/*
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 (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"syscall"

	"github.com/GoogleContainerTools/kaniko/pkg/constants"
	"github.com/GoogleContainerTools/kaniko/pkg/util"
	"github.com/sirupsen/logrus"
)

// 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
}

// Key returns a string based on the current state of the file system
func (s *Snapshotter) Key() (string, error) {
	return s.l.Key()
}

// TakeSnapshot takes a snapshot of the specified files, 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(files []string) ([]byte, error) {
	buf := bytes.NewBuffer([]byte{})
	filesAdded, err := s.snapshotFiles(buf, files)
	if err != nil {
		return nil, err
	}
	contents := buf.Bytes()
	if !filesAdded {
		return nil, nil
	}
	return contents, err
}

// TakeSnapshotFS 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) TakeSnapshotFS() ([]byte, error) {
	buf := bytes.NewBuffer([]byte{})
	filesAdded, err := s.snapShotFS(buf)
	if err != nil {
		return nil, err
	}
	contents := buf.Bytes()
	if !filesAdded {
		return nil, nil
	}
	return contents, err
}

func shouldSnapshot(file string, snapshottedFiles map[string]bool) (bool, error) {
	if val, ok := snapshottedFiles[file]; ok && val {
		return false, nil
	}
	whitelisted, err := util.CheckWhitelist(file)
	if err != nil {
		return false, fmt.Errorf("Error checking for %s in whitelist: %s", file, err)
	}
	if whitelisted && !isBuildFile(file) {
		logrus.Infof("Not adding %s to layer, as it's whitelisted", file)
		return false, nil
	}
	return true, nil
}

// snapshotFiles creates a snapshot (tar) and adds the specified files.
// It will not add files which are whitelisted.
func (s *Snapshotter) snapshotFiles(f io.Writer, files []string) (bool, error) {
	s.l.Snapshot()
	if len(files) == 0 {
		logrus.Info("No files changed in this command, skipping snapshotting.")
		return false, nil
	}
	logrus.Info("Taking snapshot of files...")
	logrus.Debugf("Taking snapshot of files %v", files)
	snapshottedFiles := make(map[string]bool)
	filesAdded := false

	t := util.NewTar(f)
	defer t.Close()

	// First add to the tar any parent directories that haven't been added
	parentDirs := []string{}
	for _, file := range files {
		parents := util.ParentDirectories(file)
		parentDirs = append(parentDirs, parents...)
	}
	for _, file := range parentDirs {
		file = filepath.Clean(file)
		shouldSnapshot, err := shouldSnapshot(file, snapshottedFiles)
		if err != nil {
			return false, fmt.Errorf("Error checking if parent dir %s can be snapshotted: %s", file, err)
		}
		if !shouldSnapshot {
			continue
		}
		snapshottedFiles[file] = true

		fileAdded, err := s.l.MaybeAdd(file)
		if err != nil {
			return false, fmt.Errorf("Unable to add parent dir %s to layered map: %s", file, err)
		}

		if fileAdded {
			err = t.AddFileToTar(file)
			if err != nil {
				return false, fmt.Errorf("Error adding parent dir %s to tar: %s", file, err)
			}
			filesAdded = true
		}
	}
	// Next add the files themselves to the tar
	for _, file := range files {
		file = filepath.Clean(file)
		shouldSnapshot, err := shouldSnapshot(file, snapshottedFiles)
		if err != nil {
			return false, fmt.Errorf("Error checking if file %s can be snapshotted: %s", file, err)
		}
		if !shouldSnapshot {
			continue
		}
		snapshottedFiles[file] = true

		if err = s.l.Add(file); err != nil {
			return false, fmt.Errorf("Unable to add file %s to layered map: %s", file, err)
		}
		if err = t.AddFileToTar(file); err != nil {
			return false, fmt.Errorf("Error adding file %s to tar: %s", file, err)
		}
		filesAdded = true
	}
	return filesAdded, nil
}

func isBuildFile(file string) bool {
	for _, buildFile := range constants.KanikoBuildFiles {
		if file == buildFile {
			return true
		}
	}
	return false
}

// shapShotFS creates a snapshot (tar) of all files in the system which are not
// whitelisted and which have changed.
func (s *Snapshotter) snapShotFS(f io.Writer) (bool, error) {
	logrus.Info("Taking snapshot of full filesystem...")

	// Some of the operations that follow (e.g. hashing) depend on the file system being synced,
	// for example the hashing function that determines if files are equal uses the mtime of the files,
	// which can lag if sync is not called. Unfortunately there can still be lag if too much data needs
	// to be flushed or the disk does its own caching/buffering.
	syscall.Sync()

	s.l.Snapshot()
	existingPaths := s.l.GetFlattenedPathsForWhiteOut()
	filesAdded := false
	t := util.NewTar(f)
	defer t.Close()

	// Save the fs state in a map to iterate over later.
	memFs := map[string]os.FileInfo{}
	filepath.Walk(s.directory, func(path string, info os.FileInfo, err error) error {
		memFs[path] = info
		return nil
	})

	// First handle whiteouts
	for p := range memFs {
		delete(existingPaths, p)
	}
	for path := range existingPaths {
		// Only add the whiteout if the directory for the file still exists.
		dir := filepath.Dir(path)
		if _, ok := memFs[dir]; ok {
			addWhiteout, err := s.l.MaybeAddWhiteout(path)
			if err != nil {
				return false, nil
			}
			if addWhiteout {
				logrus.Infof("Adding whiteout for %s", path)
				filesAdded = true
				if err := t.Whiteout(path); err != nil {
					return false, err
				}
			}
		}
	}

	// Now create the tar.
	for path := range memFs {
		whitelisted, err := util.CheckWhitelist(path)
		if err != nil {
			return false, err
		}
		if whitelisted {
			logrus.Debugf("Not adding %s to layer, as it's whitelisted", path)
			continue
		}

		// Only add to the tar if we add it to the layeredmap.
		maybeAdd, err := s.l.MaybeAdd(path)
		if err != nil {
			return false, err
		}
		if maybeAdd {
			logrus.Debugf("Adding %s to layer, because it was changed.", path)
			filesAdded = true
			if err := t.AddFileToTar(path); err != nil {
				return false, err
			}
		}
	}

	return filesAdded, nil
}