# Repay Fixed Rate

```mermaid
sequenceDiagram
  actor User
  participant Router as Router (ActionBorrow)
  participant FRLM as Fixed Rate LendingMarket (FRLM)
  participant FM as FiraMarket
  participant FW as FW
  participant CT as CouponToken (CT)

  Note over User,Router: User approves input token to Router (ERC20 approve)
  User->>Router: repay(marketParams, FRLM, FM, tokensToRepay, input)
  alt BT not expired
    Router->>FW: mintFwFromToken (input token → FW)
    FW-->>Router: FW out
    Router->>FM: swapFwForExactBt (FW → BT via AMM)
    FM-->>Router: BT out
    Router->>FRLM: approve BT, repay(marketParams, btToRepay, 0, user, "")
    FRLM-->>Router: position updated (debt reduced)
    Router-->>User: refund excess BT (if any)
  else BT expired
    Router->>FW: mintFwFromToken (input token → FW, sent to CT contract)
    FW-->>CT: FW deposited
    Router->>CT: mintBC(Router, Router) — mints both BT and CT to Router
    CT-->>Router: BT + CT out (CT is minted but economically worthless post-expiry)
    Router->>FRLM: approve BT, repay(marketParams, btToRepay, 0, user, "")
    FRLM-->>Router: position updated (debt reduced)
    Router-->>User: refund excess BT (if any)
    Note over Router: CT minted post-expiry stays in Router (zero value, never burned)
  end
```

**Key references**: `ActionBorrow.repay`.

## Details

* **Goal**: Repay debt using an input token; router converts to BT as needed.
* **Preconditions**:
  * Existing borrow: else `"AB: no borrow"`.
  * `tokensToRepay` must be ≤ current debt: else `"AB: repay too much"`.
  * Input token approval to router.
* **Expiry handling**:
  * **Pre-expiry**: Input token → FW (mint) → BT (AMM swap via FiraMarket). Repay, refund excess BT.
  * **Post-expiry**: Input token → FW (mint to CT contract) → `CT.mintBC` produces BT + CT. Only BT is used for repayment. CT is minted but NOT burned — it stays in the router with zero economic value.

## Views and events

**Views**

* Lending: `getUserPosition` (pre/post), `position(id, user)`.
* Market: `isExpired()`.
* FW: `previewDeposit`, `bcIndexStored()` for estimation on expired paths.

**Events**

* Lending: `EventsLib.Repay` (assets, shares), possibly `EventsLib.AccrueInterest`.
* Router/Misc: `MintFwFromToken`, `MintBcFromFw` when conversions occur.