order sagas

pkg/order/id.go

@@ -0,0 +1,71 @@
+package order
+
+import (
+	"crypto/rand"
+	"fmt"
+)
+
+// OrderId is a 64-bit order identifier with a compact base62 string form, the
+// same scheme the cart uses (cart.CartId) so ids are consistent across the
+// commerce services. The grain is keyed by the raw uint64.
+type OrderId uint64
+
+const base62Alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+var base62Rev [256]byte
+
+func init() {
+	for i := range base62Rev {
+		base62Rev[i] = 0xFF
+	}
+	for i := 0; i < len(base62Alphabet); i++ {
+		base62Rev[base62Alphabet[i]] = byte(i)
+	}
+}
+
+// String returns the canonical base62 encoding.
+func (id OrderId) String() string { return encodeBase62(uint64(id)) }
+
+// NewOrderId generates a cryptographically random non-zero id.
+func NewOrderId() (OrderId, error) {
+	var b [8]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		return 0, fmt.Errorf("NewOrderId: %w", err)
+	}
+	u := uint64(b[0])<<56 | uint64(b[1])<<48 | uint64(b[2])<<40 | uint64(b[3])<<32 |
+		uint64(b[4])<<24 | uint64(b[5])<<16 | uint64(b[6])<<8 | uint64(b[7])
+	if u == 0 {
+		return NewOrderId()
+	}
+	return OrderId(u), nil
+}
+
+// ParseOrderId parses a base62 string into an OrderId.
+func ParseOrderId(s string) (OrderId, bool) {
+	if len(s) == 0 || len(s) > 11 {
+		return 0, false
+	}
+	var v uint64
+	for i := 0; i < len(s); i++ {
+		d := base62Rev[s[i]]
+		if d == 0xFF {
+			return 0, false
+		}
+		v = v*62 + uint64(d)
+	}
+	return OrderId(v), true
+}
+
+func encodeBase62(u uint64) string {
+	if u == 0 {
+		return "0"
+	}
+	var buf [11]byte
+	i := len(buf)
+	for u > 0 {
+		i--
+		buf[i] = base62Alphabet[u%62]
+		u /= 62
+	}
+	return string(buf[i:])
+}