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# `x/mint`

The `x/mint` module handles the regular minting of new tokens in a configurable manner.

## Contents

* [State](#state)
    * [Minter](#minter)
    * [Params](#params)
* [Begin-Block](#begin-block)
    * [NextInflationRate](#nextinflationrate)
    * [NextAnnualProvisions](#nextannualprovisions)
    * [BlockProvision](#blockprovision)
* [Parameters](#parameters)
* [Events](#events)
    * [BeginBlocker](#beginblocker)
* [Client](#client)
    * [CLI](#cli)
    * [gRPC](#grpc)
    * [REST](#rest)

## Concepts

### The Minting Mechanism

The default minting mechanism was designed to:

* allow for a flexible inflation rate determined by market demand targeting a particular bonded-stake ratio
* effect a balance between market liquidity and staked supply

In order to best determine the appropriate market rate for inflation rewards, a
moving change rate is used.  The moving change rate mechanism ensures that if
the % bonded is either over or under the goal %-bonded, the inflation rate will
adjust to further incentivize or disincentivize being bonded, respectively. Setting the goal
%-bonded at less than 100% encourages the network to maintain some non-staked tokens
which should help provide some liquidity.

It can be broken down in the following way:

* If the actual percentage of bonded tokens is below the goal %-bonded the inflation rate will
   increase until a maximum value is reached
* If the goal % bonded (67% in Cosmos-Hub) is maintained, then the inflation
   rate will stay constant
* If the actual percentage of bonded tokens is above the goal %-bonded the inflation rate will
   decrease until a minimum value is reached

### Custom Minters

As of Cosmos SDK v0.53.0, developers can set a custom `MintFn` for the module for specialized token minting logic.

The function signature that a `MintFn` must implement is as follows:

```go
// MintFn defines the function that needs to be implemented in order to customize the minting process.
type MintFn func(ctx sdk.Context, k *Keeper) error
```

This can be passed to the `Keeper` upon creation with an additional `Option`:

```go
app.MintKeeper = mintkeeper.NewKeeper(
		appCodec,
		runtime.NewKVStoreService(keys[minttypes.StoreKey]),
		app.StakingKeeper,
		app.AccountKeeper,
		app.BankKeeper,
		authtypes.FeeCollectorName,
		authtypes.NewModuleAddress(govtypes.ModuleName).String(),
		// mintkeeper.WithMintFn(CUSTOM_MINT_FN), // custom mintFn can be added here
	)
```

#### Custom Minter DI Example

Below is a simple approach to creating a custom mint function with extra dependencies in DI configurations.
For this basic example, we will make the minter simply double the supply of `foo` coin.

First, we will define a function that takes our required dependencies, and returns a `MintFn`.

```go
// MyCustomMintFunction is a custom mint function that doubles the supply of `foo` coin.
func MyCustomMintFunction(bank bankkeeper.BaseKeeper) mintkeeper.MintFn {
	return func(ctx sdk.Context, k *mintkeeper.Keeper) error {
		supply := bank.GetSupply(ctx, "foo")
		err := k.MintCoins(ctx, sdk.NewCoins(supply.Add(supply)))
		if err != nil {
			return err
		}
		return nil
	}
}
```

Then, pass the function defined above into the `depinject.Supply` function with the required dependencies.

```go
// NewSimApp returns a reference to an initialized SimApp.
func NewSimApp(
    logger log.Logger,
    db dbm.DB,
    traceStore io.Writer,
    loadLatest bool,
    appOpts servertypes.AppOptions,
    baseAppOptions ...func(*baseapp.BaseApp),
) *SimApp {
    var (
        app        = &SimApp{}
        appBuilder *runtime.AppBuilder
        appConfig = depinject.Configs(
            AppConfig,
            depinject.Supply(
                appOpts,
                logger,
                // our custom mint function with the necessary dependency passed in.
                MyCustomMintFunction(app.BankKeeper),
            ),
        )
	)
	// ...
}
```

## State

### Minter

The minter is a space for holding current inflation information.

* Minter: `0x00 -> ProtocolBuffer(minter)`

```protobuf reference
https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/proto/cosmos/mint/v1beta1/mint.proto#L10-L24
```

### Params

The mint module stores its params in state with the prefix of `0x01`,
it can be updated with governance or the address with authority.

* Params: `mint/params -> legacy_amino(params)`

```protobuf reference
https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/proto/cosmos/mint/v1beta1/mint.proto#L26-L59
```

## Begin-Block

Minting parameters are recalculated and inflation paid at the beginning of each block.

### Inflation rate calculation

Inflation rate is calculated using an "inflation calculation function" that's
passed to the `NewAppModule` function. If no function is passed, then the SDK's
default inflation function will be used (`NextInflationRate`). In case a custom
inflation calculation logic is needed, this can be achieved by defining and
passing a function that matches `InflationCalculationFn`'s signature.

```go
type InflationCalculationFn func(ctx sdk.Context, minter Minter, params Params, bondedRatio math.LegacyDec) math.LegacyDec
```

#### NextInflationRate

The target annual inflation rate is recalculated each block.
The inflation is also subject to a rate change (positive or negative)
depending on the distance from the desired ratio (67%). The maximum rate change
possible is defined to be 13% per year, however, the annual inflation is capped
as between 7% and 20%.

```go
NextInflationRate(params Params, bondedRatio math.LegacyDec) (inflation math.LegacyDec) {
	inflationRateChangePerYear = (1 - bondedRatio/params.GoalBonded) * params.InflationRateChange
	inflationRateChange = inflationRateChangePerYear/blocksPerYr

	// increase the new annual inflation for this next block
	inflation += inflationRateChange
	if inflation > params.InflationMax {
		inflation = params.InflationMax
	}
	if inflation < params.InflationMin {
		inflation = params.InflationMin
	}

	return inflation
}
```

