/*
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 builder

import (
	"errors"
	"fmt"
	"strings"

	"github.com/go-logr/logr"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/klog/v2"

	"sigs.k8s.io/controller-runtime/pkg/client"
	"sigs.k8s.io/controller-runtime/pkg/client/apiutil"
	"sigs.k8s.io/controller-runtime/pkg/controller"
	"sigs.k8s.io/controller-runtime/pkg/handler"
	"sigs.k8s.io/controller-runtime/pkg/manager"
	"sigs.k8s.io/controller-runtime/pkg/predicate"
	"sigs.k8s.io/controller-runtime/pkg/reconcile"
	"sigs.k8s.io/controller-runtime/pkg/source"
)

// Supporting mocking out functions for testing.
var newController = controller.New
var getGvk = apiutil.GVKForObject

// project represents other forms that the we can use to
// send/receive a given resource (metadata-only, unstructured, etc).
type objectProjection int

const (
	// projectAsNormal doesn't change the object from the form given.
	projectAsNormal objectProjection = iota
	// projectAsMetadata turns this into an metadata-only watch.
	projectAsMetadata
)

// Builder builds a Controller.
type Builder struct {
	forInput         ForInput
	ownsInput        []OwnsInput
	watchesInput     []WatchesInput
	mgr              manager.Manager
	globalPredicates []predicate.Predicate
	ctrl             controller.Controller
	ctrlOptions      controller.Options
	name             string
}

// ControllerManagedBy returns a new controller builder that will be started by the provided Manager.
func ControllerManagedBy(m manager.Manager) *Builder {
	return &Builder{mgr: m}
}

// ForInput represents the information set by For method.
type ForInput struct {
	object           client.Object
	predicates       []predicate.Predicate
	objectProjection objectProjection
	err              error
}

// For defines the type of Object being *reconciled*, and configures the ControllerManagedBy to respond to create / delete /
// update events by *reconciling the object*.
// This is the equivalent of calling
// Watches(&source.Kind{Type: apiType}, &handler.EnqueueRequestForObject{}).
func (blder *Builder) For(object client.Object, opts ...ForOption) *Builder {
	if blder.forInput.object != nil {
		blder.forInput.err = fmt.Errorf("For(...) should only be called once, could not assign multiple objects for reconciliation")
		return blder
	}
	input := ForInput{object: object}
	for _, opt := range opts {
		opt.ApplyToFor(&input)
	}

	blder.forInput = input
	return blder
}

// OwnsInput represents the information set by Owns method.
type OwnsInput struct {
	object           client.Object
	predicates       []predicate.Predicate
	objectProjection objectProjection
}

// Owns defines types of Objects being *generated* by the ControllerManagedBy, and configures the ControllerManagedBy to respond to
// create / delete / update events by *reconciling the owner object*.  This is the equivalent of calling
// Watches(&source.Kind{Type: <ForType-forInput>}, &handler.EnqueueRequestForOwner{OwnerType: apiType, IsController: true}).
func (blder *Builder) Owns(object client.Object, opts ...OwnsOption) *Builder {
	input := OwnsInput{object: object}
	for _, opt := range opts {
		opt.ApplyToOwns(&input)
	}

	blder.ownsInput = append(blder.ownsInput, input)
	return blder
}

// WatchesInput represents the information set by Watches method.
type WatchesInput struct {
	src              source.Source
	eventhandler     handler.EventHandler
	predicates       []predicate.Predicate
	objectProjection objectProjection
}

// Watches exposes the lower-level ControllerManagedBy Watches functions through the builder.  Consider using
// Owns or For instead of Watches directly.
// Specified predicates are registered only for given source.
func (blder *Builder) Watches(src source.Source, eventhandler handler.EventHandler, opts ...WatchesOption) *Builder {
	input := WatchesInput{src: src, eventhandler: eventhandler}
	for _, opt := range opts {
		opt.ApplyToWatches(&input)
	}

	blder.watchesInput = append(blder.watchesInput, input)
	return blder
}

// WithEventFilter sets the event filters, to filter which create/update/delete/generic events eventually
// trigger reconciliations.  For example, filtering on whether the resource version has changed.
// Given predicate is added for all watched objects.
// Defaults to the empty list.
func (blder *Builder) WithEventFilter(p predicate.Predicate) *Builder {
	blder.globalPredicates = append(blder.globalPredicates, p)
	return blder
}

// WithOptions overrides the controller options use in doController. Defaults to empty.
func (blder *Builder) WithOptions(options controller.Options) *Builder {
	blder.ctrlOptions = options
	return blder
}

// WithLogConstructor overrides the controller options's LogConstructor.
func (blder *Builder) WithLogConstructor(logConstructor func(*reconcile.Request) logr.Logger) *Builder {
	blder.ctrlOptions.LogConstructor = logConstructor
	return blder
}

// Named sets the name of the controller to the given name.  The name shows up
// in metrics, among other things, and thus should be a prometheus compatible name
// (underscores and alphanumeric characters only).
//
// By default, controllers are named using the lowercase version of their kind.
func (blder *Builder) Named(name string) *Builder {
	blder.name = name
	return blder
}

// Complete builds the Application Controller.
func (blder *Builder) Complete(r reconcile.Reconciler) error {
	_, err := blder.Build(r)
	return err
}

// Build builds the Application Controller and returns the Controller it created.
func (blder *Builder) Build(r reconcile.Reconciler) (controller.Controller, error) {
	if r == nil {
		return nil, fmt.Errorf("must provide a non-nil Reconciler")
	}
	if blder.mgr == nil {
		return nil, fmt.Errorf("must provide a non-nil Manager")
	}
	if blder.forInput.err != nil {
		return nil, blder.forInput.err
	}

