add recurring swap example

examples/recurring_swap.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+
+from pyteal import *
+
+""" Recurring Swap
+
+This is a recurring payment contract. This contract can be set as an escrow 
+and sending tmpl_amount recurringly to tmpl_rcv as long as secret is provided.
+
+Use scenarios:
+A insurer company set up this escrow contract and funded with Algos. 
+Whenever the hospital received a record from the device, the hospital can send a 
+transaction to transfer tmpl_amount of Algos from the escrow to the hospital. 
+The hospital may be required to put some information about the record in the note 
+field for audit purpose.
+
+"""
+
+tmpl_rcv = Addr("6ZHGHH5Z5CTPCF5WCESXMGRSVK7QJETR63M3NY5FJCUYDHO57VTCMJOBGY")
+tmpl_amount = Int(500)
+tmpl_fee = 1000
+# secret_hash: replace the value with the SHA256 value of the secret
+tmpl_secret_hash = Bytes("base32", "23232323232323")
+
+fee_cond = Txn.fee() < Int(1000)
+type_cond = Txn.type_enum() == Int(1)
+recv_cond = And(Txn.close_remainder_to() == Global.zero_address(),
+                Txn.receiver() == tmpl_rcv,
+                Sha256(Arg(0)) == tmpl_secret_hash)
+
+recurring_swap = And(fee_cond, type_cond, recv_cond)
+print(recurring_swap.teal())