Borrow at a fixed rate

import {
  createWalletClient,
  http,
  parseUnits,
  zeroAddress,
  type Address,
} from "viem";
import { base } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";

// The borrower (taker of bids), i.e. your wallet address
const taker: Address = "0xYourWalletAddress";

// Create a wallet client connected to Base
// This example uses a simple EOA with a private key for brevity 
// You can substitute in any wallet solution that fits your setup
const walletClient = createWalletClient({
  account: privateKeyToAccount("0xYourPrivateKey"),
  chain: base,
  transport: http(),
});

GET https://api.morpho.org/v0/midnight/books
  ?chain_ids=8453                                                // Base
  &loan_tokens=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913        // USDC on Base
  &sort=maturity

// Response (each book is one market with its top ask/bid levels)
{
  "cursor": "eyJzb3J0Ijpb...",                                   // for pagination (null when no more pages)
  "data": [
    {
      "market_id":        "0xd92de5e7fbb...7614",                // this is the ID you will use in the next step
      "chain_id":   8453,
      "loan_token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "maturity":   1798761600,                                  // January 1, 2027
      "collaterals": [
        {          
          "token":   "0x4200...0006",                            // WETH
          "lltv":    "770000000000000000",                       // 77% LTV
          "liquidation_cursor": "250000000000000000",            // 0.25
          "oracle":  "0xOracle..."
        }
      ],

      "asks": [ /* … lending side, ignore for borrowing */ ],

      // ┌──────────────────────────────────────────────────────────────┐
      // │  FOR BORROWING → read the BIDS                               │
      // │  Bids = lenders buying units = offering to lend you money    │
      // │  You (the borrower) take these bids = sell your units        │
      // │  The bid price is what you receive per unit → your cost      │
      // └──────────────────────────────────────────────────────────────┘
      "bids": [
        {
          "tick":   4988,
          "price":  "956937000000000000",                        // ≈ 0.9569 per unit
          "units":  "8000000000",
          "assets": "7655497000",                                // ≈ 7,655 USDC on the bid
          "count":  2
        },
        {
          "tick":   4976,
          "price":  "951000000000000000",                        // ≈ 0.9510 (worse for borrower)
          "units":  "12000000000",
          "assets": "11412000000",
          "count":  4
        }
      ]
    }
  ]
}

// Select book data
const book = response.data[0];

// Obtain best bid price (highest = cheapest to borrow)
const bestBidPrice = Number(book.bids[0].price) / 1e18;          // ≈ 0.9569

// Calculate time to maturity (ttm) in seconds
const ttm = book.maturity - Date.now() / 1000;

// Calculate fixed borrow APR
const borrowAPR = (1 / bestBidPrice - 1) * (365 * 86400) / ttm;  

console.log(`Borrow APR: ${(borrowAPR * 100).toFixed(2)}%`);    

// If the rate looks good, save the market ID for the next step
const marketId = book.market_id;                                 // "0xd92de5e7fbb...7614"

GET https://api.morpho.org/v0/midnight/books/{marketId}/bids/quote
  ?assets=10000000000                             // 10,000 USDC (6 decimals)
  &slippage=0.5                                   // 0.5% slippage guard

// Response - the Router's execution plan:
{
  "data": {
    "average_best_price":  "956937000000000000",  // ≈ 0.9569
    "average_worst_price": "952152000000000000",  // with 0.5% slippage
    "available_assets":    "14000000000",         // 14,000 USDC total bid depth
    "available_units":     "14630000000",

    "takeable_offers": [
      {
        "market_id":     "0xd92de5e7fbb...7614",
        "units":         "8000000000",           // cap: up to 8,000 units from this offer
        "ratifier_data": "0x7c1e...d402",
        "offer": {
          "buy":      true,                      // buy offer (bid) (maker is lender)
          "tick":     4988,
          "maker":    "0xDave...",
          "ratifier": "0xEcrecoverRatifier...",
          // … remaining offer fields
        }
      },
      {
        "market_id": "0xd92de5e7fbb...7614",
        "units":     "6630000000",               // cap: 6,630 units — fallback
        "ratifier_data": "0xab12...e905",
        "offer": { "buy": true, "tick": 4976, "maker": "0xEve...", /* … */ }
      }
    ]
  }
}

