/*
Copyright 2020 The KubeSphere 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.
*/

// NOTE: This file is copied from k8s.io/kubernetes/plugin/pkg/auth/authorizer/rbac.

package authorizerfactory

import (
	"bytes"
	"context"
	"fmt"
	"github.com/open-policy-agent/opa/rego"
	"k8s.io/apiserver/pkg/authentication/serviceaccount"
	iamv1alpha2 "kubesphere.io/kubesphere/pkg/apis/iam/v1alpha2"
	"kubesphere.io/kubesphere/pkg/apiserver/authorization/authorizer"
	"kubesphere.io/kubesphere/pkg/apiserver/request"
	"kubesphere.io/kubesphere/pkg/models/iam/am"
	"kubesphere.io/kubesphere/pkg/utils/sliceutil"

	"k8s.io/klog"

	rbacv1 "k8s.io/api/rbac/v1"
	utilerrors "k8s.io/apimachinery/pkg/util/errors"
	"k8s.io/apiserver/pkg/authentication/user"
	rbacv1helpers "kubesphere.io/kubesphere/pkg/api/rbac/v1"
)

const (
	defaultRegoQuery    = "data.authz.allow"
	defaultRegoFileName = "authz.rego"
)

type RBACAuthorizer struct {
	am am.AccessManagementInterface
}

// authorizingVisitor short-circuits once allowed, and collects any resolution errors encountered
type authorizingVisitor struct {
	requestAttributes authorizer.Attributes

	allowed bool
	reason  string
	errors  []error
}

func (v *authorizingVisitor) visit(source fmt.Stringer, regoPolicy string, rule *rbacv1.PolicyRule, err error) bool {
	if regoPolicy != "" && regoPolicyAllows(v.requestAttributes, regoPolicy) {
		v.allowed = true
		v.reason = fmt.Sprintf("RBAC: allowed by %s", source.String())
		return false
	}
	if rule != nil && ruleAllows(v.requestAttributes, rule) {
		v.allowed = true
		v.reason = fmt.Sprintf("RBAC: allowed by %s", source.String())
		return false
	}
	if err != nil {
		v.errors = append(v.errors, err)
	}
	return true
}

type ruleAccumulator struct {
	rules  []rbacv1.PolicyRule
	errors []error
}

func (r *ruleAccumulator) visit(_ fmt.Stringer, _ string, rule *rbacv1.PolicyRule, err error) bool {
	if rule != nil {
		r.rules = append(r.rules, *rule)
	}
	if err != nil {
		r.errors = append(r.errors, err)
	}
	return true
}

func (r *RBACAuthorizer) Authorize(requestAttributes authorizer.Attributes) (authorizer.Decision, string, error) {
	ruleCheckingVisitor := &authorizingVisitor{requestAttributes: requestAttributes}

	r.visitRulesFor(requestAttributes, ruleCheckingVisitor.visit)

	if ruleCheckingVisitor.allowed {
		return authorizer.DecisionAllow, ruleCheckingVisitor.reason, nil
	}

	// Build a detailed log of the denial.
	// Make the whole block conditional so we don't do a lot of string-building we won't use.
	if klog.V(4) {
		var operation string
		if requestAttributes.IsResourceRequest() {
			b := &bytes.Buffer{}
			b.WriteString(`"`)
			b.WriteString(requestAttributes.GetVerb())
			b.WriteString(`" resource "`)
			b.WriteString(requestAttributes.GetResource())
			if len(requestAttributes.GetAPIGroup()) > 0 {
				b.WriteString(`.`)
				b.WriteString(requestAttributes.GetAPIGroup())
			}
			if len(requestAttributes.GetSubresource()) > 0 {
				b.WriteString(`/`)
				b.WriteString(requestAttributes.GetSubresource())
			}
			b.WriteString(`"`)
			if len(requestAttributes.GetName()) > 0 {
				b.WriteString(` named "`)
				b.WriteString(requestAttributes.GetName())
				b.WriteString(`"`)
			}
			operation = b.String()
		} else {
			operation = fmt.Sprintf("%q nonResourceURL %q", requestAttributes.GetVerb(), requestAttributes.GetPath())
		}

