Coverage Summary for Class: PartNumber (day03p2)

 package day03p2
 
 data class Schematic(val lines: List<String>) {
   private val numberRegex = """(\d+)""".toRegex()
 
   val partNumbers: List<PartNumber>
 
   init {
     partNumbers = lines.asSequence().flatMapIndexed { row, line ->
       numberRegex.findAll(line)
         .mapNotNull {
           val group = it.groups[1] ?: error("no group")
           val position = Position(row, group.range)
           if (!isAdjacentToSymbol(position)) {
             return@mapNotNull null
           }
           PartNumber(group.value.toInt(), position)
         }
     }
       .toList()
   }
 
   fun isAdjacentToSymbol(row: Int, indexRange: IntRange): Boolean =
     isAdjacentToSymbol(Position(row, indexRange))
 
   private fun isAdjacentToSymbol(position: Position): Boolean =
     adjacentCoordinates(position).any { isSymbol(it) }
 
   private fun isSymbol(coordinate: Coordinate): Boolean = isMatching(coordinate) { char ->
     char.isSymbol()
   }
 
   private fun isGearCandidate(coordinate: Coordinate): Boolean = isMatching(coordinate) { char ->
     char.isGearCandidate()
   }
 
   private fun isMatching(coordinate: Coordinate, matcher: (Char) -> Boolean): Boolean {
     val line = lines.getOrNull(coordinate.row) ?: return false
     val char = line.getOrNull(coordinate.col) ?: return false
     return matcher(char)
   }
 
   fun findGears(): Map<Coordinate, Set<PartNumber>> {
     val gearCandidats = mutableMapOf<Coordinate, MutableSet<PartNumber>>()
     for (partNumber in partNumbers) {
       adjacentCoordinates(partNumber.position).forEach { coordinate ->
         if (isGearCandidate(coordinate)) {
           gearCandidats.computeIfAbsent(coordinate) { mutableSetOf() }.add(partNumber)
         }
       }
     }
 
     return gearCandidats.filterValues { it.size == 2 }
   }
 
   private fun adjacentCoordinates(position: Position): Sequence<Coordinate> {
     val encapsulatingRange = position.range.encapsulatingRange()
     val leftAndRight = sequenceOf(
       Coordinate(position.row, encapsulatingRange.first),
       Coordinate(position.row, encapsulatingRange.last)
     )
     val previousRow = if (position.row > 0) {
       encapsulatingRange.asSequence().map { Coordinate(position.row - 1, it) }
     } else emptySequence()
     val nextRow = if (position.row < lines.size - 1) {
       encapsulatingRange.asSequence().map { Coordinate(position.row + 1, it) }
     } else emptySequence()
 
     return leftAndRight + previousRow + nextRow
   }
 
   fun sumOfGearRatios(): Int = findGears().asSequence()
     .sumOf { pns -> pns.value.asSequence().map { it.value }.reduce { acc, i -> acc * i } }
 
   companion object {
     fun fromString(raw: String): Schematic {
       return Schematic(raw.lines())
     }
   }
 
 }
 
 fun Char.isSymbol(): Boolean = this != '.' && !isDigit()
 
 fun Char.isGearCandidate(): Boolean = this == '*'
 
 fun IntRange.encapsulatingRange(): IntRange = first - 1..last + 1
 
 data class PartNumber(val value: Int, val position: Position)
 
 data class Position(val row: Int, val range: IntRange)
 
 data class Coordinate(val row: Int, val col: Int)