/*
Copyright 2020 The actions-runner-controller 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 controllers

import (
	"context"
	"errors"
	"fmt"
	"reflect"
	"time"

	gogithub "github.com/google/go-github/v39/github"

	"github.com/go-logr/logr"
	kerrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/client-go/tools/record"
	ctrl "sigs.k8s.io/controller-runtime"
	"sigs.k8s.io/controller-runtime/pkg/client"

	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"

	"github.com/actions-runner-controller/actions-runner-controller/api/v1alpha1"
	"github.com/actions-runner-controller/actions-runner-controller/github"
)

// RunnerReplicaSetReconciler reconciles a Runner object
type RunnerReplicaSetReconciler struct {
	client.Client
	Log          logr.Logger
	Recorder     record.EventRecorder
	Scheme       *runtime.Scheme
	GitHubClient *github.Client
	Name         string
}

// +kubebuilder:rbac:groups=actions.summerwind.dev,resources=runnerreplicasets,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=actions.summerwind.dev,resources=runnerreplicasets/finalizers,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=actions.summerwind.dev,resources=runnerreplicasets/status,verbs=get;update;patch
// +kubebuilder:rbac:groups=actions.summerwind.dev,resources=runners,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=actions.summerwind.dev,resources=runners/status,verbs=get;update;patch
// +kubebuilder:rbac:groups=core,resources=events,verbs=create;patch

func (r *RunnerReplicaSetReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
	log := r.Log.WithValues("runnerreplicaset", req.NamespacedName)

	var rs v1alpha1.RunnerReplicaSet
	if err := r.Get(ctx, req.NamespacedName, &rs); err != nil {
		return ctrl.Result{}, client.IgnoreNotFound(err)
	}

	if !rs.ObjectMeta.DeletionTimestamp.IsZero() {
		return ctrl.Result{}, nil
	}

	selector, err := metav1.LabelSelectorAsSelector(rs.Spec.Selector)
	if err != nil {
		return ctrl.Result{}, err
	}
	// Get the Runners managed by the target RunnerReplicaSet
	var allRunners v1alpha1.RunnerList
	if err := r.List(
		ctx,
		&allRunners,
		client.InNamespace(req.Namespace),
		client.MatchingLabelsSelector{Selector: selector},
	); err != nil {
		if !kerrors.IsNotFound(err) {
			return ctrl.Result{}, err
		}
	}

	var myRunners []v1alpha1.Runner

	var (
		current   int
		ready     int
		available int
	)

	for _, r := range allRunners.Items {
		// This guard is required to avoid the RunnerReplicaSet created by the controller v0.17.0 or before
		// to not treat all the runners in the namespace as its children.
		if metav1.IsControlledBy(&r, &rs) && !metav1.HasAnnotation(r.ObjectMeta, annotationKeyRegistrationOnly) {
			myRunners = append(myRunners, r)

			current += 1

			if r.Status.Phase == string(corev1.PodRunning) {
				ready += 1
				// available is currently the same as ready, as we don't yet have minReadySeconds for runners
				available += 1
			}
		}
	}

	var desired int

	if rs.Spec.Replicas != nil {
		desired = *rs.Spec.Replicas
	} else {
		desired = 1
	}

	registrationOnlyRunnerNsName := req.NamespacedName
	registrationOnlyRunnerNsName.Name = registrationOnlyRunnerNameFor(rs.Name)
	registrationOnlyRunner := v1alpha1.Runner{}
	registrationOnlyRunnerExists := false
	if err := r.Get(
		ctx,
		registrationOnlyRunnerNsName,
		&registrationOnlyRunner,
	); err != nil {
		if !kerrors.IsNotFound(err) {
			return ctrl.Result{}, err
		}
	} else {
		registrationOnlyRunnerExists = true
	}

