Add toggleable host separator lines (hotkey s)

Draw 1px yellow vertical lines between hosts when monitoring multiple
servers, making it easy to see where one host's bars end and the next
begins. Toggled with hotkey 's', persisted via 'w' to ~/.loadbarsrc.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 148 insertions, 0 deletions

diff --git a/internal/display/display_test.go b/internal/display/display_test.go
index 734e144..f5f2e39 100644
--- a/internal/display/display_test.go
+++ b/internal/display/display_test.go
@@ -1266,3 +1266,151 @@ func TestHandleKey_WriteConfig_IOAvgLine(t *testing.T) {
 		t.Error("expected ShowIOAvgLine=true in config after 'w'")
 	}
 }
+
+func TestHandleKey_ToggleSeparators(t *testing.T) {
+	cfg := defaultTestConfig()
+	state := newRunState(cfg, 200, 100)
+	if state.showSeparators {
+		t.Fatal("expected showSeparators=false initially")
+	}
+	handleKey(sdl.K_s, nil, cfg, state)
+	if !state.showSeparators {
+		t.Fatal("expected showSeparators=true after pressing s")
+	}
+	handleKey(sdl.K_s, nil, cfg, state)
+	if state.showSeparators {
+		t.Fatal("expected showSeparators=false after pressing s again")
+	}
+}
+
+func TestSeparator_TwoHosts_Enabled(t *testing.T) {
+	// Two hosts (100% system = blue) with separators enabled: yellow pixel at boundary
+	const w, h int32 = 200, 100
+
+	renderer, surface, err := createTestRenderer(w, h)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer renderer.Destroy()
+	defer surface.Free()
+
+	prev1, cur1 := makeCPUPair(100, 0, 0) // all system → blue
+	prev2, cur2 := makeCPUPair(100, 0, 0)
+
+	cfg := defaultTestConfig()
+	cfg.ShowCores = false
+	cfg.ShowMem = false
+	cfg.ShowNet = false
+	cfg.ShowSeparators = true
+
+	src := &mockSource{
+		data: map[string]*stats.HostStats{
+			"alpha": {CPU: map[string]collector.CPULine{"cpu": cur1}},
+			"beta":  {CPU: map[string]collector.CPULine{"cpu": cur2}},
+		},
+	}
+
+	state := newRunState(cfg, w, h)
+	state.prevCPU["alpha;cpu"] = prev1
+	state.prevCPU["beta;cpu"] = prev2
+
+	drawFrame(renderer, src, cfg, state)
+
+	// 2 bars at 200px → each 100px. Separator at x=100 (start of second host's bars)
+	assertPixelColor(t, surface, 100, 50, constants.Yellow, 3, "separator yellow at x=100")
+}
+
+func TestSeparator_TwoHosts_Disabled(t *testing.T) {
+	// Two hosts (100% system = blue) with separators disabled: no yellow at boundary
+	const w, h int32 = 200, 100
+
+	renderer, surface, err := createTestRenderer(w, h)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer renderer.Destroy()
+	defer surface.Free()
+
+	prev1, cur1 := makeCPUPair(100, 0, 0) // all system → blue
+	prev2, cur2 := makeCPUPair(100, 0, 0)
+
+	cfg := defaultTestConfig()
+	cfg.ShowCores = false
+	cfg.ShowMem = false
+	cfg.ShowNet = false
+	cfg.ShowSeparators = false
+
+	src := &mockSource{
+		data: map[string]*stats.HostStats{
+			"alpha": {CPU: map[string]collector.CPULine{"cpu": cur1}},
+			"beta":  {CPU: map[string]collector.CPULine{"cpu": cur2}},
+		},
+	}
+
+	state := newRunState(cfg, w, h)
+	state.prevCPU["alpha;cpu"] = prev1
+	state.prevCPU["beta;cpu"] = prev2
+
+	drawFrame(renderer, src, cfg, state)
+
+	// At x=100, should be blue (second host's system bar), NOT yellow separator
+	assertPixelColor(t, surface, 100, 50, constants.Blue, 3, "no separator, should be blue")
+}
+
+func TestSeparator_SingleHost(t *testing.T) {
+	// Single host: no separator should be drawn even when enabled
+	const w, h int32 = 100, 100
+
+	renderer, surface, err := createTestRenderer(w, h)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer renderer.Destroy()
+	defer surface.Free()
+
+	prev, cur := makeCPUPair(50, 30, 20)
+	cfg := defaultTestConfig()
+	cfg.ShowCores = false
+	cfg.ShowMem = false
+	cfg.ShowNet = false
+	cfg.ShowSeparators = true
+
+	src := &mockSource{
+		data: map[string]*stats.HostStats{
+			"host1": {CPU: map[string]collector.CPULine{"cpu": cur}},
+		},
+	}
+
+	state := newRunState(cfg, w, h)
+	state.prevCPU["host1;cpu"] = prev
+
+	drawFrame(renderer, src, cfg, state)
+
+	// No separator at the edges — just verify no yellow at x=0 or x=99
+	r, g, b := getPixelColor(surface, 0, 50)
+	if r == constants.Yellow.R && g == constants.Yellow.G && b == constants.Yellow.B {
+		t.Errorf("unexpected yellow separator at x=0 with single host")
+	}
+	r, g, b = getPixelColor(surface, 99, 50)
+	if r == constants.Yellow.R && g == constants.Yellow.G && b == constants.Yellow.B {
+		t.Errorf("unexpected yellow separator at x=99 with single host")
+	}
+}
+
+func TestHandleKey_WriteConfig_Separators(t *testing.T) {
+	// Verify that 'w' hotkey persists showSeparators to config
+	tmpDir := t.TempDir()
+	origHome := os.Getenv("HOME")
+	os.Setenv("HOME", tmpDir)
+	defer os.Setenv("HOME", origHome)
+
+	cfg := defaultTestConfig()
+	state := newRunState(cfg, 200, 100)
+	state.showSeparators = true
+
+	handleKey(sdl.K_w, nil, cfg, state)
+
+	if !cfg.ShowSeparators {
+		t.Error("expected ShowSeparators=true in config after 'w'")
+	}
+}