1 files changed, 76 insertions, 0 deletions
diff --git a/lib/buildtx.js b/lib/buildtx.js
new file mode 100644
index 00000000..351f8081
--- /dev/null
+++ b/lib/buildtx.js
@@ -0,0 +1,76 @@
+const axios = require("axios");
+const bitcoin = require("bitcoinjs-lib");
+const coinselect = require("coinselect");
+const split = require("coinselect/split");
+const api = prod ? "https://blockstream.info/api" : "http://localhost:3002";
+const SATS = 100000000;
+const network = prod
+  ? bitcoin.networks["bitcoin"]
+  : bitcoin.networks["regtest"];
+
+module.exports = async ({ address, amount, feeRate, user }) => {
+  if (!feeRate) feeRate = (await bc.estimateSmartFee(6)).feerate * SATS;
+  feeRate = Math.round(feeRate / 1000);
+
+  const payments = await db.Payment.findAll({
+    where: {
+      received: true,
+      account_id: user.account_id,
+    } 
+  });
+
+  const utxos = [];
+  for (let i = 0; i < payments.length; i++) {
+    try {
+      utxos.push(...(await axios.get(`${api}/address/${payments[i].address}/utxo`)).data);
+    } catch (e) {
+      l.error("problem fetching utxos", e.message);
+    }
+  } 
+
+  let targets = [
+    {
+      address,
+      value: amount
+    }
+  ];
+
+  let { inputs, outputs, fee } = coinselect(utxos, targets, feeRate);
+
+  if (!inputs || !outputs) {
+    l.info("utxos", amount, feeRate, utxos, inputs, outputs);
+    throw new Error("Failed to create transaction");
+  } 
+
+  let psbt = new bitcoin.Psbt({ network });
+  let total = 0;
+
+  outputs.map(({ address, value }) => {
+    total += value;
+    if (!address) {
+      address =  payments[payments.length - 1].address;
+      change.push(address);
+    } 
+
+    psbt = psbt.addOutput({
+      address,
+      value
+    });
+  });
+
+  for (let i = 0; i < inputs.length; i++) {
+    let { txid, vout } = inputs[i];
+    let nonWitnessUtxo = Buffer.from(await bc.getRawTransaction(txid), "hex");
+    psbt = psbt.addInput({
+      hash: txid,
+      index: vout,
+      nonWitnessUtxo
+    });
+  }
+
+  feeRate = Math.round(feeRate * 1000);
+  psbt = psbt.toBase64();
+
+  l.info("returning", { tx: psbt, feeRate });
+  return { tx: psbt, feeRate };
+};