/*
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 validation validates EncryptionConfiguration.
package validation

import (
	"encoding/base64"
	"fmt"
	"net/url"
	"strings"

	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apimachinery/pkg/util/validation/field"
	"k8s.io/apiserver/pkg/apis/config"
)

const (
	moreThanOneElementErr          = "more than one provider specified in a single element, should split into different list elements"
	keyLenErrFmt                   = "secret is not of the expected length, got %d, expected one of %v"
	unsupportedSchemeErrFmt        = "unsupported scheme %q for KMS provider, only unix is supported"
	unsupportedKMSAPIVersionErrFmt = "unsupported apiVersion %s for KMS provider, only v1 and v2 are supported"
	atLeastOneRequiredErrFmt       = "at least one %s is required"
	invalidURLErrFmt               = "invalid endpoint for kms provider, error: %v"
	mandatoryFieldErrFmt           = "%s is a mandatory field for a %s"
	base64EncodingErr              = "secrets must be base64 encoded"
	zeroOrNegativeErrFmt           = "%s should be a positive value"
	nonZeroErrFmt                  = "%s should be a positive value, or negative to disable"
	encryptionConfigNilErr         = "EncryptionConfiguration can't be nil"
	invalidKMSConfigNameErrFmt     = "invalid KMS provider name %s, must not contain ':'"
	duplicateKMSConfigNameErrFmt   = "duplicate KMS provider name %s, names must be unique"
	eventsGroupErr                 = "'*.events.k8s.io' objects are stored using the 'events' API group in etcd. Use 'events' instead in the config file"
	extensionsGroupErr             = "'extensions' group has been removed and cannot be used for encryption"
	starResourceErr                = "use '*.' to encrypt all the resources from core API group or *.* to encrypt all resources"
	overlapErr                     = "using overlapping resources such as 'secrets' and '*.' in the same resource list is not allowed as they will be masked"
	nonRESTAPIResourceErr          = "resources which do not have REST API/s cannot be encrypted"
	resourceNameErr                = "resource name should not contain capital letters"
	resourceAcrossGroupErr         = "encrypting the same resource across groups is not supported"
	duplicateResourceErr           = "the same resource cannot be specified multiple times"
)

var (
	// See https://golang.org/pkg/crypto/aes/#NewCipher for details on supported key sizes for AES.
	aesKeySizes = []int{16, 24, 32}

	// See https://godoc.org/golang.org/x/crypto/nacl/secretbox#Open for details on the supported key sizes for Secretbox.
	secretBoxKeySizes = []int{32}

	root = field.NewPath("resources")
)

// ValidateEncryptionConfiguration validates a v1.EncryptionConfiguration.
func ValidateEncryptionConfiguration(c *config.EncryptionConfiguration, reload bool) field.ErrorList {
	allErrs := field.ErrorList{}

	if c == nil {
		allErrs = append(allErrs, field.Required(root, encryptionConfigNilErr))
		return allErrs
	}

	if len(c.Resources) == 0 {
		allErrs = append(allErrs, field.Required(root, fmt.Sprintf(atLeastOneRequiredErrFmt, root)))
		return allErrs
	}

	// kmsProviderNames is used to track config names to ensure they are unique.
	kmsProviderNames := sets.NewString()
	for i, conf := range c.Resources {
		r := root.Index(i).Child("resources")
		p := root.Index(i).Child("providers")

		if len(conf.Resources) == 0 {
			allErrs = append(allErrs, field.Required(r, fmt.Sprintf(atLeastOneRequiredErrFmt, r)))
		}

		allErrs = append(allErrs, validateResourceOverlap(conf.Resources, r)...)
		allErrs = append(allErrs, validateResourceNames(conf.Resources, r)...)

		if len(conf.Providers) == 0 {
			allErrs = append(allErrs, field.Required(p, fmt.Sprintf(atLeastOneRequiredErrFmt, p)))
		}

		for j, provider := range conf.Providers {
			path := p.Index(j)
			allErrs = append(allErrs, validateSingleProvider(provider, path)...)

			switch {
			case provider.KMS != nil:
				allErrs = append(allErrs, validateKMSConfiguration(provider.KMS, path.Child("kms"), kmsProviderNames, reload)...)
				kmsProviderNames.Insert(provider.KMS.Name)
			case provider.AESGCM != nil:
				allErrs = append(allErrs, validateKeys(provider.AESGCM.Keys, path.Child("aesgcm").Child("keys"), aesKeySizes)...)
			case provider.AESCBC != nil:
				allErrs = append(allErrs, validateKeys(provider.AESCBC.Keys, path.Child("aescbc").Child("keys"), aesKeySizes)...)
			case provider.Secretbox != nil:
				allErrs = append(allErrs, validateKeys(provider.Secretbox.Keys, path.Child("secretbox").Child("keys"), secretBoxKeySizes)...)
			}
		}
	}

	return allErrs
}

var anyGroupAnyResource = schema.GroupResource{
	Group:    "*",
	Resource: "*",
}

