/*
Copyright 2018 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 webhook contains libraries for generating webhookconfig manifests
// from markers in Go source files.
//
// The markers take the form:
//
//  +kubebuilder:webhook:failurePolicy=<string>,groups=<[]string>,resources=<[]string>,verbs=<[]string>,versions=<[]string>,name=<string>,path=<string>,mutating=<bool>
package webhook

import (
	"fmt"
	"strings"

	admissionreg "k8s.io/api/admissionregistration/v1beta1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"

	"sigs.k8s.io/controller-tools/pkg/genall"
	"sigs.k8s.io/controller-tools/pkg/markers"
)

var (
	// ConfigDefinition s a marker for defining Webhook manifests.
	// Call ToWebhook on the value to get a Kubernetes Webhook.
	ConfigDefinition = markers.Must(markers.MakeDefinition("kubebuilder:webhook", markers.DescribesPackage, Config{}))
)

// +controllertools:marker:generateHelp:category=Webhook

// Config specifies how a webhook should be served.
//
// It specifies only the details that are intrinsic to the application serving
// it (e.g. the resources it can handle, or the path it serves on).
type Config struct {
	// Mutating marks this as a mutating webhook (it's validating only if false)
	//
	// Mutating webhooks are allowed to change the object in their response,
	// and are called *after* all validating webhooks.  Mutating webhooks may
	// choose to reject an object, similarly to a validating webhook.
	Mutating bool
	// FailurePolicy specifies what should happen if the API server cannot reach the webhook.
	//
	// It may be either "ignore" (to skip the webhook and continue on) or "fail" (to reject
	// the object in question).
	FailurePolicy string

	// Groups specifies the API groups that this webhook receives requests for.
	Groups []string
	// Resources specifies the API resources that this webhook receives requests for.
	Resources []string
	// Verbs specifies the Kubernetes API verbs that this webhook receives requests for.
	//
	// Only modification-like verbs may be specified.
	// May be "create", "update", "delete", "connect", or "*" (for all).
	Verbs []string
	// Versions specifies the API versions that this webhook receives requests for.
	Versions []string

	// Name indicates the name of this webhook configuration.
	Name string
	// Path specifies that path that the API server should connect to this webhook on.
	Path string
}

// verbToAPIVariant converts a marker's verb to the proper value for the API.
// Unrecognized verbs are passed through.
func verbToAPIVariant(verbRaw string) admissionreg.OperationType {
	switch strings.ToLower(verbRaw) {
	case strings.ToLower(string(admissionreg.Create)):
		return admissionreg.Create
	case strings.ToLower(string(admissionreg.Update)):
		return admissionreg.Update
	case strings.ToLower(string(admissionreg.Delete)):
		return admissionreg.Delete
	case strings.ToLower(string(admissionreg.Connect)):
		return admissionreg.Connect
	case strings.ToLower(string(admissionreg.OperationAll)):
		return admissionreg.OperationAll
	default:
		return admissionreg.OperationType(verbRaw)
	}
}

// ToMutatingWebhook converts this rule to its Kubernetes API form.
func (c Config) ToMutatingWebhook() (admissionreg.MutatingWebhook, error) {
	if !c.Mutating {
		return admissionreg.MutatingWebhook{}, fmt.Errorf("%s is a validating webhook", c.Name)
	}

	return admissionreg.MutatingWebhook{
		Name:          c.Name,
		Rules:         c.rules(),
		FailurePolicy: c.failurePolicy(),
		ClientConfig:  c.clientConfig(),
	}, nil
}

// ToValidatingWebhook converts this rule to its Kubernetes API form.
func (c Config) ToValidatingWebhook() (admissionreg.ValidatingWebhook, error) {
	if c.Mutating {
		return admissionreg.ValidatingWebhook{}, fmt.Errorf("%s is a mutating webhook", c.Name)
	}

	return admissionreg.ValidatingWebhook{
		Name:          c.Name,
		Rules:         c.rules(),
		FailurePolicy: c.failurePolicy(),
		ClientConfig:  c.clientConfig(),
	}, nil
}

