package main

import (
	"bytes"
	"errors"
	"flag"
	"fmt"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"time"

	"golang.org/x/term"
)

var n = flag.Duration("n", 2*time.Minute, "polling interval")

func run() error {
	cols, _, err := term.GetSize(int(os.Stdout.Fd()))
	if err != nil {
		return err
	}
	args := flag.Args()
	if len(args) < 2 {
		return errors.New("usage error")
	}
	maxStr := args[0]
	maxVal, err := strconv.Atoi(maxStr)
	if err != nil {
		return fmt.Errorf("max: %s", err)
	}
	cmd := args[1:]
	type measurement struct {
		t time.Time
		i int
	}
	var measurements []measurement
	for i := 0; ; i++ {
		outputBytes, err := exec.Command(cmd[0], cmd[1:]...).Output()
		if err != nil {
			fmt.Println(err)
			continue
		}
		output, err := strconv.Atoi(string(bytes.TrimSuffix(outputBytes, []byte("\n"))))
		if err != nil {
			fmt.Println(err)
			continue
		}
		p := output * cols / maxVal
		if i > 0 {
			fmt.Print("\033[2F\033[J")
		}
		fmt.Printf("%s>\n", strings.Repeat("=", max(p-1, 0)))
		measurements = append(measurements, measurement{time.Now(), output})
		if len(measurements) > 20 {
			measurements = measurements[1:]
		}
		deltaT := measurements[len(measurements)-1].t.Sub(measurements[0].t)
		delta := measurements[len(measurements)-1].i - measurements[0].i
		if delta == 0 {
			fmt.Println()
		} else {
			fmt.Printf("ETA: %s\n", time.Duration(float64(maxVal-output)/float64(delta)*float64(deltaT)).Round(time.Second))
		}
		time.Sleep(*n)
	}
}

func main() {
	flag.Parse()
	if err := run(); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}