	// On scale to zero, we must have fully registered registration-only runner before we start deleting other runners, hence `desired == 0`
	// On scale from zero, we must retain the registratoin-only runner until one or more other runners get registered, hence `registrationOnlyRunnerExists && available == 0`.
	// On RunnerReplicaSet creation, it have always 0 replics and no registration-only runner.
	// In this case We don't need to bother creating a registration-only runner which gets deleted soon after we have 1 or more available repolicas,
	// hence it's not `available == 0`, but `registrationOnlyRunnerExists && available == 0`.
	// See https://github.com/actions-runner-controller/actions-runner-controller/issues/516
	registrationOnlyRunnerNeeded := desired == 0 || (registrationOnlyRunnerExists && current == 0)

	if registrationOnlyRunnerNeeded {
		if registrationOnlyRunnerExists {
			if registrationOnlyRunner.Status.Phase == "" {
				log.Info("Still waiting for the registration-only runner to be registered")

				return ctrl.Result{}, nil
			}
		} else {
			// A registration-only runner does not exist and is needed, hence create it.

			runnerForScaleFromToZero, err := r.newRunner(rs)
			if err != nil {
				return ctrl.Result{}, fmt.Errorf("failed to create runner for scale from/to zero: %v", err)
			}

			runnerForScaleFromToZero.ObjectMeta.Name = registrationOnlyRunnerNsName.Name
			runnerForScaleFromToZero.ObjectMeta.GenerateName = ""
			runnerForScaleFromToZero.ObjectMeta.Labels = nil
			metav1.SetMetaDataAnnotation(&runnerForScaleFromToZero.ObjectMeta, annotationKeyRegistrationOnly, "true")

			if err := r.Client.Create(ctx, &runnerForScaleFromToZero); err != nil {
				log.Error(err, "Failed to create runner for scale from/to zero")

				return ctrl.Result{}, err
			}

			// We can continue to deleting runner pods only after the
			// registration-only runner gets registered.
			return ctrl.Result{}, nil
		}
	} else {
		// A registration-only runner exists and is not needed, hence delete it.
		if registrationOnlyRunnerExists {
			if err := r.Client.Delete(ctx, &registrationOnlyRunner); err != nil {
				log.Error(err, "Retrying soon because we failed to delete registration-only runner")

				return ctrl.Result{Requeue: true}, nil
			}
		}
	}

	if current > desired {
		n := current - desired

		log.V(0).Info(fmt.Sprintf("Deleting %d runners", n), "desired", desired, "current", current, "ready", ready)

		// get runners that are currently offline/not busy/timed-out to register
		var deletionCandidates []v1alpha1.Runner

		for _, runner := range allRunners.Items {
			busy, err := r.GitHubClient.IsRunnerBusy(ctx, runner.Spec.Enterprise, runner.Spec.Organization, runner.Spec.Repository, runner.Name)
			if err != nil {
				notRegistered := false
				offline := false

				var notFoundException *github.RunnerNotFound
				var offlineException *github.RunnerOffline
				if errors.As(err, &notFoundException) {
					log.V(1).Info("Failed to check if runner is busy. Either this runner has never been successfully registered to GitHub or it still needs more time.", "runnerName", runner.Name)
					notRegistered = true
				} else if errors.As(err, &offlineException) {
					offline = true
				} else {
					var e *gogithub.RateLimitError
					if errors.As(err, &e) {
						// We log the underlying error when we failed calling GitHub API to list or unregisters,
						// or the runner is still busy.
						log.Error(
							err,
							fmt.Sprintf(
								"Failed to check if runner is busy due to GitHub API rate limit. Retrying in %s to avoid excessive GitHub API calls",
								retryDelayOnGitHubAPIRateLimitError,
							),
						)

						return ctrl.Result{RequeueAfter: retryDelayOnGitHubAPIRateLimitError}, err
					}

					return ctrl.Result{}, err
				}

				registrationTimeout := 15 * time.Minute
				currentTime := time.Now()
				registrationDidTimeout := currentTime.Sub(runner.CreationTimestamp.Add(registrationTimeout)) > 0

