package main

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

type disc struct {
    positions, initial int
}

func main() {
    fmt.Println("Day 15 of Advent of Code 2016")
    f, err := os.Open("input")
    check(err)

    input := read_input(f)

    var discs []disc
    for _, line := range input {
        fields := strings.Fields(line)
        positions, err := strconv.Atoi(fields[3])
        check(err)
        initial, err := strconv.Atoi(fields[11][:len(fields[11])-1])
        check(err)
        discs = append(discs, disc{positions, initial})
    }

    var time int
    for time = 0; !is_success(discs, time); time++ {
    }

    fmt.Printf("Part 1: %d\n", time)

    discs = append(discs, disc{11, 0})

    var new_time int
    for new_time = 0; !is_success(discs, new_time); new_time++ {
    }

    fmt.Printf("Part 2: %d\n", new_time)
}

func is_success(ds []disc, initial_time int) bool {
    for i, disc := range ds {
        if !(rotate_disc(disc, i+initial_time+1) == 0) {
            return false
        }
    }
    return true
}

func rotate_disc(d disc, t int) int {
    return (d.initial + t) % d.positions
}

func check(e error) {
    if e != nil {
        panic(e)
    }
}

func read_input(f *os.File) []string {
    scanner := bufio.NewScanner(f)
    data := []string{}
    for scanner.Scan() {
        data = append(data, scanner.Text())
    }
    return data
}