// Package dclist parses comma-separated Telegram DC ids (int16).
package dclist

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

// ParseList parses "1,2,5" or "2". Empty string returns (nil, nil) — caller uses single-DC default.
func ParseList(s string) ([]int16, error) {
	s = strings.TrimSpace(s)
	if s == "" {
		return nil, nil
	}
	parts := strings.Split(s, ",")
	out := make([]int16, 0, len(parts))
	for _, p := range parts {
		p = strings.TrimSpace(p)
		if p == "" {
			continue
		}
		v, err := strconv.ParseInt(p, 10, 16)
		if err != nil {
			return nil, fmt.Errorf("dc id %q: %w", p, err)
		}
		if v < -32768 || v > 32767 {
			return nil, fmt.Errorf("dc id %d out of int16 range", v)
		}
		out = append(out, int16(v))
	}
	if len(out) == 0 {
		return nil, fmt.Errorf("empty dc list after parsing %q", s)
	}
	return out, nil
}