package main

import (
	"fmt"
	"io"
	"math"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"sync"
	"testing"
	"time"
	"unicode/utf8"
)

// testRedraw is the redraw interval the tests give a display, so that
// many redraws fit in a few milliseconds.
const testRedraw = time.Millisecond

// testDeadline bounds how long a test waits for a display to draw what
// it expects.
const testDeadline = 5 * time.Second

// testClock is a clock a test moves by hand, for a display that reads
// it from its own goroutine too.
type testClock struct {
	mu  sync.Mutex
	now time.Time
}

// Now returns the clock's time.
func (c *testClock) Now() time.Time {
	c.mu.Lock()
	defer c.mu.Unlock()

	return c.now
}

// Add moves the clock on by d.
func (c *testClock) Add(d time.Duration) {
	c.mu.Lock()
	defer c.mu.Unlock()

	c.now = c.now.Add(d)
}

//nolint:paralleltest // replaces the process-wide os.Stderr
func TestStderrIsTTYFalseForNonTerminals(t *testing.T) {
	r, pipe, err := os.Pipe()
	if err != nil {
		t.Fatal(err)
	}

	regular, err := os.Create(filepath.Join(t.TempDir(), "stderr"))
	if err != nil {
		t.Fatal(err)
	}

	devNull, err := os.OpenFile(os.DevNull, os.O_WRONLY, 0)
	if err != nil {
		t.Fatal(err)
	}

	saved := os.Stderr

	t.Cleanup(func() {
		os.Stderr = saved

		for _, f := range []*os.File{r, pipe, regular, devNull} {
			_ = f.Close()
		}
	})

	cases := map[string]*os.File{
		"a pipe":         pipe,
		"a regular file": regular,
		os.DevNull:       devNull,
	}

	for name, f := range cases {
		os.Stderr = f

		if stderrIsTTY() {
			t.Errorf("stderrIsTTY() = true with stderr on %s", name)
		}
	}
}

func TestPhaseLabel(t *testing.T) {
	t.Parallel()

	phases := []string{"load", "walk", "hash"}
	if got := phaseLabel(phases, "walk"); got != "[2/3] walk" {
		t.Errorf("phaseLabel = %q, want %q", got, "[2/3] walk")
	}
}

// TestProgressLine checks the line a display shows in each state, ten
// seconds into the phase, with no draw since the first and the last
// item just completed.
func TestProgressLine(t *testing.T) {
	t.Parallel()

	now := time.Now()
	ago := now.Add(-10 * time.Second)

	cases := []struct {
		p    *progress
		want string
	}{{
		p: &progress{
			label: scanPhase("load"), total: -1,
			waitingFor: countingRecords,
		},
		want: "[1/5] load: counting the records, elapsed 10s, eta unknown",
	}, {
		p: &progress{
			label: scanPhase("hash"), unit: scanUnit, total: 100, count: 20,
		},
		want: "[3/5] hash: [20/100] 20%, 2 files/s, elapsed 10s, eta 40s",
	}, {
		p:    &progress{label: scanPhase("hash"), unit: scanUnit, total: 100},
		want: "[3/5] hash: [0/100] 0%, 0 files/s, elapsed 10s, eta unknown",
	}, {
		p:    &progress{label: scanPhase("update"), unit: scanUnit, total: 0},
		want: "[4/5] update: [0/0] 100%, 0 files/s, elapsed 10s, eta 0s",
	}, {
		p: &progress{
			label: scanPhase("walk"), unit: scanUnit, total: 100,
			estimate: true, count: 20,
		},
		want: "[2/5] walk: [20/~100] 20%, 2 files/s, elapsed 10s, eta 40s",
	}, {
		// Past the estimate the walk cannot tell how long it has left.
		p: &progress{
			label: scanPhase("walk"), unit: scanUnit, total: 100,
			estimate: true, count: 120,
		},
		want: "[2/5] walk: [120/~100] 120%, 12 files/s, elapsed 10s, " +
			"eta unknown",
	}, {
		// A first scan's walk has no estimate.
		p: &progress{
			label: scanPhase("walk"), unit: scanUnit, total: -1, count: 20,
		},
		want: "[2/5] walk: 20 files, 2 files/s, elapsed 10s, eta unknown",
	}, {
		// The rate is in what the phase counts.
		p: &progress{
			label: treesPhase("group"), unit: "directories", total: 100,
			count: 20,
		},
		want: "[3/4] group: [20/100] 20%, 2 directories/s, elapsed 10s, " +
			"eta 40s",
	}}

