/*
Copyright 2017 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 reconciliation

import (
	"fmt"
	"reflect"

	"k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/kubernetes/pkg/api"
	"k8s.io/kubernetes/pkg/apis/rbac"
	"k8s.io/kubernetes/pkg/registry/rbac/validation"
)

type ReconcileOperation string

var (
	ReconcileCreate   ReconcileOperation = "create"
	ReconcileUpdate   ReconcileOperation = "update"
	ReconcileRecreate ReconcileOperation = "recreate"
	ReconcileNone     ReconcileOperation = "none"
)

type RuleOwnerModifier interface {
	Get(namespace, name string) (RuleOwner, error)
	Create(RuleOwner) (RuleOwner, error)
	Update(RuleOwner) (RuleOwner, error)
}

type RuleOwner interface {
	GetNamespace() string
	GetName() string
	GetLabels() map[string]string
	SetLabels(map[string]string)
	GetAnnotations() map[string]string
	SetAnnotations(map[string]string)
	GetRules() []rbac.PolicyRule
	SetRules([]rbac.PolicyRule)
}

type ReconcileRoleOptions struct {
	// Role is the expected role that will be reconciled
	Role RuleOwner
	// Confirm indicates writes should be performed. When false, results are returned as a dry-run.
	Confirm bool
	// RemoveExtraPermissions indicates reconciliation should remove extra permissions from an existing role
	RemoveExtraPermissions bool
	// Client is used to look up existing roles, and create/update the role when Confirm=true
	Client RuleOwnerModifier
}

type ReconcileClusterRoleResult struct {
	// Role is the reconciled role from the reconciliation operation.
	// If the reconcile was performed as a dry-run, or the existing role was protected, the reconciled role is not persisted.
	Role RuleOwner

	// MissingRules contains expected rules that were missing from the currently persisted role
	MissingRules []rbac.PolicyRule
	// ExtraRules contains extra permissions the currently persisted role had
	ExtraRules []rbac.PolicyRule

	// Operation is the API operation required to reconcile.
	// If no reconciliation was needed, it is set to ReconcileNone.
	// If options.Confirm == false, the reconcile was in dry-run mode, so the operation was not performed.
	// If result.Protected == true, the role opted out of reconciliation, so the operation was not performed.
	// Otherwise, the operation was performed.
	Operation ReconcileOperation
	// Protected indicates an existing role prevented reconciliation
	Protected bool
}

func (o *ReconcileRoleOptions) Run() (*ReconcileClusterRoleResult, error) {
	return o.run(0)
}

func (o *ReconcileRoleOptions) run(attempts int) (*ReconcileClusterRoleResult, error) {
	// This keeps us from retrying forever if a role keeps appearing and disappearing as we reconcile.
	// Conflict errors on update are handled at a higher level.
	if attempts > 2 {
		return nil, fmt.Errorf("exceeded maximum attempts")
	}

	var result *ReconcileClusterRoleResult

	existing, err := o.Client.Get(o.Role.GetNamespace(), o.Role.GetName())
	switch {
	case errors.IsNotFound(err):
		result = &ReconcileClusterRoleResult{
			Role:         o.Role,
			MissingRules: o.Role.GetRules(),
			Operation:    ReconcileCreate,
		}

	case err != nil:
		return nil, err

	default:
		result, err = computeReconciledRole(existing, o.Role, o.RemoveExtraPermissions)
		if err != nil {
			return nil, err
		}
	}

	// If reconcile-protected, short-circuit
	if result.Protected {
		return result, nil
	}
	// If we're in dry-run mode, short-circuit
	if !o.Confirm {
		return result, nil
	}

	switch result.Operation {
	case ReconcileCreate:
		created, err := o.Client.Create(result.Role)
		// If created since we started this reconcile, re-run
		if errors.IsAlreadyExists(err) {
			return o.run(attempts + 1)
		}
		if err != nil {
			return nil, err
		}
		result.Role = created

	case ReconcileUpdate:
		updated, err := o.Client.Update(result.Role)
		// If deleted since we started this reconcile, re-run
		if errors.IsNotFound(err) {
			return o.run(attempts + 1)
		}
		if err != nil {
			return nil, err
		}
		result.Role = updated

	case ReconcileNone:
		// no-op

	default:
		return nil, fmt.Errorf("invalid operation: %v", result.Operation)
	}

	return result, nil
}

// computeReconciledRole returns the role that must be created and/or updated to make the
// existing role's permissions match the expected role's permissions
func computeReconciledRole(existing, expected RuleOwner, removeExtraPermissions bool) (*ReconcileClusterRoleResult, error) {
	result := &ReconcileClusterRoleResult{Operation: ReconcileNone}

	result.Protected = (existing.GetAnnotations()[rbac.AutoUpdateAnnotationKey] == "false")

	// Start with a copy of the existing object
	changedObj, err := api.Scheme.DeepCopy(existing)
	if err != nil {
		return nil, err
	}
	result.Role = changedObj.(RuleOwner)

	// Merge expected annotations and labels
	result.Role.SetAnnotations(merge(expected.GetAnnotations(), result.Role.GetAnnotations()))
	if !reflect.DeepEqual(result.Role.GetAnnotations(), existing.GetAnnotations()) {
		result.Operation = ReconcileUpdate
	}
	result.Role.SetLabels(merge(expected.GetLabels(), result.Role.GetLabels()))
	if !reflect.DeepEqual(result.Role.GetLabels(), existing.GetLabels()) {
		result.Operation = ReconcileUpdate
	}

	// Compute extra and missing rules
	_, result.ExtraRules = validation.Covers(expected.GetRules(), existing.GetRules())
	_, result.MissingRules = validation.Covers(existing.GetRules(), expected.GetRules())

	switch {
	case !removeExtraPermissions && len(result.MissingRules) > 0:
		// add missing rules in the union case
		result.Role.SetRules(append(result.Role.GetRules(), result.MissingRules...))
		result.Operation = ReconcileUpdate

	case removeExtraPermissions && (len(result.MissingRules) > 0 || len(result.ExtraRules) > 0):
		// stomp to expected rules in the non-union case
		result.Role.SetRules(expected.GetRules())
		result.Operation = ReconcileUpdate
	}

	return result, nil
}

// merge combines the given maps with the later annotations having higher precedence
func merge(maps ...map[string]string) map[string]string {
	var output map[string]string = nil
	for _, m := range maps {
		if m != nil && output == nil {
			output = map[string]string{}
		}
		for k, v := range m {
			output[k] = v
		}
	}
	return output
}