Example p2p flashloan contract

examples/smart_contracts/flashloan.py

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+from opshin.prelude import *
+from opshin.std.fractions import *
+
+
+@dataclass
+class FlashloanParams(PlutusData):
+    CONSTR_ID = 0
+    owner: PubKeyHash
+    loan_token: Token
+    loan_fee: Fraction
+
+
+@dataclass
+class FlashloanState(PlutusData):
+    CONSTR_ID = 0
+    params: FlashloanParams
+    spent_for: TxOutRef
+
+
+@dataclass
+class FlashLend(PlutusData):
+    CONSTR_ID = 0
+    input_index: int
+    output_index: int
+
+
+@dataclass
+class FlashWithdraw(PlutusData):
+    CONSTR_ID = 1
+
+
+def validator(
+    state: FlashloanState,
+    redeemer: Union[FlashLend, FlashWithdraw],
+    context: ScriptContext,
+) -> None:
+    tx_info = context.tx_info
+    purpose: Spending = context.purpose
+    if isinstance(redeemer, FlashWithdraw):
+        assert state.params.owner in tx_info.signatories, "Only the owner can withdraw"
+    elif isinstance(redeemer, FlashLend):
+        own_input_info = tx_info.inputs[redeemer.input_index]
+        assert (
+            own_input_info.out_ref == purpose.tx_out_ref
+        ), "Input index must match the spent utxo"
+        own_input = own_input_info.resolved
+        own_output = tx_info.outputs[redeemer.output_index]
+        assert (
+            own_output.address == own_input.address
+        ), "Output must be sent back to contract"
+        assert own_output.datum == SomeOutputDatum(
+            FlashloanState(state.params, purpose.tx_out_ref)
+        )
+        loan_token = state.params.loan_token
+        for pid, name_amount_dict in own_input.value.items():
+            for name, amount in name_amount_dict.items():
+                if Token(pid, name) == loan_token:
+                    assert ge_fraction(
+                        mul_fraction(Fraction(amount, 1), state.params.loan_fee),
+                        Fraction(own_output.value[pid][name], 1),
+                    ), "Output must satisfy loan fee"
+                else:
+                    assert (
+                        own_output.value[pid][name] == amount
+                    ), "Output must have same value as input"
+        assert len(own_output.to_cbor()) <= 1000, "Output must be less than 1000 bytes"
+    else:
+        assert False, "Invalid redeemer"