# Emission Distribution

The Backstop contract is responsible for distributing emissions to backstop depositors and lending pools after it receives them from the emitter contract.

## Reward Zone

Emissions are only distributed to pools in a `reward_zone`, which the backstop contract manages, and backstop depositors designating their deposits to those pools.

### Reward Zone Length

The number of pools that can be added to the reward zone is 50. This is done to prevent liquidity fragmentation by ensuring only a select number of pools receive emissions.

### Adding Pools to the Reward Zone

Pools can be added to the Reward Zone by calling the `add_reward()` function. This function intakes a potential pool to drop from the reward zone and attempts the addition with the following process:

{% @mermaid/diagram content="flowchart LR
A\[add\_reward] --> B{"REWARD\_ZONE
current\_length
<
max\_length"}
B --->|Yes| C\[\["ADD pool\_to\_add"]]
B -->|No| D{"pool\_to\_add\_total\_tokens

>

pool\_to\_drop\_total\_tokens"}
D -->|Yes| C
D -->|Yes| E\[\["DROP pool\_to\_drop"]]
D -->|No| F\[\[PANIC!]]" %}

{% hint style="danger" %}
If the pool being added to the reward zone has not met the minimum backstop threshold `add_reward()` will fail.
{% endhint %}

{% hint style="warning" %}
If the to\_remove pool is not in the reward zone, `add_reward()` will fail.
{% endhint %}

{% hint style="warning" %}
If the pool is already in the reward zone, `add_reward()` will fail.
{% endhint %}

## Emission Management

The backstop contract facilitates both emission distribution and backstop emissions claims.

### Emission Distribution

Emissions are distributed to backstop depositors and pools by calling the `gulp_emissions()` function which:

{% hint style="info" %}
Anyone may call `gulp_emissions()` - it's expected that someone will run a bot to do so
{% endhint %}

1. Calculates the `new_emissions` received from the emitter which
   1. equal to `emitter_last_distribution_time - backstop_last_distribution_time`

{% hint style="warning" %}
At least one hour must have passed between `emitter_last_distribution_time` and `backstop_last_distribution_time` or this `gulp_emissions()` will fail. This is to prevent rounding issues
{% endhint %}

2. Calculates the amount of emissions to allocate to backstop depositors and pools
   1. Backstop depositors get 70% of new emissions
   2. Pools get 30% of new emissions
3. Sets emissions per second for backstop depositors
   1. equal to `(backstop_emissions * pool_backstop_tokens / total_backstop_tokens_in_reward_zone_pools) + remaining_emissions / 7 days)`

{% hint style="info" %}
This EPS will expire in 7 days, so emissions must be gulped every 7 days, or backstop depositors will stop receiving emissions until emissions are gulped again. Emissions not distributed during a gulp gap will be accrued in the next gulp call.
{% endhint %}

{% hint style="info" %}
Backstop deposits queued for withdrawal will not count towards either`total_backstop_tokens_in_reward_zone_pools` or `pool_backstop_tokens` in the emission distribution calculations
{% endhint %}

4. Sets emissions earned by each pool
   1. equal to `pool_emissions * pool_backstop_tokens / total_backstop_tokens_in_reward_zone_pools`

### Emission Claims

The backstop facilitates emission claims by backstop depositors. Backstop depositors can claim their emissions by calling the `claim()` function which transfers the user's earned emissions for all input pool addresses to the user and reduces the user's accrued emissions to 0.

```rust
    /// Claim backstop deposit emissions from a list of pools for `from`
    ///
    /// Returns the amount of LP tokens minted
    ///
    /// ### Arguments
    /// * `from` - The address of the user claiming emissions
    /// * `pool_addresses` - The Vec of addresses to claim backstop deposit emissions from
    /// * `min_lp_tokens_out` - The minimum amount of LP tokens to mint with the claimed BLND
    ///
    /// ### Errors
    /// If an invalid pool address is included
    fn claim(e: Env, from: Address, pool_addresses: Vec<Address>, min_lp_tokens_out: i128) -> i128;
```

All claimed emissions are automatically deposited into the backstop and allocated to the pool they were earned in.

{% hint style="info" %}
Emissions are immediately deposited into the BLND:USDC liquidity pool so the claim function intakes a min-pool-tokens-out parameter to allow users to protect themselves from being frontran if they so choose.
{% endhint %}

{% hint style="info" %}
Users can claim their emissions and deposit them on behalf of another user by specifying the user in the `to` parameter in the `claim()` function.
{% endhint %}


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