/*
   Copyright The containerd 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 aufs

import (
	"bufio"
	"context"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync"
	"syscall"

	"github.com/containerd/containerd/log"
	"github.com/containerd/containerd/mount"
	"github.com/containerd/containerd/snapshots"
	"github.com/containerd/containerd/snapshots/storage"
	"github.com/containerd/continuity/fs"

	"golang.org/x/sys/unix"
)

var (
	dirperm        sync.Once
	dirpermEnabled bool
)

type snapshotter struct {
	root string
	ms   *storage.MetaStore
}

// New creates a new snapshotter using aufs
func New(root string) (snapshots.Snapshotter, error) {
	if err := supported(); err != nil {
		return nil, err
	}
	if err := os.MkdirAll(root, 0700); err != nil {
		return nil, err
	}
	ms, err := storage.NewMetaStore(filepath.Join(root, "metadata.db"))
	if err != nil {
		return nil, err
	}
	if err := os.Mkdir(filepath.Join(root, "snapshots"), 0700); err != nil && !os.IsExist(err) {
		return nil, err
	}
	return &snapshotter{
		root: root,
		ms:   ms,
	}, nil
}

func (o *snapshotter) Stat(ctx context.Context, key string) (snapshots.Info, error) {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return snapshots.Info{}, err
	}
	defer t.Rollback()
	_, info, _, err := storage.GetInfo(ctx, key)
	if err != nil {
		return snapshots.Info{}, err
	}
	return info, nil
}

func (o *snapshotter) Update(ctx context.Context, info snapshots.Info, fieldpaths ...string) (snapshots.Info, error) {
	ctx, t, err := o.ms.TransactionContext(ctx, true)
	if err != nil {
		return snapshots.Info{}, err
	}
	info, err = storage.UpdateInfo(ctx, info, fieldpaths...)
	if err != nil {
		t.Rollback()
		return snapshots.Info{}, err
	}
	if err := t.Commit(); err != nil {
		return snapshots.Info{}, err
	}
	return info, nil
}

// Usage returns the resources taken by the snapshot identified by key.
//
// For active snapshots, this will scan the usage of directory and may take some time.
//
// For committed snapshots, the value is returned from the metadata database.
func (o *snapshotter) Usage(ctx context.Context, key string) (snapshots.Usage, error) {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return snapshots.Usage{}, err
	}
	id, info, usage, err := storage.GetInfo(ctx, key)
	t.Rollback() // transaction no longer needed at this point.
	if err != nil {
		return snapshots.Usage{}, err
	}

	upperPath := o.upperPath(id)

	if info.Kind == snapshots.KindActive {
		du, err := fs.DiskUsage(ctx, upperPath)
		if err != nil {
			// TODO(stevvooe): Consider not reporting an error in this case.
			return snapshots.Usage{}, err
		}

		usage = snapshots.Usage(du)
	}

	return usage, nil
}

func (o *snapshotter) Prepare(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
	return o.createSnapshot(ctx, snapshots.KindActive, key, parent, opts)
}

func (o *snapshotter) View(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
	return o.createSnapshot(ctx, snapshots.KindView, key, parent, opts)
}

// Mounts returns the mounts for the transaction identified by key. Can be
// called on an read-write or readonly transaction.
//
// This can be used to recover mounts after calling View or Prepare.
func (o *snapshotter) Mounts(ctx context.Context, key string) ([]mount.Mount, error) {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return nil, err
	}
	s, err := storage.GetSnapshot(ctx, key)
	t.Rollback()
	if err != nil {
		return nil, fmt.Errorf("failed to get active mount: %w", err)
	}
	return o.mounts(s), nil
}

func (o *snapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) error {
	ctx, t, err := o.ms.TransactionContext(ctx, true)
	if err != nil {
		return err
	}

	defer func() {
		if err != nil {
			if rerr := t.Rollback(); rerr != nil {
				log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
			}
		}
	}()

	// grab the existing id
	id, _, _, err := storage.GetInfo(ctx, key)
	if err != nil {
		return err
	}

	usage, err := fs.DiskUsage(ctx, o.upperPath(id))
	if err != nil {
		return err
	}

	if _, err = storage.CommitActive(ctx, key, name, snapshots.Usage(usage), opts...); err != nil {
		return fmt.Errorf("failed to commit snapshot: %w", err)
	}
	return t.Commit()
}

// Remove abandons the transaction identified by key. All resources
// associated with the key will be removed.
func (o *snapshotter) Remove(ctx context.Context, key string) (err error) {
	ctx, t, err := o.ms.TransactionContext(ctx, true)
	if err != nil {
		return err
	}
	defer func() {
		if err != nil && t != nil {
			if rerr := t.Rollback(); rerr != nil {
				log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
			}
		}
	}()

	id, _, err := storage.Remove(ctx, key)
	if err != nil {
		return fmt.Errorf("failed to remove: %w", err)
	}

	path := filepath.Join(o.root, "snapshots", id)
	renamed := filepath.Join(o.root, "snapshots", "rm-"+id)
	if err := os.Rename(path, renamed); err != nil {
		return fmt.Errorf("failed to rename: %w", err)
	}

	err = t.Commit()
	t = nil
	if err != nil {
		if err1 := os.Rename(renamed, path); err1 != nil {
			// May cause inconsistent data on disk
			log.G(ctx).WithError(err1).WithField("path", renamed).Errorf("Failed to rename after failed commit")
		}
		return fmt.Errorf("failed to commit: %w", err)
	}
	if err := os.RemoveAll(renamed); err != nil {
		// Must be cleaned up, any "rm-*" could be removed if no active transactions
		log.G(ctx).WithError(err).WithField("path", renamed).Warnf("Failed to remove root filesystem")
	}

