ULID in Kotlin

ULID.kt

/**
 * Adopted from https://github.com/JonasSchubert/kULID
 * 
 * MIT License
 *
 * Copyright (c) 2021 GuepardoApps (Jonas Schubert), Christopher J. Campo
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

import kotlin.experimental.and
import kotlin.random.Random

class ULID {
    companion object {
        private const val ULID_LENGTH = 26
        private const val DEFAULT_ENTROPY_SIZE = 10
        
        // Min and max allowed timestamp values.
        private const val MIN_TIMESTAMP = 0x0L     
        private const val MAX_TIMESTAMP = 0x0000ffffffffffffL

        // Base32 characters mapping
        private val charMapping = charArrayOf(
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k',
            'm', 'n', 'p', 'q', 'r', 's', 't', 'v', 'w', 'x',
            'y', 'z'
        )

        /**
         * Generate random ULID string using [kotlin.random.Random] instance.
         * @return ULID string
         */
        fun random(): String = generate(System.currentTimeMillis(), Random.nextBytes(DEFAULT_ENTROPY_SIZE))

        /**
         * Generate ULID from Unix epoch timestamp in millisecond and entropy bytes.
         * Throws [java.lang.IllegalArgumentException] if timestamp is less than {@value #MIN_TIME},
         * is more than {@value #MAX_TIME}, or entropy bytes is null or less than 10 bytes.
         * @param time           Unix epoch timestamp in millisecond
         * @param entropy        Entropy bytes
         * @return               ULID string
         */
        fun generate(time: Long, entropy: ByteArray): String {
            if (time < MIN_TIMESTAMP || time > MAX_TIMESTAMP || entropy.size < DEFAULT_ENTROPY_SIZE) {
                throw IllegalArgumentException("Time is too long, or entropy is less than 10 bytes or null")
            }

            val chars = CharArray(ULID_LENGTH)

            // time
            chars[0] = charMapping[time.ushr(45).toInt() and 0x1f]
            chars[1] = charMapping[time.ushr(40).toInt() and 0x1f]
            chars[2] = charMapping[time.ushr(35).toInt() and 0x1f]
            chars[3] = charMapping[time.ushr(30).toInt() and 0x1f]
            chars[4] = charMapping[time.ushr(25).toInt() and 0x1f]
            chars[5] = charMapping[time.ushr(20).toInt() and 0x1f]
            chars[6] = charMapping[time.ushr(15).toInt() and 0x1f]
            chars[7] = charMapping[time.ushr(10).toInt() and 0x1f]
            chars[8] = charMapping[time.ushr(5).toInt() and 0x1f]
            chars[9] = charMapping[time.toInt() and 0x1f]

            // entropy
            chars[10] = charMapping[(entropy[0].toShort() and 0xff).toInt().ushr(3)]
            chars[11] =
                charMapping[(entropy[0].toInt() shl 2 or (entropy[1].toShort() and 0xff).toInt().ushr(6) and 0x1f)]
            chars[12] = charMapping[((entropy[1].toShort() and 0xff).toInt().ushr(1) and 0x1f)]
            chars[13] =
                charMapping[(entropy[1].toInt() shl 4 or (entropy[2].toShort() and 0xff).toInt().ushr(4) and 0x1f)]
            chars[14] =
                charMapping[(entropy[2].toInt() shl 5 or (entropy[3].toShort() and 0xff).toInt().ushr(7) and 0x1f)]
            chars[15] = charMapping[((entropy[3].toShort() and 0xff).toInt().ushr(2) and 0x1f)]
            chars[16] =
                charMapping[(entropy[3].toInt() shl 3 or (entropy[4].toShort() and 0xff).toInt().ushr(5) and 0x1f)]
            chars[17] = charMapping[(entropy[4].toInt() and 0x1f)]
            chars[18] = charMapping[(entropy[5].toShort() and 0xff).toInt().ushr(3)]
            chars[19] =
                charMapping[(entropy[5].toInt() shl 2 or (entropy[6].toShort() and 0xff).toInt().ushr(6) and 0x1f)]
            chars[20] = charMapping[((entropy[6].toShort() and 0xff).toInt().ushr(1) and 0x1f)]
            chars[21] =
                charMapping[(entropy[6].toInt() shl 4 or (entropy[7].toShort() and 0xff).toInt().ushr(4) and 0x1f)]
            chars[22] =
                charMapping[(entropy[7].toInt() shl 5 or (entropy[8].toShort() and 0xff).toInt().ushr(7) and 0x1f)]
            chars[23] = charMapping[((entropy[8].toShort() and 0xff).toInt().ushr(2) and 0x1f)]
            chars[24] =
                charMapping[(entropy[8].toInt() shl 3 or (entropy[9].toShort() and 0xff).toInt().ushr(5) and 0x1f)]
            chars[25] = charMapping[(entropy[9].toInt() and 0x1f)]

            return String(chars).toLowerCase()
        }
    }
}

Awesome, very useful, thanks.

@petered you bet, glad you found it useful.