120 lines
4.1 KiB
TypeScript
120 lines
4.1 KiB
TypeScript
/**
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* Terminal dark/light mode detection for the 'auto' theme setting.
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*
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* Detection is based on the terminal's actual background color (queried via
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* OSC 11 by systemThemeWatcher.ts) rather than the OS appearance setting —
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* a dark terminal on a light-mode OS should still resolve to 'dark'.
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*
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* The detected theme is cached module-level so callers can resolve 'auto'
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* without awaiting the async OSC round-trip. The cache is seeded from
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* $COLORFGBG (synchronous, set by some terminals at launch) and then
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* updated by the watcher once the OSC 11 response arrives.
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*/
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import type { ThemeName, ThemeSetting } from './theme.js'
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export type SystemTheme = 'dark' | 'light'
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let cachedSystemTheme: SystemTheme | undefined
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/**
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* Get the current terminal theme. Cached after first detection; the watcher
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* updates the cache on live changes.
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*/
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export function getSystemThemeName(): SystemTheme {
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if (cachedSystemTheme === undefined) {
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cachedSystemTheme = detectFromColorFgBg() ?? 'dark'
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}
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return cachedSystemTheme
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}
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/**
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* Update the cached terminal theme. Called by the watcher when the OSC 11
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* query returns so non-React call sites stay in sync.
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*/
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export function setCachedSystemTheme(theme: SystemTheme): void {
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cachedSystemTheme = theme
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}
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/**
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* Resolve a ThemeSetting (which may be 'auto') to a concrete ThemeName.
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*/
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export function resolveThemeSetting(setting: ThemeSetting): ThemeName {
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if (setting === 'auto') {
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return getSystemThemeName()
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}
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return setting
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}
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/**
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* Parse an OSC color response data string into a theme.
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*
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* Accepts XParseColor formats returned by OSC 10/11 queries:
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* - `rgb:R/G/B` where each component is 1–4 hex digits (each scaled to
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* [0, 16^n - 1] for n digits). This is what xterm, iTerm2, Terminal.app,
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* Ghostty, kitty, Alacritty, etc. return.
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* - `#RRGGBB` / `#RRRRGGGGBBBB` (rare, but cheap to accept).
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*
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* Returns undefined for unrecognized formats so callers can fall back.
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*/
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export function themeFromOscColor(data: string): SystemTheme | undefined {
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const rgb = parseOscRgb(data)
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if (!rgb) return undefined
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// ITU-R BT.709 relative luminance. Midpoint split: > 0.5 is light.
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const luminance = 0.2126 * rgb.r + 0.7152 * rgb.g + 0.0722 * rgb.b
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return luminance > 0.5 ? 'light' : 'dark'
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}
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type Rgb = { r: number; g: number; b: number }
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function parseOscRgb(data: string): Rgb | undefined {
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// rgb:RRRR/GGGG/BBBB — each component is 1–4 hex digits.
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// Some terminals append an alpha component (rgba:…/…/…/…); ignore it.
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const rgbMatch =
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/^rgba?:([0-9a-f]{1,4})\/([0-9a-f]{1,4})\/([0-9a-f]{1,4})/i.exec(data)
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if (rgbMatch) {
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return {
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r: hexComponent(rgbMatch[1]!),
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g: hexComponent(rgbMatch[2]!),
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b: hexComponent(rgbMatch[3]!),
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}
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}
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// #RRGGBB or #RRRRGGGGBBBB — split into three equal hex runs.
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const hashMatch = /^#([0-9a-f]+)$/i.exec(data)
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if (hashMatch && hashMatch[1]!.length % 3 === 0) {
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const hex = hashMatch[1]!
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const n = hex.length / 3
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return {
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r: hexComponent(hex.slice(0, n)),
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g: hexComponent(hex.slice(n, 2 * n)),
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b: hexComponent(hex.slice(2 * n)),
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}
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}
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return undefined
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}
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/** Normalize a 1–4 digit hex component to [0, 1]. */
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function hexComponent(hex: string): number {
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const max = 16 ** hex.length - 1
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return parseInt(hex, 16) / max
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}
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/**
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* Read $COLORFGBG for a synchronous initial guess before the OSC 11
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* round-trip completes. Format is `fg;bg` (or `fg;other;bg`) where values
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* are ANSI color indices. rxvt convention: bg 0–6 or 8 are dark; bg 7
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* and 9–15 are light. Only set by some terminals (rxvt-family, Konsole,
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* iTerm2 with the option enabled), so this is a best-effort hint.
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*/
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function detectFromColorFgBg(): SystemTheme | undefined {
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const colorfgbg = process.env['COLORFGBG']
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if (!colorfgbg) return undefined
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const parts = colorfgbg.split(';')
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const bg = parts[parts.length - 1]
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if (bg === undefined || bg === '') return undefined
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const bgNum = Number(bg)
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if (!Number.isInteger(bgNum) || bgNum < 0 || bgNum > 15) return undefined
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// 0–6 and 8 are dark ANSI colors; 7 (white) and 9–15 (bright) are light.
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return bgNum <= 6 || bgNum === 8 ? 'dark' : 'light'
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}
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