package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"strconv"
	"strings"
)

type idRange struct {
	from, to uint
}

func readRanges(r io.Reader) ([]idRange, error) {
	sc := bufio.NewScanner(r)
	sc.Split(scanSimpleCSV)

	var ranges []idRange
	for sc.Scan() {
		before, after, ok := strings.Cut(sc.Text(), "-")
		if !ok {
			return nil, fmt.Errorf("range %q: missing dash", sc.Text())
		}
		from, err := strconv.ParseUint(before, 10, 0)
		if err != nil {
			return nil, fmt.Errorf("range %q: %w", sc.Text(), err)
		}
		to, err := strconv.ParseUint(after, 10, 0)
		if err != nil {
			return nil, fmt.Errorf("range %q: %w", sc.Text(), err)
		}
		if from > to {
			return nil, fmt.Errorf("range %q: refers from higher to lower", sc.Text())
		}
		ranges = append(ranges, idRange{
			from: uint(from),
			to:   uint(to),
		})
	}
	return ranges, sc.Err()
}

func scanSimpleCSV(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	if i := bytes.IndexByte(data, ','); i >= 0 {
		return i + 1, data[:i], nil
	}
	if atEOF {
		if trimmed, ok := bytes.CutSuffix(data, []byte("\r\n")); ok {
			return len(data), trimmed, nil
		}
		if trimmed, ok := bytes.CutSuffix(data, []byte{'\n'}); ok {
			return len(data), trimmed, nil
		}
		return len(data), data, nil
	}
	return 0, nil, nil
}