Switch the theme live

Widgets copy their colors when they are created, so they now get role
tokens (one unique RGB value per role) instead of colors, and a wrapper
around the tcell screen replaces the tokens with the current theme's
colors in SetContent. Changing the theme in the Config view swaps that
table; the next draw recolors everything. Poster colors that equal a
token are nudged off it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019reK4DUGYqDUjniWYJvwUW

internal/ui/theme.go

@@ -46,9 +46,6 @@ var (
 	}
 )
 
-// current is the theme in use.
-var current = darkTheme
-
 // chooseTheme resolves the ui.theme setting: "dark", "light", or "auto" (the
 // default), which follows the background color the terminal reported and is
 // dark when it did not say. The second value explains the choice for the log.
@@ -69,13 +66,34 @@ func chooseTheme(setting string, info terminalInfo) (theme, string) {
 	return darkTheme, "Theme: dark (auto: the terminal's background " + hex + " is dark)"
 }
 
-// apply makes t the colors of everything created afterwards: tview's default
-// styles (widgets copy them when they are created, so this must run before any
-// is) and the color names used in the texts, which tview looks up in tcell's
-// table: "[yellow]" means this theme's yellow, "white" its text color and
-// "black" its background (the active tab is "[black:white]").
-func (t theme) apply() {
-	current = t
+// colors lists the theme's colors in a fixed order of roles.
+func (t theme) colors() []tcell.Color {
+	return []tcell.Color{t.bg, t.text, t.border, t.field, t.fieldMuted, t.list, t.pressed, t.toast,
+		t.gray, t.yellow, t.green, t.red, t.blue, t.purple}
+}
+
+// tokens is the theme the widgets are built with: every role has a color of
+// its own that no theme uses, and themedScreen replaces it with the color of
+// the current theme while drawing. That is how the theme changes while the
+// program runs: widgets copy their colors when they are created, but what they
+// copy is a role, not a color.
+var tokens = func() theme {
+	var c [14]tcell.Color
+	for i := range c {
+		c[i] = tcell.NewRGBColor(0xa5, 0x17, int32(i))
+	}
+	return theme{name: "tokens", bg: c[0], text: c[1], border: c[2], field: c[3], fieldMuted: c[4], list: c[5], pressed: c[6], toast: c[7],
+		gray: c[8], yellow: c[9], green: c[10], red: c[11], blue: c[12], purple: c[13]}
+}()
+
+// useTokens makes the role colors the defaults of everything created
+// afterwards: tview's default styles (widgets copy them when they are created,
+// so this must run before any is) and the color names used in the texts,
+// which tview looks up in tcell's table: "[yellow]" is the theme's yellow,
+// "white" its text color and "black" its background (the active tab is
+// "[black:white]").
+func useTokens() {
+	t := tokens
 	st := &tview.Styles
 	st.PrimitiveBackgroundColor = t.bg
 	st.ContrastBackgroundColor = t.field
@@ -97,7 +115,60 @@ func (t theme) apply() {
 	}
 }
 
-// named returns the theme's color for a name used in the texts.
+// themedScreen draws with the current theme: it replaces the role colors of
+// everything set on the screen by the theme's colors. Other colors (posters,
+// the image ids of real-image posters) pass unchanged.
+type themedScreen struct {
+	tcell.Screen
+	theme   theme
+	colors  map[tcell.Color]tcell.Color
+	initErr error
+}
+
+func newThemedScreen(s tcell.Screen, t theme) *themedScreen {
+	ts := &themedScreen{Screen: s}
+	ts.setTheme(t)
+	return ts
+}
+
+// setTheme switches the colors; the next draw shows them.
+func (s *themedScreen) setTheme(t theme) {
+	s.theme = t
+	s.colors = map[tcell.Color]tcell.Color{}
+	actual := t.colors()
+	for i, tok := range tokens.colors() {
+		s.colors[tok] = actual[i]
+	}
+}
+
+func (s *themedScreen) SetContent(x, y int, primary rune, combining []rune, style tcell.Style) {
+	fg, bg, _ := style.Decompose()
+	if c, ok := s.colors[fg]; ok {
+		style = style.Foreground(c)
+	}
+	if c, ok := s.colors[bg]; ok {
+		style = style.Background(c)
+	}
+	s.Screen.SetContent(x, y, primary, combining, style)
+}
+
+// Init remembers the error, which tview's SetScreen drops.
+func (s *themedScreen) Init() error {
+	s.initErr = s.Screen.Init()
+	return s.initErr
+}
+
+// notToken nudges a picture's color that happens to equal a role color, so
+// themedScreen does not replace it.
+func notToken(c tcell.Color) tcell.Color {
+	r, g, b := c.RGB()
+	if r == 0xa5 && g == 0x17 && b < int32(len(tokens.colors())) {
+		return tcell.NewRGBColor(r, g+1, b)
+	}
+	return c
+}
+
+// named returns the role color for a name used in the texts.
 func named(name string) tcell.Color { return tcell.GetColor(name) }
 
 func hexColor(c color.RGBA) string {