/*
Copyright 2022 The Kubernetes 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"
	"fmt"
	"net/http"
	"sync"
	"time"

	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/apiserver/pkg/server/healthz"
	"k8s.io/apiserver/pkg/server/options/encryptionconfig"
	"k8s.io/apiserver/pkg/server/options/encryptionconfig/metrics"
	"k8s.io/client-go/util/workqueue"
	"k8s.io/klog/v2"
)

// workqueueKey is the dummy key used to process change in encryption config file.
const workqueueKey = "key"

// EncryptionConfigFileChangePollDuration is exposed so that integration tests can crank up the reload speed.
var EncryptionConfigFileChangePollDuration = time.Minute

// DynamicEncryptionConfigContent which can dynamically handle changes in encryption config file.
type DynamicEncryptionConfigContent struct {
	name string

	// filePath is the path of the file to read.
	filePath string

	// lastLoadedEncryptionConfigHash stores last successfully read encryption config file content.
	lastLoadedEncryptionConfigHash string

	// queue for processing changes in encryption config file.
	queue workqueue.RateLimitingInterface

	// dynamicTransformers updates the transformers when encryption config file changes.
	dynamicTransformers *encryptionconfig.DynamicTransformers

	// identity of the api server
	apiServerID string

	// can be swapped during testing
	getEncryptionConfigHash func(ctx context.Context, filepath string) (string, error)
	loadEncryptionConfig    func(ctx context.Context, filepath string, reload bool, apiServerID string) (*encryptionconfig.EncryptionConfiguration, error)
}

func init() {
	metrics.RegisterMetrics()
}

// NewDynamicEncryptionConfiguration returns controller that dynamically reacts to changes in encryption config file.
func NewDynamicEncryptionConfiguration(
	name, filePath string,
	dynamicTransformers *encryptionconfig.DynamicTransformers,
	configContentHash string,
	apiServerID string,
) *DynamicEncryptionConfigContent {
	return &DynamicEncryptionConfigContent{
		name:                           name,
		filePath:                       filePath,
		lastLoadedEncryptionConfigHash: configContentHash,
		dynamicTransformers:            dynamicTransformers,
		queue:                          workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), name),
		apiServerID:                    apiServerID,
		getEncryptionConfigHash: func(_ context.Context, filepath string) (string, error) {
			return encryptionconfig.GetEncryptionConfigHash(filepath)
		},
		loadEncryptionConfig: encryptionconfig.LoadEncryptionConfig,
	}
}

// Run starts the controller and blocks until ctx is canceled.
func (d *DynamicEncryptionConfigContent) Run(ctx context.Context) {
	defer utilruntime.HandleCrash()

	klog.InfoS("Starting controller", "name", d.name)
	defer klog.InfoS("Shutting down controller", "name", d.name)

	var wg sync.WaitGroup

	wg.Add(1)
	go func() {
		defer utilruntime.HandleCrash()
		defer wg.Done()
		defer d.queue.ShutDown()
		<-ctx.Done()
	}()

	wg.Add(1)
	go func() {
		defer utilruntime.HandleCrash()
		defer wg.Done()
		d.runWorker(ctx)
	}()

	// this function polls changes in the encryption config file by placing a dummy key in the queue.
	// the 'runWorker' function then picks up this dummy key and processes the changes.
	// the goroutine terminates when 'ctx' is canceled.
	_ = wait.PollUntilContextCancel(
		ctx,
		EncryptionConfigFileChangePollDuration,
		true,
		func(ctx context.Context) (bool, error) {
			// add dummy item to the queue to trigger file content processing.
			d.queue.Add(workqueueKey)

			// return false to continue polling.
			return false, nil
		},
	)

	wg.Wait()
}

// runWorker to process file content
func (d *DynamicEncryptionConfigContent) runWorker(ctx context.Context) {
	for d.processNextWorkItem(ctx) {
	}
}

// processNextWorkItem processes file content when there is a message in the queue.
func (d *DynamicEncryptionConfigContent) processNextWorkItem(serverCtx context.Context) bool {
	// key here is dummy item in the queue to trigger file content processing.
	key, quit := d.queue.Get()
	if quit {
		return false
	}
	defer d.queue.Done(key)

	d.processWorkItem(serverCtx, key)

	return true
}

func (d *DynamicEncryptionConfigContent) processWorkItem(serverCtx context.Context, workqueueKey interface{}) {
	var (
		updatedEffectiveConfig  bool
		err                     error
		encryptionConfiguration *encryptionconfig.EncryptionConfiguration
		configChanged           bool
	)

	// get context to close the new transformers (on error cases and on the next reload)
	// serverCtx is attached to the API server's lifecycle so we will always close transformers on shut down
	ctx, closeTransformers := context.WithCancel(serverCtx)

	defer func() {
		// TODO can work queue metrics help here?

