progress: show multiple downloads as a bar table

lineMany crammed every download onto one line as name+percent, dropping
the speed column that answers "which one is stalled" and producing ugly
double brackets for names like "[Gecko]". render N>1 as a redrawn block:
one row each (name, bar, percent, DL speed, ETA/stalled), a header with
the active count and totals, falling back to a single summary line when
the table would overflow the window. one download keeps its dashboard.

progress/progress_test.go

@@ -1,6 +1,7 @@
 package progress
 
 import (
+	"bytes"
 	"strings"
 	"testing"
 	"time"
@@ -112,6 +113,100 @@ func TestLineOneCNSD(t *testing.T) {
 	}
 }
 
+func TestBarOf(t *testing.T) {
+	tests := []struct {
+		name string
+		s    download.Stat
+		want string
+	}{
+		{"empty", download.Stat{Status: download.Active, Total: 100, Completed: 0}, "|------------|"},
+		{"half", download.Stat{Status: download.Active, Total: 100, Completed: 50}, "|######------|"},
+		{"full by complete", download.Stat{Status: download.Complete}, "|############|"},
+		{"full by seeding", download.Stat{Status: download.Seeding}, "|############|"},
+		{"unknown total is empty", download.Stat{Status: download.Active, Total: -1, Completed: 9}, "|------------|"},
+	}
+	for _, tc := range tests {
+		if got := barOf(tc.s); got != tc.want {
+			t.Errorf("%s: barOf = %q, want %q", tc.name, got, tc.want)
+		}
+	}
+}
+
+func TestPctField(t *testing.T) {
+	if got := pctField(download.Stat{Status: download.Active, Total: 100, Completed: 50}); got != " 50%" {
+		t.Errorf("active 50%% = %q, want ' 50%%'", got)
+	}
+	if got := pctField(download.Stat{Status: download.Seeding}); got != "100%" {
+		t.Errorf("seeding = %q, want 100%%", got)
+	}
+	if got := pctField(download.Stat{Status: download.Active, Total: -1}); got != "  --" {
+		t.Errorf("unknown total = %q, want '  --'", got)
+	}
+}
+
+// TestRowMetric: the two trailing fields per download state.
+func TestRowMetric(t *testing.T) {
+	r := newReporter(true)
+	if m, tail := r.rowMetric(download.Stat{Status: download.Active, Total: 100, Completed: 50}, 10, 0); !strings.HasPrefix(m, "DL:") || tail == "" {
+		t.Errorf("active downloading: metric=%q tail=%q, want DL:… + an ETA", m, tail)
+	}
+	if m, tail := r.rowMetric(download.Stat{Status: download.Seeding}, 0, 128<<10); m != "seeding" || !strings.HasPrefix(tail, "UL:") {
+		t.Errorf("seeding: metric=%q tail=%q, want seeding + UL:…", m, tail)
+	}
+	if m, _ := r.rowMetric(download.Stat{Status: download.Complete}, 0, 0); m != "done" {
+		t.Errorf("complete metric=%q, want done", m)
+	}
+}
+
+// TestBlockTableAndFallback: several downloads render as header+rows when they
+// fit, and collapse to a single summary line when the window is too short.
+func TestBlockTableAndFallback(t *testing.T) {
+	r := newReporter(true)
+	stats := []download.Stat{
+		{ID: "a", Name: "a", Status: download.Active, Total: 100, Completed: 50},
+		{ID: "b", Name: "b", Status: download.Active, Total: 100, Completed: 10},
+	}
+	r.height = 24
+	if got := r.block(stats); len(got) != 3 { // header + 2 rows
+		t.Errorf("table block = %d lines, want 3:\n%v", len(got), got)
+	}
+	r.height = 2 // header + 2 rows = 3 > 2
+	if got := r.block(stats); len(got) != 1 {
+		t.Errorf("overflow block = %d lines, want 1 summary:\n%v", len(got), got)
+	}
+}
+
+// TestRenderRedraw: the TTY path draws the block, then on the next frame moves
+// the cursor up over the previous frame and clears it before repainting.
+func TestRenderRedraw(t *testing.T) {
+	snap := []download.Stat{
+		{ID: "a", Name: "alpha", IsBT: true, Status: download.Active, Total: 100, Completed: 50},
+		{ID: "b", Name: "beta", IsBT: true, Status: download.Seeding, Total: 100, Completed: 100, Uploaded: 200},
+	}
+	var buf bytes.Buffer
+	r := &Reporter{
+		snap:  func() []download.Stat { return snap },
+		human: true, w: &buf, tty: true, width: 200, height: 24,
+		win: map[string]*speedWindow{},
+	}
+	r.render(false)
+	first := buf.String()
+	for _, want := range []string{"2 active", "alpha", "seeding", "|"} {
+		if !strings.Contains(first, want) {
+			t.Fatalf("first frame missing %q:\n%q", want, first)
+		}
+	}
+	buf.Reset()
+	r.render(false)
+	second := buf.String()
+	if !strings.Contains(second, "\x1b[2A") { // up prevLines-1 = 3-1
+		t.Errorf("second frame should move cursor up 2 lines:\n%q", second)
+	}
+	if !strings.Contains(second, "\x1b[J") {
+		t.Errorf("second frame should clear to end of screen:\n%q", second)
+	}
+}
+
 // TestShortNameRune ensures CJK names are truncated on runes, not bytes.
 func TestShortNameRune(t *testing.T) {
 	name := strings.Repeat("あ", 30) // 30 runes, 90 bytes