package logs

import (
	"context"
	"errors"
	"io"
	"log"
	"sync"
	"time"

	appsv1 "k8s.io/api/apps/v1"
	corev1 "k8s.io/api/core/v1"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/watch"
	"k8s.io/client-go/kubernetes"
)

// KubernetesClient wraps a Kubernetes clientset.
type KubernetesClient struct {
	kubernetes.Interface
}

// concurrentWriter implements an io.Writer that can be safely written to from
// multiple goroutines.
type concurrentWriter struct {
	w  io.Writer
	mu sync.Mutex
}

// Write implements io.Writer.
func (cw *concurrentWriter) Write(p []byte) (int, error) {
	cw.mu.Lock()
	defer cw.mu.Unlock()

	return cw.w.Write(p)
}

type PodWatcherInterface interface {
	WatchPods(ctx context.Context) error
	Close()
}

// PodWatcherFunc builds a PodWatcher.
type PodWatcherFunc func(KubernetesClient, string, *metav1.LabelSelector, io.Writer) PodWatcherInterface

// Watcher watches a deployment and tails the logs for its currently active
// pods.
type Watcher struct {
	deployName     string
	container      string
	strictExist    bool
	clientset      KubernetesClient
	deployment     *appsv1.Deployment
	podWatcher     PodWatcherInterface
	podWatcherFunc PodWatcherFunc
	errChan        chan error
	dst            *concurrentWriter
}

// NewWatcher creates a new Watcher.
func NewWatcher(deployName string, container string, strictExist bool, clientset KubernetesClient, podWatcherFunc PodWatcherFunc, dst io.Writer) *Watcher {
	return &Watcher{
		deployName:     deployName,
		container:      container,
		strictExist:    strictExist,
		clientset:      clientset,
		podWatcherFunc: podWatcherFunc,
		errChan:        make(chan error),
		dst:            &concurrentWriter{w: dst},
	}
}

// Watch watches a deployment.
func (w *Watcher) Watch(ctx context.Context) error {
	deploymentsClient := w.clientset.AppsV1().Deployments(corev1.NamespaceDefault)

	// Check if the deployment exists before we commence watching, to allow us to
	// return an error if needed.
	_, err := deploymentsClient.Get(ctx, w.deployName, metav1.GetOptions{})
	var statusErr *apierrors.StatusError
	if errors.As(err, &statusErr) && statusErr.Status().Reason == metav1.StatusReasonNotFound {
		if w.strictExist {
			return err
		}
		log.Printf(`deployment "%s" does not exist, waiting`, w.deployName)
	}

	opts := metav1.ListOptions{Watch: true, FieldSelector: "metadata.name=" + w.deployName}
	deploymentsWatcher, err := deploymentsClient.Watch(ctx, opts)
	if err != nil {
		return err
	}
	defer deploymentsWatcher.Stop()

	ticker := time.NewTicker(time.Second)
	defer ticker.Stop()

	for {
		select {
		case evt := <-deploymentsWatcher.ResultChan():
			switch evt.Type {
			case watch.Added, watch.Modified:
				deployment := evt.Object.(*appsv1.Deployment)
				w.addDeployment(ctx, deployment)
			case watch.Deleted:
				w.removeDeployment()
			}
		case err := <-w.errChan:
			return err
		case <-ctx.Done():
			return ctx.Err()
		}
	}
}

func (w *Watcher) addDeployment(ctx context.Context, deployment *appsv1.Deployment) {
	if w.deployment != nil && w.deployment.UID == deployment.UID {
		return
	}

	w.removeDeployment()

	log.Println("[DeploymentWatcher] add deployment")

	w.deployment = deployment
	w.podWatcher = w.podWatcherFunc(
		w.clientset,
		w.container,
		deployment.Spec.Selector,
		w.dst,
	)

	go func() {
		if err := w.podWatcher.WatchPods(ctx); err != nil {
			w.errChan <- err
		}
	}()
}

func (w *Watcher) removeDeployment() {
	if w.podWatcher != nil {
		log.Println("[DeploymentWatcher] remove deployment")
		w.podWatcher.Close()
		w.podWatcher = nil
	}
	w.deployment = nil
}