/* Example from Solidity by Example
   http://solidity.readthedocs.io/en/develop/common-patterns.html

   contract WithdrawalContract {
     address public richest
     uint public mostSent

      mapping (address => uint) pendingWithdrawals

      function WithdrawalContract() payable {
        richest = msg.sender
        mostSent = msg.value
      }

      function becomeRichest() payable returns (bool) {
        if (msg.value > mostSent) {
            pendingWithdrawals[richest] += msg.value
            richest = msg.sender
            mostSent = msg.value
            return true
        } else {
            return false
        }
      }

      function withdraw() {
        uint amount = pendingWithdrawals[msg.sender]
        // Remember to zero the pending refund before
        // sending to prevent re-entrancy attacks
        pendingWithdrawals[msg.sender] = 0
        msg.sender.transfer(amount)
      }
  }

*/

contract WithdrawalContract =

  record state = { richest  : address,
                   mostSent : uint,
                   pendingWithdrawals : map(address, uint) }

  function becomeRichest() : result(bool) =
      if (call().value > state.mostSent)
        let totalAmount : uint = Map.get_(state.richest, pendingWithdrawals) + call().value
        {state = state{ pendingWithdrawals = Map.insert(state.richest, call().value, state.pendingWithdrawals),
                        richest  = call().sender,
                        mostSent = call().value },
         result = true}
      else
        {result = false}

  function withdraw() =
      let amount : uint = Map.get_(call().sender, state.pendingWithdrawals)
      { state.pendingWithdrawals = Map.insert(call().sender, 0, state.pendingWithdrawals),
        transactions = spend_tx(amount, call().sender) }