/*
Copyright 2025 The Kubeflow Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package controller

import (
	"context"
	"iter"
	"slices"
	"time"

	"github.com/go-logr/logr"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/client-go/tools/events"
	"k8s.io/client-go/util/workqueue"
	"k8s.io/klog/v2"
	ctrl "sigs.k8s.io/controller-runtime"
	"sigs.k8s.io/controller-runtime/pkg/builder"
	"sigs.k8s.io/controller-runtime/pkg/client"
	"sigs.k8s.io/controller-runtime/pkg/controller"
	ctrlutil "sigs.k8s.io/controller-runtime/pkg/controller/controllerutil"
	"sigs.k8s.io/controller-runtime/pkg/event"
	"sigs.k8s.io/controller-runtime/pkg/handler"
	"sigs.k8s.io/controller-runtime/pkg/reconcile"
	"sigs.k8s.io/controller-runtime/pkg/source"

	trainer "github.com/kubeflow/trainer/v2/pkg/apis/trainer/v1alpha1"
	"github.com/kubeflow/trainer/v2/pkg/constants"
	idxer "github.com/kubeflow/trainer/v2/pkg/runtime/indexer"
	"github.com/kubeflow/trainer/v2/pkg/util/trainjob"
)

const (
	updateChBuffer = 10
)

type TrainingRuntimeReconciler struct {
	log                      logr.Logger
	client                   client.Client
	recorder                 events.EventRecorder
	nonRuntimeObjectUpdateCh chan event.TypedGenericEvent[iter.Seq[types.NamespacedName]]
}

var _ reconcile.Reconciler = (*TrainingRuntimeReconciler)(nil)
var _ TrainJobWatcher = (*TrainingRuntimeReconciler)(nil)

func NewTrainingRuntimeReconciler(cli client.Client, recorder events.EventRecorder) *TrainingRuntimeReconciler {
	return &TrainingRuntimeReconciler{
		log:                      ctrl.Log.WithName("trainingruntime-controller"),
		client:                   cli,
		recorder:                 recorder,
		nonRuntimeObjectUpdateCh: make(chan event.TypedGenericEvent[iter.Seq[types.NamespacedName]], updateChBuffer),
	}
}

// +kubebuilder:rbac:groups=trainer.kubeflow.org,resources=trainingruntimes,verbs=get;list;watch;update;patch
// +kubebuilder:rbac:groups=trainer.kubeflow.org,resources=trainingruntimes/finalizers,verbs=get;update;patch

func (r *TrainingRuntimeReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
	var runtime trainer.TrainingRuntime
	if err := r.client.Get(ctx, req.NamespacedName, &runtime); err != nil {
		return ctrl.Result{}, client.IgnoreNotFound(err)
	}
	log := ctrl.LoggerFrom(ctx).WithValues("trainingRuntime", klog.KObj(&runtime))
	ctrl.LoggerInto(ctx, log)
	log.V(2).Info("Reconciling TrainingRuntime")

	trainJobs := &trainer.TrainJobList{}
	if err := r.client.List(ctx, trainJobs, client.InNamespace(runtime.Namespace), client.MatchingFields{
		idxer.TrainJobRuntimeRefKey: runtime.Name,
	}); err != nil {
		return ctrl.Result{}, err
	}

	prevRuntime := runtime.DeepCopy()
	if !ctrlutil.ContainsFinalizer(&runtime, constants.ResourceInUseFinalizer) && len(trainJobs.Items) != 0 {
		ctrlutil.AddFinalizer(&runtime, constants.ResourceInUseFinalizer)
		return ctrl.Result{}, r.client.Patch(ctx, &runtime, client.MergeFrom(prevRuntime))
	} else if !runtime.DeletionTimestamp.IsZero() && len(trainJobs.Items) == 0 {
		ctrlutil.RemoveFinalizer(&runtime, constants.ResourceInUseFinalizer)
		return ctrl.Result{}, r.client.Patch(ctx, &runtime, client.MergeFrom(prevRuntime))
	}
	return ctrl.Result{}, nil
}

func (r *TrainingRuntimeReconciler) NotifyTrainJobUpdate(oldJob, newJob *trainer.TrainJob) {
	var runtimeNSName *types.NamespacedName
	switch {
	case oldJob != nil && newJob != nil:
		// UPDATE Event.
		if trainjob.RuntimeRefIsTrainingRuntime(newJob.Spec.RuntimeRef) {
			runtimeNSName = &types.NamespacedName{Namespace: newJob.Namespace, Name: newJob.Spec.RuntimeRef.Name}
		}
	case oldJob == nil:
		// CREATE Event.
		if trainjob.RuntimeRefIsTrainingRuntime(newJob.Spec.RuntimeRef) {
			runtimeNSName = &types.NamespacedName{Namespace: newJob.Namespace, Name: newJob.Spec.RuntimeRef.Name}
		}
	default:
		// DELETE Event.
		if trainjob.RuntimeRefIsTrainingRuntime(oldJob.Spec.RuntimeRef) {
			runtimeNSName = &types.NamespacedName{Namespace: oldJob.Namespace, Name: oldJob.Spec.RuntimeRef.Name}
		}
	}
	if runtimeNSName != nil {
		r.nonRuntimeObjectUpdateCh <- event.TypedGenericEvent[iter.Seq[types.NamespacedName]]{
			Object: slices.Values([]types.NamespacedName{*runtimeNSName}),
		}
	}
}

type nonRuntimeObjectHandler struct{}

var _ handler.TypedEventHandler[iter.Seq[types.NamespacedName], reconcile.Request] = (*nonRuntimeObjectHandler)(nil)

func (h *nonRuntimeObjectHandler) Create(context.Context, event.TypedCreateEvent[iter.Seq[types.NamespacedName]], workqueue.TypedRateLimitingInterface[reconcile.Request]) {
}
func (h *nonRuntimeObjectHandler) Update(context.Context, event.TypedUpdateEvent[iter.Seq[types.NamespacedName]], workqueue.TypedRateLimitingInterface[reconcile.Request]) {
}
func (h *nonRuntimeObjectHandler) Delete(context.Context, event.TypedDeleteEvent[iter.Seq[types.NamespacedName]], workqueue.TypedRateLimitingInterface[reconcile.Request]) {
}
func (h *nonRuntimeObjectHandler) Generic(_ context.Context, e event.TypedGenericEvent[iter.Seq[types.NamespacedName]], q workqueue.TypedRateLimitingInterface[reconcile.Request]) {
	for nsName := range e.Object {
		q.AddAfter(reconcile.Request{NamespacedName: nsName}, time.Second)
	}
}

func (r *TrainingRuntimeReconciler) SetupWithManager(mgr ctrl.Manager, options controller.Options) error {
	return builder.TypedControllerManagedBy[reconcile.Request](mgr).
		Named("trainingruntime_controller").
		WithOptions(options).
		WatchesRawSource(source.TypedKind(
			mgr.GetCache(),
			&trainer.TrainingRuntime{},
			&handler.TypedEnqueueRequestForObject[*trainer.TrainingRuntime]{},
		)).
		WatchesRawSource(source.Channel(r.nonRuntimeObjectUpdateCh, &nonRuntimeObjectHandler{})).
		Complete(r)
}