		var scope string
		if ns := requestAttributes.GetNamespace(); len(ns) > 0 {
			scope = fmt.Sprintf("in namespace %q", ns)
		} else if ws := requestAttributes.GetWorkspace(); len(ws) > 0 {
			scope = fmt.Sprintf("in workspace %q", ws)
		} else if requestAttributes.GetResourceScope() == request.ClusterScope {
			scope = "cluster scope"
		} else {
			scope = "global-wide"
		}

		klog.Infof("RBAC: no rules authorize user %q with groups %q to %s %s", requestAttributes.GetUser().GetName(), requestAttributes.GetUser().GetGroups(), operation, scope)
	}

	reason := ""
	if len(ruleCheckingVisitor.errors) > 0 {
		reason = fmt.Sprintf("RBAC: %v", utilerrors.NewAggregate(ruleCheckingVisitor.errors))
	}
	return authorizer.DecisionNoOpinion, reason, nil
}

func NewRBACAuthorizer(am am.AccessManagementInterface) *RBACAuthorizer {
	return &RBACAuthorizer{am: am}
}

func ruleAllows(requestAttributes authorizer.Attributes, rule *rbacv1.PolicyRule) bool {
	if requestAttributes.IsResourceRequest() {
		combinedResource := requestAttributes.GetResource()
		if len(requestAttributes.GetSubresource()) > 0 {
			combinedResource = requestAttributes.GetResource() + "/" + requestAttributes.GetSubresource()
		}

		return rbacv1helpers.VerbMatches(rule, requestAttributes.GetVerb()) &&
			rbacv1helpers.APIGroupMatches(rule, requestAttributes.GetAPIGroup()) &&
			rbacv1helpers.ResourceMatches(rule, combinedResource, requestAttributes.GetSubresource()) &&
			rbacv1helpers.ResourceNameMatches(rule, requestAttributes.GetName())
	}

	return rbacv1helpers.VerbMatches(rule, requestAttributes.GetVerb()) &&
		rbacv1helpers.NonResourceURLMatches(rule, requestAttributes.GetPath())
}

func regoPolicyAllows(requestAttributes authorizer.Attributes, regoPolicy string) bool {
	// Call the rego.New function to create an object that can be prepared or evaluated
	//  After constructing a new rego.Rego object you can call PrepareForEval() to obtain an executable query
	query, err := rego.New(rego.Query(defaultRegoQuery), rego.Module(defaultRegoFileName, regoPolicy)).PrepareForEval(context.Background())

	if err != nil {
		klog.Warningf("syntax error:%s, content: %s", err, regoPolicy)
		return false
	}

	// The policy decision is contained in the results returned by the Eval() call. You can inspect the decision and handle it accordingly.
	results, err := query.Eval(context.Background(), rego.EvalInput(requestAttributes))

	if err != nil {
		klog.Warningf("syntax error:%s, content: %s", err, regoPolicy)
		return false
	}

	if len(results) > 0 && results[0].Expressions[0].Value == true {
		return true
	}

	return false
}

func (r *RBACAuthorizer) rulesFor(requestAttributes authorizer.Attributes) ([]rbacv1.PolicyRule, error) {
	visitor := &ruleAccumulator{}
	r.visitRulesFor(requestAttributes, visitor.visit)
	return visitor.rules, utilerrors.NewAggregate(visitor.errors)
}

func (r *RBACAuthorizer) visitRulesFor(requestAttributes authorizer.Attributes, visitor func(source fmt.Stringer, regoPolicy string, rule *rbacv1.PolicyRule, err error) bool) {

	if globalRoleBindings, err := r.am.ListGlobalRoleBindings(""); err != nil {
		if !visitor(nil, "", nil, err) {
			return
		}
	} else {
		sourceDescriber := &globalRoleBindingDescriber{}
		for _, globalRoleBinding := range globalRoleBindings {
			subjectIndex, applies := appliesTo(requestAttributes.GetUser(), globalRoleBinding.Subjects, "")
			if !applies {
				continue
			}
			regoPolicy, rules, err := r.am.GetRoleReferenceRules(globalRoleBinding.RoleRef, "")
			if err != nil {
				visitor(nil, "", nil, err)
				continue
			}
			sourceDescriber.binding = globalRoleBinding
			sourceDescriber.subject = &globalRoleBinding.Subjects[subjectIndex]
			if !visitor(sourceDescriber, regoPolicy, nil, nil) {
				return
			}
			for i := range rules {
				if !visitor(sourceDescriber, "", &rules[i], nil) {
					return
				}
			}
		}

