/*
The MIT License (MIT)

Copyright © 2025 pacman64

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the “Software”), to deal
in the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

/*
To compile a smaller-sized command-line app, you can use the `go` command as
follows:

go build -ldflags "-s -w" -trimpath timer.go
*/

package main

import (
	"bufio"
	"io"
	"os"
	"os/exec"
	"os/signal"
	"strconv"
	"sync"
	"time"
)

// Note: the code is avoiding using the fmt package to save hundreds of
// kilobytes on the resulting executable, which is a noticeable difference.

const (
	// gap has the spaces between current timer value and current date/time
	gap = `    `

	// clear has enough spaces in it to cover any chronograph output
	clear = "\r" + `                                              ` + "\r"

	dateTimeFormat = `2006-01-02 15:04:05 Jan Mon`

	forceQuitCode = 255
)

const (
	// every = 100 * time.Millisecond
	// chronoFormat = `15:04:05.0`

	// every = 500 * time.Millisecond
	// chronoFormat = `15:04:05`

	every        = 1000 * time.Millisecond
	chronoFormat = `15:04:05`
)

const info = `
timer [options...] [command...] [args...]


Run a live timer/chronograph on stderr, always showing below all lines
from stdin, which update stdout as they come.

When stdin (or the command run) is over, this app simply quits showing how
long it ran, by extending its last visible timer line on stderr.

You can also use this app without piping anything to its stdin or giving it
any command to run, acting as a simple live clock until you force-quit it,
via Control+C, or end the stdin stream via Control+D.

To ensure any stderr lines don't clash with the chronograph output line,
you can also run this app with arguments to have it run a command, thus
guaranteeing the subtask's stdout and stderr lines show without ever being
mixed up.

Note: by default this app assumes command output is plain-text lines, so a
command's non-empty binary stdout may be corrupted in subtle ways; use the
binary option to avoid that.

The options are, available both in single and double-dash versions

    -b         treat stdin or a command's stdout as generic binary data
    -bin       treat stdin or a command's stdout as generic binary data
    -binary    treat stdin or a command's stdout as generic binary data

    -h         show this help message
    -help      show this help message
`

func main() {
	bin := false
	args := os.Args[1:]

	if len(args) > 0 {
		switch args[0] {
		case `-h`, `--h`, `-help`, `--help`:
			os.Stdout.WriteString(info[1:])
			return

		case `-b`, `--b`, `-bin`, `--bin`, `-binary`, `--binary`:
			bin = true
			args = args[1:]
		}
	}

	if len(args) > 0 && args[0] == `--` {
		args = args[1:]
	}

	if len(args) > 0 {
		os.Exit(runTask(args[0], args[1:], bin))
	}

	err := chronograph(os.Stdin, nil, bin)
	if quit, ok := err.(justQuit); ok {
		os.Exit(quit.exitCode)
	}

	if err != nil {
		showError(err)
		os.Exit(1)
	}
}

// justQuit is a custom error-type which isn't for showing, but for quitting
// the app right away instead
type justQuit struct {
	exitCode int
}

// Error is only to satisfy the error interface, and not for showing
func (justQuit) Error() string {
	return `quitting right away`
}

// runTask handles running the app in `subtask-mode`
func runTask(name string, args []string, bin bool) (exitCode int) {
	cmd := exec.Command(name, args...)
	cmd.Stdin = os.Stdin

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		showError(err)
		return 1
	}
	defer stdout.Close()

	stderr, err := cmd.StderrPipe()
	if err != nil {
		showError(err)
		return 1
	}
	defer stderr.Close()

	if err := cmd.Start(); err != nil {
		showError(err)
		return 1
	}

	err = chronograph(stdout, stderr, bin)
	if quit, ok := err.(justQuit); ok {
		return quit.exitCode
	}
	if err != nil {
		showError(err)
	}

	if err := cmd.Wait(); err != nil {
		showError(err)
	}
	return cmd.ProcessState.ExitCode()
}

func showError(err error) {
	if err != nil {
		os.Stderr.WriteString(err.Error())
		os.Stderr.WriteString("\n")
	}
}

// readBytes is the binary-mode alternative to func readLines for a command's
// standard output
func readBytes(r io.Reader, chunks chan []byte) error {
	defer close(chunks)

	if r == nil {
		return nil
	}

	var buf [16 * 1024]byte

	for {
		n, err := r.Read(buf[:])

		if err == io.EOF {
			if n > 0 {
				chunks <- buf[:n]
			}
			return nil
		}

		if err != nil {
			return err
		}

		if n < 1 {
			continue
		}

		chunks <- buf[:n]
	}
}

// readLines is run twice asynchronously, so that both stdin and stderr lines
// are handled independently, which matters when running a subtask
func readLines(r io.Reader, lines chan []byte) error {
	defer close(lines)

