> For the complete documentation index, see [llms.txt](https://docs.essencefinance.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.essencefinance.io/development/smart-contracts/peg/ipegstabilitymodule.md).

# IPegStabilityModule

The Chi PSM is a contract which holds a reserve of assets in order to exchange CHI at $1 of underlying assets with a fee. `mint()` - buy CHI for $1 of underlying tokens `redeem()` - sell CHI back for $1 of the same

The contract has a reservesThreshold() of underlying meant to stand ready for redemptions. Any surplus reserves can be sent into the PCV using `allocateSurplus()`

The contract is a PCVDeposit - to track reserves OracleRef - to determine price of underlying, and RateLimitedMinter - to stop infinite mints and related issues (but this is in the implementation due to inheritance-linearization difficulties)

Inspired by MakerDAO PSM, code written without reference

## Functions

### mint

```solidity
function mint(
    address to,
    uint256 amountIn,
    uint256 minAmountOut
) external returns (uint256 amountChiOut)
```

mint `amountChiOut` CHI to address `to` for `amountIn` underlying tokens

see getMintAmountOut() to pre-calculate amount out

#### Parameters

| Name           | Type    | Description |
| -------------- | ------- | ----------- |
| `to`           | address |             |
| `amountIn`     | uint256 |             |
| `minAmountOut` | uint256 |             |

### redeem

```solidity
function redeem(
    address to,
    uint256 amountChiIn,
    uint256 minAmountOut
) external returns (uint256 amountOut)
```

redeem `amountChiIn` CHI for `amountOut` underlying tokens and send to address `to`

see getRedeemAmountOut() to pre-calculate amount out

#### Parameters

| Name           | Type    | Description |
| -------------- | ------- | ----------- |
| `to`           | address |             |
| `amountChiIn`  | uint256 |             |
| `minAmountOut` | uint256 |             |

### allocateSurplus

```solidity
function allocateSurplus() external
```

send any surplus reserves to the PCV allocation

### setMintFee

```solidity
function setMintFee(
    uint256 newMintFeeBasisPoints
) external
```

set the mint fee vs oracle price in basis point terms

#### Parameters

| Name                    | Type    | Description |
| ----------------------- | ------- | ----------- |
| `newMintFeeBasisPoints` | uint256 |             |

### setRedeemFee

```solidity
function setRedeemFee(
    uint256 newRedeemFeeBasisPoints
) external
```

set the redemption fee vs oracle price in basis point terms

#### Parameters

| Name                      | Type    | Description |
| ------------------------- | ------- | ----------- |
| `newRedeemFeeBasisPoints` | uint256 |             |

### setReservesThreshold

```solidity
function setReservesThreshold(
    uint256 newReservesThreshold
) external
```

set the ideal amount of reserves for the contract to hold for redemptions

#### Parameters

| Name                   | Type    | Description |
| ---------------------- | ------- | ----------- |
| `newReservesThreshold` | uint256 |             |

### setSurplusTarget

```solidity
function setSurplusTarget(
    contract IPCVDeposit newTarget
) external
```

set the target for sending surplus reserves

#### Parameters

| Name        | Type                 | Description |
| ----------- | -------------------- | ----------- |
| `newTarget` | contract IPCVDeposit |             |

### getMintAmountOut

```solidity
function getMintAmountOut(
    uint256 amountIn
) external returns (uint256 amountChiOut)
```

calculate the amount of CHI out for a given `amountIn` of underlying

#### Parameters

| Name       | Type    | Description |
| ---------- | ------- | ----------- |
| `amountIn` | uint256 |             |

### getRedeemAmountOut

```solidity
function getRedeemAmountOut(
    uint256 amountChiIn
) external returns (uint256 amountOut)
```

calculate the amount of underlying out for a given `amountChiIn` of CHI

#### Parameters

| Name          | Type    | Description |
| ------------- | ------- | ----------- |
| `amountChiIn` | uint256 |             |

### getMaxMintAmountOut

```solidity
function getMaxMintAmountOut() external returns (uint256)
```

the maximum mint amount out

### hasSurplus

```solidity
function hasSurplus() external returns (bool)
```

a flag for whether the current balance is above (true) or below and equal (false) to the reservesThreshold