func validateResourceOverlap(resources []string, fieldPath *field.Path) field.ErrorList {
	if len(resources) < 2 { // cannot have overlap with a single resource
		return nil
	}

	var allErrs field.ErrorList

	r := make([]schema.GroupResource, 0, len(resources))
	for _, resource := range resources {
		r = append(r, schema.ParseGroupResource(resource))
	}

	var hasOverlap, hasDuplicate bool

	for i, r1 := range r {
		for j, r2 := range r {
			if i == j {
				continue
			}

			if r1 == r2 && !hasDuplicate {
				hasDuplicate = true
				continue
			}

			if hasOverlap {
				continue
			}

			if r1 == anyGroupAnyResource {
				hasOverlap = true
				continue
			}

			if r1.Group != r2.Group {
				continue
			}

			if r1.Resource == "*" || r2.Resource == "*" {
				hasOverlap = true
				continue
			}
		}
	}

	if hasDuplicate {
		allErrs = append(
			allErrs,
			field.Invalid(
				fieldPath,
				resources,
				duplicateResourceErr,
			),
		)
	}

	if hasOverlap {
		allErrs = append(
			allErrs,
			field.Invalid(
				fieldPath,
				resources,
				overlapErr,
			),
		)
	}

	return allErrs
}

func validateResourceNames(resources []string, fieldPath *field.Path) field.ErrorList {
	var allErrs field.ErrorList

	for j, res := range resources {
		jj := fieldPath.Index(j)

		// check if resource name has capital letters
		if hasCapital(res) {
			allErrs = append(
				allErrs,
				field.Invalid(
					jj,
					resources[j],
					resourceNameErr,
				),
			)
			continue
		}

		// check if resource is '*'
		if res == "*" {
			allErrs = append(
				allErrs,
				field.Invalid(
					jj,
					resources[j],
					starResourceErr,
				),
			)
			continue
		}

		// check if resource is:
		// 'apiserveripinfo' OR
		// 'serviceipallocations' OR
		// 'servicenodeportallocations' OR
		if res == "apiserveripinfo" ||
			res == "serviceipallocations" ||
			res == "servicenodeportallocations" {
			allErrs = append(
				allErrs,
				field.Invalid(
					jj,
					resources[j],
					nonRESTAPIResourceErr,
				),
			)
			continue
		}

		// check if group is 'events.k8s.io'
		gr := schema.ParseGroupResource(res)
		if gr.Group == "events.k8s.io" {
			allErrs = append(
				allErrs,
				field.Invalid(
					jj,
					resources[j],
					eventsGroupErr,
				),
			)
			continue
		}

		// check if group is 'extensions'
		if gr.Group == "extensions" {
			allErrs = append(
				allErrs,
				field.Invalid(
					jj,
					resources[j],
					extensionsGroupErr,
				),
			)
			continue
		}

		// disallow resource.* as encrypting the same resource across groups does not make sense
		if gr.Group == "*" && gr.Resource != "*" {
			allErrs = append(
				allErrs,
				field.Invalid(
					jj,
					resources[j],
					resourceAcrossGroupErr,
				),
			)
			continue
		}
	}

	return allErrs
}

func validateSingleProvider(provider config.ProviderConfiguration, fieldPath *field.Path) field.ErrorList {
	allErrs := field.ErrorList{}
	found := 0

	if provider.KMS != nil {
		found++
	}
	if provider.AESGCM != nil {
		found++
	}
	if provider.AESCBC != nil {
		found++
	}
	if provider.Secretbox != nil {
		found++
	}
	if provider.Identity != nil {
		found++
	}

	if found == 0 {
		return append(allErrs, field.Invalid(fieldPath, provider, "provider does not contain any of the expected providers: KMS, AESGCM, AESCBC, Secretbox, Identity"))
	}

	if found > 1 {
		return append(allErrs, field.Invalid(fieldPath, provider, moreThanOneElementErr))
	}

	return allErrs
}

func validateKeys(keys []config.Key, fieldPath *field.Path, expectedLen []int) field.ErrorList {
	allErrs := field.ErrorList{}

	if len(keys) == 0 {
		allErrs = append(allErrs, field.Required(fieldPath, fmt.Sprintf(atLeastOneRequiredErrFmt, "keys")))
		return allErrs
	}

	for i, key := range keys {
		allErrs = append(allErrs, validateKey(key, fieldPath.Index(i), expectedLen)...)
	}

	return allErrs
}

func validateKey(key config.Key, fieldPath *field.Path, expectedLen []int) field.ErrorList {
	allErrs := field.ErrorList{}

	if key.Name == "" {
		allErrs = append(allErrs, field.Required(fieldPath.Child("name"), fmt.Sprintf(mandatoryFieldErrFmt, "name", "key")))
	}

	if key.Secret == "" {
		allErrs = append(allErrs, field.Required(fieldPath.Child("secret"), fmt.Sprintf(mandatoryFieldErrFmt, "secret", "key")))
		return allErrs
	}