		if !updatedEffectiveConfig {
			// avoid leaking if we're not using the newly constructed transformers (due to an error or them not being changed)
			closeTransformers()
		}

		if updatedEffectiveConfig && err == nil {
			metrics.RecordEncryptionConfigAutomaticReloadSuccess(d.apiServerID)
		}

		if err != nil {
			metrics.RecordEncryptionConfigAutomaticReloadFailure(d.apiServerID)
			utilruntime.HandleError(fmt.Errorf("error processing encryption config file %s: %v", d.filePath, err))
			// add dummy item back to the queue to trigger file content processing.
			d.queue.AddRateLimited(workqueueKey)
		}
	}()

	encryptionConfiguration, configChanged, err = d.processEncryptionConfig(ctx)
	if err != nil {
		return
	}
	if !configChanged {
		return
	}

	if len(encryptionConfiguration.HealthChecks) != 1 {
		err = fmt.Errorf("unexpected number of healthz checks: %d. Should have only one", len(encryptionConfiguration.HealthChecks))
		return
	}
	// get healthz checks for all new KMS plugins.
	if err = d.validateNewTransformersHealth(ctx, encryptionConfiguration.HealthChecks[0], encryptionConfiguration.KMSCloseGracePeriod); err != nil {
		return
	}

	// update transformers.
	// when reload=true there must always be one healthz check.
	d.dynamicTransformers.Set(
		encryptionConfiguration.Transformers,
		closeTransformers,
		encryptionConfiguration.HealthChecks[0],
		encryptionConfiguration.KMSCloseGracePeriod,
	)

	// update local copy of recent config content once update is successful.
	d.lastLoadedEncryptionConfigHash = encryptionConfiguration.EncryptionFileContentHash
	klog.V(2).InfoS("Loaded new kms encryption config content", "name", d.name)

	updatedEffectiveConfig = true
}

// loadEncryptionConfig processes the next set of content from the file.
func (d *DynamicEncryptionConfigContent) processEncryptionConfig(ctx context.Context) (
	_ *encryptionconfig.EncryptionConfiguration,
	configChanged bool,
	_ error,
) {
	contentHash, err := d.getEncryptionConfigHash(ctx, d.filePath)
	if err != nil {
		return nil, false, err
	}

	// check if encryptionConfig is different from the current. Do nothing if they are the same.
	if contentHash == d.lastLoadedEncryptionConfigHash {
		klog.V(4).InfoS("Encryption config has not changed (before load)", "name", d.name)
		return nil, false, nil
	}

	// this code path will only execute if reload=true. So passing true explicitly.
	encryptionConfiguration, err := d.loadEncryptionConfig(ctx, d.filePath, true, d.apiServerID)
	if err != nil {
		return nil, false, err
	}

	// check if encryptionConfig is different from the current (again to avoid TOCTOU). Do nothing if they are the same.
	if encryptionConfiguration.EncryptionFileContentHash == d.lastLoadedEncryptionConfigHash {
		klog.V(4).InfoS("Encryption config has not changed (after load)", "name", d.name)
		return nil, false, nil
	}

	return encryptionConfiguration, true, nil
}

// minKMSPluginCloseGracePeriod can be lowered in unit tests to make the health check poll faster
var minKMSPluginCloseGracePeriod = 10 * time.Second

func (d *DynamicEncryptionConfigContent) validateNewTransformersHealth(
	ctx context.Context,
	kmsPluginHealthzCheck healthz.HealthChecker,
	kmsPluginCloseGracePeriod time.Duration,
) error {
	// test if new transformers are healthy
	var healthCheckError error

	if kmsPluginCloseGracePeriod < minKMSPluginCloseGracePeriod {
		kmsPluginCloseGracePeriod = minKMSPluginCloseGracePeriod
	}

	// really make sure that the immediate check does not hang
	var cancel context.CancelFunc
	ctx, cancel = context.WithTimeout(ctx, kmsPluginCloseGracePeriod)
	defer cancel()

	pollErr := wait.PollImmediateWithContext(ctx, 100*time.Millisecond, kmsPluginCloseGracePeriod, func(ctx context.Context) (bool, error) {
		// create a fake http get request to health check endpoint
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, fmt.Sprintf("/healthz/%s", kmsPluginHealthzCheck.Name()), nil)
		if err != nil {
			return false, err
		}

		healthCheckError = kmsPluginHealthzCheck.Check(req)
		return healthCheckError == nil, nil
	})
	if pollErr != nil {
		return fmt.Errorf("health check for new transformers failed, polling error %v: %w", pollErr, healthCheckError)
	}
	klog.V(2).InfoS("Health check succeeded")
	return nil
}
