Increment nested number in DynamoDB

DynamoDBNestedIncrement.kt

import com.amazonaws.services.dynamodbv2.document.PrimaryKey
import com.amazonaws.services.dynamodbv2.document.api.UpdateItemApi
import com.amazonaws.services.dynamodbv2.model.ConditionalCheckFailedException

fun UpdateItemApi.nestedIncrement(key: PrimaryKey, attribute: String, path: List<String>, increment: Int) {
    tryToIncrement(key, listOf(attribute) + path, increment)
}

private fun List<String>.toPathExpression(): String =
    mapIndexed { index, _ -> "#p$index" }.joinToString(".")

private fun List<String>.toNameMap(): Map<String, String> =
    mapIndexed { index, name -> "#p$index" to name }.toMap()

private fun UpdateItemApi.tryToIncrement(key: PrimaryKey, path: List<String>, increment: Int) {
    val pathExpression = path.toPathExpression()
    val attributesMap = path.toNameMap()

    try {
        updateItem(
            key,
            "SET $pathExpression = $pathExpression + :inc",
            "attribute_exists($pathExpression)",
            attributesMap,
            mapOf(":inc" to increment)
        )
    } catch (e: ConditionalCheckFailedException) {
        tryToCreateMap(key, path, increment)
    }
}

private fun UpdateItemApi.tryToCreateMap(key: PrimaryKey, path: List<String>, value: Any) {
    val pathExpression = path.toPathExpression()
    val attributesMap = path.toNameMap()

    val upperPath = path.dropLast(1)
    val upperPathExpression = upperPath.toPathExpression()

    if (upperPath.isNotEmpty()) {
        try {
            updateItem(
                key,
                "SET $pathExpression = :new",
                "attribute_exists($upperPathExpression)",
                attributesMap,
                mapOf(":new" to value)
            )
        } catch (e: ConditionalCheckFailedException) {
            val lastName = path.last()
            tryToCreateMap(key, upperPath, mapOf(lastName to value))
        }
    } else {
        updateItem(
            key,
            "SET $pathExpression = :new",
            attributesMap,
            mapOf(":new" to value)
        )
    }
}