package main

import (
	"fmt"
	"os"
	"time"

	"github.com/schollz/progressbar/v3"
)

// plainInterval is the minimum time between progress lines when stderr
// is not a TTY.
const plainInterval = 5 * time.Second

// barThrottle caps how often the TTY progress bar redraws.
const barThrottle = 100 * time.Millisecond

// walkSpinnerType selects the progressbar library's spinner style used
// for the walk pass, which has no known total.
const walkSpinnerType = 14

// percentScale converts a fraction to a percentage.
const percentScale = 100

// stderrIsTTY reports whether stderr is attached to a terminal.
func stderrIsTTY() bool {
	fi, err := os.Stderr.Stat()
	if err != nil {
		return false
	}

	return fi.Mode()&os.ModeCharDevice != 0
}

// progress renders one scan pass's progress on stderr. On a TTY it
// delegates to the progressbar library (spinner style when the total is
// unknown, full bar with count/percent/rate/elapsed/ETA otherwise). When
// stderr is not a TTY it emits no ANSI redraws: it prints a plain
// one-line update no more often than every plainInterval.
//
// All methods must be called from the main goroutine only.
type progress struct {
	label string
	total int64 // -1 when unknown (walk pass)
	bar   *progressbar.ProgressBar
	count int64
	start time.Time
	last  time.Time
}

func newProgress(label string, total int64) *progress {
	p := &progress{label: label, total: total, start: time.Now()}
	if !stderrIsTTY() {
		return p
	}

	opts := []progressbar.Option{
		progressbar.OptionSetWriter(os.Stderr),
		progressbar.OptionSetDescription(label),
		progressbar.OptionShowCount(),
		progressbar.OptionShowIts(),
		progressbar.OptionSetItsString("files"),
		progressbar.OptionSetElapsedTime(true),
		progressbar.OptionThrottle(barThrottle),
	}
	if total >= 0 {
		opts = append(opts,
			progressbar.OptionSetPredictTime(true),
			progressbar.OptionShowElapsedTimeOnFinish(),
		)
	} else {
		opts = append(opts,
			progressbar.OptionSetPredictTime(false),
			progressbar.OptionSpinnerType(walkSpinnerType),
		)
	}

	p.bar = progressbar.NewOptions64(total, opts...)

	return p
}

// increment records one completed item and refreshes the display.
func (p *progress) increment() {
	p.count++
	if p.bar != nil {
		_ = p.bar.Add(1)

		return
	}

	if time.Since(p.last) >= plainInterval {
		p.last = time.Now()
		fmt.Fprintln(os.Stderr, p.plainLine())
	}
}

// warnf prints a one-line warning to stderr without corrupting the bar.
func (p *progress) warnf(format string, args ...any) {
	if p.bar != nil {
		_ = p.bar.Clear()
	}

	fmt.Fprintf(os.Stderr, format+"\n", args...)
}

// finish terminates the pass's display.
func (p *progress) finish() {
	if p.bar != nil {
		_ = p.bar.Finish()

		fmt.Fprintln(os.Stderr)

		return
	}

	fmt.Fprintln(os.Stderr, p.plainLine())
}

// plainLine formats a non-TTY progress line.
func (p *progress) plainLine() string {
	elapsed := time.Since(p.start)
	if p.total < 0 {
		return fmt.Sprintf("%s: %d files, elapsed %s",
			p.label, p.count, elapsed.Round(time.Second))
	}

	pct := float64(percentScale)
	if p.total > 0 {
		pct = percentScale * float64(p.count) / float64(p.total)
	}

	rate := 0.0
	if s := elapsed.Seconds(); s > 0 {
		rate = float64(p.count) / s
	}

	eta := "?"

	if rate > 0 && p.count <= p.total {
		remaining := time.Duration(float64(p.total-p.count) / rate * float64(time.Second))
		eta = remaining.Round(time.Second).String()
	}

	return fmt.Sprintf("%s: [%d/%d] %.0f%% %.0f files/s elapsed %s eta %s",
		p.label, p.count, p.total, pct, rate,
		elapsed.Round(time.Second), eta)
}