Monorepo scaffolding (#16)

* Change scaffolding

* Fix gh action

common/bip68.go

@@ -0,0 +1,57 @@
+package common
+
+import (
+	"encoding/hex"
+	"fmt"
+)
+
+const (
+	SEQUENCE_LOCKTIME_MASK         = 0x0000ffff
+	SEQUENCE_LOCKTIME_TYPE_FLAG    = 1 << 22
+	SEQUENCE_LOCKTIME_GRANULARITY  = 9
+	SECONDS_MOD                    = 1 << SEQUENCE_LOCKTIME_GRANULARITY
+	SECONDS_MAX                    = SEQUENCE_LOCKTIME_MASK << SEQUENCE_LOCKTIME_GRANULARITY
+	SEQUENCE_LOCKTIME_DISABLE_FLAG = 1 << 31
+)
+
+func closerToModulo512(x uint) uint {
+	return x - (x % 512)
+}
+
+// BIP68Encode returns the encoded sequence locktime for the given number of seconds.
+func BIP68Encode(seconds uint) ([]byte, error) {
+	seconds = closerToModulo512(seconds)
+	if seconds > SECONDS_MAX {
+		return nil, fmt.Errorf("seconds too large, max is %d", SECONDS_MAX)
+	}
+	if seconds%SECONDS_MOD != 0 {
+		return nil, fmt.Errorf("seconds must be a multiple of %d", SECONDS_MOD)
+	}
+
+	asNumber := SEQUENCE_LOCKTIME_TYPE_FLAG | (seconds >> SEQUENCE_LOCKTIME_GRANULARITY)
+	hexString := fmt.Sprintf("%x", asNumber)
+	reversed, err := hex.DecodeString(hexString)
+	if err != nil {
+		return nil, err
+	}
+	for i, j := 0, len(reversed)-1; i < j; i, j = i+1, j-1 {
+		reversed[i], reversed[j] = reversed[j], reversed[i]
+	}
+	return reversed, nil
+}
+
+func BIP68Decode(sequence []byte) (uint, error) {
+	var asNumber int64
+	for i := len(sequence) - 1; i >= 0; i-- {
+		asNumber = asNumber<<8 | int64(sequence[i])
+	}
+
+	if asNumber&SEQUENCE_LOCKTIME_DISABLE_FLAG != 0 {
+		return 0, fmt.Errorf("sequence is disabled")
+	}
+	if asNumber&SEQUENCE_LOCKTIME_TYPE_FLAG != 0 {
+		seconds := asNumber & SEQUENCE_LOCKTIME_MASK << SEQUENCE_LOCKTIME_GRANULARITY
+		return uint(seconds), nil
+	}
+	return 0, fmt.Errorf("sequence is encoded as block number")
+}