package profile

import (
	"crypto/rand"
	"fmt"
)

// ProfileId is a 64-bit profile identifier with a compact base62 string form,
// the same scheme the cart and order use so ids are consistent across services.
type ProfileId 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 ProfileId) String() string { return encodeBase62(uint64(id)) }

// NewProfileId generates a cryptographically random non-zero id.
func NewProfileId() (ProfileId, error) {
	var b [8]byte
	if _, err := rand.Read(b[:]); err != nil {
		return 0, fmt.Errorf("NewProfileId: %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 NewProfileId()
	}
	return ProfileId(u), nil
}

// ParseProfileId parses a base62 string into a ProfileId.
func ParseProfileId(s string) (ProfileId, 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 ProfileId(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:])
}