MindSift/frontend/src/lib/theme.ts

import type { UserTheme } from './types';

// Built-in themes are compiled CSS files (src/themes/); custom themes are user CSS from the server,
// injected at runtime and addressed as "custom:<id>"
export type ThemeId = string;

export interface ThemeOption {
  id: ThemeId;
  name: string;
  subtitle: string;
  file: string;
  previewBg: string;
  previewPanel: string;
  previewAccent: string;
  previewText: string;
  isRounded: boolean;
  isCustom?: boolean;
}

export const THEME_STORAGE_KEY = 'mindsift_active_theme';
// CSS of the active custom theme, so it applies on boot before the API answers (no flash)
const CUSTOM_CSS_CACHE_KEY = 'mindsift_custom_theme_css';
const CUSTOM_STYLE_ID = 'mindsift-custom-theme';
export const CUSTOM_THEME_PREFIX = 'custom:';

export const AVAILABLE_THEMES: ThemeOption[] = [
  {
    id: 'dark',
    name: 'MindSift Dark (Standard)',
    subtitle: 'Monochrom, dunkel & eckig (0px)',
    file: 'src/themes/theme-dark.css',
    previewBg: '#121316',
    previewPanel: '#1a1c20',
    previewAccent: '#2563eb',
    previewText: '#f4f4f5',
    isRounded: false,
  },
  {
    id: 'light',
    name: 'MindSift Light (Tagmodus)',
    subtitle: 'Helles Papier-Design & klare Kontraste',
    file: 'src/themes/theme-light.css',
    previewBg: '#f3f4f6',
    previewPanel: '#ffffff',
    previewAccent: '#2563eb',
    previewText: '#111827',
    isRounded: false,
  },
  {
    id: 'high-contrast',
    name: 'High Contrast (Scharf)',
    subtitle: 'Tiefschwarz (#000) & weiße Konturen',
    file: 'src/themes/theme-high-contrast.css',
    previewBg: '#000000',
    previewPanel: '#09090b',
    previewAccent: '#38bdf8',
    previewText: '#ffffff',
    isRounded: false,
  },
  {
    id: 'soft',
    name: 'Soft Slate (Abgerundet)',
    subtitle: 'Schiefer-Blau mit weichen Radien (10px)',
    file: 'src/themes/theme-soft.css',
    previewBg: '#0f172a',
    previewPanel: '#1e293b',
    previewAccent: '#3b82f6',
    previewText: '#f8fafc',
    isRounded: true,
  },
];

export const isCustomThemeId = (id: ThemeId) => id.startsWith(CUSTOM_THEME_PREFIX);
export const customThemeId = (t: UserTheme): ThemeId => CUSTOM_THEME_PREFIX + t.id;

// Comments are ignored when reading the CSS (the template mentions [data-theme="mein-theme"] in one)
const stripComments = (css: string) => css.replace(/\/\*[\s\S]*?\*\//g, '');

const readCssVar = (css: string, name: string): string | undefined =>
  stripComments(css).match(new RegExp(`--${name}\\s*:\\s*([^;]+);`))?.[1].trim();

// The CSS decides its own [data-theme="…"]; without one it targets plain :root
const themeAttribute = (css: string): string =>
  stripComments(css).match(/data-theme\s*=\s*["']?([\w-]+)/)?.[1] || 'custom';

// Light background -> no Tailwind dark class
function isLightColor(color?: string): boolean {
  const hex = color?.match(/^#([0-9a-f]{3}|[0-9a-f]{6})$/i)?.[1];
  if (!hex) return false;
  const full = hex.length === 3 ? hex.split('').map((c) => c + c).join('') : hex;
  const [r, g, b] = [0, 2, 4].map((i) => parseInt(full.slice(i, i + 2), 16));
  return 0.2126 * r + 0.7152 * g + 0.0722 * b > 140;
}

export function customThemeOption(t: UserTheme): ThemeOption {
  const radius = readCssVar(t.css, 'radius-card');
  return {
    id: customThemeId(t),
    name: t.name,
    subtitle: 'Eigenes Theme',
    file: 'Eigenes Theme (gespeichert auf dem Server)',
    previewBg: readCssVar(t.css, 'bg-app') || '#121316',
    previewPanel: readCssVar(t.css, 'bg-panel') || '#1a1c20',
    previewAccent: readCssVar(t.css, 'accent-primary') || '#2563eb',
    previewText: readCssVar(t.css, 'text-main') || '#f4f4f5',
    isRounded: !!radius && !/^0(px)?$/.test(radius),
    isCustom: true,
  };
}

function injectCustomCss(css: string | null): void {
  if (typeof document === 'undefined') return;
  let el = document.getElementById(CUSTOM_STYLE_ID) as HTMLStyleElement | null;
  if (css === null) {
    el?.remove();
    return;
  }
  if (!el) {
    el = document.createElement('style');
    el.id = CUSTOM_STYLE_ID;
  }
  el.textContent = css;
  // Last in <head>, so it wins over the compiled themes
  document.head.appendChild(el);
}

function applyToDocument(themeId: ThemeId, customCss: string | null): void {
  if (typeof document === 'undefined') return;
  injectCustomCss(customCss);
  const root = document.documentElement;
  const attr = customCss !== null ? themeAttribute(customCss) : themeId;
  root.setAttribute('data-theme', attr);
  const light = customCss !== null ? isLightColor(readCssVar(customCss, 'bg-app')) : themeId === 'light';
  root.classList.toggle('dark', !light);
}

function store(key: string, value: string | null): void {
  try {
    if (value === null) localStorage.removeItem(key);
    else localStorage.setItem(key, value);
  } catch {
    // ignore
  }
}

function load(key: string): string | null {
  try {
    return localStorage.getItem(key);
  } catch {
    return null;
  }
}

export function getActiveTheme(): ThemeId {
  const saved = load(THEME_STORAGE_KEY);
  if (saved && AVAILABLE_THEMES.some((t) => t.id === saved)) return saved;
  if (saved && isCustomThemeId(saved) && load(CUSTOM_CSS_CACHE_KEY)) return saved;
  return 'dark';
}

// customCss is required for custom themes and ignored for built-in ones
export function setActiveTheme(themeId: ThemeId, customCss?: string): void {
  const css = isCustomThemeId(themeId) ? customCss ?? null : null;
  const effectiveId = isCustomThemeId(themeId) && css === null ? 'dark' : themeId;
  store(THEME_STORAGE_KEY, effectiveId);
  store(CUSTOM_CSS_CACHE_KEY, css);
  applyToDocument(effectiveId, css);
}

export function initThemeOnBoot(): ThemeId {
  const active = getActiveTheme();
  applyToDocument(active, isCustomThemeId(active) ? load(CUSTOM_CSS_CACHE_KEY) : null);
  return active;
}