	return nil
}

// Walk the committed snapshots.
func (o *snapshotter) Walk(ctx context.Context, fn snapshots.WalkFunc, filters ...string) error {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return err
	}
	defer t.Rollback()
	return storage.WalkInfo(ctx, fn, filters...)
}

func (o *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, key, parent string, opts []snapshots.Opt) ([]mount.Mount, error) {
	var (
		path        string
		snapshotDir = filepath.Join(o.root, "snapshots")
	)

	td, err := os.MkdirTemp(snapshotDir, "new-")
	if err != nil {
		return nil, fmt.Errorf("failed to create temp dir: %w", err)
	}
	defer func() {
		if err != nil {
			if td != "" {
				if err1 := os.RemoveAll(td); err1 != nil {
					err = fmt.Errorf("remove failed %v: %w", err1, err)
				}
			}
			if path != "" {
				if err1 := os.RemoveAll(path); err1 != nil {
					err = fmt.Errorf("failed to remove path %v: %w", err1, err)
				}
			}
		}
	}()

	fs := filepath.Join(td, "fs")
	if err = os.MkdirAll(fs, 0755); err != nil {
		return nil, err
	}

	ctx, t, err := o.ms.TransactionContext(ctx, true)
	if err != nil {
		return nil, err
	}

	s, err := storage.CreateSnapshot(ctx, kind, key, parent, opts...)
	if err != nil {
		if rerr := t.Rollback(); rerr != nil {
			log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
		}
		return nil, fmt.Errorf("failed to create active: %w", err)
	}

	if len(s.ParentIDs) > 0 {
		st, err := os.Stat(filepath.Join(o.upperPath(s.ParentIDs[0])))
		if err != nil {
			if rerr := t.Rollback(); rerr != nil {
				log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
			}
			return nil, fmt.Errorf("failed to stat parent: %w", err)
		}

		stat := st.Sys().(*syscall.Stat_t)

		if err := os.Lchown(fs, int(stat.Uid), int(stat.Gid)); err != nil {
			if rerr := t.Rollback(); rerr != nil {
				log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
			}
			return nil, fmt.Errorf("failed to chown: %w", err)
		}
	}

	path = filepath.Join(snapshotDir, s.ID)
	if err = os.Rename(td, path); err != nil {
		if rerr := t.Rollback(); rerr != nil {
			log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
		}
		return nil, fmt.Errorf("failed to rename: %w", err)
	}
	td = ""

	if err = t.Commit(); err != nil {
		return nil, fmt.Errorf("commit failed: %w", err)
	}

	return o.mounts(s), nil
}

func (o *snapshotter) mounts(s storage.Snapshot) []mount.Mount {
	if len(s.ParentIDs) == 0 {
		// if we only have one layer/no parents then just return a bind mount
		roFlag := "rw"
		if s.Kind == snapshots.KindView {
			roFlag = "ro"
		}

		return []mount.Mount{
			{
				Source: o.upperPath(s.ID),
				Type:   "bind",
				Options: []string{
					roFlag,
					"rbind",
				},
			},
		}
	}

	aufsOptions := []string{
		"br",
	}

	if s.Kind == snapshots.KindActive {
		aufsOptions = append(aufsOptions,
			fmt.Sprintf("%s=rw", o.upperPath(s.ID)),
		)
	} else if len(s.ParentIDs) == 1 {
		return []mount.Mount{
			{
				Source: o.upperPath(s.ParentIDs[0]),
				Type:   "bind",
				Options: []string{
					"ro",
					"rbind",
				},
			},
		}
	}

	for i := range s.ParentIDs {
		aufsOptions = append(aufsOptions, fmt.Sprintf("%s=ro+wh", o.upperPath(s.ParentIDs[i])))
	}
	options := []string{
		"dio",
		"xino=/dev/shm/aufs.xino",
	}
	if useDirperm() {
		options = append(options, "dirperm1")
	}

	options = append(options, strings.Join(aufsOptions, ":"))
	return []mount.Mount{
		{
			Type:    "aufs",
			Source:  "none",
			Options: options,
		},
	}

}

func (o *snapshotter) upperPath(id string) string {
	return filepath.Join(o.root, "snapshots", id, "fs")
}

func supported() error {
	// modprobe the aufs module before checking
	var probeError error
	cmd := exec.Command("modprobe", "aufs")
	out, err := cmd.CombinedOutput()
	if err != nil {
		probeError = fmt.Errorf(" (modprobe aufs failed: %v %q)", err, out)
	}

	f, err := os.Open("/proc/filesystems")
	if err != nil {
		return err
	}
	defer f.Close()

	s := bufio.NewScanner(f)
	for s.Scan() {
		if strings.Contains(s.Text(), "aufs") {
			return nil
		}
	}
	return fmt.Errorf("aufs is not supported: %w", probeError)
}

// useDirperm checks dirperm1 mount option can be used with the current
// version of aufs.
func useDirperm() bool {
	dirperm.Do(func() {
		base, err := os.MkdirTemp("", "docker-aufs-base")
		if err != nil {
			return
		}
		defer os.RemoveAll(base)

		union, err := os.MkdirTemp("", "docker-aufs-union")
		if err != nil {
			return
		}
		defer os.RemoveAll(union)

		opts := fmt.Sprintf("br:%s,dirperm1,xino=/dev/shm/aufs.xino", base)
		if err := unix.Mount("none", union, "aufs", 0, opts); err != nil {
			return
		}
		dirpermEnabled = true
		unix.Unmount(union, 0)
	})
	return dirpermEnabled
}

func (o *snapshotter) Close() error {
	return o.ms.Close()
}