	for _, tc := range cases {
		tc.p.start, tc.p.rateStart, tc.p.lastItem = ago, ago, now
		tc.p.drawn = []drawnCount{{at: ago}}

		if got, _ := tc.p.line(now, math.MaxInt, true); got != tc.want {
			t.Errorf("line = %q, want %q", got, tc.want)
		}
	}
}

// TestLineFitsRoom checks how a line is fitted to the room it has, ten
// seconds into the phase, and fifty into a phase with no file read for
// the last 42: it leaves out the rate, or what the phase waits for,
// then what it says of the stall, and is cut only when what is left is
// still too wide.
func TestLineFitsRoom(t *testing.T) {
	t.Parallel()

	now := time.Now()
	ago := now.Add(-10 * time.Second)
	hash := &progress{
		label: scanPhase("hash"), unit: scanUnit, total: 100, count: 20,
		start: ago, rateStart: ago, lastItem: now,
		drawn: []drawnCount{{at: ago}},
	}
	content := &progress{
		label: scanPhase("content"), total: -1,
		waitingFor: searchingDatabase, start: ago, rateStart: ago,
	}

	started := now.Add(-50 * time.Second)
	stalled := &progress{
		label: scanPhase("hash"), unit: scanUnit, total: 100, count: 20,
		doing: readingFiles, start: started, rateStart: started,
		lastItem: now.Add(-42 * time.Second),
		drawn:    []drawnCount{{at: now.Add(-rateWindow), count: 20}},
	}

	cases := []struct {
		p       *progress
		room    int
		percent bool
		want    string
		fits    bool
	}{{
		p: hash, room: 57, percent: true,
		want: "[3/5] hash: [20/100] 20%, 2 files/s, elapsed 10s, eta 40s",
		fits: true,
	}, {
		p: hash, room: 56, percent: true,
		want: "[3/5] hash: [20/100] 20%, elapsed 10s, eta 40s",
		fits: true,
	}, {
		p: hash, room: 45, percent: true,
		want: "[3/5] hash: [20/100] 20%, elapsed 10s, eta 40",
		fits: false,
	}, {
		// Before the library's bar, which shows the percent.
		p: hash, room: 57, percent: false,
		want: "[3/5] hash: [20/100], 2 files/s, elapsed 10s, eta 40s",
		fits: true,
	}, {
		p: content, room: 40, percent: true,
		want: "[5/5] content: elapsed 10s, eta unknown",
		fits: true,
	}, {
		p: stalled, room: 101, percent: true,
		want: "[3/5] hash: [20/100] 20%, 0 files/s, no files finished for " +
			"42s, reading files, elapsed 50s, eta 3m20s",
		fits: true,
	}, {
		p: stalled, room: 100, percent: true,
		want: "[3/5] hash: [20/100] 20%, no files finished for 42s, " +
			"reading files, elapsed 50s, eta 3m20s",
		fits: true,
	}, {
		p: stalled, room: 89, percent: true,
		want: "[3/5] hash: [20/100] 20%, elapsed 50s, eta 3m20s",
		fits: true,
	}}

	for _, tc := range cases {
		got, fits := tc.p.line(now, tc.room, tc.percent)
		if got != tc.want || fits != tc.fits {
			t.Errorf("line(%d, %t) = %q, %t, want %q, %t",
				tc.room, tc.percent, got, fits, tc.want, tc.fits)
		}
	}
}

