Kotlin SpannableStringBuilder DSL

DSL

package tylerwalker.io.dsl

import android.graphics.Color
import android.text.Spannable
import android.text.SpannableStringBuilder
import android.text.style.ForegroundColorSpan

class Atom(val content: SpannableStringBuilder) {
    operator fun String.unaryPlus() { content.append(this) }

        fun append(block: Atom.() -> Unit) =
            apply {
                block()
            }

    fun red(block: Atom.() -> Unit) =
        apply {
            val redPaint = ForegroundColorSpan(Color.rgb(255, 0, 0))

            val start = content.lastIndex + 1

            block()

            val end = content.lastIndex

            if (end >= start) {
                content.setSpan(redPaint, start, end + 1, Spannable.SPAN_INCLUSIVE_INCLUSIVE)
            }
        }

        private val redPaint = ForegroundColorSpan(Color.rgb(255, 0, 0))
}

operator fun Atom.plus(other: Atom): Atom = Atom(content.append(other.content))

fun spannable(block: Atom.() -> Unit) =
    Atom(SpannableStringBuilder("")).run {
        block()
        content
    }