add link id generation

linkgen/linkgen.go

@@ -0,0 +1,125 @@
+package linkgen
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+
+	"github.com/parkan/go-hauk/config"
+	"github.com/parkan/go-hauk/store"
+)
+
+const (
+	alphaLower     = "0123456789abcdefghijklmnopqrstuvwxyz"
+	alphaMixed     = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
+	alphaUpper     = "123456789ABCDEFGHIJKLMNPQRSTUVWXYZ"
+	prefixLocdata  = "locdata-"
+)
+
+type Generator struct {
+	store store.Store
+	style config.LinkStyle
+}
+
+func New(s store.Store, style config.LinkStyle) *Generator {
+	return &Generator{store: s, style: style}
+}
+
+func (g *Generator) Generate(ctx context.Context) (string, error) {
+	for {
+		s, err := g.generate()
+		if err != nil {
+			return "", err
+		}
+		exists, err := g.store.Exists(ctx, prefixLocdata+s)
+		if err != nil {
+			return "", err
+		}
+		if !exists {
+			return s, nil
+		}
+	}
+}
+
+func (g *Generator) generate() (string, error) {
+	switch g.style {
+	case config.LinkUUIDv4:
+		return uuidV4()
+	case config.Link16Hex:
+		return hexString(8)
+	case config.Link16Lower:
+		return randomString(alphaLower, 16)
+	case config.Link16Mixed:
+		return randomString(alphaMixed, 16)
+	case config.Link16Upper:
+		return randomString(alphaUpper, 16)
+	case config.Link32Hex:
+		return hexString(16)
+	case config.Link32Lower:
+		return randomString(alphaLower, 32)
+	case config.Link32Mixed:
+		return randomString(alphaMixed, 32)
+	case config.Link32Upper:
+		return randomString(alphaUpper, 32)
+	case config.Link4Plus4Lower:
+		return fourPlusFour(alphaLower)
+	case config.Link4Plus4Mixed:
+		return fourPlusFour(alphaMixed)
+	case config.Link4Plus4Upper:
+		fallthrough
+	default:
+		return fourPlusFour(alphaUpper)
+	}
+}
+
+func uuidV4() (string, error) {
+	b := make([]byte, 16)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	b[6] = (b[6] & 0x0f) | 0x40
+	b[8] = (b[8] & 0x3f) | 0x80
+	h := hex.EncodeToString(b)
+	return fmt.Sprintf("%s-%s-%s-%s-%s", h[0:8], h[8:12], h[12:16], h[16:20], h[20:32]), nil
+}
+
+func hexString(n int) (string, error) {
+	b := make([]byte, n)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(b), nil
+}
+
+func randomString(alpha string, length int) (string, error) {
+	b := make([]byte, length)
+	for i := 0; i < length; i++ {
+		idx, err := randInt(len(alpha))
+		if err != nil {
+			return "", err
+		}
+		b[i] = alpha[idx]
+	}
+	return string(b), nil
+}
+
+func fourPlusFour(alpha string) (string, error) {
+	s, err := randomString(alpha, 8)
+	if err != nil {
+		return "", err
+	}
+	return s[:4] + "-" + s[4:], nil
+}
+
+func randInt(max int) (int, error) {
+	b := make([]byte, 1)
+	for {
+		if _, err := rand.Read(b); err != nil {
+			return 0, err
+		}
+		if int(b[0]) < 256-(256%max) {
+			return int(b[0]) % max, nil
+		}
+	}
+}