From 5e2d455b728acedb5d6220f5d156190b73068601 Mon Sep 17 00:00:00 2001
From: fiatjaf <fiatjaf@gmail.com>
Date: Wed, 29 Jan 2025 12:47:07 -0300
Subject: [PATCH] nip60: a helper to get amount from a bolt11 invoice.

---
 nip60/helpers.go      | 56 +++++++++++++++++++++++++++++++++++++++++++
 nip60/helpers_test.go | 37 ++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)
 create mode 100644 nip60/helpers_test.go

diff --git a/nip60/helpers.go b/nip60/helpers.go
index e7db1d9..c941fd7 100644
--- a/nip60/helpers.go
+++ b/nip60/helpers.go
@@ -7,6 +7,8 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"strconv"
+	"strings"
 
 	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/btcec/v2/schnorr"
@@ -201,3 +203,57 @@ func parseKeysetKeys(keys nut01.KeysMap) (map[uint64]*btcec.PublicKey, error) {
 	}
 	return parsedKeys, nil
 }
+
+func getSatoshisAmountFromBolt11(bolt11 string) (uint64, error) {
+	if len(bolt11) < 50 {
+		return 0, fmt.Errorf("invalid invoice, too short")
+	}
+	bolt11 = bolt11[0:50]
+	idx := strings.LastIndex(bolt11, "1")
+	if idx == -1 {
+		return 0, fmt.Errorf("invalid invoice")
+	}
+	hrp := bolt11[0:idx]
+	amount, ok := strings.CutPrefix(hrp, "lnbc")
+	if !ok {
+		return 0, fmt.Errorf("invalid invoice")
+	}
+	if len(amount) < 1 {
+		return 0, nil
+	}
+
+	// if last character is a digit, then the amount can just be interpreted as BTC
+	char := amount[len(amount)-1]
+	digit := char - '0'
+	isDigit := digit >= 0 && digit <= 9
+
+	cutPoint := len(amount) - 1
+	if isDigit {
+		cutPoint++
+	}
+
+	// if not a digit, it must be part of the known units
+	num := amount[:cutPoint]
+	if len(num) < 1 {
+		return 0, nil
+	}
+
+	am, err := strconv.ParseUint(num, 10, 64)
+	if err != nil {
+		return 0, err
+	}
+
+	switch char {
+	case 'm':
+		return am * 100000, nil
+	case 'u':
+		return am * 100, nil
+	case 'n':
+		return am / 10, nil
+	case 'p':
+		return am / 10000, nil
+	default:
+		// is BTC
+		return am * 100000000, nil
+	}
+}
diff --git a/nip60/helpers_test.go b/nip60/helpers_test.go
new file mode 100644
index 0000000..042aeea
--- /dev/null
+++ b/nip60/helpers_test.go
@@ -0,0 +1,37 @@
+package nip60
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestBolt11Parsing(t *testing.T) {
+	for _, tc := range []struct {
+		bolt11   string
+		sats     uint64
+		hasError bool
+	}{
+		{"", 0, true},
+		{"lnbc50n1pne523ypp57rn4l2ne673c093g72nm4pum2mkxjm0v2c0pjc9je909axyutdlqdq2f38xy6t5wvcqzpgxqrrssrzjq0nfr7qlprzkl2rke380tj0gkunm66pv7dtqt0396jrq02qz2fs98apyqqqqqqqqqgqqqqqqqqqqqzsqxgsp5rgp9fa9d8unmg949ztty48dgptke8f8zflt7af8d4yknamp2ymdq9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgqmatchtjjsyvk45mwwg2mvf8xshxhk2gveslvc27dda6dkp0kfc3hhs06e3c966h3z9j9aran0q8ncm6n458xdca3j5nsrke4saxrfmsqu7suv5", 5, false},