### NextAnnualProvisions

Calculate the annual provisions based on current total supply and inflation
rate. This parameter is calculated once per block.

```go
NextAnnualProvisions(params Params, totalSupply math.LegacyDec) (provisions math.LegacyDec) {
	return Inflation * totalSupply
```

### BlockProvision

Calculate the provisions generated for each block based on current annual provisions. The provisions are then minted by the `mint` module's `ModuleMinterAccount` and then transferred to the `auth`'s `FeeCollector` `ModuleAccount`.

```go
BlockProvision(params Params) sdk.Coin {
	provisionAmt = AnnualProvisions/ params.BlocksPerYear
	return sdk.NewCoin(params.MintDenom, provisionAmt.Truncate())
```


## Parameters

The minting module contains the following parameters:

| Key                 | Type            | Example                |
|---------------------|-----------------|------------------------|
| MintDenom           | string          | "uatom"                |
| InflationRateChange | string (dec)    | "0.130000000000000000" |
| InflationMax        | string (dec)    | "0.200000000000000000" |
| InflationMin        | string (dec)    | "0.070000000000000000" |
| GoalBonded          | string (dec)    | "0.670000000000000000" |
| BlocksPerYear       | string (uint64) | "6311520"              |


## Events

The minting module emits the following events:

### BeginBlocker

| Type | Attribute Key     | Attribute Value    |
|------|-------------------|--------------------|
| mint | bonded_ratio      | {bondedRatio}      |
| mint | inflation         | {inflation}        |
| mint | annual_provisions | {annualProvisions} |
| mint | amount            | {amount}           |


## Client

### CLI

A user can query and interact with the `mint` module using the CLI.

#### Query

The `query` commands allows users to query `mint` state.

```shell
simd query mint --help
```

##### annual-provisions

The `annual-provisions` command allows users to query the current minting annual provisions value

```shell
simd query mint annual-provisions [flags]
```

Example:

```shell
simd query mint annual-provisions
```

Example Output:

```shell
22268504368893.612100895088410693
```

##### inflation

The `inflation` command allows users to query the current minting inflation value

```shell
simd query mint inflation [flags]
```

Example:

```shell
simd query mint inflation
```

Example Output:

```shell
0.199200302563256955
```

##### params

The `params` command allows users to query the current minting parameters

```shell
simd query mint params [flags]
```

Example:

```yml
blocks_per_year: "4360000"
goal_bonded: "0.670000000000000000"
inflation_max: "0.200000000000000000"
inflation_min: "0.070000000000000000"
inflation_rate_change: "0.130000000000000000"
mint_denom: stake
```

### gRPC

A user can query the `mint` module using gRPC endpoints.

#### AnnualProvisions

The `AnnualProvisions` endpoint allows users to query the current minting annual provisions value

```shell
/cosmos.mint.v1beta1.Query/AnnualProvisions
```

Example:

```shell
grpcurl -plaintext localhost:9090 cosmos.mint.v1beta1.Query/AnnualProvisions
```

Example Output:

```json
{
  "annualProvisions": "1432452520532626265712995618"
}
```

#### Inflation

The `Inflation` endpoint allows users to query the current minting inflation value

```shell
/cosmos.mint.v1beta1.Query/Inflation
```

Example:

```shell
grpcurl -plaintext localhost:9090 cosmos.mint.v1beta1.Query/Inflation
```

Example Output:

```json
{
  "inflation": "130197115720711261"
}
```

#### Params

The `Params` endpoint allows users to query the current minting parameters

```shell
/cosmos.mint.v1beta1.Query/Params
```

Example:

```shell
grpcurl -plaintext localhost:9090 cosmos.mint.v1beta1.Query/Params
```

Example Output:

```json
{
  "params": {
    "mintDenom": "stake",
    "inflationRateChange": "130000000000000000",
    "inflationMax": "200000000000000000",
    "inflationMin": "70000000000000000",
    "goalBonded": "670000000000000000",
    "blocksPerYear": "6311520"
  }
}
```

### REST

A user can query the `mint` module using REST endpoints.

#### annual-provisions

```shell
/cosmos/mint/v1beta1/annual_provisions
```

Example:

```shell
curl "localhost:1317/cosmos/mint/v1beta1/annual_provisions"
```

Example Output:

```json
{
  "annualProvisions": "1432452520532626265712995618"
}
```

#### inflation

```shell
/cosmos/mint/v1beta1/inflation
```

Example:

```shell
curl "localhost:1317/cosmos/mint/v1beta1/inflation"
```

Example Output:

```json
{
  "inflation": "130197115720711261"
}
```

#### params

```shell
/cosmos/mint/v1beta1/params
```

Example:

```shell
curl "localhost:1317/cosmos/mint/v1beta1/params"
```

Example Output:

```json
{
  "params": {
    "mintDenom": "stake",
    "inflationRateChange": "130000000000000000",
    "inflationMax": "200000000000000000",
    "inflationMin": "70000000000000000",
    "goalBonded": "670000000000000000",
    "blocksPerYear": "6311520"
  }
}
```
