package godns

import (
	"fmt"
	"net"
	"strings"
)

// TSIG is caller-supplied key material. go-dns does not generate keys.
type TSIG struct {
	Name      string // key name presented to BIND
	Algorithm string // BIND algorithm name, e.g. hmac-sha256
	Secret    string // base64 secret from the Key File
}

// Client is a session against one nameserver and zone, authenticated with TSIG.
type Client struct {
	server string
	zone   string
	tsig   TSIG
}

// NewClient validates ASCII zone names and required TSIG fields.
// server is host or host:port; port 53 is assumed when omitted.
func NewClient(server, zone string, key TSIG) (*Client, error) {
	if strings.TrimSpace(server) == "" {
		return nil, fmt.Errorf("server is required")
	}
	if err := asciiName("zone", zone); err != nil {
		return nil, err
	}
	if err := validateTSIG(key); err != nil {
		return nil, err
	}
	addr, err := withDNSPort(server)
	if err != nil {
		return nil, err
	}
	return &Client{server: addr, zone: strings.TrimSpace(zone), tsig: key}, nil
}

// validateTSIG requires name, algorithm, and secret, and an ASCII key name.
func validateTSIG(key TSIG) error {
	if strings.TrimSpace(key.Name) == "" {
		return fmt.Errorf("TSIG name is required")
	}
	if strings.TrimSpace(key.Algorithm) == "" {
		return fmt.Errorf("TSIG algorithm is required")
	}
	if strings.TrimSpace(key.Secret) == "" {
		return fmt.Errorf("TSIG secret is required")
	}
	if err := asciiName("TSIG name", key.Name); err != nil {
		return err
	}
	return nil
}

// withDNSPort appends :53 when server has no port.
func withDNSPort(server string) (string, error) {
	host := strings.TrimSpace(server)
	if _, _, err := net.SplitHostPort(host); err == nil {
		return host, nil
	}
	// net.SplitHostPort fails for bare IPv6; require brackets or a hostname/IPv4.
	if strings.Count(host, ":") > 1 && !strings.HasPrefix(host, "[") {
		return "", fmt.Errorf("IPv6 server must be [host]:port or wrapped in brackets")
	}
	return net.JoinHostPort(host, "53"), nil
}

// asciiName rejects empty or non-ASCII DNS names.
func asciiName(label, name string) error {
	trimmed := strings.TrimSpace(name)
	if trimmed == "" {
		return fmt.Errorf("%s is required", label)
	}
	for i := 0; i < len(trimmed); i++ {
		if trimmed[i] > 127 {
			return fmt.Errorf("%s must be ASCII, got %q", label, name)
		}
	}
	return nil
}