+		{"lnbc10500n1pne5tn3pp53wha2waf6g8zac853ay43uscfm9xy3k6ntz0lft72vajyna8695qdq2f38xy6t5wvcqzpgxqrrssrzjq0nfr7qlprzkl2rke380tj0gkunm66pv7dtqt0396jrq02qz2fs98apyqqqqqqqqqgqqqqqqqqqqqzsqxgsp5vapxxnr2wd3780qwmexe24hfcd2m87hsnn8z9xt9u0kmlwq084aq9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgq7vljmxfwsxsmf773ad5fhghe4s840t4set4ypyan2tnzwsldxktquw9lzhtlzj3zldma79hgr6ftp7hst8jh0km3p63vtsfugadtmkgp8wtkzp", 1050, false},
+		{"lnbc778970n1pne5t5jpp5yazceq5p3sr2dfvp283zqy4xd5jea9vwvc4ptw3m47qlkyzpzdtsdq2f38xy6t5wvcqzpgxqrrssrzjq0nfr7qlprzkl2rke380tj0gkunm66pv7dtqt0396jrq02qz2fs98apyqqqqqqqqqgqqqqqqqqqqqzsqxgsp5ssfackh9ys9ggc4h7ag3panc8wu3gqh84ghnkfd24khyy5pmjx6q9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgqdupshqq328498wk3evxh0ext6y5svfsnyauqvcse3l7u3lmk9s5yftmn7ec4l3d5aqd702je4g7aeng2nyjy0qcv23ue9ddn3ga3llsqzlnjv3", 77897, false},
+		{"lnbc700u1pne5t4upp5qkxcf9xsmn3p2r55dm386vlp52cvtgjyrv450z6ft2kj6lsmm6asdq2f38xy6t5wvcqzpgxqrrssrzjq0nfr7qlprzkl2rke380tj0gkunm66pv7dtqt0396jrq02qz2fs98apyqqqqqqqqqgqqqqqqqqqqqzsqxgsp5r2ynl9fycj5eega7tzuae5nu8umwawv30glw2c6gh45ymaryxdjs9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgqx8d2dr05fmaelmfmxyd6snlyenx25pl6jaxlcm9vqvq89t2smwv8au8j24fwxjswz4j2vcvnmhkaja4dhxf9y49jvwgd7xasgp3tppcp27zlr0", 70000, false},
+		{"lnbc2600u1pne5tkepp5q2g379zdf7k35ylf4r4f7hc47e9eazxlv3z55ydjnmtj8gt0vy8qdq2f38xy6t5wvcqzpgxqrrssrzjq0nfr7qlprzkl2rke380tj0gkunm66pv7dtqt0396jrq02qz2fs98apyqqqqqqqqqgqqqqqqqqqqqzsqxgsp5p45aam8azmegj747j8lwmdcjd6uj2f8mjpwh34qjye2h67g3azwq9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgq649a6ztfcqtalz3lfukesxep9tkaew90d80l6sds8cnppsqd0yx4jkttyuzw5k8erygzh36k6n3j5x4q3caqxsg3vy52j6va8879x4qqxlk7p5", 260000, false},
+		{"lnbc400m1pne5thjpp57slr93076zkczq08nvufgp6td6yafr9su3hqr2w2jl64p8e7k4jsdq2f38xy6t5wvcqzpgxqrrssrzjq0nfr7qlprzkl2rke380tj0gkunm66pv7dtqt0396jrq02qz2fs98apyqqqqqqqqqgqqqqqqqqqqqzsqxgsp55grhezefgcgjsddk4lp4jc564pwu5cp0zddg5f6tygt7xe57g47s9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgqf0xtyv62a4v9sjze3ftgdhwpgskhe3hlvwyjnhvt74grzsmpftvzdrlnh02cfg00st26pv7vgkxpknny52s3cuccwpm29l5yarq5fcqpfn7eh9", 40000000, false},
+		{"lnbc81pne5tcdpp59qnlzkzyjz0wy0z7fvjxe67u75cpknzfzahwqzm640ly0yrs982sdq2f38xy6t5wvcqzpgxqrrssrzjq0nfr7qlprzkl2rke380tj0gkunm66pv7dtqt0396jrq02qz2fs98apyqqqqqqqqqgqqqqqqqqqqqzsqxgsp5lrljv8ce4c64l77gj4gffg5gc8nlrnngk85twzvp35l92jwwravq9p4gqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqysgq5a8yyyreke9x5u4up22tzknum43hqyza9y808hmvftcvj7t7m5lzdrz53mhdh6snxxwd4r0x2cgw9crlzm4pdln80hphwfzpuj869nqq73w8r3", 800000000, false},
+		{"lnbc5n1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq", 0, false},
+		{"lnbc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq", 0, false},
+	} {
+		t.Run(fmt.Sprintf("%d = %s", tc.sats, tc.bolt11), func(t *testing.T) {
+			sats, err := getSatoshisAmountFromBolt11(tc.bolt11)
+			if tc.hasError {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+			require.Equal(t, int(tc.sats), int(sats))
+		})
+	}
+}