/*
Copyright 2018 Google LLC

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 snapshot

import (
	"archive/tar"
	"bytes"
	"github.com/GoogleCloudPlatform/k8s-container-builder/pkg/util"
	"github.com/sirupsen/logrus"

	"io"
	"io/ioutil"
	"os"
	"path/filepath"
)

// Snapshotter holds the root directory from which to take snapshots, and a list of snapshots taken
type Snapshotter struct {
	l         *LayeredMap
	directory string
}

// NewSnapshotter creates a new snapshotter rooted at d
func NewSnapshotter(l *LayeredMap, d string) *Snapshotter {
	return &Snapshotter{l: l, directory: d}
}

// Init initializes a new snapshotter
func (s *Snapshotter) Init() error {
	if _, err := s.snapShotFS(ioutil.Discard); err != nil {
		return err
	}
	return nil
}

// TakeSnapshot takes a snapshot of the filesystem, avoiding directories in the whitelist, and creates
// a tarball of the changed files. Return contents of the tarball, and whether or not any files were changed
func (s *Snapshotter) TakeSnapshot() ([]byte, bool, error) {
	buf := bytes.NewBuffer([]byte{})
	filesAdded, err := s.snapShotFS(buf)
	if err != nil {
		return nil, filesAdded, err
	}
	contents, err := ioutil.ReadAll(buf)
	if err != nil {
		return nil, filesAdded, err
	}
	return contents, filesAdded, err
}

// TakeSnapshotOfFiles takes a snapshot of specific files
// Used for ADD/COPY commands, when we know which files have changed
func (s *Snapshotter) TakeSnapshotOfFiles(files []string) ([]byte, error) {
	logrus.Infof("Taking snapshot of files %s", files)
	s.l.Snapshot()
	if len(files) == 0 {
		logrus.Info("No files changed in this command, skipping snapshotting.")
		return nil, nil
	}
	buf := bytes.NewBuffer([]byte{})
	w := tar.NewWriter(buf)
	defer w.Close()
	for _, file := range files {
		info, err := os.Stat(file)
		if err != nil {
			return nil, err
		}
		if util.PathInWhitelist(file, s.directory) {
			logrus.Debugf("Not adding %s to layer, as it is whitelisted", file)
			continue
		}
		// Only add to the tar if we add it to the layeredmap.
		maybeAdd, err := s.l.MaybeAdd(file)
		if err != nil {
			return nil, err
		}
		if maybeAdd {
			util.AddToTar(file, info, w)
		}
	}
	return ioutil.ReadAll(buf)
}

func (s *Snapshotter) snapShotFS(f io.Writer) (bool, error) {
	s.l.Snapshot()
	filesAdded := false
	w := tar.NewWriter(f)
	defer w.Close()

	err := filepath.Walk(s.directory, func(path string, info os.FileInfo, err error) error {
		if util.PathInWhitelist(path, s.directory) {
			logrus.Debugf("Not adding %s to layer, as it's whitelisted", path)
			return nil
		}

		// Only add to the tar if we add it to the layeredmap.
		maybeAdd, err := s.l.MaybeAdd(path)
		if err != nil {
			return err
		}
		if maybeAdd {
			filesAdded = true
			return util.AddToTar(path, info, w)
		}
		return nil
	})
	return filesAdded, err
}