arr-tui/internal/ui/theme.go

package ui

import (
	"image/color"

	"github.com/gdamore/tcell/v2"
	"github.com/rivo/tview"
)

// theme is a complete set of colors, so the program looks the same whatever
// palette the terminal's color theme has (themes often make "black" a grey
// that is not their background, and light themes put dark grey slabs under
// white text). Every color is one of the fixed entries 16-255 of the
// 256-color table, so terminals without 24-bit color show exactly these too
// (the nearest match of an exact color is itself, and the first 16 entries,
// which themes change, never equal them).
type theme struct {
	name string

	bg, text, border  tcell.Color
	field, fieldMuted tcell.Color // input fields and buttons; placeholders on them
	list              tcell.Color // open dropdown lists (drawn with bg-colored text)
	pressed           tcell.Color // text of a pressed button (on the text color)
	toast             tcell.Color // background of the popups

	// The accent colors, used by name in the texts ("[yellow]...").
	gray, yellow, green, red, blue, purple tcell.Color
}

func c256(i int) tcell.Color { return tcell.PaletteColor(i).TrueColor() }

var (
	darkTheme = theme{
		name: "dark",
		bg:   c256(232), text: c256(253), border: c256(246),
		field: c256(236), fieldMuted: c256(245),
		list: c256(110), pressed: c256(25), toast: c256(236),
		gray: c256(245), yellow: c256(221), green: c256(113), red: c256(203), blue: c256(75), purple: c256(141),
	}
	lightTheme = theme{
		name: "light",
		bg:   c256(255), text: c256(234), border: c256(243),
		field: c256(252), fieldMuted: c256(245),
		list: c256(67), pressed: c256(255), toast: c256(252),
		gray: c256(243), yellow: c256(130), green: c256(28), red: c256(160), blue: c256(26), purple: c256(91),
	}
)

// 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.
func chooseTheme(setting string, info terminalInfo) (theme, string) {
	switch setting {
	case "dark":
		return darkTheme, "Theme: dark"
	case "light":
		return lightTheme, "Theme: light"
	}
	if !info.hasBG {
		return darkTheme, "Theme: dark (auto: the terminal did not report its background color)"
	}
	hex := hexColor(info.bg)
	if luminance(info.bg) > 0.5 {
		return lightTheme, "Theme: light (auto: the terminal's background " + hex + " is light)"
	}
	return darkTheme, "Theme: dark (auto: the terminal's background " + hex + " is dark)"
}

// 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
	st.MoreContrastBackgroundColor = t.list
	st.BorderColor, st.TitleColor, st.GraphicsColor = t.border, t.text, t.border
	st.PrimaryTextColor = t.text
	st.SecondaryTextColor = t.yellow
	st.TertiaryTextColor = t.green
	st.InverseTextColor = t.pressed
	st.ContrastSecondaryTextColor = t.fieldMuted

	for name, c := range map[string]tcell.Color{
		"white": t.text, "black": t.bg,
		"gray": t.gray, "grey": t.gray,
		"yellow": t.yellow, "green": t.green, "red": t.red,
		"blue": t.blue, "purple": t.purple,
	} {
		tcell.ColorNames[name] = c
	}
}

// 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 {
	const digits = "0123456789abcdef"
	b := []byte{'#', 0, 0, 0, 0, 0, 0}
	for i, v := range []uint8{c.R, c.G, c.B} {
		b[1+2*i], b[2+2*i] = digits[v>>4], digits[v&15]
	}
	return string(b)
}