feat: simple defi vault (#37)

* feat: simple defi vault

* feat: add Simple defi vault description

* fix: typo

* fix: simple vault wrapped IERC20Dispatcher

listings/ch01-applications/simple_vault/.gitignore

@@ -0,0 +1 @@
+target

listings/ch01-applications/simple_vault/Scarb.toml

@@ -0,0 +1,11 @@
+[package]
+name = "simple_vault"
+version = "0.1.0"
+
+# See more keys and their definitions at https://docs.swmansion.com/scarb/docs/reference/manifest
+
+[dependencies]
+starknet = "1.1.0"
+
+[[target.starknet-contract]]
+allowed-libfuncs-list.name = "experimental_v0.1.0"

listings/ch01-applications/simple_vault/src/lib.cairo

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+mod simple_vault;

listings/ch01-applications/simple_vault/src/simple_vault.cairo

@@ -0,0 +1,109 @@
+use starknet::{ContractAddress};
+
+// In order to make contract calls within our Vault,
+// we need to have the ABI of the remote contract defined to import the Dispatcher
+#[abi]
+trait IERC20 {
+    #[view]
+    fn name() -> felt252;
+
+    #[view]
+    fn symbol() -> felt252;
+
+    #[view]
+    fn decimals() -> u8;
+
+    #[view]
+    fn total_supply() -> u256;
+
+    #[view]
+    fn balance_of(account: ContractAddress) -> u256;
+
+    #[view]
+    fn allowance(owner: ContractAddress, spender: ContractAddress) -> u256;
+
+    #[external]
+    fn transfer(recipient: ContractAddress, amount: u256) -> bool;
+
+    #[external]
+    fn transfer_from(sender: ContractAddress, recipient: ContractAddress, amount: u256) -> bool;
+
+    #[external]
+    fn approve(spender: ContractAddress, amount: u256) -> bool;
+}
+
+#[contract]
+mod SimpleVault {
+    use super::{IERC20Dispatcher, IERC20DispatcherTrait};
+    use starknet::{
+        ContractAddress,
+        get_caller_address,
+        get_contract_address
+    };
+
+    struct Storage {
+        _token: IERC20Dispatcher,
+        _total_supply: u256,
+        _balance_of: LegacyMap<ContractAddress, u256>
+    }
+
+    #[constructor]
+    fn constructor(token: ContractAddress) {
+        _token::write(IERC20Dispatcher { contract_address: token });
+    }
+
+    fn _mint(to: ContractAddress, shares: u256) {
+        _total_supply::write(_total_supply::read() + shares);
+        _balance_of::write(to, _balance_of::read(to) + shares);
+    }
+
+    fn _burn(from: ContractAddress, shares: u256) {
+        _total_supply::write(_total_supply::read() - shares);
+        _balance_of::write(from, _balance_of::read(from) - shares);
+    }
+
+    #[external]
+    fn deposit(amount: u256) {
+        // a = amount
+        // B = balance of token before deposit
+        // T = total supply
+        // s = shares to mint
+        //
+        // (T + s) / T = (a + B) / B 
+        //
+        // s = aT / B
+        let caller = get_caller_address();
+        let this = get_contract_address();
+
+        let mut shares = 0;
+        if _total_supply::read() == 0 {
+            shares = amount;
+        } else {
+            let balance = _token::read().balance_of(this);
+            shares = (amount * _total_supply::read()) / balance;
+        }
+
+        _mint(caller, shares);
+        _token::read().transfer_from(caller, this, amount);
+    }
+
+    #[external]
+    fn withdraw(shares: u256) {
+        // a = amount
+        // B = balance of token before withdraw
+        // T = total supply
+        // s = shares to burn
+        //
+        // (T - s) / T = (B - a) / B 
+        //
+        // a = sB / T
+        let caller = get_caller_address();
+        let this = get_contract_address();
+
+        let balance = _token::read().balance_of(this);
+        let amount = (shares * balance) / _total_supply::read();
+        _burn(caller, shares);
+        _token::read().transfer(caller, amount);
+    }
+}
+

src/SUMMARY.md

@@ -13,3 +13,4 @@ Summary
 
 - [Applications](./ch01-00-applications.md)
   - [Upgradeable Contract](./ch01-01-upgradeable_contract.md)
+  - [Defi Vault](./ch01-02-simple_vault.md)

src/ch01-02-simple_vault.md

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+# Simple Defi Vault
+
+This is the Cairo adaptation of the [Solidity by example Vault](https://solidity-by-example.org/defi/vault/).
+Here's how it works:
+
+- When a user deposits a token, the contract calculates the amount of shares to mint.
+
+- When a user withdraws, the contract burns their shares, calculates the yield, and withdraw both the yield and the initial amount of token deposited.
+
+```rust
+{{#include ../listings/ch01-applications/simple_vault/src/simple_vault.cairo}}
+```
+
+> **Note**
+> As of version v1.1.0, we need to enable `experimental_v0.1.0` libfuncs to use `u256_divmod_safe` as it hasn't been audited yet.
+> It'll be included in v2.0.0.