package config

import (
	"fmt"
	"net/url"
	"strings"
)

// Resolve turns a short topic, host/topic, or absolute URL into an origin and
// a single topic name. defaultHost is used only for short names.
func Resolve(topic, defaultHost string) (origin, name string, err error) {
	topic = strings.TrimSpace(topic)
	if topic == "" {
		return "", "", fmt.Errorf("empty topic")
	}
	if !strings.Contains(topic, "://") && strings.Contains(topic, "/") {
		return Resolve("https://"+topic, "")
	}
	if strings.Contains(topic, "://") {
		u, err := url.Parse(topic)
		if err != nil || u.Host == "" || (u.Scheme != "https" && u.Scheme != "http") {
			return "", "", fmt.Errorf("invalid topic URL %q", topic)
		}
		path := strings.Trim(u.Path, "/")
		if path == "" {
			return "", "", fmt.Errorf("topic URL %q has no topic", topic)
		}
		base := u.Scheme + "://" + u.Host
		if i := strings.LastIndex(path, "/"); i >= 0 {
			base += "/" + path[:i]
			path = path[i+1:]
		}
		if err := checkName(path); err != nil {
			return "", "", err
		}
		return base, path, nil
	}
	if err := checkName(topic); err != nil {
		return "", "", err
	}
	origin, err = normalizeOrigin(defaultHost)
	if err != nil {
		return "", "", fmt.Errorf("topic %q: %w", topic, err)
	}
	return origin, topic, nil
}

func checkName(name string) error {
	if name == "" || strings.Contains(name, ",") || strings.ContainsAny(name, " \t") {
		return fmt.Errorf("invalid topic name %q", name)
	}
	return nil
}

func normalizeOrigin(host string) (string, error) {
	host = strings.TrimSpace(host)
	if host == "" {
		return "", fmt.Errorf("no default-host")
	}
	if !strings.Contains(host, "://") {
		host = "https://" + host
	}
	u, err := url.Parse(strings.TrimRight(host, "/"))
	if err != nil || u.Host == "" || (u.Scheme != "https" && u.Scheme != "http") {
		return "", fmt.Errorf("invalid host %q", host)
	}
	origin := u.Scheme + "://" + u.Host
	if path := strings.Trim(u.Path, "/"); path != "" {
		origin += "/" + path
	}
	return origin, nil
}