# Stablecoinswap API

## addLiquidity

{% hint style="info" %}
Adding liquidity is free. However, removing liquidity bears the same fee as the swap operation. This is to prevent users from bypassing the trading fee by depositing liquidity in one token and instantly withdrawing it in another token.
{% endhint %}

{% tabs %}
{% tab title="Smart Contract" %}

```python
def addLiquidity(
    token_address: address, 
    erc20_token_amount: uint256, 
    deadline: timestamp
) -> bool
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.addLiquidity(token_address, amount, deadline).send({ from: user_address }, callback)
```

{% endtab %}
{% endtabs %}

| Parameter            | Type    |                   Description |
| -------------------- | ------- | ----------------------------: |
| token\_address       | address | Address of ERC20 token to add |
| erc20\_token\_amount | uint256 |  How many ERC20 tokens to add |
| deadline             | uint256 |          Transaction deadline |

| Returns |                                                  |
| ------- | -----------------------------------------------: |
| uint256 | The amount of STL tokens received by the sender. |

## removeLiquidity

{% tabs %}
{% tab title="Smart Contract" %}

```python
def removeLiquidity(
    token_address: address, 
    stableswap_token_amount: uint256, 
    erc20_min_output_amount: uint256, 
    deadline: timestamp
) -> bool
```

{% endtab %}

{% tab title="Web3" %}

```
 contract.methods.removeLiquidity(token_address, amount, min_output_amount, deadline).send({ from: user_address }, callback)
```

{% endtab %}
{% endtabs %}

| Parameter                  | Type    |                        Description |
| -------------------------- | ------- | ---------------------------------: |
| token\_address             | address |   Address of ERC20 token to remove |
| stableswap\_token\_amount  | uint256 |     Amount of STL tokens to redeem |
| erc20\_min\_output\_amount | uint256 | Minimum ERC20 tokens output amount |
| deadline                   | uint256 |               Transaction deadline |

| Returns |                                                    |
| ------- | -------------------------------------------------: |
| uint256 | The amount of erc20 tokens received by the sender. |

## swapTokens

{% tabs %}
{% tab title="Smart Contract" %}

```python
def swapTokens(
    input_token: address,
    output_token: address, 
    erc20_input_amount: uint256, 
    erc20_min_output_amount: uint256, 
    deadline: timestamp
) -> bool
```

{% endtab %}

{% tab title="Web3" %}

```
contract.methods.swapTokens(input_token_address, output_token_address, input_amount, min_output_amount, deadline).send({ from: this.currentAddress() }, callback)
```

{% endtab %}
{% endtabs %}

| Parameter                  | Type    |                        Description |
| -------------------------- | ------- | ---------------------------------: |
| input\_token               | address |      Address of input  ERC20 token |
| output\_token              | address |      Address of output ERC20 token |
| erc20\_input\_amount       | uint256 |  Amount of ERC20 input tokens sold |
| erc20\_min\_output\_amount | uint256 | Minimum ERC20 output tokens to buy |
| deadline                   | uint256 |               Transaction deadline |

| Returns |                                                    |
| ------- | -------------------------------------------------: |
| uint256 | The amount of erc20 tokens received by the sender. |

## tokenExchangeRateAfterFees

{% tabs %}
{% tab title="Smart Contract" %}

```python
@constant
def tokenExchangeRateAfterFees(
    input_token_address: address, 
    output_token_address: address
) -> uint256
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.tokenExchangeRateAfterFees(input_token_address, output_token_address).call()
```

{% endtab %}
{% endtabs %}

| Parameter              | Type    |                    Description |
| ---------------------- | ------- | -----------------------------: |
| input\_token\_address  | address | Address of ERC20 token to sell |
| output\_token\_address | address |  Address of ERC20 token to buy |

| Returns |                                                                                                                                                                                                              |
| ------- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------: |
| uint265 | <p>Exchange rate multiplied by 10^22.</p><p></p><p> Note that due to rounding, the fees could be slightly higher for the tokens with smaller decimal precision and/or if the exchange amount is too low.</p> |

## tokenOutputAmountAfterFees

{% tabs %}
{% tab title="Smart Contract" %}

```python
@constant
def tokenOutputAmountAfterFees(
    input_token_amount: uint256, 
    input_token_address: address, 
    output_token_address: address
) -> uint256
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.tokenOutputAmountAfterFees(amount, input_token_address, output_token_address).call()
```

{% endtab %}
{% endtabs %}

| Parameter              | Type    |                    Description |
| ---------------------- | ------- | -----------------------------: |
| input\_token\_amount   | uint256 |  Amount of ERC20 token to sell |
| input\_token\_address  | address | Address of ERC20 token to sell |
| output\_token\_address | address |  Address of ERC20 token to buy |

| Returns |                                                                  |
| ------- | ---------------------------------------------------------------: |
| uint256 | How many tokens can be bought for a given amount of input tokens |

## poolOwnership

{% tabs %}
{% tab title="Smart Contract" %}

```python
@constant
def poolOwnership(user_address: address) -> decimal
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.poolOwnership(address).call()
```

{% endtab %}
{% endtabs %}

| Parameter     | Type    |       Description |
| ------------- | ------- | ----------------: |
| user\_address | address | Address of a user |

| Returns               |                                                |
| --------------------- | ---------------------------------------------: |
| fixed168x10 (uint168) | Share of total liquidity belonging to the user |

## fees

{% tabs %}
{% tab title="Smart Contract" %}

```python
@constant
def fees(fee_name: string[32]) -> decimal
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.fees(fee_name).call()
```

{% endtab %}
{% endtabs %}

| Parameter | Type   |              Description |
| --------- | ------ | -----------------------: |
| fee\_name | string | 'ownerFee' or 'tradeFee' |

| Returns               |                                   |
| --------------------- | --------------------------------: |
| fixed168x10 (uint168) | Fee value (i.e. 0.001 means 0.1%) |

## inputTokens

{% tabs %}
{% tab title="Smart Contract" %}

```python
inputTokens: public(map(address, bool))
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.inputTokens(address).call()
```

{% endtab %}
{% endtabs %}

| Parameter | Type    |            Description |
| --------- | ------- | ---------------------: |
| address   | address | Address of ERC20 token |

| Returns |                                                             |
| ------- | ----------------------------------------------------------: |
| bool    | True if an address is in the list of available input tokens |

## outputTokens

{% tabs %}
{% tab title="Smart Contract" %}

```python
outputTokens: public(map(address, bool))
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.outputTokens(address).call()
```

{% endtab %}
{% endtabs %}

| Parameter | Type    |            Description |
| --------- | ------- | ---------------------: |
| address   | address | Address of ERC20 token |

| Returns |                                                              |
| ------- | -----------------------------------------------------------: |
| bool    | True if an address is in the list of available output tokens |

## priceOracleAddress

{% tabs %}
{% tab title="Smart Contract" %}

```python
priceOracleAddress: public(address)
```

{% endtab %}

{% tab title="Web3" %}

```javascript
contract.methods.priceOracleAddress().call()
```

{% endtab %}
{% endtabs %}

| Returns |                                   |
| ------- | --------------------------------: |
| address | Address of a priceoracle contract |