joinSwapPoolAmountOut

Author: Ramarti

model/balancer_pool.py

@@ -1,5 +1,5 @@
 from collections import namedtuple
-from decimal import Decimal
+from decimal import Decimal, ROUND_HALF_DOWN
 
 from model.balancer_constants import MIN_FEE, MAX_BOUND_TOKENS, INIT_POOL_SUPPLY, EXIT_FEE, MAX_IN_RATIO, MAX_OUT_RATIO
 from model.balancer_math import BalancerMath
@@ -294,3 +294,36 @@ def join_swap_extern_amount_in(self, token_in: str, token_amount_in: Decimal, mi
         # _pushPoolShare(msg.sender, pool_amount_out);
         # _pullUnderlying(token_in, msg.sender, token_amount_in);
         return pool_amount_out
+
+    
+
+    def join_swap_pool_amount_out(self, token_in: str, pool_amount_out: Decimal, max_amount_in: Decimal) -> Decimal:
+        if not self._records[token_in].bound:
+            raise Exception("ERR_NOT_BOUND")
+        
+        in_record = self._records[token_in]
+
+        token_amount_in = self.calc_single_in_given_pool_out(
+          token_balance_in = in_record.balance,
+          token_weight_in = in_record.denorm,
+          pool_supply = self.pool_token_supply,
+          total_weight = self.total_weight,
+          pool_amount_out = pool_amount_out,
+          swap_fee = self._swap_fee)
+
+        if token_amount_in == 0:
+          raise Exception("ERR_MATH_APPROX")
+
+        if token_amount_in > max_amount_in:
+          raise Exception("ERR_LIMIT_IN")
+
+        if token_amount_in > in_record.balance * MAX_IN_RATIO:
+          raise Exception("ERR_MAX_IN_RATIO")
+        
+        in_record.balance = in_record.balance + token_amount_in
+        self._mint_pool_share(pool_amount_out)
+        # _pushPoolShare(msg.sender, poolAmountOut);
+        # _pullUnderlying(tokenIn, msg.sender, tokenAmountIn);
+
+        return token_amount_in
+        

tests/test_balancer_pool.py

@@ -105,5 +105,20 @@ def test_join_swap_extern_amount_in(self):
         self.assertAlmostEqual(p_ao, Decimal('2.309727440687574969'))
         self.assertAlmostEqual(pool.pool_token_supply, Decimal('135.224857816660897462'))
 
+    def test_join_join_swap_pool_amount_out(self):
+        pool = BalancerPool(initial_pool_supply=Decimal('100'))
+        pool.bind('WETH', Decimal('4'), Decimal('10'))
+        pool.bind('DAI', Decimal('12'), Decimal('11'))
+        swap_fee = Decimal('0.001')
+        pool.set_swap_fee(swap_fee)
+        p_ao = Decimal('2.2')
+        t_ai = pool.join_swap_pool_amount_out(token_in='DAI', pool_amount_out=p_ao, max_amount_in=Decimal('1000'))
+        self.assertAlmostEqual(pool.pool_token_supply, Decimal('102.2'))
+        self.assertAlmostEqual(t_ai, Decimal('0.509279173873455029'))
+        self.assertAlmostEqual(pool.get_balance('DAI'), Decimal('12.509279173873455029'))
+        self.assertAlmostEqual(pool.get_balance('WETH'), Decimal('4'))
+
+
+
 if __name__ == '__main__':
     unittest.main()