		if requestAttributes.GetResourceScope() == request.GlobalScope {
			return
		}
	}

	if requestAttributes.GetResourceScope() == request.WorkspaceScope ||
		requestAttributes.GetResourceScope() == request.NamespaceScope ||
		requestAttributes.GetResourceScope() == request.DevOpsScope {

		var workspace string
		var err error
		// all of resource under namespace and devops belong to workspace
		if requestAttributes.GetResourceScope() == request.NamespaceScope {
			if workspace, err = r.am.GetNamespaceControlledWorkspace(requestAttributes.GetNamespace()); err != nil {
				if !visitor(nil, "", nil, err) {
					return
				}
			}
		} else if requestAttributes.GetResourceScope() == request.DevOpsScope {
			if workspace, err = r.am.GetDevOpsControlledWorkspace(requestAttributes.GetDevOps()); err != nil {
				if !visitor(nil, "", nil, err) {
					return
				}
			}
		}

		if workspace == "" {
			workspace = requestAttributes.GetWorkspace()
		}

		if workspaceRoleBindings, err := r.am.ListWorkspaceRoleBindings("", workspace); err != nil {
			if !visitor(nil, "", nil, err) {
				return
			}
		} else {
			sourceDescriber := &workspaceRoleBindingDescriber{}
			for _, workspaceRoleBinding := range workspaceRoleBindings {
				subjectIndex, applies := appliesTo(requestAttributes.GetUser(), workspaceRoleBinding.Subjects, "")
				if !applies {
					continue
				}
				regoPolicy, rules, err := r.am.GetRoleReferenceRules(workspaceRoleBinding.RoleRef, "")
				if err != nil {
					visitor(nil, "", nil, err)
					continue
				}
				sourceDescriber.binding = workspaceRoleBinding
				sourceDescriber.subject = &workspaceRoleBinding.Subjects[subjectIndex]
				if !visitor(sourceDescriber, regoPolicy, nil, nil) {
					return
				}
				for i := range rules {
					if !visitor(sourceDescriber, "", &rules[i], nil) {
						return
					}
				}
			}
		}
	}

	if requestAttributes.GetResourceScope() == request.NamespaceScope ||
		requestAttributes.GetResourceScope() == request.DevOpsScope {

		namespace := requestAttributes.GetNamespace()
		// list devops role binding
		if requestAttributes.GetResourceScope() == request.DevOpsScope {
			if relatedNamespace, err := r.am.GetDevOpsRelatedNamespace(requestAttributes.GetDevOps()); err != nil {
				if !visitor(nil, "", nil, err) {
					return
				}
			} else {
				namespace = relatedNamespace
			}
		}

		if roleBindings, err := r.am.ListRoleBindings("", namespace); err != nil {
			if !visitor(nil, "", nil, err) {
				return
			}
		} else {
			sourceDescriber := &roleBindingDescriber{}
			for _, roleBinding := range roleBindings {
				subjectIndex, applies := appliesTo(requestAttributes.GetUser(), roleBinding.Subjects, namespace)
				if !applies {
					continue
				}
				regoPolicy, rules, err := r.am.GetRoleReferenceRules(roleBinding.RoleRef, namespace)
				if err != nil {
					visitor(nil, "", nil, err)
					continue
				}
				sourceDescriber.binding = roleBinding
				sourceDescriber.subject = &roleBinding.Subjects[subjectIndex]
				if !visitor(sourceDescriber, regoPolicy, nil, nil) {
					return
				}
				for i := range rules {
					if !visitor(sourceDescriber, "", &rules[i], nil) {
						return
					}
				}
			}
		}
	}

