# BC Oracle

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**Source:** `src/fira_bonding/oracles/BCOracleLib.sol`, `src/fira_bonding/oracles/BCLpOracle.sol`
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## BCOracleLib

### BT pricing

Pre-expiry, BT price is derived from the TWAP `ln(impliedRate)`:

```
btToAssetRate = 1 / exp(lnImpliedRate × timeToExpiry / YEAR)
```

This is the present value of 1 unit of underlying, discounted at the TWAP implied rate. Post-expiry, BT is worth exactly 1 asset unit.

### CT pricing

CT value is `1 - btToAssetRate`. Since BT + CT = 1 asset unit by construction, CT captures the remainder.

### FW solvency adjustment

If the FW exchange rate drops below the BC index, the FW wrapper is insolvent. In this case, BT and CT rates are scaled down by `fwIndex / bcIndex`, preventing the oracle from reporting prices that assume full solvency.

### TWAP calculation

`getMarketLnImpliedRate(market, duration)` queries two cumulative observations, takes the difference, and divides by duration for a manipulation-resistant time-weighted average.

## BCLpOracle

A convenience contract wrapping both `BCOracleLib` and `LpOracleLib` as external view functions. Deployed once per chain to save bytecode in contracts that need oracle prices.

Provides `getOracleState(market, duration)` to check whether a market has enough observation cardinality for the requested TWAP window and whether the oldest observation is old enough.