package me.ccampo.librepoker.engine.util

import me.ccampo.librepoker.engine.model.Card
import me.ccampo.librepoker.engine.model.Hand
import me.ccampo.librepoker.engine.model.HandScore
import me.ccampo.librepoker.engine.model.HandType

/**
 * @author <NAME>
 */

/**
 * First sort the cards in descending order, and then put any pairs/sets/quads
 * of cards in front. Example, A K 4 J 4 becomes 4 4 J K A
 *
 * See: https://stackoverflow.com/questions/42380183/algorithm-to-give-a-value-to-a-5-card-poker-hand
 */
fun evaluate(hand: Hand): HandScore {
  val groups = hand.cards
    .sortedByDescending { it.face.weight }
    .groupBy { it.face }
    .toSortedMap(compareByDescending { it.weight })

  val type = when (groups.size) {
    2 -> if (groups.any { it.value.size == 4 }) HandType.FOUR_OF_A_KIND else HandType.FULL_HOUSE
    3 -> if (groups.any { it.value.size == 3 }) HandType.THREE_OF_A_KIND else HandType.TWO_PAIR
    4 -> HandType.PAIR
    else -> {
      val flush = hand.isFlush()
      val straight = hand.isStraight()
      when {
        flush && straight -> if (hand.cards.sumBy { it.face.weight } == 60) HandType.ROYAL_FLUSH else HandType.STRAIGHT_FLUSH
        flush -> HandType.FLUSH
        straight -> HandType.STRAIGHT
        else -> HandType.HIGH_CARD
      }
    }
  }

  val score = groups.values
    .sortedByDescending { it.size }
    .flatten()
    .fold(type.rank, { score, card -> (score shl 4) + card.face.weight })

  return HandScore(type, score)
}

fun sort(cards: List<Card>): List<Card> {
  return cards
    .sortedByDescending { it.face.weight }
    .groupBy { it.face }
    .toSortedMap(compareByDescending { it.weight })
    .values
    .sortedByDescending { it.size }
    .flatten()
}

fun getBestHand(cards: List<Card>): Hand {
  return cards.combinations(5).map { Hand(it) }.maxBy { it.score.score }!!
}

private fun <T> List<T>.combinations(n: Int): List<List<T>> {
  fun <T> combinations(l: List<T>, n: Int): List<List<T>> {
    val result = mutableListOf<List<T>>()
    when {
      n > l.size -> throw IllegalArgumentException("Value n must be less than or equal to the list size")
      n == l.size -> result.add(l)
      n == 0 -> result.add(emptyList())
      n < l.size -> result.addAll(combinations(l.tail, n) + combinations(l.tail, n - 1).map { it + l.head })
    }
    return result
  }
  return combinations(this, n)
}

private val <T> List<T>.tail: List<T> get() = drop(1)

private val <T> List<T>.head: T get() = first()
