type state =
  record
    goal     : nat;
    deadline : timestamp;
    backers  : map (address, nat);
    funded   : bool
  end

entrypoint donate (storage store : state;
                   const sender  : address;
                   const amount  : mutez)
  : storage * list (operation) is
  var operations : list (operation) := []
  begin
    if now > store.deadline then
      fail "Deadline passed"
    else
      if store.backers.[sender] = None then
        store :=
          copy store with
            record
              backers = map_add store.backers (sender, amount)
            end
      else null
  end with (store, operations)

entrypoint get_funds (storage store : state; const sender : address)
  : storage * list (operation) is
  var operations : list (operation) := []
  begin
    if sender = owner then
      if now >= store.deadline then
        if balance >= store.goal then
          begin
            store := copy store with record funded = true end;
            operations := [Transfer (owner, balance)]
          end
        else fail "Below target"
      else fail "Too soon"
    else null
  end with (store, operations)

entrypoint claim (storage store : state; const sender : address)
  : storage * list (operation) is
  var operations : list (operation) := [];
  var amount : mutez := 0
  begin
    if now <= store.deadline then
      fail "Too soon"
    else
      match store.backers.[sender] with
        None ->
          fail "Not a backer"
      | Some amount ->
          if balance >= store.goal || store.funded then
            fail "Cannot refund"
          else
            begin
              amount := store.backers.[sender];
              store :=
                copy store with
                  record
                    backers = map_remove store.backers sender
                  end;
              operations := [Transfer (sender, amount)]
            end
      end
  end with (store, operations)