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/* IPRD Group 2022 */
package org.jetbrains.base64

private val BASE64_ALPHABET: String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
private val BASE64_MASK: Byte = 0x3f
private val BASE64_PAD: Char = '='
private val BASE64_INVERSE_ALPHABET = IntArray(256) {
  BASE64_ALPHABET.indexOf(it.toChar())
}

private fun Int.toBase64(): Char = BASE64_ALPHABET[this]

actual object Base64Factory {
  actual fun createEncoder(): Base64Encoder = NativeBase64Encoder
}

object NativeBase64Encoder : Base64Encoder {
  override fun encode(src: ByteArray): ByteArray {
    fun ByteArray.getOrZero(index: Int): Int = if (index >= size) 0 else get(index).toInt()
    // 4n / 3 is expected Base64 payload
    val result = ArrayList(4 * src.size / 3)
    var index = 0
    while (index < src.size) {
      val symbolsLeft = src.size - index
      val padSize = if (symbolsLeft >= 3) 0 else (3 - symbolsLeft) * 8 / 6
      val chunk = (src.getOrZero(index) shl 16) or (src.getOrZero(index + 1) shl 8) or src.getOrZero(index + 2)
      index += 3

      for (i in 3 downTo padSize) {
        val char = (chunk shr (6 * i)) and BASE64_MASK.toInt()
        result.add(char.toBase64().code.toByte())
      }
      // Fill the pad with '='
      repeat(padSize) { result.add(BASE64_PAD.code.toByte()) }
    }

    return result.toByteArray()
  }
}