/*
Copyright 2019 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 builder

import (
	"errors"
	"net/http"
	"net/url"
	"regexp"
	"strings"

	"github.com/go-logr/logr"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/client-go/rest"
	"k8s.io/klog/v2"

	"sigs.k8s.io/controller-runtime/pkg/client/apiutil"
	"sigs.k8s.io/controller-runtime/pkg/manager"
	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
	"sigs.k8s.io/controller-runtime/pkg/webhook/conversion"
)

// WebhookBuilder builds a Webhook.
type WebhookBuilder struct {
	apiType                   runtime.Object
	customDefaulter           admission.CustomDefaulter
	customDefaulterOpts       []admission.DefaulterOption
	customValidator           admission.CustomValidator
	customPath                string
	customValidatorCustomPath string
	customDefaulterCustomPath string
	gvk                       schema.GroupVersionKind
	mgr                       manager.Manager
	config                    *rest.Config
	recoverPanic              *bool
	logConstructor            func(base logr.Logger, req *admission.Request) logr.Logger
	err                       error
}

// WebhookManagedBy returns a new webhook builder.
func WebhookManagedBy(m manager.Manager) *WebhookBuilder {
	return &WebhookBuilder{mgr: m}
}

// TODO(droot): update the GoDoc for conversion.

// For takes a runtime.Object which should be a CR.
// If the given object implements the admission.Defaulter interface, a MutatingWebhook will be wired for this type.
// If the given object implements the admission.Validator interface, a ValidatingWebhook will be wired for this type.
func (blder *WebhookBuilder) For(apiType runtime.Object) *WebhookBuilder {
	if blder.apiType != nil {
		blder.err = errors.New("For(...) should only be called once, could not assign multiple objects for webhook registration")
	}
	blder.apiType = apiType
	return blder
}

// WithDefaulter takes an admission.CustomDefaulter interface, a MutatingWebhook with the provided opts (admission.DefaulterOption)
// will be wired for this type.
func (blder *WebhookBuilder) WithDefaulter(defaulter admission.CustomDefaulter, opts ...admission.DefaulterOption) *WebhookBuilder {
	blder.customDefaulter = defaulter
	blder.customDefaulterOpts = opts
	return blder
}

// WithValidator takes a admission.CustomValidator interface, a ValidatingWebhook will be wired for this type.
func (blder *WebhookBuilder) WithValidator(validator admission.CustomValidator) *WebhookBuilder {
	blder.customValidator = validator
	return blder
}

// WithLogConstructor overrides the webhook's LogConstructor.
func (blder *WebhookBuilder) WithLogConstructor(logConstructor func(base logr.Logger, req *admission.Request) logr.Logger) *WebhookBuilder {
	blder.logConstructor = logConstructor
	return blder
}

// RecoverPanic indicates whether panics caused by the webhook should be recovered.
// Defaults to true.
func (blder *WebhookBuilder) RecoverPanic(recoverPanic bool) *WebhookBuilder {
	blder.recoverPanic = &recoverPanic
	return blder
}

// WithCustomPath overrides the webhook's default path by the customPath
// Deprecated: WithCustomPath should not be used anymore.
// Please use WithValidatorCustomPath or WithDefaulterCustomPath instead.
func (blder *WebhookBuilder) WithCustomPath(customPath string) *WebhookBuilder {
	blder.customPath = customPath
	return blder
}

// WithValidatorCustomPath overrides the path of the Validator.
func (blder *WebhookBuilder) WithValidatorCustomPath(customPath string) *WebhookBuilder {
	blder.customValidatorCustomPath = customPath
	return blder
}

// WithDefaulterCustomPath overrides the path of the Defaulter.
func (blder *WebhookBuilder) WithDefaulterCustomPath(customPath string) *WebhookBuilder {
	blder.customDefaulterCustomPath = customPath
	return blder
}

// Complete builds the webhook.
func (blder *WebhookBuilder) Complete() error {
	// Set the Config
	blder.loadRestConfig()

	// Configure the default LogConstructor
	blder.setLogConstructor()

	// Set the Webhook if needed
	return blder.registerWebhooks()
}

func (blder *WebhookBuilder) loadRestConfig() {
	if blder.config == nil {
		blder.config = blder.mgr.GetConfig()
	}
}

func (blder *WebhookBuilder) setLogConstructor() {
	if blder.logConstructor == nil {
		blder.logConstructor = func(base logr.Logger, req *admission.Request) logr.Logger {
			log := base.WithValues(
				"webhookGroup", blder.gvk.Group,
				"webhookKind", blder.gvk.Kind,
			)
			if req != nil {
				return log.WithValues(
					blder.gvk.Kind, klog.KRef(req.Namespace, req.Name),
					"namespace", req.Namespace, "name", req.Name,
					"resource", req.Resource, "user", req.UserInfo.Username,
					"requestID", req.UID,
				)
			}
			return log
		}
	}
}

func (blder *WebhookBuilder) isThereCustomPathConflict() bool {
	return (blder.customPath != "" && blder.customDefaulter != nil && blder.customValidator != nil) || (blder.customPath != "" && blder.customDefaulterCustomPath != "") || (blder.customPath != "" && blder.customValidatorCustomPath != "")
}

func (blder *WebhookBuilder) registerWebhooks() error {
	typ, err := blder.getType()
	if err != nil {
		return err
	}

	blder.gvk, err = apiutil.GVKForObject(typ, blder.mgr.GetScheme())
	if err != nil {
		return err
	}

	if blder.isThereCustomPathConflict() {
		return errors.New("only one of CustomDefaulter or CustomValidator should be set when using WithCustomPath. Otherwise, WithDefaulterCustomPath() and WithValidatorCustomPath() should be used")
	}
	if blder.customPath != "" {
		// isThereCustomPathConflict() already checks for potential conflicts.
		// Since we are sure that only one of customDefaulter or customValidator will be used,
		// we can set both customDefaulterCustomPath and validatingCustomPath.
		blder.customDefaulterCustomPath = blder.customPath
		blder.customValidatorCustomPath = blder.customPath
	}

