// Package config provides application configuration via Viper.
package config

import (
	"fmt"
	"strings"

	"golang.org/x/net/publicsuffix"
)

// ClassifyTarget determines whether a DNS name is an apex domain
// (eTLD+1) or a hostname (subdomain of an eTLD+1). Returns
// "domain" or "hostname". Returns an error if the name is itself
// a public suffix (e.g. "co.uk") or otherwise invalid.
func ClassifyTarget(name string) (string, error) {
	// Normalize: lowercase, strip trailing dot.
	name = strings.ToLower(strings.TrimSuffix(name, "."))

	if name == "" {
		return "", fmt.Errorf("empty target name")
	}

	apex, err := publicsuffix.EffectiveTLDPlusOne(name)
	if err != nil {
		return "", fmt.Errorf(
			"invalid target %q: %w", name, err,
		)
	}

	if name == apex {
		return "domain", nil
	}

	return "hostname", nil
}

// classifyTargets splits a list of DNS names into apex domains
// and hostnames using the Public Suffix List.
func classifyTargets(
	targets []string,
) (domains, hostnames []string, err error) {
	for _, target := range targets {
		kind, classifyErr := ClassifyTarget(target)
		if classifyErr != nil {
			return nil, nil, classifyErr
		}

		switch kind {
		case "domain":
			domains = append(domains, strings.ToLower(
				strings.TrimSuffix(target, "."),
			))
		case "hostname":
			hostnames = append(hostnames, strings.ToLower(
				strings.TrimSuffix(target, "."),
			))
		}
	}

	return domains, hostnames, nil
}