From 5de2155a63ae97e5bc5c81a839c779b60fadbb5c Mon Sep 17 00:00:00 2001
From: Ben Hauser <ben@hauser.id>
Date: Mon, 1 Mar 2021 19:28:59 +0400
Subject: [PATCH 1/2] feat: migrator

---
 contracts/PoolMigrator.vy | 44 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 contracts/PoolMigrator.vy

diff --git a/contracts/PoolMigrator.vy b/contracts/PoolMigrator.vy
new file mode 100644
index 0000000..5c12f7a
--- /dev/null
+++ b/contracts/PoolMigrator.vy
@@ -0,0 +1,44 @@
+# @version 0.2.11
+"""
+@title Pool Migrator
+@author Curve.fi
+@notice Zap for moving liquidity between Curve factory pools in a single transaction
+@license MIT
+"""
+
+interface ERC20:
+    def approve(_spender: address, _amount: uint256): nonpayable
+
+interface Swap:
+    def transferFrom(_owner: address, _spender: address, _amount: uint256) -> bool: nonpayable
+    def add_liquidity(_amounts: uint256[2], _min_mint_amount: uint256, _receiver: address) -> uint256: nonpayable
+    def remove_liquidity(_burn_amount: uint256, _min_amounts: uint256[2]) -> uint256[2]: nonpayable
+    def coins(i: uint256) -> address: view
+
+
+# pool -> coins are approved?
+is_approved: HashMap[address, bool]
+
+
+@external
+def migrate_to_new_pool(_old_pool: address, _new_pool: address, _amount: uint256) -> uint256:
+    """
+    @notice Migrate liquidity between two pools
+    @dev Each pool must be deployed by the curve factory and contain identical
+         assets. The migrator must have approval to transfer `_old_pool` tokens
+         on behalf of the caller.
+    @param _old_pool Address of the pool to migrate from
+    @param _new_pool Address of the pool to migrate into
+    @param _amount Number of `_old_pool` LP tokens to migrate
+    @return uint256 Number of `_new_pool` LP tokens received
+    """
+    Swap(_old_pool).transferFrom(msg.sender, self, _amount)
+    amounts: uint256[2] = Swap(_old_pool).remove_liquidity(_amount, [0, 0])
+
+    if not self.is_approved[_new_pool]:
+        for i in range(2):
+            coin: address = Swap(_new_pool).coins(i)
+            ERC20(coin).approve(_new_pool, MAX_UINT256)
+        self.is_approved[_new_pool] = True
+
+    return Swap(_new_pool).add_liquidity(amounts, 0, msg.sender)

From 380dfae56d857d56a6f6b213e0e103e3b656b2d5 Mon Sep 17 00:00:00 2001
From: Ben Hauser <ben@hauser.id>
Date: Mon, 1 Mar 2021 19:29:05 +0400
Subject: [PATCH 2/2] tests: migrator

---
 tests/test_migrator.py | 78 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 tests/test_migrator.py

diff --git a/tests/test_migrator.py b/tests/test_migrator.py
new file mode 100644
index 0000000..f5909b1
--- /dev/null
+++ b/tests/test_migrator.py
@@ -0,0 +1,78 @@
+import brownie
+import pytest
+
+pytestmark = pytest.mark.usefixtures("add_initial_liquidity", "mint_bob", "approve_bob")
+
+
+@pytest.fixture(scope="module")
+def swap2(MetaImplementationUSD, alice, base_pool, factory, coin):
+    tx = factory.deploy_metapool(
+        base_pool, "Test Swap", "TST", coin, 200, 4000000, {"from": alice}
+    )
+    yield MetaImplementationUSD.at(tx.return_value)
+
+
+@pytest.fixture(scope="module")
+def migrator(PoolMigrator, alice, swap):
+    contract = PoolMigrator.deploy({"from": alice})
+    swap.approve(contract, 2 ** 256 - 1, {"from": alice})
+    yield contract
+
+
+def test_migrate(alice, migrator, swap, swap2):
+    balance = swap.balanceOf(alice)
+    migrator.migrate_to_new_pool(swap, swap2, balance, {"from": alice})
+
+    assert swap.balanceOf(alice) == 0
+    assert swap2.balanceOf(alice) == balance
+
+    assert swap.balanceOf(migrator) == 0
+    assert swap2.balanceOf(migrator) == 0
+
+
+def test_migrate_partial(alice, migrator, swap, swap2, coin):
+    balance = swap.balanceOf(alice)
+    migrator.migrate_to_new_pool(swap, swap2, balance // 4, {"from": alice})
+
+    assert swap.balanceOf(alice) == balance - balance // 4
+    assert abs(swap2.balanceOf(alice) - balance // 4) < 8 + (10 ** 18 - coin.decimals())
+
+    assert swap.balanceOf(migrator) == 0
+    assert swap2.balanceOf(migrator) == 0
+
+
+def test_migrate_multiple(alice, migrator, swap, swap2, coin):
+    balance = swap.balanceOf(alice)
+    for i in range(4):
+        migrator.migrate_to_new_pool(swap, swap2, balance // 4, {"from": alice})
+
+    assert swap.balanceOf(alice) < 5
+    assert abs(swap2.balanceOf(alice) - balance) < 8 + (10 ** 18 - coin.decimals())
+
+    assert swap.balanceOf(migrator) == 0
+    assert swap2.balanceOf(migrator) == 0
+
+
+def test_migrate_bidirectional(alice, migrator, swap, swap2):
+    balance = swap.balanceOf(alice)
+    migrator.migrate_to_new_pool(swap, swap2, balance, {"from": alice})
+    swap2.approve(migrator, 2 ** 256 - 1, {"from": alice})
+    migrator.migrate_to_new_pool(swap2, swap, balance, {"from": alice})
+
+    assert abs(swap.balanceOf(alice) - balance) < 4
+    assert swap2.balanceOf(alice) == 0
+
+    assert swap.balanceOf(migrator) == 0
+    assert swap2.balanceOf(migrator) == 0
+
+
+def test_migration_wrong_pool(alice, migrator, swap, swap_btc):
+    balance = swap.balanceOf(alice)
+    with brownie.reverts():
+        migrator.migrate_to_new_pool(swap, swap_btc, balance, {"from": alice})
+
+
+def test_insufficient_balance(alice, migrator, swap, swap2):
+    balance = swap.balanceOf(alice)
+    with brownie.reverts():
+        migrator.migrate_to_new_pool(swap, swap2, balance + 1, {"from": alice})