package notes

import (

"github.com/kballard/go-shellquote"

"github.com/pkg/errors"

"io"

"os"

"os/exec"

)

// PagerWriter is a wrapper of pager command to paging output to writer with pager command such as

// `less` or `more`. Starting process, writing input to process, waiting process finishes may cause

// an error. If one of them causes an error, later operations won't be performed. Instead, the prior

// error is returned.

type PagerWriter struct {

cmd *exec.Cmd

stdin io.WriteCloser

// Cmdline is a string of command line which was spawned

Cmdline string

// Err is an error instance which occurred while paging.

Err error

}

// Wait waits until underlying pager process finishes

func (pager *PagerWriter) Wait() error {

if pager.Err != nil {

return pager.Err

}

pager.stdin.Close()

err := pager.cmd.Wait()

pager.Err = err

return err

}

// Write writes given payload to underlying pager process's stdin

func (pager *PagerWriter) Write(p []byte) (int, error) {

if pager.Err != nil {

return 0, pager.Err

}

n, err := pager.stdin.Write(p)

pager.Err = err

return n, err

}

// StartPagerWriter creates a new PagerWriter instance and spawns underlying pager process with given

// command. pagerCmd can contain options like "less -R". When the command cannot be parsed as shell

// arguments or starting underlying pager process fails, this function returns an error

func StartPagerWriter(pagerCmd string, stdout io.Writer) (*PagerWriter, error) {

cmdline, err := shellquote.Split(pagerCmd)

if err != nil {

return nil, errors.Wrap(err, "Cannot parsing $NOTES_CLI_PAGER as shell command line")

}

cmd := exec.Command(cmdline[0], cmdline[1:]...)

cmd.Stderr = os.Stderr

cmd.Stdout = stdout

stdin, err := cmd.StdinPipe()

if err != nil {

return nil, errors.Wrap(err, "Cannot create pipe stdin to pager command. Please check $NOTES_CLI_PAGER")

}

if err = cmd.Start(); err != nil {

err = errors.Wrapf(err, "Cannot start pager command '%s'. Please check $NOTES_CLI_PAGER is correct", pagerCmd)

}

return &PagerWriter{

Cmdline: pagerCmd,

cmd: cmd,

stdin: stdin,

Err: err,

}, err

}