nomino/gen_rand.go

package nomino

import (
	"crypto/rand"
	"strings"

	"github.com/deatil/go-encoding/base62"
	"github.com/google/uuid"
)

// UUIDer is an interface for generating UUIDs, by the [UUID] [Generator].
// It is recommended that you use either the [UUIDv4] or [UUIDv7] variables.
type UUIDer interface {
	UUID() (uuid.UUID, error)
}

// UUIDFunc is a function that generates a UUID.
type UUIDFunc func() (uuid.UUID, error)

// UUID allows [UUIDFunc] to be used as a [UUIDer].
func (u UUIDFunc) UUID() (uuid.UUID, error) {
	return u()
}

var (
	// UUIDv1. You probably don't want to use this. It is included for completeness sake.
	UUIDv1 = UUIDFunc(uuid.NewUUID)
	// UUIDv4 is the default.
	UUIDv4 = UUIDFunc(uuid.NewRandom)
	// UUIDv6 is primarily a replacement for UUIDv1. You probably should use 4 or 7.
	UUIDv6 = UUIDFunc(uuid.NewV6)
	// UUIDv7 should be used if you want it sortable by time.
	UUIDv7 = UUIDFunc(uuid.NewV7)
)

// UUID generates a UUID. If nil is passed as an argument,
// a UUIDv4 is generated.
func UUID(u UUIDer) Generator {
	if u == nil {
		u = UUIDv4
	}
	return func(*Config) (string, error) {
		uu, err := u.UUID()
		if err != nil {
			return "", err
		}
		return uu.String(), nil
	}
}

type randConf struct {
	length int
}

// RandomOption is an option for the [Random] [Generator].
type RandomOption func(*randConf)

// RandomLength controls the length of the string generated by [Random].
func RandomLength(length int) RandomOption {
	return func(c *randConf) {
		c.length = length
	}
}

func getRandomBytes(l int) []byte {
	key := make([]byte, l)
	_, _ = rand.Read(key)
	e := base62.StdEncoding.Encode(key)
	return e[:l]
}

func fillBuffer(buff *strings.Builder, length int) {
	for buff.Len() < length {
		buff.Write(getRandomBytes(length - buff.Len()))
	}
}

// Random generates a random string containing the characters A-Za-z0-9.
// By default, it will be eight characters long.
func Random(opts ...RandomOption) Generator {
	c := randConf{8}
	for _, opt := range opts {
		opt(&c)
	}
	return func(*Config) (string, error) {
		var buff strings.Builder
		buff.Grow(c.length)
		fillBuffer(&buff, c.length)
		return buff.String(), nil
	}
}