diff --git a/lib/bottom.ex b/lib/bottom.ex
index e2386de..4bde983 100644
--- a/lib/bottom.ex
+++ b/lib/bottom.ex
@@ -15,4 +15,57 @@ defmodule Tetris.Bottom do
     Enum.any?(points, &collides?(bottom,&1))
   end
 
+  def complete_ys(bottom) do
+    bottom
+    |> Map.keys
+    |> Enum.map(&elem(&1, 1))
+    |> Enum.uniq
+    |> Enum.filter(fn row -> complete?(bottom, row) end)
+  end
+
+  def complete?(bottom, row) do
+    count =
+      bottom
+      |> Map.keys
+      |> Enum.filter(fn {_x,y} -> y == row end)
+      |> Enum.count
+
+    count == 10
+  end
+
+  def collapse_row(bottom, row) do
+    bad_keys =
+      bottom
+      |> Map.keys
+      |> Enum.filter(fn {_x,y} -> y == row end)
+
+    bottom
+    |> Map.drop(bad_keys)
+    |> Enum.map(&move_bad_points_up(&1, row))
+    |> Map.new
+
+  end
+
+  def move_bad_points_up({{x, y}, {x, y, colour}}, row) when y < row do
+    #move_bad_poitns_down ???
+    {{x, y+1}, {x, y+1, colour}}
+  end
+  def move_bad_points_up(key_value, _row)  do
+    key_value
+  end
+
+  def full_collapse(bottom) do
+    # a bottom less completed row
+    rows =
+      bottom
+      |> complete_ys()
+      |> Enum.sort
+
+    new_bottom =
+       Enum.reduce(rows, bottom, &collapse_row(&2, &1))
+
+    {Enum.count(rows), new_bottom}
+  end
+
+
 end
diff --git a/lib/tetris.ex b/lib/tetris.ex
index 4039349..625b50b 100644
--- a/lib/tetris.ex
+++ b/lib/tetris.ex
@@ -8,7 +8,59 @@ defmodule Tetris do
 
   end
 
-  def try_move(brick, bottom, f) do
+
+
+  def drop(brick, bottom, colour) do
+    new_brick =
+      Brick.down(brick)
+    maybe_do_drop(
+      Bottom.collides?(bottom, prepare(new_brick)),
+      bottom,
+      brick,
+      new_brick,
+      colour
+    )
+  end
+
+  def maybe_do_drop(true=_collided,bottom, old_brick, _new_block, colour) do
+    new_brick = Brick.new_random
+
+    points =
+      old_brick
+      |> prepare
+      |> Points.with_colour(colour)
+
+    {count, new_bottom} =
+      bottom
+      |> Bottom.merge(points)
+      |> Bottom.full_collapse
+
+    %{
+      brick: new_brick,
+      bottom:  new_bottom,
+      score: score(count),
+      game_over: Bottom.collides?(new_bottom, prepare(new_brick))
+    }
+  end
+  def maybe_do_drop(false=_collided,bottom, _old_brick, new_block, _colour) do
+    %{
+      brick: new_block,
+      bottom:  bottom,
+      score: 1,
+      game_over: false
+    }
+  end
+
+  def score(0), do: 0
+  def score(count) do
+    100 * round(:math.pow(2, count))
+  end
+
+  def try_left(brick, bottom), do: try_move(brick,bottom, &Brick.left/1)
+  def try_right(brick, bottom), do: try_move(brick,bottom, &Brick.right/1)
+  def try_spin(brick, bottom), do: try_move(brick,bottom, &Brick.spin_90/1)
+
+  defp try_move(brick, bottom, f) do
     new_brick = f.(brick)
 
     if Bottom.collides?(bottom, prepare(new_brick)) do
@@ -17,9 +69,4 @@ defmodule Tetris do
         new_brick
     end
   end
-
-  def try_left(brick, bottom), do: try_move(brick,bottom, &Brick.left/1)
-  def try_right(brick, bottom), do: try_move(brick,bottom, &Brick.right/1)
-  def try_spin(brick, bottom), do: try_move(brick,bottom, &Brick.spin_90/1)
-
 end
diff --git a/test/bottom_test.exs b/test/bottom_test.exs
index 857c95f..513a9bc 100644
--- a/test/bottom_test.exs
+++ b/test/bottom_test.exs
@@ -26,4 +26,39 @@ defmodule BottomTest do
     }
     assert actual == expected
   end
+
+  test "compute complete ys" do
+    bottom = new_bottom(20, [{{19, 19}, {19, 19, :red}}])
+
+    assert complete_ys(bottom) == [20]
+  end
+
+  test "collapse single row" do
+    bottom = new_bottom(20, [{{19, 19}, {19, 19, :red}}])
+    actual = Map.keys(collapse_row(bottom, 20))
+    refute {19,19} in actual
+    assert {19, 20} in actual
+    assert Enum.count(actual) == 1
+    #IO.inspect collapse_row(bottom, 20)
+  end
+
+
+  test "full collapse with single row" do
+    bottom = new_bottom(20, [{{19, 19}, {19, 19, :red}}])
+    {actual_count, actual_bottom} = full_collapse(bottom)
+    assert actual_count == 1
+    assert {19,20} in Map.keys(actual_bottom)
+  end
+
+
+
+  def new_bottom(complete_row, xtras) do
+    (xtras ++
+    (1..10
+    |> Enum.map( fn x ->
+        {{x, complete_row}, {x,complete_row, :red}}
+      end)))
+    |> Map.new
+  end
+
 end
diff --git a/test/tetris_test.exs b/test/tetris_test.exs
index bedade2..7ee8807 100644
--- a/test/tetris_test.exs
+++ b/test/tetris_test.exs
@@ -22,5 +22,49 @@ defmodule TetrisTest do
     assert actual == brick
   end
 
+  test "drops without merging" do
+    brick = Brick.new(%{location: {5,5}})
+    bottom = %{}
+
+    expected = %{
+      brick: Brick.down(brick),
+      bottom: %{},
+      score: 1,
+      game_over: false
+    }
+
+    actual = drop(brick, bottom, :red)
+
+    assert actual == expected
+  end
+
+  test "drops and merges" do
+    brick = Brick.new(%{location: {5,16}})
+    bottom = %{}
+
+    %{score: score, bottom: actual_bottom} =
+      Tetris.drop(brick, bottom, :red)
+
+    assert Map.get(actual_bottom, {7,20}) ==  {7,20, :red}
+    assert score == 0
+  end
+
+  test "drops and merges with collapse" do
+    brick = Brick.new(%{location: {5,16}})
+    bottom =
+      for x <- 1..10,  y <- 17..20, x != 7 do
+        {{x,y}, {x,y, :red}}
+      end
+      |> Map.new
+
+
+    %{score: score, bottom: actual_bottom} =
+      Tetris.drop(brick, bottom, :red)
+
+    assert actual_bottom == %{}
+    assert score == 1600
+  end
+
+
 
 end