package main

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

func main() {
	fmt.Println(part1([]int64{1, 10, 100, 2024}), 37327623)
	fmt.Println(part1(readData("data.txt")), 13004408787)
	fmt.Println(part2([]int64{1, 2, 3, 2024}), 23)
	fmt.Println(part2(readData("data.txt")))
}

func part1(init []int64) (result int64) {
	for _, n := range init {
		for range 2000 {
			n = next(n)
		}
		result += n
	}
	return
}

func makeChangeId(memory [4]int, i int) (result int) {
	for j := range 4 {
		result = result*19 + memory[(i+j)%4] + 9
	}
	return
}

func part2(init []int64) int {
	priceForChangeId := make([]int, 19*19*19*19)
	for _, n := range init {
		seenChange := make([]bool, 19*19*19*19)
		prevPrice := n % 10
		memory := [4]int{0, 0, 0, 0}
		for i := range 2000 {
			n2 := next(n)
			price := n2 % 10
			change := price - prevPrice
			memory[i%4] = int(change)
			if i >= 3 {
				changeId := makeChangeId(memory, i)
				if !seenChange[changeId] {
					seenChange[changeId] = true
					priceForChangeId[changeId] += int(price)
				}
			}
			n, prevPrice = n2, price
		}
	}
	return slices.Max(priceForChangeId)
}

func prune(a int64) int64 {
	return a % 16777216
}

func next(a int64) int64 {
	a = prune((a << 6) ^ a)
	a = prune((a >> 5) ^ a)
	a = prune((a << 11) ^ a)
	return a
}

func readData(fileName string) (numbers []int64) {
	fp, _ := os.Open(fileName)
	scanner := bufio.NewScanner(fp)

	for scanner.Scan() {
		n, _ := strconv.ParseInt(scanner.Text(), 10, 64)
		numbers = append(numbers, n)
	}

	return
}