/*
   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 cgroups

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"

	specs "github.com/opencontainers/runtime-spec/specs-go"
)

func NewCputset(root string) *cpusetController {
	return &cpusetController{
		root: filepath.Join(root, string(Cpuset)),
	}
}

type cpusetController struct {
	root string
}

func (c *cpusetController) Name() Name {
	return Cpuset
}

func (c *cpusetController) Path(path string) string {
	return filepath.Join(c.root, path)
}

func (c *cpusetController) Create(path string, resources *specs.LinuxResources) error {
	if err := c.ensureParent(c.Path(path), c.root); err != nil {
		return err
	}
	if err := os.MkdirAll(c.Path(path), defaultDirPerm); err != nil {
		return err
	}
	if err := c.copyIfNeeded(c.Path(path), filepath.Dir(c.Path(path))); err != nil {
		return err
	}
	if resources.CPU != nil {
		for _, t := range []struct {
			name  string
			value string
		}{
			{
				name:  "cpus",
				value: resources.CPU.Cpus,
			},
			{
				name:  "mems",
				value: resources.CPU.Mems,
			},
		} {
			if t.value != "" {
				if err := ioutil.WriteFile(
					filepath.Join(c.Path(path), fmt.Sprintf("cpuset.%s", t.name)),
					[]byte(t.value),
					defaultFilePerm,
				); err != nil {
					return err
				}
			}
		}
	}
	return nil
}

func (c *cpusetController) Update(path string, resources *specs.LinuxResources) error {
	return c.Create(path, resources)
}

func (c *cpusetController) getValues(path string) (cpus []byte, mems []byte, err error) {
	if cpus, err = ioutil.ReadFile(filepath.Join(path, "cpuset.cpus")); err != nil && !os.IsNotExist(err) {
		return
	}
	if mems, err = ioutil.ReadFile(filepath.Join(path, "cpuset.mems")); err != nil && !os.IsNotExist(err) {
		return
	}
	return cpus, mems, nil
}

// ensureParent makes sure that the parent directory of current is created
// and populated with the proper cpus and mems files copied from
// it's parent.
func (c *cpusetController) ensureParent(current, root string) error {
	parent := filepath.Dir(current)
	if _, err := filepath.Rel(root, parent); err != nil {
		return nil
	}
	// Avoid infinite recursion.
	if parent == current {
		return fmt.Errorf("cpuset: cgroup parent path outside cgroup root")
	}
	if cleanPath(parent) != root {
		if err := c.ensureParent(parent, root); err != nil {
			return err
		}
	}
	if err := os.MkdirAll(current, defaultDirPerm); err != nil {
		return err
	}
	return c.copyIfNeeded(current, parent)
}

// copyIfNeeded copies the cpuset.cpus and cpuset.mems from the parent
// directory to the current directory if the file's contents are 0
func (c *cpusetController) copyIfNeeded(current, parent string) error {
	var (
		err                      error
		currentCpus, currentMems []byte
		parentCpus, parentMems   []byte
	)
	if currentCpus, currentMems, err = c.getValues(current); err != nil {
		return err
	}
	if parentCpus, parentMems, err = c.getValues(parent); err != nil {
		return err
	}
	if isEmpty(currentCpus) {
		if err := ioutil.WriteFile(
			filepath.Join(current, "cpuset.cpus"),
			parentCpus,
			defaultFilePerm,
		); err != nil {
			return err
		}
	}
	if isEmpty(currentMems) {
		if err := ioutil.WriteFile(
			filepath.Join(current, "cpuset.mems"),
			parentMems,
			defaultFilePerm,
		); err != nil {
			return err
		}
	}
	return nil
}

func isEmpty(b []byte) bool {
	return len(bytes.Trim(b, "\n")) == 0
}
