/*
Copyright The containerd Authors.
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

    https://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 (
	"context"
	"fmt"
	"io"
	"os"
	"sync"
	"syscall"

	"github.com/containerd/fifo"
	runc "github.com/containerd/go-runc"
)

// TODO(random-liu): This file can be a util.

var bufPool = sync.Pool{
	New: func() interface{} {
		buffer := make([]byte, 32<<10)
		return &buffer
	},
}

func copyPipes(ctx context.Context, rio runc.IO, stdin, stdout, stderr string, wg, cwg *sync.WaitGroup) error {
	var sameFile io.WriteCloser
	for _, i := range []struct {
		name string
		dest func(wc io.WriteCloser, rc io.Closer)
	}{
		{
			name: stdout,
			dest: func(wc io.WriteCloser, rc io.Closer) {
				wg.Add(1)
				cwg.Add(1)
				go func() {
					cwg.Done()
					p := bufPool.Get().(*[]byte)
					defer bufPool.Put(p)
					io.CopyBuffer(wc, rio.Stdout(), *p)
					wg.Done()
					wc.Close()
					if rc != nil {
						rc.Close()
					}
				}()
			},
		}, {
			name: stderr,
			dest: func(wc io.WriteCloser, rc io.Closer) {
				wg.Add(1)
				cwg.Add(1)
				go func() {
					cwg.Done()
					p := bufPool.Get().(*[]byte)
					defer bufPool.Put(p)
					io.CopyBuffer(wc, rio.Stderr(), *p)
					wg.Done()
					wc.Close()
					if rc != nil {
						rc.Close()
					}
				}()
			},
		},
	} {
		ok, err := isFifo(i.name)
		if err != nil {
			return err
		}
		var (
			fw io.WriteCloser
			fr io.Closer
		)
		if ok {
			if fw, err = fifo.OpenFifo(ctx, i.name, syscall.O_WRONLY, 0); err != nil {
				return fmt.Errorf("gvisor-containerd-shim: opening %s failed: %s", i.name, err)
			}
			if fr, err = fifo.OpenFifo(ctx, i.name, syscall.O_RDONLY, 0); err != nil {
				return fmt.Errorf("gvisor-containerd-shim: opening %s failed: %s", i.name, err)
			}
		} else {
			if sameFile != nil {
				i.dest(sameFile, nil)
				continue
			}
			if fw, err = os.OpenFile(i.name, syscall.O_WRONLY|syscall.O_APPEND, 0); err != nil {
				return fmt.Errorf("gvisor-containerd-shim: opening %s failed: %s", i.name, err)
			}
			if stdout == stderr {
				sameFile = fw
			}
		}
		i.dest(fw, fr)
	}
	if stdin == "" {
		return nil
	}
	f, err := fifo.OpenFifo(ctx, stdin, syscall.O_RDONLY|syscall.O_NONBLOCK, 0)
	if err != nil {
		return fmt.Errorf("gvisor-containerd-shim: opening %s failed: %s", stdin, err)
	}
	cwg.Add(1)
	go func() {
		cwg.Done()
		p := bufPool.Get().(*[]byte)
		defer bufPool.Put(p)

		io.CopyBuffer(rio.Stdin(), f, *p)
		rio.Stdin().Close()
		f.Close()
	}()
	return nil
}

// isFifo checks if a file is a fifo
// if the file does not exist then it returns false
func isFifo(path string) (bool, error) {
	stat, err := os.Stat(path)
	if err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	}
	if stat.Mode()&os.ModeNamedPipe == os.ModeNamedPipe {
		return true, nil
	}
	return false, nil
}