/**
 * @file fontSize — the two text sizes Settings → Appearance offers (issue #79),
 * viewer preferences kept in `localStorage` and synced to the account like the
 * theme (`lib/userPrefs.ts` PREF_KEYS):
 * - `agenthub.ui.fontSize`: the interface's size, the ROOT font size in px.
 *   Tailwind's sizes and spacing are rem, and `index.css` re-states every
 *   `text-[Npx]` class the app uses in rem, so the whole UI follows it.
 *   `index.html` applies it before first paint (same key, same range).
 *   Capped at 18px: the diff view pins its rows at `ROW_PX` (16px).
 * - `agenthub.terminal.fontSize`: xterm's cell font size in px (default 13).
 * A write fires `FONT_SIZE_EVENT`, which open terminals listen for to re-fit.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

export const UI_FONT_SIZE_KEY = "agenthub.ui.fontSize";
export const TERMINAL_FONT_SIZE_KEY = "agenthub.terminal.fontSize";
/** Fired on `window` after either size changes (this tab or a hydrate). */
export const FONT_SIZE_EVENT = "agenthub-font-size";

/** The interface sizes, root px; 16 is the browser's own default. */
export const UI_FONT_SIZES = [14, 16, 17, 18] as const;
export type UiFontSize = (typeof UI_FONT_SIZES)[number];
export const DEFAULT_UI_FONT_SIZE: UiFontSize = 16;

export const TERMINAL_FONT_SIZES = [11, 12, 13, 14, 15, 16, 18, 20] as const;
export const DEFAULT_TERMINAL_FONT_SIZE = 13;

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

function write(key: string, value: number) {
  try {
    window.localStorage.setItem(key, String(value));
  } catch {
    /* storage blocked — this page still applies it */
  }
  window.dispatchEvent(new Event(FONT_SIZE_EVENT));
}

export function readUiFontSize(): UiFontSize {
  const n = Number(read(UI_FONT_SIZE_KEY));
  return (UI_FONT_SIZES as readonly number[]).includes(n)
    ? (n as UiFontSize)
    : DEFAULT_UI_FONT_SIZE;
}

/** Paint the stored interface size on `<html>` (the default leaves it unset). */
export function applyUiFontSize(size: UiFontSize = readUiFontSize()) {
  const root = document.documentElement;
  if (size === DEFAULT_UI_FONT_SIZE) root.style.removeProperty("font-size");
  else root.style.fontSize = `${size}px`;
}

export function writeUiFontSize(size: UiFontSize) {
  applyUiFontSize(size);
  write(UI_FONT_SIZE_KEY, size);
}

export function readTerminalFontSize(): number {
  const n = Number(read(TERMINAL_FONT_SIZE_KEY));
  return (TERMINAL_FONT_SIZES as readonly number[]).includes(n) ? n : DEFAULT_TERMINAL_FONT_SIZE;
}

export function writeTerminalFontSize(size: number) {
  write(TERMINAL_FONT_SIZE_KEY, size);
}