# Stable

The `x/stable` module manages the minting and burning of a native stablecoin, backed by a basket of accepted collateral assets.

## Key Features

1. **Minting and Burning**:
   * Allows minting of the native stablecoin against approved collateral.
   * Allows burning of the native stablecoin to redeem collateral.
2. **Collateral Management**:
   * Supports a configurable basket of accepted collateral assets, typically IBC denoms.
3. **Permissioned Control**:
   * Restricts mint and burn operations to a whitelist of authorized addresses.
4. **Dynamic Exchange Rate**:
   * Calculates exchange rates dynamically based on the `exponent` (decimal places) of the involved tokens, ensuring fair value exchange.
5. **On-Chain Auditability**:
   * Provides full transparency of all operations and balances for easy auditing.

## Core Concepts

> **Note:** The following section covers advanced topics intended for experienced users or developers.

### Parameters

The `stable` module's behavior is controlled by a set of on-chain parameters:

* **`authority_addresses`** (string\[]): A list of addresses authorized to execute `MsgMint` and `MsgBurn`.
* **`accepted_denoms`** (string\[]): A whitelist of collateral asset denominations that can be deposited to mint the stablecoin. These are typically IBC denoms.
* **`stable_denom`** (string): The denomination of the native stablecoin minted by the module (e.g., `uusdrise`).

### Exchange Rate Calculation

The exchange rate between the collateral asset and the native stablecoin is not hardcoded. Instead, it is calculated dynamically using the `exponent` field from the `DenomMetadata` stored in the `x/bank` module.

If `DenomMetadata` is not found for a given token, its exponent is assumed to be `0`. This ensures a fair exchange rate for tokens based on their specified decimal places.

## Workflow: Minting and Burning

### Sequence Diagram

{% @mermaid/diagram content="sequenceDiagram
participant Authority as Authorized Address
participant StableModule as x/stable Module
participant BankModule as x/bank Module

```
note over Authority, BankModule: Mint Process
Authority->>StableModule: MsgMint
activate StableModule
StableModule->>BankModule: Transfer collateral from Authority to Module Account
StableModule->>BankModule: Mint stablecoin to Module Account
StableModule->>BankModule: Send stablecoin from Module Account to Authority
deactivate StableModule

note over Authority, BankModule: Burn Process
Authority->>StableModule: MsgBurn
activate StableModule
StableModule->>BankModule: Transfer stablecoin from Authority to Module Account
StableModule->>BankModule: Burn stablecoin from Module Account
StableModule->>BankModule: Send collateral from Module Account to Authority
deactivate StableModule" %}
```

## Messages

The module supports the following messages:

* **MsgMint**
  * **Action**: An authorized sender deposits collateral to mint the native stablecoin.
  * **Process**: 1. Verifies the `sender` is in `authority_addresses`. 2. Confirms all deposited denoms are in `accepted_denoms`. 3. Transfers collateral from the sender to the module account. 4. Calculates the corresponding amount of `stable_denom` to mint using the exponent-based exchange rate. 5. Mints the calculated amount of `stable_denom` and sends it to the `sender`.
* **MsgBurn**
  * **Action**: An authorized sender burns the native stablecoin to receive a chosen collateral asset.
  * **Process**: 1. Verifies the `sender` is an authority. 2. Confirms the requested `output_denom` is in `accepted_denoms`. 3. Transfers the `input_amount` of stablecoin from the sender to the module and burns it. 4. Calculates the corresponding amount of `output_denom` to return using the exponent-based exchange rate. 5. Transfers the calculated collateral amount from the module account to the `sender`.

## Queries

The module provides various query endpoints:

* **Params**: Query the current module parameters.
* **ModuleAccountBalance**: Query the balance of all collateral assets held by the module account.

## Auditability

All mint and burn operations, collateral balances held by the module, and the total supply of the stablecoin are publicly accessible on-chain. This design ensures that the stablecoin is always transparently and verifiably collateralized by the assets held in the module account.

See [Github](https://github.com/sunriselayer/sunrise/tree/stable/x/stable) for details.