/*
Copyright 2014 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 admission

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"reflect"
	"sort"
	"sync"

	"github.com/golang/glog"
)

// Factory is a function that returns an Interface for admission decisions.
// The config parameter provides an io.Reader handler to the factory in
// order to load specific configurations. If no configuration is provided
// the parameter is nil.
type Factory func(config io.Reader) (Interface, error)

// All registered admission options.
var (
	pluginsMutex sync.Mutex
	plugins      = make(map[string]Factory)

	// PluginEnabledFn checks whether a plugin is enabled.  By default, if you ask about it, it's enabled.
	PluginEnabledFn = func(name string, config io.Reader) bool {
		return true
	}
)

// PluginEnabledFunc is a function type that can provide an external check on whether an admission plugin may be enabled
type PluginEnabledFunc func(name string, config io.Reader) bool

// GetPlugins enumerates the names of all registered plugins.
func GetPlugins() []string {
	pluginsMutex.Lock()
	defer pluginsMutex.Unlock()
	keys := []string{}
	for k := range plugins {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	return keys
}

// RegisterPlugin registers a plugin Factory by name. This
// is expected to happen during app startup.
func RegisterPlugin(name string, plugin Factory) {
	pluginsMutex.Lock()
	defer pluginsMutex.Unlock()
	_, found := plugins[name]
	if found {
		glog.Fatalf("Admission plugin %q was registered twice", name)
	}
	glog.V(1).Infof("Registered admission plugin %q", name)
	plugins[name] = plugin
}

// getPlugin creates an instance of the named plugin.  It returns `false` if the
// the name is not known. The error is returned only when the named provider was
// known but failed to initialize.  The config parameter specifies the io.Reader
// handler of the configuration file for the cloud provider, or nil for no configuration.
func getPlugin(name string, config io.Reader) (Interface, bool, error) {
	pluginsMutex.Lock()
	defer pluginsMutex.Unlock()
	f, found := plugins[name]
	if !found {
		return nil, false, nil
	}

	config1, config2, err := splitStream(config)
	if err != nil {
		return nil, true, err
	}
	if !PluginEnabledFn(name, config1) {
		return nil, true, nil
	}

	ret, err := f(config2)
	return ret, true, err
}

// splitStream reads the stream bytes and constructs two copies of it.
func splitStream(config io.Reader) (io.Reader, io.Reader, error) {
	if config == nil || reflect.ValueOf(config).IsNil() {
		return nil, nil, nil
	}

	configBytes, err := ioutil.ReadAll(config)
	if err != nil {
		return nil, nil, err
	}

	return bytes.NewBuffer(configBytes), bytes.NewBuffer(configBytes), nil
}

// NewFromPlugins returns an admission.Interface that will enforce admission control decisions of all
// the given plugins.
func NewFromPlugins(pluginNames []string, configProvider ConfigProvider, pluginInitializer PluginInitializer) (Interface, error) {
	plugins := []Interface{}
	for _, pluginName := range pluginNames {
		pluginConfig, err := configProvider.ConfigFor(pluginName)
		if err != nil {
			return nil, err
		}

		plugin, err := InitPlugin(pluginName, pluginConfig, pluginInitializer)
		if err != nil {
			return nil, err
		}
		if plugin != nil {
			plugins = append(plugins, plugin)
		}
	}
	return chainAdmissionHandler(plugins), nil
}

// InitPlugin creates an instance of the named interface.
func InitPlugin(name string, config io.Reader, pluginInitializer PluginInitializer) (Interface, error) {
	if name == "" {
		glog.Info("No admission plugin specified.")
		return nil, nil
	}

	plugin, found, err := getPlugin(name, config)
	if err != nil {
		return nil, fmt.Errorf("Couldn't init admission plugin %q: %v", name, err)
	}
	if !found {
		return nil, fmt.Errorf("Unknown admission plugin: %s", name)
	}

	pluginInitializer.Initialize(plugin)
	// ensure that plugins have been properly initialized
	if err := Validate(plugin); err != nil {
		return nil, err
	}

	return plugin, nil
}

// Validate will call the Validate function in each plugin if they implement
// the Validator interface.
func Validate(plugin Interface) error {
	if validater, ok := plugin.(Validator); ok {
		err := validater.Validate()
		if err != nil {
			return err
		}
	}
	return nil
}

type PluginInitializers []PluginInitializer

func (pp PluginInitializers) Initialize(plugin Interface) {
	for _, p := range pp {
		p.Initialize(plugin)
	}
}