package day20

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func printNumbers(numbers []int, nexts []int) {
	current := 0

	for nexts[current] == -1 {
		current += 1
	}

	first := numbers[current]
	fmt.Printf("%d", first)
	current = nexts[current]
	for numbers[current] != first {
		fmt.Printf(" %d", numbers[current])
		current = nexts[current]
	}
	fmt.Println()
}

func removeIndex(idx int, prevs []int, nexts []int) (before int, after int) {
	before = prevs[idx]
	after = nexts[idx]

	nexts[before] = after
	prevs[after] = before
	prevs[idx] = -1
	nexts[idx] = -1

	return
}

func insertAfter(idx int, after int, prevs []int, nexts []int) {
	afterNext := nexts[after]
	prevs[idx] = after
	nexts[idx] = afterNext
	prevs[afterNext] = idx
	nexts[after] = idx
}

func insertBefore(idx int, before int, prevs []int, nexts []int) {
	beforePrev := prevs[before]
	prevs[idx] = beforePrev
	nexts[idx] = before
	prevs[before] = idx
	nexts[beforePrev] = idx
}

func shift(count int, idx int, prevs []int, nexts []int) {
	count %= len(prevs) - 1
	for count != 0 {
		before, after := removeIndex(idx, prevs, nexts)
		if count > 0 {
			insertAfter(idx, after, prevs, nexts)
			count -= 1
		} else {
			insertBefore(idx, before, prevs, nexts)
			count += 1
		}
	}
}

func indexPast(count int, current int, nexts []int) int {
	for count > 0 {
		current = nexts[current]
		count -= 1
	}
	return current
}

func Run(filename string, keyString string, countString string) {
	file, err := os.Open(filename)
	if err != nil {
		fmt.Println("Error opening file:", err)
		return
	}

	key, err := strconv.Atoi(keyString)
	if err != nil {
		fmt.Println("Invalid key value", err)
		return
	}

	roundCount, err := strconv.Atoi(countString)
	if err != nil {
		fmt.Println("Invalid round count", err)
		return
	}

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)
	numbers := []int{}
	nexts := []int{}
	prevs := []int{}
	zeroIndex := -1

	for scanner.Scan() {
		line := scanner.Text()
		x, err := strconv.Atoi(line)
		if err != nil {
			fmt.Println("Couldn't parse number", line)
			return
		}
		numbers = append(numbers, x*key)
		nexts = append(nexts, 0)
		prevs = append(prevs, 0)

		if x == 0 {
			zeroIndex = len(numbers) - 1
		}
	}

	for idx := range nexts {
		nexts[idx] = (idx + 1) % len(nexts)
		if idx == 0 {
			prevs[idx] = len(prevs) - 1
		} else {
			prevs[idx] = idx - 1
		}
	}
	file.Close()

	for round := 0; round < roundCount; round++ {
		for idx := range numbers {
			fmt.Println("Working round", round+1, "index", idx, "with value/count", numbers[idx])
			shift(numbers[idx], idx, prevs, nexts)
			//printNumbers(numbers, nexts)
		}
	}

	idx1k := indexPast(1000, zeroIndex, nexts)
	idx2k := indexPast(1000, idx1k, nexts)
	idx3k := indexPast(1000, idx2k, nexts)
	val1k := numbers[idx1k]
	val2k := numbers[idx2k]
	val3k := numbers[idx3k]
	fmt.Println("Value 1k after 0", val1k, "2k", val2k, "3k", val3k, "sum", val1k+val2k+val3k)
}