// TestSetTotalStartsRate checks that setTotal starts a phase's rate,
// its ETA and its time with no record read from when the total becomes
// known, not from when the phase started waiting for it.
func TestSetTotalStartsRate(t *testing.T) {
	t.Parallel()

	clock := &testClock{now: time.Now()}
	waited := clock.Now().Add(-20 * time.Second)
	p := &progress{
		now: clock.Now, label: scanPhase("load"), unit: scanUnit, total: -1,
		doing: readingDatabase, start: waited, rateStart: waited,
		lastItem: waited, drawn: []drawnCount{{at: waited}},
	}

	p.setTotal(100)

	// Ten seconds after the total came, no record has been read yet.
	clock.Add(10 * time.Second)

	want := "[1/5] load: [0/100] 0%, 0 files/s, no files finished for 10s, " +
		"reading the database, elapsed 30s, eta unknown"
	if got, _ := p.line(clock.Now(), math.MaxInt, true); got != want {
		t.Errorf("line = %q, want %q", got, want)
	}

	// Then 20 are.
	for range 20 {
		p.increment()
	}

	want = "[1/5] load: [20/100] 20%, 2 files/s, elapsed 30s, eta 40s"
	if got, _ := p.line(clock.Now(), math.MaxInt, true); got != want {
		t.Errorf("line = %q, want %q", got, want)
	}
}

// awaitOutput waits until stderr holds want at least times times, and
// fails the test if it never does.
func awaitOutput(t *testing.T, stderr func() string, want string,
	times int,
) {
	t.Helper()

	deadline := time.Now().Add(testDeadline)
	for strings.Count(stderr(), want) < times {
		if time.Now().After(deadline) {
			t.Fatalf("stderr = %q, want %q at least %d times",
				stderr(), want, times)
		}

		time.Sleep(testRedraw)
	}
}

// TestPlainProgressPrintsAtStartAndEnd checks that when stderr is not a
// terminal a phase prints its line the moment it starts, before its
// first item, nothing for the items it completes before plainInterval
// has passed, and its line again as it ends.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestPlainProgressPrintsAtStartAndEnd(t *testing.T) {
	stderr := captureStderr(t)
	p := newProgress(progressParams{
		label: scanPhase("hash"), unit: scanUnit, total: 1000,
	})

	for range 1000 {
		p.increment()
	}

	p.finish()

	lines := strings.Split(strings.TrimSuffix(stderr(), "\n"), "\n")

	want := "[3/5] hash: [0/1000] 0%, 0 files/s, elapsed 0s, eta unknown"
	if len(lines) != 2 || lines[0] != want ||
		!strings.HasPrefix(lines[1], "[3/5] hash: [1000/1000] 100%, ") {
		t.Errorf("stderr lines = %q, want %q, then the line at 1000",
			lines, want)
	}
}

// TestPlainProgressPrintsWhileWaiting checks that a phase waiting with
// no completed items still prints a line every interval.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestPlainProgressPrintsWhileWaiting(t *testing.T) {
	stderr := captureStderr(t)
	p := startProgress(progressParams{
		label: scanPhase("load"), total: -1,
		waitingFor: countingRecords,
	}, nil, testRedraw, time.Now)

	awaitOutput(t, stderr,
		"[1/5] load: counting the records, elapsed 0s, eta unknown\n", 3)
	p.finish()
}

// TestPlainProgressStalledProducer checks that a phase whose files stop
// coming, as when one large file is being read or a disk is slow, goes
// on printing its line every interval: the rate falls to 0 once no file
// has been read for rateWindow, and once none has for stallTime the
// line says so, and what the phase is doing. The test moves the
// display's clock by hand.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestPlainProgressStalledProducer(t *testing.T) {
	stderr := captureStderr(t)
	clock := &testClock{now: time.Now()}
	p := startProgress(progressParams{
		label: scanPhase("hash"), unit: scanUnit, total: 100,
		doing: readingFiles,
	}, nil, testRedraw, clock.Now)

	// Pass or fail, the display ends before stderr is put back.
	t.Cleanup(p.finish)

