package compare

import (
	"strconv"
	"strings"
)

const maxItems = 2

func Parse(raw string) []int {
	if raw == "" {
		return nil
	}
	var ids []int
	for _, part := range strings.Split(raw, ",") {
		id, err := strconv.Atoi(strings.TrimSpace(part))
		if err != nil || id <= 0 {
			continue
		}
		ids = appendUnique(ids, id)
	}
	return ids
}

func Format(ids []int) string {
	if len(ids) == 0 {
		return ""
	}
	parts := make([]string, len(ids))
	for i, id := range ids {
		parts[i] = strconv.Itoa(id)
	}
	return strings.Join(parts, ",")
}

func Add(raw string, id int) string {
	if id <= 0 {
		return raw
	}
	ids := Parse(raw)
	ids = appendUnique(ids, id)
	if len(ids) > maxItems {
		ids = ids[len(ids)-maxItems:]
	}
	return Format(ids)
}

func Remove(raw string, id int) string {
	ids := Parse(raw)
	var next []int
	for _, v := range ids {
		if v != id {
			next = append(next, v)
		}
	}
	return Format(next)
}

func appendUnique(ids []int, id int) []int {
	for _, v := range ids {
		if v == id {
			return ids
		}
	}
	return append(ids, id)
}