// rules returns the configuration of what operations on what
// resources/subresources a webhook should care about.
func (c Config) rules() []admissionreg.RuleWithOperations {
	whConfig := admissionreg.RuleWithOperations{
		Rule: admissionreg.Rule{
			APIGroups:   c.Groups,
			APIVersions: c.Versions,
			Resources:   c.Resources,
		},
		Operations: make([]admissionreg.OperationType, len(c.Verbs)),
	}

	for i, verbRaw := range c.Verbs {
		whConfig.Operations[i] = verbToAPIVariant(verbRaw)
	}

	// fix the group names, since letting people type "core" is nice
	for i, group := range whConfig.APIGroups {
		if group == "core" {
			whConfig.APIGroups[i] = ""
		}
	}

	return []admissionreg.RuleWithOperations{whConfig}
}

// failurePolicy converts the string value to the proper value for the API.
// Unrecognized values are passed through.
func (c Config) failurePolicy() *admissionreg.FailurePolicyType {
	var failurePolicy admissionreg.FailurePolicyType
	switch strings.ToLower(c.FailurePolicy) {
	case strings.ToLower(string(admissionreg.Ignore)):
		failurePolicy = admissionreg.Ignore
	case strings.ToLower(string(admissionreg.Fail)):
		failurePolicy = admissionreg.Fail
	default:
		failurePolicy = admissionreg.FailurePolicyType(c.FailurePolicy)
	}
	return &failurePolicy
}

// clientConfig returns the client config for a webhook.
func (c Config) clientConfig() admissionreg.WebhookClientConfig {
	path := c.Path
	return admissionreg.WebhookClientConfig{
		Service: &admissionreg.ServiceReference{
			Name:      "webhook-service",
			Namespace: "system",
			Path:      &path,
		},
		// OpenAPI marks the field as required before 1.13 because of a bug that got fixed in
		// https://github.com/kubernetes/api/commit/e7d9121e9ffd63cea0288b36a82bcc87b073bd1b
		// Put "\n" as an placeholder as a workaround til 1.13+ is almost everywhere.
		CABundle: []byte("\n"),
	}
}

// +controllertools:marker:generateHelp

// Generator generates (partial) {Mutating,Validating}WebhookConfiguration objects.
type Generator struct{}

func (Generator) RegisterMarkers(into *markers.Registry) error {
	if err := into.Register(ConfigDefinition); err != nil {
		return err
	}
	into.AddHelp(ConfigDefinition, Config{}.Help())
	return nil
}

func (Generator) Generate(ctx *genall.GenerationContext) error {
	var mutatingCfgs []admissionreg.MutatingWebhook
	var validatingCfgs []admissionreg.ValidatingWebhook
	for _, root := range ctx.Roots {
		markerSet, err := markers.PackageMarkers(ctx.Collector, root)
		if err != nil {
			root.AddError(err)
		}

		for _, cfg := range markerSet[ConfigDefinition.Name] {
			cfg := cfg.(Config)
			if cfg.Mutating {
				w, _ := cfg.ToMutatingWebhook()
				mutatingCfgs = append(mutatingCfgs, w)
			} else {
				w, _ := cfg.ToValidatingWebhook()
				validatingCfgs = append(validatingCfgs, w)
			}
		}
	}

	var objs []interface{}
	if len(mutatingCfgs) > 0 {
		objs = append(objs, &admissionreg.MutatingWebhookConfiguration{
			TypeMeta: metav1.TypeMeta{
				Kind:       "MutatingWebhookConfiguration",
				APIVersion: admissionreg.SchemeGroupVersion.String(),
			},
			ObjectMeta: metav1.ObjectMeta{
				Name: "mutating-webhook-configuration",
			},
			Webhooks: mutatingCfgs,
		})
	}

	if len(validatingCfgs) > 0 {
		objs = append(objs, &admissionreg.ValidatingWebhookConfiguration{
			TypeMeta: metav1.TypeMeta{
				Kind:       "ValidatingWebhookConfiguration",
				APIVersion: admissionreg.SchemeGroupVersion.String(),
			},
			ObjectMeta: metav1.ObjectMeta{
				Name: "validating-webhook-configuration",
			},
			Webhooks: validatingCfgs,
		})

	}

	if err := ctx.WriteYAML("manifests.yaml", objs...); err != nil {
		return err
	}

	return nil
}
