package main

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

func proccessLines(path string, f func(string) (stop bool, err error)) error {
	file, err := os.Open(path)
	if err != nil {
		return err
	}
	defer file.Close()
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		stop, err := f(scanner.Text())
		if stop || err != nil {
			return err
		}
	}
	if err := scanner.Err(); err != nil {
		return err
	}
	return nil
}

func part1() {
	seen := map[int]bool{}
	err := proccessLines("./aoc-d1-input.txt", func(line string) (bool, error) {
		num, err := strconv.Atoi(line)
		if err != nil {
			return true, err
		}
		pair := 2020 - num
		if _, ok := seen[pair]; ok {
			fmt.Printf("Found pair! %d + %d = 2020 Product = %d\n", num, pair, num*pair)
			return true, nil
		}
		seen[num] = true
		return false, nil
	})
	if err != nil {
		log.Fatal(err)
	}
}

type numberPair struct {
	A, B int
}

func part2() {
	singles := map[int]bool{}
	doubles := map[int]numberPair{}
	err := proccessLines("./aoc-d1-input.txt", func(line string) (bool, error) {
		num, err := strconv.Atoi(line)
		if err != nil {
			return true, err
		}
		remain := 2020 - num
		if pair, ok := doubles[remain]; ok {
			fmt.Printf("Found set! %d + %d + %d = 2020 Prouct = %d\n", num, pair.A, pair.B, num*pair.A*pair.B)
			return true, nil
		}
		for single := range singles {
			doubles[num+single] = numberPair{num, single}
		}
		singles[num] = true
		return false, nil
	})
	if err != nil {
		log.Fatal(err)
	}
}

func main() {
	part1()
	part2()
}