package day1

import java.io.File

object Day1 {

    fun calculateOne(input : List<String>) = input
        .filter(String::isNotBlank)
        .fold(0, addMagicNumber())

    fun calculateTwo(input : List<String>) = input
        .filter(String::isNotBlank)
        .map(::replaceElvenNumbers)
        .fold(0, addMagicNumber())

    private fun addMagicNumber() = { accumulator: Int, line: String ->
        val firstDigit = NUMBER_REGEX.findAll(line).first().value
        val secondDigit = NUMBER_REGEX.findAll(line).last().value
        val total = (firstDigit + secondDigit).toInt() + accumulator
        total
    }

    private fun replaceElvenNumbers(string: String): String =
        string.mapIndexed { index, _ ->
            readElvenNumberAtStart(string.substring(index))
        }.joinToString(separator = "")

    private fun readElvenNumberAtStart(string: String) = when {
        string.isBlank() -> ""
        string[0].isDigit() -> string[0].toString()
        string.startsWith("one") -> "1"
        string.startsWith("two") -> "2"
        string.startsWith("three") -> "3"
        string.startsWith("four") -> "4"
        string.startsWith("five") -> "5"
        string.startsWith("six") -> "6"
        string.startsWith("seven") -> "7"
        string.startsWith("eight") -> "8"
        string.startsWith("nine") -> "9"
        else -> ""
    }

    fun answerOne() =
        File("src/main/resources/day1/input.txt")
            .readLines()
            .let(::calculateOne)

    fun answerTwo() =
        File("src/main/resources/day1/input.txt")
            .readLines()
            .let(::calculateTwo)

    private val NUMBER_REGEX = Regex("\\d")

}