package year25

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"strings"
)

func Day3Part1(r io.Reader, l *log.Logger) (any, error) {
	return Day3(r, l, 2)
}
func Day3Part2(r io.Reader, l *log.Logger) (any, error) {
	return Day3(r, l, 12)
}
func Day3(r io.Reader, logger *log.Logger, size int) (int64, error) {
	scanner := bufio.NewScanner(r)
	scanner.Split(bufio.ScanLines)
	var sum int64

	findLargetDigit := func(digits []rune) (rune, int) {
		largestDigit := rune(0)
		index := 0

		for i := len(digits) - 1; i >= 0; i-- {
			if digits[i] >= largestDigit {
				largestDigit = digits[i]
				index = i
			}
		}
		return rune(largestDigit) - '0', index
	}

	for scanner.Scan() {
		text := strings.TrimSpace(scanner.Text())
		if text == "" {
			continue
		}
		line := []rune(text)
		parts := make([]byte, size)

		for index := range parts {
			digit, start := findLargetDigit(line[:len(line)+index-len(parts)+1])
			line = line[start+1:]
			if digit < 0 || digit > 9 {
				return 0, fmt.Errorf("ivalid char '%c' in line %s", digit, text)
			} else {
				parts[index] = byte(digit)
			}
		}
		logger.Println("line: ", text)

		var partSum int64
		for _, part := range parts {
			partSum *= 10
			partSum += int64(part)
		}
		logger.Println("got:  ", partSum)
		logger.Println()
		sum += partSum
	}

	return sum, scanner.Err()
}