	secret, err := base64.StdEncoding.DecodeString(key.Secret)
	if err != nil {
		allErrs = append(allErrs, field.Invalid(fieldPath.Child("secret"), "REDACTED", base64EncodingErr))
		return allErrs
	}

	lenMatched := false
	for _, l := range expectedLen {
		if len(secret) == l {
			lenMatched = true
			break
		}
	}

	if !lenMatched {
		allErrs = append(allErrs, field.Invalid(fieldPath.Child("secret"), "REDACTED", fmt.Sprintf(keyLenErrFmt, len(secret), expectedLen)))
	}

	return allErrs
}

func validateKMSConfiguration(c *config.KMSConfiguration, fieldPath *field.Path, kmsProviderNames sets.String, reload bool) field.ErrorList {
	allErrs := field.ErrorList{}

	allErrs = append(allErrs, validateKMSConfigName(c, fieldPath.Child("name"), kmsProviderNames, reload)...)
	allErrs = append(allErrs, validateKMSTimeout(c, fieldPath.Child("timeout"))...)
	allErrs = append(allErrs, validateKMSEndpoint(c, fieldPath.Child("endpoint"))...)
	allErrs = append(allErrs, validateKMSCacheSize(c, fieldPath.Child("cachesize"))...)
	allErrs = append(allErrs, validateKMSAPIVersion(c, fieldPath.Child("apiVersion"))...)
	return allErrs
}

func validateKMSCacheSize(c *config.KMSConfiguration, fieldPath *field.Path) field.ErrorList {
	allErrs := field.ErrorList{}

	// In defaulting, we set the cache size to the default value only when API version is v1.
	// So, for v2 API version, we expect the cache size field to be nil.
	if c.APIVersion != "v1" && c.CacheSize != nil {
		allErrs = append(allErrs, field.Invalid(fieldPath, *c.CacheSize, "cachesize is not supported in v2"))
	}
	if c.APIVersion == "v1" && *c.CacheSize == 0 {
		allErrs = append(allErrs, field.Invalid(fieldPath, *c.CacheSize, fmt.Sprintf(nonZeroErrFmt, "cachesize")))
	}

	return allErrs
}

func validateKMSTimeout(c *config.KMSConfiguration, fieldPath *field.Path) field.ErrorList {
	allErrs := field.ErrorList{}
	if c.Timeout.Duration <= 0 {
		allErrs = append(allErrs, field.Invalid(fieldPath, c.Timeout, fmt.Sprintf(zeroOrNegativeErrFmt, "timeout")))
	}

	return allErrs
}

func validateKMSEndpoint(c *config.KMSConfiguration, fieldPath *field.Path) field.ErrorList {
	allErrs := field.ErrorList{}
	if len(c.Endpoint) == 0 {
		return append(allErrs, field.Invalid(fieldPath, "", fmt.Sprintf(mandatoryFieldErrFmt, "endpoint", "kms")))
	}

	u, err := url.Parse(c.Endpoint)
	if err != nil {
		return append(allErrs, field.Invalid(fieldPath, c.Endpoint, fmt.Sprintf(invalidURLErrFmt, err)))
	}

	if u.Scheme != "unix" {
		return append(allErrs, field.Invalid(fieldPath, c.Endpoint, fmt.Sprintf(unsupportedSchemeErrFmt, u.Scheme)))
	}

	return allErrs
}

func validateKMSAPIVersion(c *config.KMSConfiguration, fieldPath *field.Path) field.ErrorList {
	allErrs := field.ErrorList{}
	if c.APIVersion != "v1" && c.APIVersion != "v2" {
		allErrs = append(allErrs, field.Invalid(fieldPath, c.APIVersion, fmt.Sprintf(unsupportedKMSAPIVersionErrFmt, "apiVersion")))
	}

	return allErrs
}

func validateKMSConfigName(c *config.KMSConfiguration, fieldPath *field.Path, kmsProviderNames sets.String, reload bool) field.ErrorList {
	allErrs := field.ErrorList{}
	if c.Name == "" {
		allErrs = append(allErrs, field.Required(fieldPath, fmt.Sprintf(mandatoryFieldErrFmt, "name", "provider")))
	}

	// kms v2 providers are not allowed to have a ":" in their name
	if c.APIVersion != "v1" && strings.Contains(c.Name, ":") {
		allErrs = append(allErrs, field.Invalid(fieldPath, c.Name, fmt.Sprintf(invalidKMSConfigNameErrFmt, c.Name)))
	}

	// kms v2 providers name must always be unique across all kms providers (v1 and v2)
	// kms v1 provider names must be unique across all kms providers (v1 and v2) when hot reloading of encryption configuration is enabled (reload=true)
	if reload || c.APIVersion != "v1" {
		if kmsProviderNames.Has(c.Name) {
			allErrs = append(allErrs, field.Invalid(fieldPath, c.Name, fmt.Sprintf(duplicateKMSConfigNameErrFmt, c.Name)))
		}
	}

	return allErrs
}

func hasCapital(input string) bool {
	return strings.ToLower(input) != input
}