// Interpreting the quote
const quote = response.data;
const avgPrice = Number(quote.average_best_price) / 1e18; // 0.9569
const borrowAPR = (1 / avgPrice - 1) * (365 * 86400) / ttm;

// To borrow 10,000 USDC at price ≈ 0.9569 you sell ≈ 10,450 units
// At maturity you repay 10,450 USDC → net cost ≈ 450 USDC
const unitsToSell = Math.ceil(10000e6 / avgPrice);

function apiOfferToAbi(apiOffer: any) {
  return {
    market: {
      chainId:        BigInt(apiOffer.market.chain_id),
      midnight:       apiOffer.market.midnight,
      loanToken:      apiOffer.market.loan_token,
      collateralParams: apiOffer.market.collaterals.map((c: any) => ({
        token:  c.token,
        lltv:   BigInt(c.lltv),
        liquidationCursor: BigInt(c.liquidation_cursor),
        oracle: c.oracle,
      })),
      maturity:       BigInt(apiOffer.market.maturity),
      rcfThreshold:   BigInt(apiOffer.market.rcf_threshold),
      enterGate:      apiOffer.market.enter_gate,
      liquidatorGate: apiOffer.market.liquidator_gate,
    },
    buy:                       apiOffer.buy,
    maker:                     apiOffer.maker,
    maxUnits:                  BigInt(apiOffer.max_units),
    maxAssets:                 BigInt(apiOffer.max_assets),
    start:                     BigInt(apiOffer.start),
    expiry:                    BigInt(apiOffer.expiry),
    tick:                      BigInt(apiOffer.tick),
    group:                     apiOffer.group,
    callback:                  apiOffer.callback,
    callbackData:              apiOffer.callback_data,
    receiverIfMakerIsSeller:   apiOffer.receiver_if_maker_is_seller,
    ratifier:                  apiOffer.ratifier,
    reduceOnly:                apiOffer.reduce_only,
    continuousFeeCap:          BigInt(apiOffer.continuous_fee_cap),
  };
}

const takeableOffers = quote.takeable_offers;

// Map API offers → ABI-ready structs via helper
const takes = takeableOffers.map((t) => ({
  offer: apiOfferToAbi(t.offer),
  ratifierData: t.ratifier_data,
  units: BigInt(t.units),
}));

npm install @morpho-org/midnight-sdk viem

import { MidnightApi, type MidnightApiTake } from "@morpho-org/midnight-sdk/api";
import { parseUnits } from "viem";

const marketId = "0xd92de5e7fbb...7614";   // from browsing books in Step 1

// SDK wraps the quote endpoint and maps the response into ABI-ready take objects (uses Morpho's router by default, no config needed)
const quote = await MidnightApi.fetchBookQuote({
  marketId,
  side:     "bids",                        // borrower takes bids
  assets:   parseUnits("10000", 6),        // 10,000 USDC to borrow
  slippage: "0.5",                         // 0.5% slippage guard
});

// quote.data contains:
//   .averageBestPrice  (BigInt)
//   .averageWorstPrice (BigInt)
//   .availableAssets   (BigInt)
//   .availableUnits    (BigInt)
//   .takeableOffers    (MidnightApiTake[], ABI-ready)

// ABI-ready takes
const takes: MidnightApiTake[] = quote.data.takeableOffers;

// Compute your borrowing cost
const avgPrice = Number(quote.data.averageBestPrice) / 1e18;
const borrowAPR = (1 / avgPrice - 1) * (365 * 86400) / ttm;

import {
  erc20Abi, maxUint256, createPublicClient, encodeAbiParameters, parseAbiParameters, parseSignature, parseUnits, http,
} from "viem";
import { base } from "viem/chains";

const MIDNIGHT_BUNDLES = "0x6688dEc8878f43905e11B3C6Bc025E098133144f";   // MidnightBundles contract
const USDC             = "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913";   // USDC on Base
const WETH             = "0x4200000000000000000000000000000000000006";   // WETH on Base
const MIDNIGHT         = "0x...";                                        // Midnight contract