	// 20 files read as the phase starts, then none.
	for range 20 {
		p.increment()
	}

	clock.Add(5 * time.Second)
	awaitOutput(t, stderr,
		"[3/5] hash: [20/100] 20%, 4 files/s, elapsed 5s, eta 20s\n", 3)

	clock.Add(time.Second)
	awaitOutput(t, stderr,
		"[3/5] hash: [20/100] 20%, 0 files/s, elapsed 6s, eta 24s\n", 3)

	clock.Add(4 * time.Second)
	awaitOutput(t, stderr,
		"[3/5] hash: [20/100] 20%, 0 files/s, no files finished for 10s, "+
			"reading files, elapsed 10s, eta 40s\n", 3)
}

// TestPlainProgressRateAfterStall draws a phase's plain line by hand, a
// little over plainInterval after the line before, as a late tick
// does, through a stall and a burst of files after it: the rate covers
// the files read since the line before, while the ETA comes from the
// phase's average.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestPlainProgressRateAfterStall(t *testing.T) {
	stderr := captureStderr(t)
	clock := &testClock{now: time.Now()}

	// No timed draws: the test draws.
	p := startProgress(progressParams{
		label: scanPhase("hash"), unit: scanUnit, total: 1000,
		doing: readingFiles,
	}, nil, time.Hour, clock.Now)

	late := plainInterval + time.Millisecond

	clock.Add(late)
	p.draw()
	clock.Add(late)
	p.draw()

	for range 100 {
		p.increment()
	}

	clock.Add(late)
	p.finish()

	want := []string{
		"[3/5] hash: [0/1000] 0%, 0 files/s, elapsed 0s, eta unknown",
		"[3/5] hash: [0/1000] 0%, 0 files/s, elapsed 5s, eta unknown",
		"[3/5] hash: [0/1000] 0%, 0 files/s, no files finished for 10s, " +
			"reading files, elapsed 10s, eta unknown",
		"[3/5] hash: [100/1000] 10%, 20 files/s, elapsed 15s, eta 2m15s",
	}

	lines := strings.Split(strings.TrimSuffix(stderr(), "\n"), "\n")
	if !slices.Equal(lines, want) {
		t.Errorf("stderr lines = %q, want %q", lines, want)
	}
}

// TestProgressRateAfterStallRedrawn draws a phase by hand every
// redrawInterval, as a terminal does, through a stall of stallTime and
// a burst of files after it: the rate covers the files read over the
// last rateWindow, and falls to 0 once the burst is older than that,
// while the ETA comes from the phase's average. Plain lines show each
// draw.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestProgressRateAfterStallRedrawn(t *testing.T) {
	stderr := captureStderr(t)
	clock := &testClock{now: time.Now()}

	// No timed draws: the test draws.
	p := startProgress(progressParams{
		label: scanPhase("hash"), unit: scanUnit, total: 1000,
		doing: readingFiles,
	}, nil, time.Hour, clock.Now)

	// redraw draws the display every redrawInterval for d.
	redraw := func(d time.Duration) {
		for range d / redrawInterval {
			clock.Add(redrawInterval)
			p.draw()
		}
	}

	redraw(stallTime)

	for range 50 {
		p.increment()
	}

	redraw(rateWindow + redrawInterval)
	p.finish()

	want := "[3/5] hash: [50/1000] 5%, 10 files/s, elapsed 15s, eta 4m45s\n" +
		"[3/5] hash: [50/1000] 5%, 0 files/s, elapsed 15s, eta 4m47s\n"
	if !strings.Contains(stderr(), want) {
		t.Errorf("stderr = %q, want the lines %q", stderr(), want)
	}
}

// lastFrame returns what a terminal shows of the frames a display drew:
// the last one. The library starts each frame with a carriage return
// and erases the previous one with spaces first.
func lastFrame(out string) string {
	var shown string

	for frame := range strings.SplitSeq(out, "\r") {
		if strings.TrimSpace(frame) != "" {
			shown = frame
		}
	}

	return shown
}

// TestTerminalRedrawsWhileWaiting checks that the terminal display of a
// phase, spinner or bar, keeps being drawn while the phase waits for its
// next item, with the elapsed time as of now, and shows every item
// completed before the wait. stderr is not a terminal here, so the
// displays take it to be fallbackWidth wide.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestTerminalRedrawsWhileWaiting(t *testing.T) {
	stderr := captureStderr(t)

