package main

import (
	"fmt"
	"log"
	"os"

	"git.annabunch.es/annabunches/adventofcode/2020/lib/util"
)

type SumTracker map[int][]Tuple

type Tuple struct {
	First, Second int
}

func checkValue(sumMap SumTracker, value int) bool {
	_, ok := sumMap[value]
	return ok
}

func addSums(sumMap SumTracker, values []int, index int) {
	for i := index - 25; i < index; i++ {
		sum := values[i] + values[index]
		sumMap[sum] = append(sumMap[sum], Tuple{First: i, Second: index})
	}
}

func removeSums(sumMap SumTracker, index int) {
	for sum, tupleList := range sumMap {
		newList := make([]Tuple, 0)

		for _, tuple := range tupleList {
			if !(tuple.First == index || tuple.Second == index) {
				newList = append(newList, tuple)
			}
		}
		sumMap[sum] = newList
		if len(sumMap[sum]) == 0 {
			delete(sumMap, sum)
		}
	}
}

// find and return the slice of values that sums to sum
func findListSum(values []int, sum int) []int {
	i := 0
	j := 0
	total := 0
	for total != sum {
		for total < sum {
			if j >= len(values) {
				log.Panicf("Couldn't find a match.")
			}

			total += values[j]
			j++
		}

		for total > sum {
			total -= values[i]
			i++
		}
	}

	return values[i:j]
}

func sumMinMax(values []int) int {
	min := values[0]
	max := values[0]

	for _, x := range values {
		if x < min {
			min = x
		}

		if x > max {
			max = x
		}
	}

	return min + max
}

func main() {
	step := os.Args[1]
	values := util.InputParserInts(os.Args[2])

	var badValue int
	sumMap := make(SumTracker)

	// build up the preamble
	for i := 0; i < 25; i++ {
		for j := i + 1; j < 25; j++ {
			sum := values[i] + values[j]
			if _, ok := sumMap[sum]; !ok {
				sumMap[sum] = make([]Tuple, 0)
			}

			sumMap[sum] = append(sumMap[sum], Tuple{First: i, Second: j})
		}
	}

	for i := 25; i < len(values); i++ {
		if !checkValue(sumMap, values[i]) {
			badValue = values[i]
			break
		}
		addSums(sumMap, values, i)
		removeSums(sumMap, i-25)
	}

	switch step {
	case "1":
		fmt.Println(badValue)
	case "2":
		sumValues := findListSum(values, badValue)
		fmt.Println(sumMinMax(sumValues))
	}
}