import { LS, readAccountMerged, writeAccount } from "./storage";

type Mode = "dark" | "light";
export type Scheme = "midnight" | "forest" | "slate" | "matrix" | "fjord";

// The scheme set (docs/DESIGN.md, decision B2): each earns its place with its own hue family, and its
// accent stays ≥ 30° of OKLCH hue away from danger / warn / success. theme.contract.test.ts measures
// every scheme's tokens in index.css against that rule and WCAG contrast.
export const SCHEMES: { id: Scheme; name: string; swatch: string }[] = [
  { id: "midnight", name: "Midnight", swatch: "#6d8cff" },
  { id: "forest", name: "Forest", swatch: "#22d3ee" },
  { id: "slate", name: "Slate", swatch: "#e879f9" },
  { id: "matrix", name: "Matrix", swatch: "#86a05a" },
  // A TRIAL outside B2 (Midnight's hue family, DESIGN.md decision log 2026-09-25): folded into
  // Midnight or removed once the owner has tried it; a stored "fjord" then lands on the default.
  { id: "fjord", name: "Fjord", swatch: "#5aa1cb" },
];

export interface ThemePrefs {
  mode: Mode;
  scheme: Scheme;
  fontScale: number;
  /** Show the per-scheme background image (dark theme only); off = flat colour. */
  bgImage: boolean;
  /** How strongly the background image is faded out, 0–100% (higher = fainter). */
  bgFade: number;
}

export const DEFAULT_THEME: ThemePrefs = {
  mode: "dark",
  scheme: "midnight",
  fontScale: 1.06,
  bgImage: true,
  bgFade: 60,
};

/** A stored theme (this browser's copy or the account's server prefs) as the app can apply it: only
 *  the known keys, and a scheme or mode that no longer exists (YouTube and Starship were retired in
 *  E28) falls back to the default instead of painting an unstyled page. */
export function normalizeTheme(raw: Partial<Record<keyof ThemePrefs, unknown>>): ThemePrefs {
  const d = DEFAULT_THEME;
  const num = (v: unknown, fallback: number) =>
    typeof v === "number" && Number.isFinite(v) ? v : fallback;
  return {
    mode: raw.mode === "light" || raw.mode === "dark" ? raw.mode : d.mode,
    scheme: SCHEMES.some((s) => s.id === raw.scheme) ? (raw.scheme as Scheme) : d.scheme,
    fontScale: num(raw.fontScale, d.fontScale),
    bgImage: typeof raw.bgImage === "boolean" ? raw.bgImage : d.bgImage,
    bgFade: num(raw.bgFade, d.bgFade),
  };
}

export function applyTheme(t: ThemePrefs): void {
  const el = document.documentElement;
  el.dataset.theme = t.mode;
  el.dataset.scheme = t.scheme;
  el.style.setProperty("--font-scale", String(t.fontScale));
  el.style.setProperty("--bg-fade", `${t.bgFade}%`);
}

export function loadLocalTheme(): ThemePrefs {
  return normalizeTheme(readAccountMerged(LS.theme, DEFAULT_THEME));
}

export function saveLocalTheme(t: ThemePrefs): void {
  writeAccount(LS.theme, t);
}