/*
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 flexvolume

import (
	"github.com/golang/glog"
	"k8s.io/kubernetes/pkg/volume"

	"os"

	"fmt"
	"path/filepath"
	"sync"
	"time"

	"github.com/fsnotify/fsnotify"
	"k8s.io/apimachinery/pkg/util/errors"
	utilfs "k8s.io/kubernetes/pkg/util/filesystem"
)

type flexVolumeProber struct {
	mutex           sync.Mutex
	pluginDir       string // Flexvolume driver directory
	watcher         utilfs.FSWatcher
	probeNeeded     bool      // Must only read and write this through testAndSetProbeNeeded.
	lastUpdated     time.Time // Last time probeNeeded was updated.
	watchEventCount int
	factory         PluginFactory
	fs              utilfs.Filesystem
}

const (
	// TODO (cxing) Tune these params based on test results.
	// watchEventLimit is the max allowable number of processed watches within watchEventInterval.
	watchEventInterval = 5 * time.Second
	watchEventLimit    = 20
)

func GetDynamicPluginProber(pluginDir string) volume.DynamicPluginProber {
	return &flexVolumeProber{
		pluginDir: pluginDir,
		watcher:   utilfs.NewFsnotifyWatcher(),
		factory:   pluginFactory{},
		fs:        &utilfs.DefaultFs{},
	}
}

func (prober *flexVolumeProber) Init() error {
	prober.testAndSetProbeNeeded(true)
	prober.lastUpdated = time.Now()

	if err := prober.createPluginDir(); err != nil {
		return err
	}
	if err := prober.initWatcher(); err != nil {
		return err
	}

	return nil
}

// Probes for Flexvolume drivers.
// If a filesystem update has occurred since the last probe, updated = true
// and the list of probed plugins is returned.
// Otherwise, update = false and probedPlugins = nil.
//
// If an error occurs, updated and plugins are set arbitrarily.
func (prober *flexVolumeProber) Probe() (updated bool, plugins []volume.VolumePlugin, err error) {
	probeNeeded := prober.testAndSetProbeNeeded(false)

	if !probeNeeded {
		return false, nil, nil
	}

	files, err := prober.fs.ReadDir(prober.pluginDir)
	if err != nil {
		return false, nil, fmt.Errorf("Error reading the Flexvolume directory: %s", err)
	}

	plugins = []volume.VolumePlugin{}
	allErrs := []error{}
	for _, f := range files {
		// only directories with names that do not begin with '.' are counted as plugins
		// and pluginDir/dirname/dirname should be an executable
		// unless dirname contains '~' for escaping namespace
		// e.g. dirname = vendor~cifs
		// then, executable will be pluginDir/dirname/cifs
		if f.IsDir() && filepath.Base(f.Name())[0] != '.' {
			plugin, pluginErr := prober.factory.NewFlexVolumePlugin(prober.pluginDir, f.Name())
			if pluginErr != nil {
				pluginErr = fmt.Errorf(
					"Error creating Flexvolume plugin from directory %s, skipping. Error: %s",
					f.Name(), pluginErr)
				allErrs = append(allErrs, pluginErr)
				continue
			}

			plugins = append(plugins, plugin)
		}
	}

	return true, plugins, errors.NewAggregate(allErrs)
}

func (prober *flexVolumeProber) handleWatchEvent(event fsnotify.Event) error {
	// event.Name is the watched path.
	if filepath.Base(event.Name)[0] == '.' {
		// Ignore files beginning with '.'
		return nil
	}

	eventPathAbs, err := filepath.Abs(event.Name)
	if err != nil {
		return err
	}

	pluginDirAbs, err := filepath.Abs(prober.pluginDir)
	if err != nil {
		return err
	}

	// If the Flexvolume plugin directory is removed, need to recreate it
	// in order to keep it under watch.
	if eventOpIs(event, fsnotify.Remove) && eventPathAbs == pluginDirAbs {
		if err := prober.createPluginDir(); err != nil {
			return err
		}
		if err := prober.addWatchRecursive(pluginDirAbs); err != nil {
			return err
		}
	} else if eventOpIs(event, fsnotify.Create) {
		if err := prober.addWatchRecursive(eventPathAbs); err != nil {
			return err
		}
	}

	prober.updateProbeNeeded()

	return nil
}

func (prober *flexVolumeProber) updateProbeNeeded() {
	// Within 'watchEventInterval' seconds, a max of 'watchEventLimit' watch events is processed.
	// The watch event will not be registered if the limit is reached.
	// This prevents increased disk usage from Probe() being triggered too frequently (either
	// accidentally or maliciously).
	if time.Since(prober.lastUpdated) > watchEventInterval {
		// Update, then reset the timer and watch count.
		prober.testAndSetProbeNeeded(true)
		prober.lastUpdated = time.Now()
		prober.watchEventCount = 1
	} else if prober.watchEventCount < watchEventLimit {
		prober.testAndSetProbeNeeded(true)
		prober.watchEventCount++
	}
}

// Recursively adds to watch all directories inside and including the file specified by the given filename.
// If the file is a symlink to a directory, it will watch the symlink but not any of the subdirectories.
//
// Each file or directory change triggers two events: one from the watch on itself, another from the watch
// on its parent directory.
func (prober *flexVolumeProber) addWatchRecursive(filename string) error {
	addWatch := func(path string, info os.FileInfo, err error) error {
		if err == nil && info.IsDir() {
			if err := prober.watcher.AddWatch(path); err != nil {
				glog.Errorf("Error recursively adding watch: %v", err)
			}
		}
		return nil
	}
	return prober.fs.Walk(filename, addWatch)
}

// Creates a new filesystem watcher and adds watches for the plugin directory
// and all of its subdirectories.
func (prober *flexVolumeProber) initWatcher() error {
	err := prober.watcher.Init(func(event fsnotify.Event) {
		if err := prober.handleWatchEvent(event); err != nil {
			glog.Errorf("Flexvolume prober watch: %s", err)
		}
	}, func(err error) {
		glog.Errorf("Received an error from watcher: %s", err)
	})
	if err != nil {
		return fmt.Errorf("Error initializing watcher: %s", err)
	}

	if err := prober.addWatchRecursive(prober.pluginDir); err != nil {
		return fmt.Errorf("Error adding watch on Flexvolume directory: %s", err)
	}

	prober.watcher.Run()

	return nil
}

// Creates the plugin directory, if it doesn't already exist.
func (prober *flexVolumeProber) createPluginDir() error {
	if _, err := prober.fs.Stat(prober.pluginDir); os.IsNotExist(err) {
		glog.Warningf("Flexvolume plugin directory at %s does not exist. Recreating.", prober.pluginDir)
		err := prober.fs.MkdirAll(prober.pluginDir, 0755)
		if err != nil {
			return fmt.Errorf("Error (re-)creating driver directory: %s", err)
		}
	}

	return nil
}

func (prober *flexVolumeProber) testAndSetProbeNeeded(newval bool) (oldval bool) {
	prober.mutex.Lock()
	defer prober.mutex.Unlock()
	oldval, prober.probeNeeded = prober.probeNeeded, newval
	return
}

func eventOpIs(event fsnotify.Event, op fsnotify.Op) bool {
	return event.Op&op == op
}
