 0, 0, 0])
+    ]
+    model = Model.new(tiles, 2, 2)
+    model.solve
+    model.iterate
+    model.iterate
+    model.iterate
+
+    assert model.complete?
+
+    model.prepend_empty_row
+
+    assert_equal 4, model.grid.size
+    assert_equal 1, model.grid[0].entropy
+    assert_equal 1, model.grid[1].entropy
+    assert_predicate model.grid[0], :collapsed?
+    assert_predicate model.grid[0], :collapsed?
+    assert_equal 3, model.grid[2].entropy
+    assert_equal 3, model.grid[3].entropy
+    refute_predicate model.grid[2], :collapsed?
+    refute_predicate model.grid[3], :collapsed?
+
+    assert_equal 2, model.width
+    assert_equal 2, model.height
+    assert_equal 2 * 2, model.grid.size
+    assert_equal 3, model.max_entropy
+    assert_equal 50, model.percent
+  end
 end