package generate

import (
	"crypto/rand"
	"encoding/binary"
	"encoding/hex"
	"strings"
	"time"
)

// ID generates a 24 character hex string from 8 bytes of current time
// in ns and 4 bytes of crypto-random. In practical terms, that makes
// them orderable.
func ID() string {
	bytes := make([]byte, 12)
	binary.BigEndian.PutUint64(bytes, uint64(time.Now().UnixNano()))
	rand.Read(bytes[8:])

	return strings.ToLower(hex.EncodeToString(bytes))
}

// FriendlyID generates a human-friendly ID that has a higher uniqueness,
// and a limited alphabet designed for human readability and manual copying.
//
// There are 7.98e+22 IDs in a 16-length ID, which means that if there are
// 10,000 items, you're as likely to guess one as winning the grand prize
// of the biggest lotteries around the world billions of times in a row.
func FriendlyID(length int) string {
	const alphabet = "0123456789abcdfghjkmpqrtvxy"
	const alphabetLength = byte(len(alphabet))

	// Generate random bytes
	results := make([]byte, length)
	rand.Read(results)

	// Truncate it within the alphabet
	for i := 0; i < 16; i++ {
		results[i] = alphabet[results[i]%alphabetLength]
	}

	return string(results)
}

// SessionID generates a 48 character hex string with crypto/rand
func SessionID() string {
	bytes := make([]byte, 24)
	rand.Read(bytes)

	return strings.ToLower(hex.EncodeToString(bytes))
}