				if notRegistered && registrationDidTimeout {
					log.Info(
						"Runner failed to register itself to GitHub in timely manner. "+
							"Marking the runner for scale down. "+
							"CAUTION: If you see this a lot, you should investigate the root cause. "+
							"See https://github.com/actions-runner-controller/actions-runner-controller/issues/288",
						"runnerCreationTimestamp", runner.CreationTimestamp,
						"currentTime", currentTime,
						"configuredRegistrationTimeout", registrationTimeout,
					)

					deletionCandidates = append(deletionCandidates, runner)
				}

				// offline runners should always be a great target for scale down
				if offline {
					deletionCandidates = append(deletionCandidates, runner)
				}
			} else if !busy {
				deletionCandidates = append(deletionCandidates, runner)
			}
		}

		if len(deletionCandidates) < n {
			n = len(deletionCandidates)
		}

		log.V(0).Info(fmt.Sprintf("Deleting %d runner(s)", n), "desired", desired, "current", current, "ready", ready)

		for i := 0; i < n; i++ {
			if err := r.Client.Delete(ctx, &deletionCandidates[i]); client.IgnoreNotFound(err) != nil {
				log.Error(err, "Failed to delete runner resource")

				return ctrl.Result{}, err
			}

			r.Recorder.Event(&rs, corev1.EventTypeNormal, "RunnerDeleted", fmt.Sprintf("Deleted runner '%s'", deletionCandidates[i].Name))
			log.Info("Deleted runner")
		}
	} else if desired > current {
		n := desired - current

		log.V(0).Info(fmt.Sprintf("Creating %d runner(s)", n), "desired", desired, "available", current, "ready", ready)

		for i := 0; i < n; i++ {
			newRunner, err := r.newRunner(rs)
			if err != nil {
				log.Error(err, "Could not create runner")

				return ctrl.Result{}, err
			}

			if err := r.Client.Create(ctx, &newRunner); err != nil {
				log.Error(err, "Failed to create runner resource")

				return ctrl.Result{}, err
			}
		}
	}

	var status v1alpha1.RunnerReplicaSetStatus

	status.Replicas = &current
	status.AvailableReplicas = &available
	status.ReadyReplicas = &ready

	if !reflect.DeepEqual(rs.Status, status) {
		updated := rs.DeepCopy()
		updated.Status = status

		if err := r.Status().Patch(ctx, updated, client.MergeFrom(&rs)); err != nil {
			log.Info("Failed to update runnerreplicaset status. Retrying immediately", "error", err.Error())
			return ctrl.Result{
				Requeue: true,
			}, nil
		}
	}

	return ctrl.Result{}, nil
}

func (r *RunnerReplicaSetReconciler) newRunner(rs v1alpha1.RunnerReplicaSet) (v1alpha1.Runner, error) {
	objectMeta := rs.Spec.Template.ObjectMeta.DeepCopy()

	objectMeta.GenerateName = rs.ObjectMeta.Name + "-"
	objectMeta.Namespace = rs.ObjectMeta.Namespace

	runner := v1alpha1.Runner{
		TypeMeta:   metav1.TypeMeta{},
		ObjectMeta: *objectMeta,
		Spec:       rs.Spec.Template.Spec,
	}

	if err := ctrl.SetControllerReference(&rs, &runner, r.Scheme); err != nil {
		return runner, err
	}

	return runner, nil
}

func (r *RunnerReplicaSetReconciler) SetupWithManager(mgr ctrl.Manager) error {
	name := "runnerreplicaset-controller"
	if r.Name != "" {
		name = r.Name
	}

	r.Recorder = mgr.GetEventRecorderFor(name)

	return ctrl.NewControllerManagedBy(mgr).
		For(&v1alpha1.RunnerReplicaSet{}).
		Owns(&v1alpha1.Runner{}).
		Named(name).
		Complete(r)
}

func registrationOnlyRunnerNameFor(rsName string) string {
	return rsName + "-registration-only"
}