	// Set the ControllerManagedBy
	if err := blder.doController(r); err != nil {
		return nil, err
	}

	// Set the Watch
	if err := blder.doWatch(); err != nil {
		return nil, err
	}

	return blder.ctrl, nil
}

func (blder *Builder) project(obj client.Object, proj objectProjection) (client.Object, error) {
	switch proj {
	case projectAsNormal:
		return obj, nil
	case projectAsMetadata:
		metaObj := &metav1.PartialObjectMetadata{}
		gvk, err := getGvk(obj, blder.mgr.GetScheme())
		if err != nil {
			return nil, fmt.Errorf("unable to determine GVK of %T for a metadata-only watch: %w", obj, err)
		}
		metaObj.SetGroupVersionKind(gvk)
		return metaObj, nil
	default:
		panic(fmt.Sprintf("unexpected projection type %v on type %T, should not be possible since this is an internal field", proj, obj))
	}
}

func (blder *Builder) doWatch() error {
	// Reconcile type
	typeForSrc, err := blder.project(blder.forInput.object, blder.forInput.objectProjection)
	if err != nil {
		return err
	}
	src := &source.Kind{Type: typeForSrc}
	hdler := &handler.EnqueueRequestForObject{}
	allPredicates := append(blder.globalPredicates, blder.forInput.predicates...)
	if err := blder.ctrl.Watch(src, hdler, allPredicates...); err != nil {
		return err
	}

	// Watches the managed types
	if len(blder.ownsInput) > 0 && blder.forInput.object == nil {
		return errors.New("Owns() can only be used together with For()")
	}
	for _, own := range blder.ownsInput {
		typeForSrc, err := blder.project(own.object, own.objectProjection)
		if err != nil {
			return err
		}
		src := &source.Kind{Type: typeForSrc}
		hdler := &handler.EnqueueRequestForOwner{
			OwnerType:    blder.forInput.object,
			IsController: true,
		}
		allPredicates := append([]predicate.Predicate(nil), blder.globalPredicates...)
		allPredicates = append(allPredicates, own.predicates...)
		if err := blder.ctrl.Watch(src, hdler, allPredicates...); err != nil {
			return err
		}
	}

	// Do the watch requests
	if len(blder.watchesInput) == 0 && blder.forInput.object == nil {
		return errors.New("there are no watches configured, controller will never get triggered. Use For(), Owns() or Watches() to set them up")
	}
	for _, w := range blder.watchesInput {
		allPredicates := append([]predicate.Predicate(nil), blder.globalPredicates...)
		allPredicates = append(allPredicates, w.predicates...)

		// If the source of this watch is of type *source.Kind, project it.
		if srckind, ok := w.src.(*source.Kind); ok {
			typeForSrc, err := blder.project(srckind.Type, w.objectProjection)
			if err != nil {
				return err
			}
			srckind.Type = typeForSrc
		}

		if err := blder.ctrl.Watch(w.src, w.eventhandler, allPredicates...); err != nil {
			return err
		}
	}
	return nil
}

func (blder *Builder) getControllerName(gvk schema.GroupVersionKind, hasGVK bool) (string, error) {
	if blder.name != "" {
		return blder.name, nil
	}
	if !hasGVK {
		return "", errors.New("one of For() or Named() must be called")
	}
	return strings.ToLower(gvk.Kind), nil
}

func (blder *Builder) doController(r reconcile.Reconciler) error {
	globalOpts := blder.mgr.GetControllerOptions()

	ctrlOptions := blder.ctrlOptions
	if ctrlOptions.Reconciler == nil {
		ctrlOptions.Reconciler = r
	}

	// Retrieve the GVK from the object we're reconciling
	// to prepopulate logger information, and to optionally generate a default name.
	var gvk schema.GroupVersionKind
	hasGVK := blder.forInput.object != nil
	if hasGVK {
		var err error
		gvk, err = getGvk(blder.forInput.object, blder.mgr.GetScheme())
		if err != nil {
			return err
		}
	}

	// Setup concurrency.
	if ctrlOptions.MaxConcurrentReconciles == 0 && hasGVK {
		groupKind := gvk.GroupKind().String()

		if concurrency, ok := globalOpts.GroupKindConcurrency[groupKind]; ok && concurrency > 0 {
			ctrlOptions.MaxConcurrentReconciles = concurrency
		}
	}

	// Setup cache sync timeout.
	if ctrlOptions.CacheSyncTimeout == 0 && globalOpts.CacheSyncTimeout != nil {
		ctrlOptions.CacheSyncTimeout = *globalOpts.CacheSyncTimeout
	}

	controllerName, err := blder.getControllerName(gvk, hasGVK)
	if err != nil {
		return err
	}

	// Setup the logger.
	if ctrlOptions.LogConstructor == nil {
		log := blder.mgr.GetLogger().WithValues(
			"controller", controllerName,
		)
		if hasGVK {
			log = log.WithValues(
				"controllerGroup", gvk.Group,
				"controllerKind", gvk.Kind,
			)
		}

		ctrlOptions.LogConstructor = func(req *reconcile.Request) logr.Logger {
			log := log
			if req != nil {
				if hasGVK {
					log = log.WithValues(gvk.Kind, klog.KRef(req.Namespace, req.Name))
				}
				log = log.WithValues(
					"namespace", req.Namespace, "name", req.Name,
				)
			}
			return log
		}
	}

	// Build the controller and return.
	blder.ctrl, err = newController(controllerName, blder.mgr, ctrlOptions)
	return err
}