package controlapi

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"math/big"
	"time"
)

const crockford = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"

func newULID(prefix string, now time.Time) (string, error) {
	value := make([]byte, 16)
	milliseconds := uint64(now.UTC().UnixMilli())
	value[0] = byte(milliseconds >> 40)
	value[1] = byte(milliseconds >> 32)
	value[2] = byte(milliseconds >> 24)
	value[3] = byte(milliseconds >> 16)
	value[4] = byte(milliseconds >> 8)
	value[5] = byte(milliseconds)
	if _, err := rand.Read(value[6:]); err != nil {
		return "", errors.New("generate identifier randomness")
	}
	number := new(big.Int).SetBytes(value)
	base := big.NewInt(32)
	remainder := new(big.Int)
	encoded := make([]byte, 26)
	for index := len(encoded) - 1; index >= 0; index-- {
		number.QuoRem(number, base, remainder)
		encoded[index] = crockford[remainder.Int64()]
	}
	return prefix + string(encoded), nil
}

func newTraceID() (string, error) {
	value := make([]byte, 16)
	if _, err := rand.Read(value); err != nil {
		return "", errors.New("generate trace identifier")
	}
	return "trace_" + hex.EncodeToString(value), nil
}