	cases := []struct {
		params progressParams
		want   string // how the line shows a count of 50
	}{
		{
			progressParams{label: scanPhase("walk"), unit: scanUnit, total: -1},
			"50 files,",
		},
		{
			progressParams{label: scanPhase("hash"), unit: scanUnit, total: 100},
			"[50/100],",
		},
	}

	for _, tc := range cases {
		before := len(stderr())
		since := func() string { return stderr()[before:] }
		p := startProgress(tc.params, terminalWidth, testRedraw, time.Now)

		for range 50 {
			p.increment()
		}

		// An hour into the phase, without waiting an hour.
		p.mu.Lock()
		p.start = p.start.Add(-time.Hour)
		p.mu.Unlock()

		awaitOutput(t, since, "elapsed 1h0m0s", 1)
		p.finish()

		if shown := lastFrame(since()); !strings.Contains(shown, tc.want) {
			t.Errorf("terminal shows %q, want %q", shown, tc.want)
		}
	}
}

// drawLate draws the display params describes on a terminal width
// columns wide as it starts and once more as it ends, with count items
// done two and a half hours into the phase, the last just now, and
// returns what it wrote to stderr.
func drawLate(stderr func() string, params progressParams, width int,
	count int64,
) string {
	before := len(stderr())
	clock := &testClock{now: time.Now()}

	// No timed draws come between the two.
	p := startProgress(params, func() int { return width }, time.Hour,
		clock.Now)

	// Without counting the items one by one or waiting the hours.
	clock.Add(150 * time.Minute)

	p.mu.Lock()
	p.count, p.lastItem = count, clock.Now()
	p.mu.Unlock()

	p.finish()

	return stderr()[before:]
}

// TestTerminalLinesKeepETA checks the line each display shows on an
// 80-column terminal at a large scan's counts and times, and the line
// of trees' read phase at the same counts: the rate is left out, so
// that the elapsed time and the ETA stay whole.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestTerminalLinesKeepETA(t *testing.T) {
	stderr := captureStderr(t)

	cases := []struct {
		params progressParams
		want   string
	}{{
		// Past its estimate, the walk cannot tell how long it has left.
		params: progressParams{
			label: scanPhase("walk"), unit: scanUnit, total: 1200000,
			estimate: true,
		},
		want: "[2/5] walk: [1234567/~1200000] 103%, elapsed 2h30m0s, " +
			"eta unknown",
	}, {
		params: progressParams{
			label: scanPhase("hash"), unit: scanUnit, total: 9876543,
		},
		want: "[3/5] hash: [1234567/9876543] 12%, elapsed 2h30m0s, " +
			"eta 17h30m0s",
	}, {
		params: progressParams{
			label: scanPhase("content"), unit: scanUnit, total: 9876543,
		},
		want: "[5/5] content: [1234567/9876543] 12%, elapsed 2h30m0s, " +
			"eta 17h30m0s",
	}, {
		params: progressParams{
			label: treesPhase("read"), unit: "records", total: 9876543,
		},
		want: "[2/4] read: [1234567/9876543] 12%, elapsed 2h30m0s, " +
			"eta 17h30m0s",
	}}

	for _, tc := range cases {
		out := drawLate(stderr, tc.params, 80, 1234567)
		if shown := lastFrame(out); !strings.Contains(shown, tc.want) {
			t.Errorf("terminal shows %q, want %q", shown, tc.want)
		}
	}
}

// TestTerminalLinesFitWidth draws a large scan's bar display and a small
// scan's, two and a half hours into the phase, on terminals from 120
// columns down to 40, and checks that every line stays clear of the
// terminal's last column. A line that reaches it wraps, and every
// redraw then leaves a line behind. The bar is drawn where it has room,
// as at 120 columns, and left out where it has none.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestTerminalLinesFitWidth(t *testing.T) {
	stderr := captureStderr(t)

	for _, width := range []int{120, 100, 80, 72, 60, 50, 40} {
		for _, total := range []int64{9876543, 20000} {
			params := progressParams{
				label: scanPhase("content"), unit: scanUnit, total: total,
			}
			out := drawLate(stderr, params, width, total/8)

			if width == 120 && !strings.Contains(out, "% |") {
				t.Errorf("no bar on a terminal %d wide: %q", width, out)
			}

			lines := strings.FieldsFuncSeq(out, func(r rune) bool {
				return r == '\r' || r == '\n'
			})

			for line := range lines {
				if n := utf8.RuneCountInString(line); n >= width {
					t.Errorf("a line of %d columns on a terminal %d wide: %q",
						n, width, line)
				}
			}
		}
	}
}

