// Copyright 2019 The gVisor 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 proc

import (
	"sort"
	"strconv"

	"gvisor.dev/gvisor/pkg/abi/linux"
	"gvisor.dev/gvisor/pkg/sentry/context"
	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
	"gvisor.dev/gvisor/pkg/sentry/kernel"
	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
	"gvisor.dev/gvisor/pkg/sentry/vfs"
	"gvisor.dev/gvisor/pkg/syserror"
)

const defaultPermission = 0444

// InoGenerator generates unique inode numbers for a given filesystem.
type InoGenerator interface {
	NextIno() uint64
}

// tasksInode represents the inode for /proc/ directory.
//
// +stateify savable
type tasksInode struct {
	kernfs.InodeNotSymlink
	kernfs.InodeDirectoryNoNewChildren
	kernfs.InodeAttrs
	kernfs.OrderedChildren

	inoGen InoGenerator
	pidns  *kernel.PIDNamespace
}

var _ kernfs.Inode = (*tasksInode)(nil)

func newTasksInode(inoGen InoGenerator, k *kernel.Kernel, pidns *kernel.PIDNamespace) (*tasksInode, *kernfs.Dentry) {
	root := auth.NewRootCredentials(pidns.UserNamespace())
	contents := map[string]*kernfs.Dentry{
		//"cpuinfo":     newCPUInfo(ctx, msrc),
		//"filesystems": seqfile.NewSeqFileInode(ctx, &filesystemsData{}, msrc),
		"loadavg":     newDentry(root, inoGen.NextIno(), defaultPermission, &loadavgData{}),
		"meminfo":     newDentry(root, inoGen.NextIno(), defaultPermission, &meminfoData{k: k}),
		"mounts":      kernfs.NewStaticSymlink(root, inoGen.NextIno(), defaultPermission, "self/mounts"),
		"self":        newSelfSymlink(root, inoGen.NextIno(), defaultPermission, pidns),
		"stat":        newDentry(root, inoGen.NextIno(), defaultPermission, &statData{k: k}),
		"thread-self": newThreadSelfSymlink(root, inoGen.NextIno(), defaultPermission, pidns),
		//"uptime":      newUptime(ctx, msrc),
		//"version": newVersionData(root, inoGen.NextIno(), k),
		"version": newDentry(root, inoGen.NextIno(), defaultPermission, &versionData{k: k}),
	}

	inode := &tasksInode{
		pidns:  pidns,
		inoGen: inoGen,
	}
	inode.InodeAttrs.Init(root, inoGen.NextIno(), linux.ModeDirectory|0555)

	dentry := &kernfs.Dentry{}
	dentry.Init(inode)

	inode.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
	links := inode.OrderedChildren.Populate(dentry, contents)
	inode.IncLinks(links)

	return inode, dentry
}

// Lookup implements kernfs.inodeDynamicLookup.
func (i *tasksInode) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
	// Try to lookup a corresponding task.
	tid, err := strconv.ParseUint(name, 10, 64)
	if err != nil {
		return nil, syserror.ENOENT
	}

	task := i.pidns.TaskWithID(kernel.ThreadID(tid))
	if task == nil {
		return nil, syserror.ENOENT
	}

	taskDentry := newTaskInode(i.inoGen, task, i.pidns, true)
	return taskDentry.VFSDentry(), nil
}

// Valid implements kernfs.inodeDynamicLookup.
func (i *tasksInode) Valid(ctx context.Context) bool {
	return true
}

// IterDirents implements kernfs.inodeDynamicLookup.
//
// TODO(gvisor.dev/issue/1195): Use tgid N offset = TGID_OFFSET + N.
func (i *tasksInode) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, offset, relOffset int64) (int64, error) {
	var tids []int

	// Collect all tasks. Per linux we only include it in directory listings if
	// it's the leader. But for whatever crazy reason, you can still walk to the
	// given node.
	for _, tg := range i.pidns.ThreadGroups() {
		if leader := tg.Leader(); leader != nil {
			tids = append(tids, int(i.pidns.IDOfThreadGroup(tg)))
		}
	}

	if len(tids) == 0 {
		return offset, nil
	}
	if relOffset >= int64(len(tids)) {
		return offset, nil
	}

	sort.Ints(tids)
	for _, tid := range tids[relOffset:] {
		dirent := vfs.Dirent{
			Name:    strconv.FormatUint(uint64(tid), 10),
			Type:    linux.DT_DIR,
			Ino:     i.inoGen.NextIno(),
			NextOff: offset + 1,
		}
		if !cb.Handle(dirent) {
			return offset, nil
		}
		offset++
	}
	return offset, nil
}

// Open implements kernfs.Inode.
func (i *tasksInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) {
	fd := &kernfs.GenericDirectoryFD{}
	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, flags)
	return fd.VFSFileDescription(), nil
}

func (i *tasksInode) Stat(vsfs *vfs.Filesystem) linux.Statx {
	stat := i.InodeAttrs.Stat(vsfs)

	// Add dynamic children to link count.
	for _, tg := range i.pidns.ThreadGroups() {
		if leader := tg.Leader(); leader != nil {
			stat.Nlink++
		}
	}

	return stat
}