package generate

import (
	"crypto/rand"
	"encoding/binary"
	mathRand "math/rand"
	"strconv"
)

const alphabet = "0123456789abcdefghijklmnopqrstuvwxyz"

func generateWeak(length int, prefix string) string {
	result := prefix
	for len(result) < length {
		result += string(alphabet[mathRand.Intn(len(alphabet))])
	}

	return result
}

// Generate generates an ID either strongly or weakly depending on the system.
func Generate(length int, prefix string) string {
	var buffer [32]byte

	result := prefix
	offset := 0

	_, err := rand.Read(buffer[:32])
	if err != nil {
		return generateWeak(length, prefix)
	}

	for len(result) < length {
		result += strconv.FormatUint(binary.LittleEndian.Uint64(buffer[offset:]), 36)
		offset += 8

		if offset >= 32 {
			_, err = rand.Read(buffer[:32])
			if err != nil {
				return generateWeak(length, prefix)
			}

			offset = 0
		}
	}

	return result[:length]
}