// TestTerminalNarrowedRedrawsInPlace draws a large scan's display, two
// and a half hours into the phase, on a terminal 120 columns wide, then
// makes the terminal narrower than that line and draws it again a few
// times. Nothing written after that, the erase before each redraw
// included, may reach the narrower terminal's last column: it would
// wrap, and every redraw would leave a line behind. At these widths the
// spinner stays a spinner and the bar stays a bar.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestTerminalNarrowedRedrawsInPlace(t *testing.T) {
	stderr := captureStderr(t)

	cases := []struct {
		params progressParams
		narrow int
	}{
		{
			progressParams{label: scanPhase("walk"), unit: scanUnit, total: -1},
			60,
		},
		{
			progressParams{
				label: scanPhase("hash"), unit: scanUnit, total: 9876543,
			},
			90,
		},
	}

	for _, tc := range cases {
		width := 120
		clock := &testClock{now: time.Now()}

		// No timed draws: the test draws.
		p := startProgress(tc.params, func() int { return width }, time.Hour,
			clock.Now)

		clock.Add(150 * time.Minute)

		p.mu.Lock()
		p.count, p.lastItem = 1234567, clock.Now()
		p.mu.Unlock()

		p.draw()

		width = tc.narrow
		before := len(stderr())

		p.draw()
		p.draw()
		p.finish()

		lines := strings.FieldsFuncSeq(stderr()[before:], func(r rune) bool {
			return r == '\r' || r == '\n'
		})

		for line := range lines {
			if n := utf8.RuneCountInString(line); n >= width {
				t.Errorf("%d columns written on a terminal made %d wide: %q",
					n, width, line)
			}
		}
	}
}

// TestProgressWarningsOnOwnLines drives the terminal displays, spinner
// and bar, through a run of warnings with no items between them, as when
// the walk meets many unreadable paths, for many redraws: every warning
// must land on a line of its own, never inside a redraw.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestProgressWarningsOnOwnLines(t *testing.T) {
	stderr := captureStderr(t)

	cases := []progressParams{
		{label: scanPhase("walk"), total: -1},
		{label: scanPhase("hash"), total: 10},
	}

	issued := 0

	for _, params := range cases {
		p := startProgress(params, terminalWidth, testRedraw, time.Now)

		// No pause between warnings: one written straight to stderr is
		// garbled only if a redraw lands while it is being written.
		for start := time.Now(); time.Since(start) < 50*testRedraw; issued++ {
			p.warnf("warning")
		}

		p.finish()
	}

	// A terminal shows each line as the text after its last carriage
	// return.
	shown := 0

	for line := range strings.SplitSeq(stderr(), "\n") {
		if !strings.Contains(line, "warning") {
			continue
		}

		shown++

		if text := line[strings.LastIndex(line, "\r")+1:]; text != "warning" {
			t.Errorf("terminal shows %q, want %q", text, "warning")
		}
	}

	if shown != issued {
		t.Errorf("%d warning lines, want %d", shown, issued)
	}
}

// TestProgressWriterRowsOnOwnLines drives the terminal displays,
// spinner and bar, through a run of rows written through the display's
// writer to the same terminal, as stdout is in a plain "sfdupes trees",
// each written out at once, for many redraws: the terminal must show
// every row whole, in order, on a line of its own.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestProgressWriterRowsOnOwnLines(t *testing.T) {
	stderr := captureStderr(t)

	cases := []progressParams{
		{
			label: treesPhase("open"), total: -1,
			waitingFor: "opening the database",
		},
		{label: treesPhase("write"), unit: "groups", total: 10},
	}

	var want []string

	for _, params := range cases {
		p := startProgress(params, terminalWidth, testRedraw, time.Now)
		out := p.writer(os.Stderr)

