// Package bind contains helpers for driving BIND9 pods: executing rndc and
// nsupdate over the Kubernetes exec subresource, and rendering named.conf.
package bind

import (
	"bytes"
	"context"
	"fmt"

	corev1 "k8s.io/api/core/v1"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/kubernetes/scheme"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/remotecommand"
)

// ContainerName is the BIND container name within each pod.
const ContainerName = "bind"

// Executor runs commands inside BIND pods via the exec subresource.
type Executor struct {
	config    *rest.Config
	clientset kubernetes.Interface
}

// NewExecutor builds an Executor from a controller-runtime rest config.
func NewExecutor(cfg *rest.Config) (*Executor, error) {
	cs, err := kubernetes.NewForConfig(cfg)
	if err != nil {
		return nil, fmt.Errorf("build clientset: %w", err)
	}
	return &Executor{config: cfg, clientset: cs}, nil
}

// Exec runs command in the BIND container of pod, optionally feeding stdin, and
// returns stdout. A non-zero exit or transport error yields an error that
// includes stderr.
func (e *Executor) Exec(ctx context.Context, namespace, pod string, command []string, stdin string) (string, error) {
	req := e.clientset.CoreV1().RESTClient().Post().
		Resource("pods").
		Name(pod).
		Namespace(namespace).
		SubResource("exec").
		VersionedParams(&corev1.PodExecOptions{
			Container: ContainerName,
			Command:   command,
			Stdin:     stdin != "",
			Stdout:    true,
			Stderr:    true,
		}, scheme.ParameterCodec)

	exec, err := remotecommand.NewSPDYExecutor(e.config, "POST", req.URL())
	if err != nil {
		return "", fmt.Errorf("spdy executor: %w", err)
	}

	var stdout, stderr bytes.Buffer
	opts := remotecommand.StreamOptions{Stdout: &stdout, Stderr: &stderr}
	if stdin != "" {
		opts.Stdin = bytes.NewBufferString(stdin)
	}
	if err := exec.StreamWithContext(ctx, opts); err != nil {
		return stdout.String(), fmt.Errorf("exec %v: %w (stderr: %s)", command, err, stderr.String())
	}
	return stdout.String(), nil
}