package main

import (
	"cmp"
	"flag"
	"fmt"
	"log"
	"math"
	"os"
)

func main() {
	debug := flag.Bool("debug", false, "Debug.")
	flag.Parse()

	f := os.Stdin
	if flag.NArg() > 0 {
		var err error
		f, err = os.Open(flag.Arg(0))
		if err != nil {
			log.Fatal(err)
		}
		defer f.Close()
	}

	banks, err := readBatteries(f)
	if err != nil {
		log.Fatal(err)
	}

	var sum1, sum2 uint
	for _, bank := range banks {
		power1 := bestPowerPart1(bank)
		power2 := bestPowerPart2(bank)
		if *debug {
			for _, b := range bank {
				fmt.Print(b)
			}
			fmt.Println(":", power1, power2)
		}
		sum1 += power1
		sum2 += power2
	}

	fmt.Println("sum (part 1):", sum1)
	fmt.Println("sum (part 2):", sum2)
}

func bestPowerPart1(bank []uint8) uint {
	// i := maxIndex(bank[:len(bank)-1])
	// j := maxIndex(bank[i+1:]) + i + 1
	// return uint(bank[i])*10 + uint(bank[j])
	return bestPower(bank, 2)
}

func bestPowerPart2(bank []uint8) uint {
	return bestPower(bank, 12)
}

func bestPower(bank []uint8, batteries int) uint {
	if len(bank) < batteries {
		panic(fmt.Sprintf("bank (%d) is smaller than requested batteries (%d)", len(bank), batteries))
	}
	var joltage uint
	var i int
	for j := batteries - 1; j >= 0; j-- {
		k := maxIndex(bank[i : len(bank)-j])
		k += i
		i = k + 1
		joltage += uint(bank[k]) * uint(math.Pow10(j))
	}
	return joltage
}

func maxIndex[S ~[]E, E cmp.Ordered](x S) int {
	if len(x) < 1 {
		panic("maxIndex: empty list")
	}
	i := 0
	for j := 1; j < len(x); j++ {
		if x[j] > x[i] {
			i = j
		}
	}
	return i
}