// Path 1: approve()
// 1. Let MidnightBundles pull WETH during the buy
// 2. maxUint256 = standing allowance
await walletClient.writeContract({
  account: taker, address: WETH, abi: erc20Abi,
  functionName: "approve", args: [MIDNIGHT_BUNDLES, maxUint256],
});

// Variable to set the loanTokenPermit variable to (bundler argument) in the Execute step that follows 
const collateralPermitNone   = { kind: 0, data: "0x" } as const;

// --------------------------------------------------------------

// Path 2: EIP-2612
// For a permit-capable COLLATERAL token only (WETH has no permit() but example assumes COLLATERAL of choise has permit())
const COLLATERAL = "0x...";                                               // a permit-capable collateral token
const collateralAmount = parseUnits("1", 18);                             // 1 unit of collateral 
const publicClient = createPublicClient({ chain: base, transport: http() });

const deadline = BigInt(Math.floor(Date.now() / 1000) + 3600);

// Read the taker's current EIP-2612 nonce from the USDC contract
const nonce = await publicClient.readContract({
  address: COLLATERAL,
  abi: [{ name: "nonces", type: "function", stateMutability: "view",
          inputs: [{ name: "owner", type: "address" }],
          outputs: [{ type: "uint256" }] }],
  functionName: "nonces",
  args: [taker],
});

const sig = await walletClient.signTypedData({
  account: taker,
  // TODO: Replace token name and version based on the COLLATERAL choice
  domain: { name: "<Token Name>", version: "<v>", chainId: 8453, verifyingContract: COLLATERAL },
  types: { Permit: [
    { name: "owner",    type: "address" },
    { name: "spender",  type: "address" },
    { name: "value",    type: "uint256" },
    { name: "nonce",    type: "uint256" },
    { name: "deadline", type: "uint256" },
  ] },
  primaryType: "Permit",
  message: { owner: taker, spender: MIDNIGHT_BUNDLES,
             value: collateralAmount, nonce, deadline },
});

const { r, s, v } = parseSignature(sig);

// Variable to set the loanTokenPermit variable to (bundler argument) in the Execute step that follows 
const collateralPermitERC2612 = {
  kind: 1,                                                                  // 1 = ERC2612
  data: encodeAbiParameters(
    parseAbiParameters("uint256 deadline, uint8 v, bytes32 r, bytes32 s"),
    [deadline, Number(v), r, s],
  ),
} as const;

// --------------------------------------------------------------

// Path 3: Permit2
// One-time setup (once per token, ever): approve Permit2 on collateral asset (i.e. WETH)
const PERMIT2 = "0x000000000022D473030F116dDEE9F6B43aC78BA3";               

// One-time setup: approve Permit2 on WETH. After this, every future authorization is just a signature
await walletClient.writeContract({
  account: taker, address: WETH, abi: erc20Abi,
  functionName: "approve", args: [PERMIT2, maxUint256],
});

// Per-borrow: sign a Permit2 SignatureTransfer (offchain, no gas)
const nonce    = BigInt(Date.now());                                        // unordered nonce (Permit2 uses a bitmap)
const deadline = BigInt(Math.floor(Date.now() / 1000) + 3600);

const sig = await walletClient.signTypedData({
  account: taker,
  domain: { name: "Permit2", chainId: 8453, verifyingContract: PERMIT2 },
  types: {
    PermitTransferFrom: [
      { name: "permitted", type: "TokenPermissions" },
      { name: "spender",   type: "address" },
      { name: "nonce",     type: "uint256" },
      { name: "deadline",  type: "uint256" },
    ],
    TokenPermissions: [
      { name: "token",  type: "address" },
      { name: "amount", type: "uint256" },
    ],
  },
  primaryType: "PermitTransferFrom",
  message: {
    permitted: { token: WETH, amount: collateralAmount },
    spender: MIDNIGHT_BUNDLES,    
    nonce,
    deadline,
  },
});