	if clusterRoleBindings, err := r.am.ListClusterRoleBindings(""); err != nil {
		if !visitor(nil, "", nil, err) {
			return
		}
	} else {
		sourceDescriber := &clusterRoleBindingDescriber{}
		for _, clusterRoleBinding := range clusterRoleBindings {
			subjectIndex, applies := appliesTo(requestAttributes.GetUser(), clusterRoleBinding.Subjects, "")
			if !applies {
				continue
			}
			regoPolicy, rules, err := r.am.GetRoleReferenceRules(clusterRoleBinding.RoleRef, "")
			if err != nil {
				visitor(nil, "", nil, err)
				continue
			}
			sourceDescriber.binding = clusterRoleBinding
			sourceDescriber.subject = &clusterRoleBinding.Subjects[subjectIndex]
			if !visitor(sourceDescriber, regoPolicy, nil, nil) {
				return
			}
			for i := range rules {
				if !visitor(sourceDescriber, "", &rules[i], nil) {
					return
				}
			}
		}
	}
}

// appliesTo returns whether any of the bindingSubjects applies to the specified subject,
// and if true, the index of the first subject that applies
func appliesTo(user user.Info, bindingSubjects []rbacv1.Subject, namespace string) (int, bool) {
	for i, bindingSubject := range bindingSubjects {
		if appliesToUser(user, bindingSubject, namespace) {
			return i, true
		}
	}
	return 0, false
}

func appliesToUser(user user.Info, subject rbacv1.Subject, namespace string) bool {
	switch subject.Kind {
	case rbacv1.UserKind:
		return user.GetName() == subject.Name

	case rbacv1.GroupKind:
		return sliceutil.HasString(user.GetGroups(), subject.Name)

	case rbacv1.ServiceAccountKind:
		// default the namespace to namespace we're working in if its available.  This allows rolebindings that reference
		// SAs in th local namespace to avoid having to qualify them.
		saNamespace := namespace
		if len(subject.Namespace) > 0 {
			saNamespace = subject.Namespace
		}
		if len(saNamespace) == 0 {
			return false
		}
		// use a more efficient comparison for RBAC checking
		return serviceaccount.MatchesUsername(saNamespace, subject.Name, user.GetName())
	default:
		return false
	}
}

type globalRoleBindingDescriber struct {
	binding *iamv1alpha2.GlobalRoleBinding
	subject *rbacv1.Subject
}

func (d *globalRoleBindingDescriber) String() string {
	return fmt.Sprintf("GlobalRoleBinding %q of %s %q to %s",
		d.binding.Name,
		d.binding.RoleRef.Kind,
		d.binding.RoleRef.Name,
		describeSubject(d.subject, ""),
	)
}

type clusterRoleBindingDescriber struct {
	binding *rbacv1.ClusterRoleBinding
	subject *rbacv1.Subject
}

func (d *clusterRoleBindingDescriber) String() string {
	return fmt.Sprintf("ClusterRoleBinding %q of %s %q to %s",
		d.binding.Name,
		d.binding.RoleRef.Kind,
		d.binding.RoleRef.Name,
		describeSubject(d.subject, ""),
	)
}

type workspaceRoleBindingDescriber struct {
	binding *iamv1alpha2.WorkspaceRoleBinding
	subject *rbacv1.Subject
}

func (d *workspaceRoleBindingDescriber) String() string {
	return fmt.Sprintf("GlobalRoleBinding %q of %s %q to %s",
		d.binding.Name,
		d.binding.RoleRef.Kind,
		d.binding.RoleRef.Name,
		describeSubject(d.subject, ""),
	)
}

type roleBindingDescriber struct {
	binding *rbacv1.RoleBinding
	subject *rbacv1.Subject
}

func (d *roleBindingDescriber) String() string {
	return fmt.Sprintf("RoleBinding %q of %s %q to %s",
		d.binding.Name+"/"+d.binding.Namespace,
		d.binding.RoleRef.Kind,
		d.binding.RoleRef.Name,
		describeSubject(d.subject, d.binding.Namespace),
	)
}

func describeSubject(s *rbacv1.Subject, bindingNamespace string) string {
	switch s.Kind {
	case rbacv1.ServiceAccountKind:
		if len(s.Namespace) > 0 {
			return fmt.Sprintf("%s %q", s.Kind, s.Name+"/"+s.Namespace)
		}
		return fmt.Sprintf("%s %q", s.Kind, s.Name+"/"+bindingNamespace)
	default:
		return fmt.Sprintf("%s %q", s.Kind, s.Name)
	}
}