### reservesSurplus

```solidity
function reservesSurplus() external returns (int256)
```

an integer representing the positive surplus or negative deficit of contract balance vs reservesThreshold

### reservesThreshold

```solidity
function reservesThreshold() external returns (uint256)
```

the ideal amount of reserves for the contract to hold for redemptions

### mintFeeBasisPoints

```solidity
function mintFeeBasisPoints() external returns (uint256)
```

the mint fee vs oracle price in basis point terms

### redeemFeeBasisPoints

```solidity
function redeemFeeBasisPoints() external returns (uint256)
```

the redemption fee vs oracle price in basis point terms

### underlyingToken

```solidity
function underlyingToken() external returns (contract IERC20)
```

the underlying token exchanged for CHI

### surplusTarget

```solidity
function surplusTarget() external returns (contract IPCVDeposit)
```

the PCV deposit target to send surplus reserves

### MAX\_FEE

```solidity
function MAX_FEE() external returns (uint256)
```

the max mint and redeem fee in basis points

## Events

### AllocateSurplus

```solidity
event AllocateSurplus(
    address caller,
    uint256 amount
)
```

event emitted when excess PCV is allocated

#### Parameters

| Name             | Type    | Description |
| ---------------- | ------- | ----------- |
| `caller`         | address |             |
| `amount`         | uint256 |             |
| ### MaxFeeUpdate |         |             |

```solidity
event MaxFeeUpdate(
    uint256 oldMaxFee,
    uint256 newMaxFee
)
```

event emitted when a new max fee is set

#### Parameters

| Name              | Type    | Description |
| ----------------- | ------- | ----------- |
| `oldMaxFee`       | uint256 |             |
| `newMaxFee`       | uint256 |             |
| ### MintFeeUpdate |         |             |

```solidity
event MintFeeUpdate(
    uint256 oldMintFee,
    uint256 newMintFee
)
```

event emitted when a new mint fee is set

#### Parameters

| Name                | Type    | Description |
| ------------------- | ------- | ----------- |
| `oldMintFee`        | uint256 |             |
| `newMintFee`        | uint256 |             |
| ### RedeemFeeUpdate |         |             |

```solidity
event RedeemFeeUpdate(
    uint256 oldRedeemFee,
    uint256 newRedeemFee
)
```

event emitted when a new redeem fee is set

#### Parameters

| Name                        | Type    | Description |
| --------------------------- | ------- | ----------- |
| `oldRedeemFee`              | uint256 |             |
| `newRedeemFee`              | uint256 |             |
| ### ReservesThresholdUpdate |         |             |

```solidity
event ReservesThresholdUpdate(
    uint256 oldReservesThreshold,
    uint256 newReservesThreshold
)
```

event emitted when reservesThreshold is updated

#### Parameters

| Name                    | Type    | Description |
| ----------------------- | ------- | ----------- |
| `oldReservesThreshold`  | uint256 |             |
| `newReservesThreshold`  | uint256 |             |
| ### SurplusTargetUpdate |         |             |

```solidity
event SurplusTargetUpdate(
    contract IPCVDeposit oldTarget,
    contract IPCVDeposit newTarget
)
```

event emitted when surplus target is updated

#### Parameters

| Name        | Type                 | Description |
| ----------- | -------------------- | ----------- |
| `oldTarget` | contract IPCVDeposit |             |
| `newTarget` | contract IPCVDeposit |             |
| ### Redeem  |                      |             |

```solidity
event Redeem(
    address to,
    uint256 amountChiIn,
    uint256 amountAssetOut
)
```

event emitted upon a redemption

#### Parameters

| Name             | Type    | Description |
| ---------------- | ------- | ----------- |
| `to`             | address |             |
| `amountChiIn`    | uint256 |             |
| `amountAssetOut` | uint256 |             |
| ### Mint         |         |             |

```solidity
event Mint(
    address to,
    uint256 amountIn,
    uint256 amountChiOut
)
```

event emitted when chi gets minted

#### Parameters

| Name           | Type    | Description |
| -------------- | ------- | ----------- |
| `to`           | address |             |
| `amountIn`     | uint256 |             |
| `amountChiOut` | uint256 |             |


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