	// Register webhook(s) for type
	err = blder.registerDefaultingWebhook()
	if err != nil {
		return err
	}

	err = blder.registerValidatingWebhook()
	if err != nil {
		return err
	}

	err = blder.registerConversionWebhook()
	if err != nil {
		return err
	}
	return blder.err
}

// registerDefaultingWebhook registers a defaulting webhook if necessary.
func (blder *WebhookBuilder) registerDefaultingWebhook() error {
	mwh := blder.getDefaultingWebhook()
	if mwh != nil {
		mwh.LogConstructor = blder.logConstructor
		path := generateMutatePath(blder.gvk)
		if blder.customDefaulterCustomPath != "" {
			generatedCustomPath, err := generateCustomPath(blder.customDefaulterCustomPath)
			if err != nil {
				return err
			}
			path = generatedCustomPath
		}

		// Checking if the path is already registered.
		// If so, just skip it.
		if !blder.isAlreadyHandled(path) {
			log.Info("Registering a mutating webhook",
				"GVK", blder.gvk,
				"path", path)
			blder.mgr.GetWebhookServer().Register(path, mwh)
		}
	}

	return nil
}

func (blder *WebhookBuilder) getDefaultingWebhook() *admission.Webhook {
	if defaulter := blder.customDefaulter; defaulter != nil {
		w := admission.WithCustomDefaulter(blder.mgr.GetScheme(), blder.apiType, defaulter, blder.customDefaulterOpts...)
		if blder.recoverPanic != nil {
			w = w.WithRecoverPanic(*blder.recoverPanic)
		}
		return w
	}
	return nil
}

// registerValidatingWebhook registers a validating webhook if necessary.
func (blder *WebhookBuilder) registerValidatingWebhook() error {
	vwh := blder.getValidatingWebhook()
	if vwh != nil {
		vwh.LogConstructor = blder.logConstructor
		path := generateValidatePath(blder.gvk)
		if blder.customValidatorCustomPath != "" {
			generatedCustomPath, err := generateCustomPath(blder.customValidatorCustomPath)
			if err != nil {
				return err
			}
			path = generatedCustomPath
		}

		// Checking if the path is already registered.
		// If so, just skip it.
		if !blder.isAlreadyHandled(path) {
			log.Info("Registering a validating webhook",
				"GVK", blder.gvk,
				"path", path)
			blder.mgr.GetWebhookServer().Register(path, vwh)
		}
	}

	return nil
}

func (blder *WebhookBuilder) getValidatingWebhook() *admission.Webhook {
	if validator := blder.customValidator; validator != nil {
		w := admission.WithCustomValidator(blder.mgr.GetScheme(), blder.apiType, validator)
		if blder.recoverPanic != nil {
			w = w.WithRecoverPanic(*blder.recoverPanic)
		}
		return w
	}
	return nil
}

func (blder *WebhookBuilder) registerConversionWebhook() error {
	ok, err := conversion.IsConvertible(blder.mgr.GetScheme(), blder.apiType)
	if err != nil {
		log.Error(err, "conversion check failed", "GVK", blder.gvk)
		return err
	}
	if ok {
		if !blder.isAlreadyHandled("/convert") {
			blder.mgr.GetWebhookServer().Register("/convert", conversion.NewWebhookHandler(blder.mgr.GetScheme()))
		}
		log.Info("Conversion webhook enabled", "GVK", blder.gvk)
	}

	return nil
}

func (blder *WebhookBuilder) getType() (runtime.Object, error) {
	if blder.apiType != nil {
		return blder.apiType, nil
	}
	return nil, errors.New("For() must be called with a valid object")
}

func (blder *WebhookBuilder) isAlreadyHandled(path string) bool {
	if blder.mgr.GetWebhookServer().WebhookMux() == nil {
		return false
	}
	h, p := blder.mgr.GetWebhookServer().WebhookMux().Handler(&http.Request{URL: &url.URL{Path: path}})
	if p == path && h != nil {
		return true
	}
	return false
}

func generateMutatePath(gvk schema.GroupVersionKind) string {
	return "/mutate-" + strings.ReplaceAll(gvk.Group, ".", "-") + "-" +
		gvk.Version + "-" + strings.ToLower(gvk.Kind)
}

func generateValidatePath(gvk schema.GroupVersionKind) string {
	return "/validate-" + strings.ReplaceAll(gvk.Group, ".", "-") + "-" +
		gvk.Version + "-" + strings.ToLower(gvk.Kind)
}

const webhookPathStringValidation = `^((/[a-zA-Z0-9-_]+)+|/)$`

var validWebhookPathRegex = regexp.MustCompile(webhookPathStringValidation)

func generateCustomPath(customPath string) (string, error) {
	if !validWebhookPathRegex.MatchString(customPath) {
		return "", errors.New("customPath \"" + customPath + "\" does not match this regex: " + webhookPathStringValidation)
	}
	return customPath, nil
}
