acceptance_state={
 not_grabbed=0,
 would_accept=1,
 would_not_accept=2,
 no_move=3
}
cursor=klass()
function cursor:init(board)
 self.ruleset=board.ruleset
 self.board=board
 self.hover_x=self.ruleset.n_slots\2
 self.hover_y=1
 self.saved_hover_x_y=nil
 self.grabbed=nil
end

function cursor:acceptance_state()
 local hover=self:hover_slot()
 if self.grabbed then
  if hover==self.grabbed then
   return acceptance_state.no_move
  end
  local source=self.board.slots[self.grabbed]
  local target=self.board.slots[self:hover_slot()]
  local card=source:peek()
  if target:would_accept(card) then
   return acceptance_state.would_accept,source,target
  else
   return acceptance_state.would_not_accept
  end
 else
  if (self.board.slots[hover]:peek()) return acceptance_state.not_grabbed
  return acceptance_state.would_not_accept
 end
end

function cursor:save_hover()
 self.saved_hover_x_y={self.hover_x,self.hover_y}
end

function cursor:restore_hover()
 self.wants_to_restore_hover=true
end

function cursor:actually_restore_hover()
 if (not self.saved_hover_x_y) return
 self.wants_to_restore_hover=false

 -- try restoring hover x
 local old_hover_x,old_hover_y=self.hover_x,self.hover_y
 self.hover_x,self.hover_y=unpack(self.saved_hover_x_y)

 -- try very hard to be in a valid spot
 for i in all{
  function() self.hover_x,self.hover_y=old_hover_x,old_hover_y end,
  function() self:move_x(-1) end,
  function() self:move_y(1) end,
  function() self:move_x(-1) end,
  function() self:move_y(-1) end
 } do
  if (self:acceptance_state()!=acceptance_state.would_not_accept) return
  i()
 end
end

function cursor:toggle_grab()
 local acc,src,tar=self:acceptance_state()
 local slot=self:hover_slot()
 if acc==acceptance_state.not_grabbed then
  if (not self.board.watcher:intercept("grab",slot)) sounds:dire() return
  if (self.board.slots[slot]:peek()) self.grabbed=slot
  self:save_hover()
  sounds:menu()
 elseif acc==acceptance_state.would_accept then
  if (not self.board.watcher:intercept("drop",slot)) sounds:dire() return
  self.board:pre_move(src:peek())
  local card=src:pop()
  tar:add(card)
  self.grabbed=nil
  self.board:on_move(card)
  self:restore_hover()
  sounds:menu()
 elseif acc==acceptance_state.no_move or acc==acceptance_state.would_not_accept then
  self:drop_grab()
 else
  assert(false,"invalid acceptance state")
 end
end

function cursor:drop_grab()
 if (not self.board.watcher:intercept("cancel")) sounds:dire() return
 self.grabbed=nil
 self:restore_hover()
 sounds:menu()
end

function cursor:update()
 if (self.wants_to_restore_hover) self:actually_restore_hover()
end

function cursor:move_x(dx)
 if (self.hover_y==0) return
 if (dx==0) return
 local orig_x=self.hover_x
 while true do
  self.hover_x+=dx
  self.hover_x%=self.ruleset.n_slots 
  if (self.hover_x==orig_x) return
  if (self:acceptance_state()!=acceptance_state.would_not_accept) return true
 end
 return 
end

function cursor:move_y(dy)
 local old_y=self.hover_y
 if (self.hover_y==0 and dy==1) self.hover_y=1
 if (self.hover_y==1 and dy==-1) self.hover_y=0
 if (self:acceptance_state()==acceptance_state.would_not_accept) if (not self:move_x(-1)) self.hover_y=old_y
end

function cursor:hover_slot()
 if (self.hover_y==0) return self.ruleset.n_slots+1
 return self.hover_x+1
end

function cursor:grabbed_card()
 if self.grabbed then
  local slot=self.board.slots[self.grabbed]
  return slot:peek()
 end
 return nil
end

function cursor:draw_at(l,i)
 local card=self:grabbed_card()
 local acc=self:acceptance_state()

 if card then
  i+=1
  local x,y=l:place_card(i)
  local card_fg=self.ruleset.deck:draw_card(x,y,card,{rotate=l.rotated})
  local fg=card_fg
  draw_layout_hint(l,i,9,false)
 else
  local filled=false
  if (i<1) i=1 filled=true
  draw_layout_hint(l,i,12,filled)
 end
end