		// No pause between rows: one is garbled only if a redraw lands
		// on its line.
		for start := time.Now(); time.Since(start) < 50*testRedraw; {
			row := fmt.Sprintf("row %d", len(want))
			want = append(want, row)

			_, err := fmt.Fprintln(out, row)
			if err == nil {
				err = out.Flush()
			}

			if err != nil {
				t.Fatal(err)
			}
		}

		p.finish()
	}

	// A terminal shows each line as the text after its last carriage
	// return.
	var shown []string

	for line := range strings.SplitSeq(stderr(), "\n") {
		if strings.Contains(line, "row ") {
			shown = append(shown, line[strings.LastIndex(line, "\r")+1:])
		}
	}

	if len(shown) != len(want) {
		t.Fatalf("terminal shows %d rows, want %d", len(shown), len(want))
	}

	for i := range want {
		if shown[i] != want[i] {
			t.Fatalf("terminal shows %q, want %q", shown[i], want[i])
		}
	}
}

// TestProgressWriterStalledStdoutKeepsLines writes a row larger than a
// pipe holds through the display's writer to a pipe nobody reads yet,
// as stdout is when its reader has stopped while stderr goes to a file:
// while the write waits, the display must go on printing its line.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestProgressWriterStalledStdoutKeepsLines(t *testing.T) {
	stderr := captureStderr(t)

	r, w, err := os.Pipe()
	if err != nil {
		t.Fatal(err)
	}

	t.Cleanup(func() {
		_ = w.Close()
		_ = r.Close()
	})

	p := startProgress(progressParams{label: treesPhase("write"), total: 1},
		nil, testRedraw, time.Now)
	out := p.writer(w)
	written := make(chan error, 1)

	go func() {
		_, writeErr := fmt.Fprintln(out, strings.Repeat("x", ioBufSize))
		written <- writeErr
	}()

	// Pass or fail, the pipe is then read so that the write ends, and
	// the display ends before stderr is put back.
	t.Cleanup(func() {
		go func() {
			_, _ = io.Copy(io.Discard, r)
		}()

		writeErr := <-written
		if writeErr != nil {
			t.Error(writeErr)
		}

		p.finish()
	})

	// The first byte read shows that the write has started; the rest
	// of the row waits until the pipe is read.
	_, err = r.Read(make([]byte, 1))
	if err != nil {
		t.Fatal(err)
	}

	line := "[4/4] write: "
	awaitOutput(t, stderr, line, strings.Count(stderr(), line)+3)
}

// TestTerminalStoppedShortKeepsCount checks that the terminal display
// of a phase that stops before its total, as an interrupted one does,
// is left showing the count it stopped at rather than a full bar.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestTerminalStoppedShortKeepsCount(t *testing.T) {
	stderr := captureStderr(t)
	p := startProgress(progressParams{label: scanPhase("hash"), total: 10},
		terminalWidth, redrawInterval, time.Now)

	p.increment()
	p.increment()
	p.finish()

	if shown := lastFrame(stderr()); !strings.Contains(shown, "[2/10],") {
		t.Errorf("terminal shows %q, want a count of 2 of 10", shown)
	}
}

// TestWarningAfterLastItemKeepsBar checks that a warning printed after
// a phase's last item, as for a failed read of the last file, leaves the
// phase's full bar on the terminal below the warning.
//
//nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
func TestWarningAfterLastItemKeepsBar(t *testing.T) {
	stderr := captureStderr(t)
	p := startProgress(progressParams{label: scanPhase("hash"), total: 2},
		terminalWidth, testRedraw, time.Now)

	p.increment()
	p.increment()

	awaitOutput(t, stderr, "[2/2],", 1)
	p.warnf("warning")
	p.finish()

	if shown := lastFrame(stderr()); !strings.Contains(shown, "[2/2],") {
		t.Errorf("terminal shows %q, want a count of 2 of 2", shown)
	}
}