// Theme: dark (default) + light, persisted. When the user hasn't pinned a
// theme we follow the OS via CSS `prefers-color-scheme`; pinning sets an
// explicit `data-theme` on <html> that overrides the media query.
//
// Palette: orthogonal to light/dark. Each palette ships both a dark and a
// light token set in styles.css; `data-palette` on <html> selects it, and
// graphite — the default — is the bare document with no attribute.

type Theme = "light" | "dark";
const KEY = "maestro-theme";

/** Every `data-palette` value, in picker order. Graphite is the default. */
export const PALETTES = [
  "graphite",
  "ice-cyan",
  "periwinkle",
  "amber-phosphor",
  "ember",
  "orchid",
] as const;
export type Palette = (typeof PALETTES)[number];
const PALETTE_KEY = "maestro-palette";

function stored(): Theme | null {
  const v = localStorage.getItem(KEY);
  return v === "light" || v === "dark" ? v : null;
}

function systemTheme(): Theme {
  return window.matchMedia("(prefers-color-scheme: light)").matches
    ? "light"
    : "dark";
}

/** The theme actually showing right now (pinned or system). */
export function resolvedTheme(): Theme {
  return stored() ?? systemTheme();
}

function storedPalette(): Palette | null {
  const v = localStorage.getItem(PALETTE_KEY);
  return (PALETTES as readonly string[]).includes(v ?? "")
    ? (v as Palette)
    : null;
}

/** The palette in force (stored or the graphite default). */
export function resolvedPalette(): Palette {
  return document.documentElement.dataset.palette as Palette | undefined
    ?? storedPalette()
    ?? "graphite";
}

/** Pin a palette. Graphite is the bare document, so it clears the attribute. */
export function setPalette(p: Palette): void {
  localStorage.setItem(PALETTE_KEY, p);
  if (p === "graphite") delete document.documentElement.dataset.palette;
  else document.documentElement.dataset.palette = p;
}

/** Apply the pinned theme + palette at boot (no-ops when unpinned). */
export function initTheme(): void {
  // Dev-only `?theme=light|dark` override for visual review; stripped in prod.
  if (import.meta.env.DEV) {
    const q = new URLSearchParams(location.search).get("theme");
    if (q === "light" || q === "dark") {
      document.documentElement.dataset.theme = q;
      applyStoredPalette();
      return;
    }
  }
  const pinned = stored();
  if (pinned) document.documentElement.dataset.theme = pinned;
  applyStoredPalette();
}

function applyStoredPalette(): void {
  const p = storedPalette();
  if (p && p !== "graphite") document.documentElement.dataset.palette = p;
}

function setTheme(t: Theme): void {
  localStorage.setItem(KEY, t);
  document.documentElement.dataset.theme = t;
}

/** A header button that flips between light and dark. */
export function createThemeToggle(): HTMLButtonElement {
  const btn = document.createElement("button");
  btn.type = "button";
  btn.className = "btn btn-ghost btn-icon theme-toggle";
  btn.innerHTML = `<span class="moon" aria-hidden="true">☾</span><span class="sun" aria-hidden="true">☀</span>`;
  const sync = () => {
    const next = resolvedTheme() === "dark" ? "light" : "dark";
    btn.setAttribute("aria-label", `Switch to ${next} theme`);
    btn.title = `Switch to ${next} theme`;
  };
  sync();
  btn.addEventListener("click", () => {
    setTheme(resolvedTheme() === "dark" ? "light" : "dark");
    sync();
  });
  return btn;
}

/** A footer dropdown that picks the colour palette. */
export function createPaletteSelect(): HTMLSelectElement {
  const select = document.createElement("select");
  select.className = "palette-select";
  select.setAttribute("aria-label", "Colour palette");
  select.title = "Colour palette";
  for (const p of PALETTES) {
    const opt = document.createElement("option");
    opt.value = p;
    opt.textContent = p;
    select.appendChild(opt);
  }
  select.value = resolvedPalette();
  select.addEventListener("change", () => {
    setPalette(select.value as Palette);
  });
  return select;
}