package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
	"time"
)

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func partOne() {
	f, _ := os.Open("input")
	reader := bufio.NewReader(f)
	scanner := bufio.NewScanner(reader)

	busWaitTimes := map[int]int{}
	shortestWait := -1

	// don't actually need loop logic for a two-line input
	scanner.Scan()
	ts := scanner.Text()
	currentTimestamp, _ := strconv.Atoi(ts)

	scanner.Scan()
	buses := strings.Split(scanner.Text(), ",")
	for _, b := range buses {
		if b != "x" {
			j, _ := strconv.Atoi(b)
			busWaitTimes[j] = (((currentTimestamp / j) + 1) * j) - currentTimestamp
			if shortestWait == -1 || busWaitTimes[shortestWait] > busWaitTimes[j] {
				shortestWait = j
			}
		}
	}

	fmt.Println(busWaitTimes[shortestWait] * shortestWait)
}

type bus struct {
	route  float64
	offset float64
}

func partTwo() {
	f, _ := os.Open("input")
	reader := bufio.NewReader(f)
	scanner := bufio.NewScanner(reader)

	buses := []bus{}

	scanner.Scan() // discard first line
	scanner.Scan()
	line := strings.Split(scanner.Text(), ",")
	for i, b := range line {
		if b != "x" {
			j, _ := strconv.Atoi(b)
			buses = append(buses, bus{
				route:  float64(j),
				offset: float64(i),
			})
		}
	}

	t := float64(0)
	offset := buses[0].route
loop:
	t = t + offset
	offset = 1
	for i := range buses {
		if math.Remainder(t+buses[i].offset, buses[i].route) != 0 {
			goto loop
		} else {
			offset = offset * buses[i].route
		}
	}

	fmt.Println(int(t))
}