package bind

import (
	"context"
	"fmt"
	"strings"
)

// TSIGCreds carries the material needed to authenticate a dynamic update.
type TSIGCreds struct {
	Name      string // TSIG key name
	Algorithm string // e.g. hmac-sha256
	Secret    string // base64-encoded key
}

// RecordUpdate describes a desired record set to apply to a zone.
type RecordUpdate struct {
	FQDN   string   // fully-qualified owner name, trailing dot recommended
	Type   string   // RR type
	TTL    int32    // record TTL
	Values []string // RDATA entries
	Delete bool     // when true, delete instead of add
	// PerValue operates on individual records rather than the whole RRset: adds
	// leave existing records in place, deletes remove only the listed Values.
	// Required at a zone apex, where BIND silently ignores an RRset-wide delete
	// of NS or SOA and would turn a replace into an append.
	PerValue bool
}

// NSUpdate applies a set of record changes to zone by executing nsupdate on the
// primary pod, targeting the local server and authenticating with creds. All
// changes are sent in a single atomic transaction.
func (e *Executor) NSUpdate(ctx context.Context, namespace, pod, zone string, creds TSIGCreds, updates []RecordUpdate) error {
	cmd := []string{NsupdateBin, "-y", fmt.Sprintf("%s:%s:%s", creds.Algorithm, creds.Name, creds.Secret)}
	if out, err := e.Exec(ctx, namespace, pod, cmd, nsupdateScript(zone, updates)); err != nil {
		return fmt.Errorf("nsupdate zone %s: %w (out: %s)", zone, err, out)
	}
	return nil
}

// ApexNS returns the zone's currently published apex NS names, so the operator
// can converge the RRset rather than append to it. The query is TSIG-signed with
// the same creds as an update: a zone behind a view whose match-clients is a key
// is unreachable to an unsigned query, which named answers REFUSED (with an empty
// body and a zero exit status), and the caller must not read that as "no NS".
func (e *Executor) ApexNS(ctx context.Context, namespace, pod, zone string, creds TSIGCreds) ([]string, error) {
	cmd := []string{
		DigBin, "-y", fmt.Sprintf("%s:%s:%s", creds.Algorithm, creds.Name, creds.Secret),
		"+short", "+time=5", "+tries=1", "@127.0.0.1", dot(zone), "NS",
	}
	out, err := e.Exec(ctx, namespace, pod, cmd, "")
	if err != nil {
		return nil, fmt.Errorf("query apex NS of %s: %w (out: %s)", zone, err, out)
	}
	return parseDigNames(out), nil
}

// parseDigNames picks the answers out of `dig +short` output: one fully-qualified
// name per line. Anything without a trailing dot is not a name, and dig prefixes
// its diagnostics (a missing or mismatched TSIG key among them) with ';'.
func parseDigNames(out string) []string {
	var names []string
	for _, line := range strings.Split(out, "\n") {
		line = strings.TrimSpace(line)
		if strings.HasPrefix(line, ";") || !strings.HasSuffix(line, ".") {
			continue
		}
		names = append(names, line)
	}
	return names
}

// nsupdateScript renders the nsupdate input for a set of changes.
func nsupdateScript(zone string, updates []RecordUpdate) string {
	var b strings.Builder
	b.WriteString("server 127.0.0.1\n")
	fmt.Fprintf(&b, "zone %s\n", dot(zone))
	for _, u := range updates {
		switch {
		case u.PerValue && u.Delete:
			for _, v := range u.Values {
				fmt.Fprintf(&b, "update delete %s %s %s\n", dot(u.FQDN), u.Type, v)
			}
		case u.PerValue:
			for _, v := range u.Values {
				fmt.Fprintf(&b, "update add %s %d %s %s\n", dot(u.FQDN), u.TTL, u.Type, v)
			}
		default:
			// Replace semantics: clear the RRset first, then add the values.
			fmt.Fprintf(&b, "update delete %s %s\n", dot(u.FQDN), u.Type)
			if u.Delete {
				continue
			}
			for _, v := range u.Values {
				fmt.Fprintf(&b, "update add %s %d %s %s\n", dot(u.FQDN), u.TTL, u.Type, v)
			}
		}
	}
	b.WriteString("send\n")
	return b.String()
}

// dot ensures a name is fully qualified with a trailing dot.
func dot(name string) string {
	if name == "" || name == "@" {
		return "@"
	}
	if strings.HasSuffix(name, ".") {
		return name
	}
	return name + "."
}