// Variable to set the loanTokenPermit variable to (bundler argument) in the Execute step that follows 
const collateralPermit2 = {
  kind: 2,                                                                   // 2 = Permit2
  data: encodeAbiParameters(
    parseAbiParameters("uint256 nonce, uint256 deadline, bytes signature"),
    [nonce, deadline, sig],
  ),
} as const;

// --------------------------------------------------------------
// Authorize MidnightBundles to act on your position (one-time boolean, persists across future actions)
await walletClient.writeContract({
  account: taker,
  address: MIDNIGHT,
  abi: midnightAbi,
  functionName: "setIsAuthorized",
  args: [MIDNIGHT_BUNDLES, true],
});

import { createWalletClient, http, parseUnits, zeroAddress, maxUint256 } from "viem";
import { base } from "viem/chains";
import { midnightBundlesAbi } from "@morpho-org/midnight-sdk";

const MIDNIGHT_BUNDLES = "0x6688dEc8878f43905e11B3C6Bc025E098133144f";        // MidnightBundles contract on Base
const WETH = "0x4200000000000000000000000000000000000006";                    // WETH contract address

// Borrower sells units to receive USDC, depositing WETH as collateral
const targetSellerAssets = parseUnits("10000", 6);                            // want 10,000 USDC

const worstAcceptablePrice = 0.95;                                            // worst price per unit you'll accept

// Calculate maxUnits to set your own price guard (cap your debt obligation by specifying the maximum number of units you're willing to sell) from worst acceptable borrow rate
// If price drops below 0.95, you'd need to sell more units than this so the bundle reverts instead of giving you a worse rate
const maxUnits = BigInt(Math.ceil(10_000e6 / worstAcceptablePrice));

// Calculate collateral needed for the debt you want to take using the market's LLTV, and the oracle price of the collateral asset:
// 1. Retrieve the collateral's LLTV from the "Browse markets" step: collaterals[0].lltv = "770000000000000000" → 77% (WETH's LLTV for this market)
// 2. Fetch your desireable debt at maturity (maxUnits ≈ 10,527 USDC)
// 3. Estimate the minimum collateral value needed for this configuration (debt / LLTV = 10,527 / 0.77 ≈ 13,671 USDC)
// 4. At WETH ≈ $3,000, minimum debt for this position is ≈ 4.56 WETH (at the liquidation boundary)
// 5. Add a safety buffer (i.e. ~10% headroom above minimum) on that to get to 5 WETH
const collateralAmount   = parseUnits("5", 18);                               // 5 WETH collateral

// Deadline: the transaction reverts if not included before this timestamp
const deadline = BigInt(Math.floor(Date.now() / 1000) + 3600);               // 1 hour from now

// Collateral is referenced by index into the market's collateralParams[] NOT by token address.
// Here collateralIndex 0 = collateralParams[0] = WETH.
// See Authorizations section for different permit inputs (i.e. collateralPermitNone, collateralPermitERC2612, collateralPermit2)
// The permit is per collateral asset and per-supply action; { kind: 0 } means "already approved on the bundle".
const collateralSupplies = [
  { collateralIndex: 0n, assets: collateralAmount, permit: collateralPermitNone },
];

const hash = await walletClient.writeContract({
  account: taker,
  address: MIDNIGHT_BUNDLES,
  abi: midnightBundlesAbi,
  functionName: "midnightBundlesV1SupplyCollateralAndSellWithAssetsTarget",
  args: [
    targetSellerAssets,  // USDC to receive
    maxUnits,            // revert if more units sold than this (rate protection)
    taker,               // taker — the borrower's address
    false,               // reduceOnly (false for a new borrow position)
    taker,               // receiver (where the borrowed USDC is sent)
    collateralSupplies,  // CollateralSupply[] — WETH to deposit as collateral
    takes,               // takes (takeable offers from the quote)
    0n,                  // referralFeePct (0 = none)
    zeroAddress,         // referralFeeRecipient (none)
    maxUint256,          // maxContinuousFee (type(uint256).max disables the check)
    deadline             // deadline (reverts if tx is included after this timestamp)
  ],
});

console.log("Borrow tx:", hash);