/*
Copyright 2014 Google Inc. All rights reserved.

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 kubectl

import (
	"fmt"
	"strconv"

	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/client"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/util/wait"
)

// ResizePrecondition describes a condition that must be true for the resize to take place
// If CurrentSize == -1, it is ignored.
// If CurrentResourceVersion is the empty string, it is ignored.
// Otherwise they must equal the values in the replication controller for it to be valid.
type ResizePrecondition struct {
	Size            int
	ResourceVersion string
}

// A PreconditionError is returned when a replication controller fails to match
// the resize preconditions passed to kubectl.
type PreconditionError struct {
	Precondition  string
	ExpectedValue string
	ActualValue   string
}

func (pe PreconditionError) Error() string {
	return fmt.Sprintf("Expected %s to be %s, was %s", pe.Precondition, pe.ExpectedValue, pe.ActualValue)
}

type ControllerResizeErrorType int

const (
	ControllerResizeGetFailure ControllerResizeErrorType = iota
	ControllerResizeUpdateFailure
)

// A ControllerResizeError is returned when a the resize request passes
// preconditions but fails to actually resize the controller.
type ControllerResizeError struct {
	FailureType     ControllerResizeErrorType
	ResourceVersion string
	ActualError     error
}

func (c ControllerResizeError) Error() string {
	return fmt.Sprintf(
		"Resizing the controller failed with: %s; Current resource version %s",
		c.ActualError, c.ResourceVersion)
}

// Validate ensures that the preconditions match.  Returns nil if they are valid, an error otherwise
func (precondition *ResizePrecondition) Validate(controller *api.ReplicationController) error {
	if precondition.Size != -1 && controller.Spec.Replicas != precondition.Size {
		return PreconditionError{"replicas", strconv.Itoa(precondition.Size), strconv.Itoa(controller.Spec.Replicas)}
	}
	if precondition.ResourceVersion != "" && controller.ResourceVersion != precondition.ResourceVersion {
		return PreconditionError{"resource version", precondition.ResourceVersion, controller.ResourceVersion}
	}
	return nil
}

type Resizer interface {
	Resize(namespace, name string, preconditions *ResizePrecondition, newSize uint) (string, error)
}

func ResizerFor(kind string, c client.Interface) (Resizer, error) {
	switch kind {
	case "ReplicationController":
		return &ReplicationControllerResizer{c}, nil
	}
	return nil, fmt.Errorf("no resizer has been implemented for %q", kind)
}

type ReplicationControllerResizer struct {
	client.Interface
}

// ResizeCondition is a closure around Resize that facilitates retries via util.wait
func ResizeCondition(r Resizer, precondition *ResizePrecondition, namespace, name string, count uint) wait.ConditionFunc {
	return func() (bool, error) {
		_, err := r.Resize(namespace, name, precondition, count)
		switch e, _ := err.(ControllerResizeError); err.(type) {
		case nil:
			return true, nil
		case ControllerResizeError:
			if e.FailureType == ControllerResizeUpdateFailure {
				return false, nil
			}
		}
		return false, err
	}
}

func (resize *ReplicationControllerResizer) Resize(namespace, name string, preconditions *ResizePrecondition, newSize uint) (string, error) {
	rc := resize.ReplicationControllers(namespace)
	controller, err := rc.Get(name)
	if err != nil {
		return "", ControllerResizeError{ControllerResizeGetFailure, "Unknown", err}
	}

	if preconditions != nil {
		if err := preconditions.Validate(controller); err != nil {
			return "", err
		}
	}

	controller.Spec.Replicas = int(newSize)
	// TODO: do retry on 409 errors here?
	if _, err := rc.Update(controller); err != nil {
		return "", ControllerResizeError{ControllerResizeUpdateFailure, controller.ResourceVersion, err}
	}
	// TODO: do a better job of printing objects here.
	return "resized", nil
}