contracts/chequebook: add chequebook contract wrapper

The wrapper code is adapted from the swarm/services/chequebook package
with the following mostly cosmetic changes:

* The code now uses the new Go API interfaces to query balances. Some
  minor functional changes were required to make this work.
* The package no longer depends on swarm/services/swap/swap. References
  to swap.Promise are replaced by interface{}, the base type of Promise.
  This is temporary.
* The contract wrapper has been regenerated with latest abigen
  and solc v0.3.6.
* There is a new generator that creates the 'deployed code' variable.
* Documentation comments now follow the recommended godoc style.
* [CHEQUEBOOK] log prefixes are gone.
* LGPL license headers have been added to all files.

1 files changed, 43 insertions, 0 deletions

diff --git a/contracts/chequebook/contract/chequebook.sol b/contracts/chequebook/contract/chequebook.sol
new file mode 100644
index 000000000..cb19d0b27
--- /dev/null
+++ b/contracts/chequebook/contract/chequebook.sol
@@ -0,0 +1,43 @@
+import "mortal";
+
+/// @title Chequebook for Ethereum micropayments
+/// @author Daniel A. Nagy <daniel@ethdev.com>
+contract chequebook is mortal {
+    // Cumulative paid amount in wei to each beneficiary
+    mapping (address => uint256) public sent;
+
+    /// @notice Overdraft event
+    event Overdraft(address deadbeat);
+
+    /// @notice Cash cheque
+    ///
+    /// @param beneficiary beneficiary address
+    /// @param amount cumulative amount in wei
+    /// @param sig_v signature parameter v
+    /// @param sig_r signature parameter r
+    /// @param sig_s signature parameter s
+    /// The digital signature is calculated on the concatenated triplet of contract address, beneficiary address and cumulative amount
+    function cash(address beneficiary, uint256 amount,
+        uint8 sig_v, bytes32 sig_r, bytes32 sig_s) {
+        // Check if the cheque is old.
+        // Only cheques that are more recent than the last cashed one are considered.
+        if(amount <= sent[beneficiary]) return;
+        // Check the digital signature of the cheque.
+        bytes32 hash = sha3(address(this), beneficiary, amount);
+        if(owner != ecrecover(hash, sig_v, sig_r, sig_s)) return;
+        // Attempt sending the difference between the cumulative amount on the cheque
+        // and the cumulative amount on the last cashed cheque to beneficiary.
+        if (amount - sent[beneficiary] >= this.balance) {
+            if (beneficiary.send(amount - sent[beneficiary])) {
+                // Upon success, update the cumulative amount.
+                sent[beneficiary] = amount;
+            }
+        } else {
+            // Upon failure, punish owner for writing a bounced cheque.
+            // owner.sendToDebtorsPrison();
+            Overdraft(owner);
+            // Compensate beneficiary.
+            suicide(beneficiary);
+        }
+    }
+}