Jetpack compose text visual transformation

DateVisualTransformation.kt

import androidx.compose.ui.text.input.VisualTransformation
import androidx.compose.ui.text.input.TransformedText
import androidx.compose.ui.text.input.OffsetMapping
import androidx.compose.ui.text.AnnotatedString

/**
 * Visually transform a string as YYYY-MM-DD.
 */
object DateVisualTransformation : VisualTransformation {
  fun transform(original: String): String {
    val trimmed: String = original.take(8)
    if (trimmed.length < 4) return trimmed
    if (trimmed.length == 4) return "$trimmed-"
    val (year, monthAndOrDate) = trimmed.chunked(4)
    if (trimmed.length == 5 ) return "$year-$monthAndOrDate"
    if(trimmed.length == 6) return "$year-$monthAndOrDate-"
    val (month, date) = monthAndOrDate.chunked(2)
    return "$year-$month-$date"
  }
  
  override fun filter(text: AnnotatedString): TransformedText {
    return TransformedText(AnnotatedString(transform(text.text)),
      object : OffsetMapping {
        override fun originalToTransformed(offset: Int): Int {
          if (offset <= 3) return offset
          if (offset <= 5) return offset + 1
          if (offset <= 7) return offset + 2
          return 10
        }

        override fun transformedToOriginal(offset: Int): Int {
          if (offset <= 4) return offset
          if (offset <= 7) return offset - 1
          if (offset <= 10) return offset - 2
          return 8
        }
      })
  }
}