// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>

package at

import (
	"fmt"
	"strconv"
	"strings"
)

func parse_scroll_amount(amt string) ([]interface{}, error) {
	var ans = make([]interface{}, 2)
	if amt == "start" || amt == "end" {
		ans[0] = amt
		ans[1] = nil
	} else {
		pages := strings.Contains(amt, "p")
		unscroll := strings.Contains(amt, "u")
		var mult float64 = 1
		if strings.HasSuffix(amt, "-") && !unscroll {
			mult = -1
			q, err := strconv.ParseFloat(strings.TrimRight(amt, "+-plu"), 64)
			if err != nil {
				return ans, err
			}
			if !pages && q != float64(int(q)) {
				return ans, fmt.Errorf("The number must be an integer")
			}
			ans[0] = q * mult
			if pages {
				ans[1] = "p"
			} else if unscroll {
				ans[1] = "u"
			} else {
				ans[1] = "l"
			}
		}
	}
	return ans, nil
}