	// when not handling a subtask, this func will be called with a nil
	// reader, since without a subtask, there's no stderr to read from
	if r == nil {
		return nil
	}

	const gb = 1024 * 1024 * 1024
	sc := bufio.NewScanner(r)
	sc.Buffer(nil, 8*gb)

	for sc.Scan() {
		lines <- sc.Bytes()
	}
	return sc.Err()
}

// chronograph runs a live chronograph, showing the time elapsed: 2 input
// sources for lines are handled concurrently, one destined for the app's
// stdout, the other for the app's stderr, without interfering with the
// chronograph lines, which also show on stderr
func chronograph(stdout io.Reader, stderr io.Reader, bin bool) error {
	start := time.Now()
	t := time.NewTicker(every)
	// s is a buffer used to minimize actual writes to final stdout/stderr
	s := make([]byte, 0, 1024)

	// start showing the timer right away
	s = startChronoLine(s[:0], start, start)
	os.Stderr.Write(s)

	// stopped is a special event to handle force-quitting the app
	stopped := make(chan os.Signal, 1)
	defer close(stopped)
	signal.Notify(stopped, os.Interrupt)

	// errors will no longer travel when both input streams are over
	errors := make(chan error)
	var waitAllOutput sync.WaitGroup
	waitAllOutput.Add(2)

	// binary-mode only concerns stdin or stdout, and never stderr
	readOutput := readLines
	if bin {
		readOutput = readBytes
	}

	// relay stdout data asynchronously
	outChunks := make(chan []byte)
	go func() {
		defer waitAllOutput.Done()
		if stdout != nil {
			errors <- readOutput(stdout, outChunks)
		}
	}()

	// relay stderr data asynchronously
	errLines := make(chan []byte)
	go func() {
		defer waitAllOutput.Done()
		if stderr != nil {
			errors <- readLines(stderr, errLines)
		}
	}()

	// quit is a special event which happens when both input streams are over
	quit := make(chan struct{})
	defer close(quit)
	go func() {
		waitAllOutput.Wait()
		close(errors)
		quit <- struct{}{}
	}()

	for {
		select {
		case now := <-t.C:
			s = append(s[:0], clear...)
			s = startChronoLine(s, start, now)
			os.Stderr.Write(s)

		case chunk := <-outChunks:
			if chunk == nil {
				// filter out junk for needlessly-chatty pipes, while still
				// keeping actual empty lines
				continue
			}

			// write-order of the next 3 steps matters, to avoid mixing up
			// lines since stdout and stderr lines can show up together, if
			// not handled correctly

			os.Stderr.WriteString(clear)

			s = append(s[:0], chunk...)
			// add an extra line-feed byte only when in plain-text mode
			if !bin {
				s = append(s, '\n')
			}

			// assume (final) stdout write errors are due to a closed pipe,
			// so quit this app successfully right away
			if _, err := os.Stdout.Write(s); err != nil {
				t.Stop()
				s = startChronoLine(s[:0], start, time.Now())
				s = endChronoLine(s, start)
				os.Stderr.Write(s)
				return nil
			}

			s = startChronoLine(s[:0], start, time.Now())
			os.Stderr.Write(s)

		case line := <-errLines:
			if line == nil {
				// filter out junk for needlessly-chatty pipes, while still
				// keeping actual empty lines
				continue
			}

			s = append(append(append(s[:0], clear...), line...), '\n')
			s = startChronoLine(s, start, time.Now())
			s = endChronoLine(s, start)
			os.Stderr.Write(s)

		case err := <-errors:
			if err == nil {
				continue
			}
			os.Stderr.WriteString(clear)
			showError(err)
			s = startChronoLine(s[:0], start, time.Now())
			os.Stderr.Write(s)

		case <-quit:
			os.Stderr.Write(endChronoLine(s[:0], start))
			return justQuit{0}

		case <-stopped:
			t.Stop()
			os.Stderr.Write(endChronoLine(s[:0], start))
			return justQuit{forceQuitCode}
		}
	}
}

func startChronoLine(buf []byte, start, now time.Time) []byte {
	dt := now.Sub(start)
	buf = time.Time{}.Add(dt).AppendFormat(buf, chronoFormat)
	buf = append(buf, gap...)
	buf = now.AppendFormat(buf, dateTimeFormat)
	return buf
}

func endChronoLine(buf []byte, start time.Time) []byte {
	secs := time.Since(start).Seconds()
	buf = append(buf, gap...)
	buf = strconv.AppendFloat(buf, secs, 'f', 4, 64)
	buf = append(buf, " seconds\n"...)
	return buf
}