package pipeline

import (
	"os/exec"
	"io"
)

type Pipe struct {
	Cmds []exec.Cmd
}

func (pl *Pipe) preStart() error {
	for _, cmd := range pl.Cmds[:len(pl.Cmds)-2] {
		if err := cmd.Start(); err != nil {
			return err
		}
	}
	return nil
}

func (pl *Pipe) Start() error {
	for _, cmd := range pl.Cmds {
		if err := cmd.Start(); err != nil {
			return err
		}
	}
	return nil
}

func (pl *Pipe) Wait() error {
	for _, cmd := range pl.Cmds {
		if err := cmd.Wait(); err != nil {
			return err
		}
	}
	return nil
}

func (pl *Pipe) Run() error {
	if err := pl.Start(); err != nil {
		return err
	}
	return pl.Wait()
}

func (pl *Pipe) CombinedOutput() ([]byte, error) {
	if err := pl.preStart(); err != nil {
		return nil, err
	}
	return pl.Cmds[len(pl.Cmds)-1].CombinedOutput()
}

func (pl *Pipe) Output() ([]byte, error) {
	if err := pl.preStart(); err != nil {
		return nil, err
	}
	return pl.Cmds[len(pl.Cmds)-1].Output()
}

func (pl *Pipe) StdinPipe() (io.WriteCloser, error) {
	return pl.Cmds[0].StdinPipe()
}

func (pl *Pipe) StdoutPipe() (io.ReadCloser, error) {
	return pl.Cmds[len(pl.Cmds)-1].StdoutPipe()
}

var _ = &Pipe{}

func Pipeline(cmds ...exec.Cmd) (*Pipe, error) {
	pl := &Pipe{cmds}
	for i := range pl.Cmds[:len(pl.Cmds)-2] {
		out, err := pl.Cmds[i].StdoutPipe()
		if err != nil {
			return nil, err
		}
		pl.Cmds[i+1].Stdin = out
	}
	return pl, nil
}