/** Keyboard-shortcut overlay (`?`), the web counterpart of the TUI's help
 *  overlay. It renders the command registry (`commands.ts`) — the same list
 *  that dispatches the keys — so a binding can never be documented as one
 *  thing and do another. */

import {
  CommandSet,
  defineCommands,
  keyCaps,
  publishedCommands,
  type Command,
} from "./commands.js";

let open: { el: HTMLElement; dispose: () => void } | null = null;

export function isHelpOpen(): boolean {
  return open !== null;
}

export function closeHelp(): void {
  open?.dispose();
}

export function toggleHelp(): void {
  if (open) closeHelp();
  else openHelp();
}

/** Mount the overlay. Opening while already open is a no-op re-render, so a
 *  stray second call can never stack two dialogs. */
export function openHelp(): HTMLElement {
  closeHelp();

  const el = document.createElement("div");
  el.className = "help-overlay";
  el.setAttribute("role", "dialog");
  el.setAttribute("aria-modal", "true");
  el.setAttribute("aria-label", "Keyboard shortcuts");

  const panel = document.createElement("div");
  panel.className = "help-panel";

  const head = document.createElement("header");
  head.className = "help-head";
  const title = document.createElement("h2");
  title.className = "help-title";
  title.textContent = "Keyboard shortcuts";
  const close = document.createElement("button");
  close.type = "button";
  close.className = "help-close";
  close.setAttribute("aria-label", "Close");
  close.textContent = "✕";
  close.addEventListener("click", closeHelp);
  head.append(title, close);
  panel.appendChild(head);

  for (const group of groupedCommands()) {
    const section = document.createElement("section");
    section.className = "help-group";
    const heading = document.createElement("h3");
    heading.className = "help-group-title";
    heading.textContent = group.title;
    const list = document.createElement("dl");
    list.className = "help-list";
    for (const cmd of group.items) {
      const row = document.createElement("div");
      row.className = "help-row";
      row.dataset.commandId = cmd.id;
      const keys = document.createElement("dt");
      keys.className = "help-keys";
      for (const key of keyCaps(cmd.keys[0])) {
        const cap = document.createElement("kbd");
        cap.textContent = key;
        keys.appendChild(cap);
      }
      const desc = document.createElement("dd");
      desc.className = "help-desc";
      desc.textContent = cmd.label;
      row.append(keys, desc);
      list.appendChild(row);
    }
    section.append(heading, list);
    panel.appendChild(section);
  }

  // A press on the scrim closes; one inside the panel is left alone.
  el.addEventListener("click", (ev) => {
    if (!panel.contains(ev.target as Node)) closeHelp();
  });
  el.appendChild(panel);
  document.body.appendChild(el);

  const dispose = () => {
    if (open?.el !== el) return;
    open = null;
    el.remove();
  };
  open = { el, dispose };
  close.focus();
  return el;
}

/** The registry's commands, in registry order, bucketed into the help
 *  overlay's sections. Groups appear in the order their first command does. */
export function groupedCommands(): { title: string; items: Command[] }[] {
  const groups: { title: string; items: Command[] }[] = [];
  for (const cmd of publishedCommands()) {
    let group = groups.find((g) => g.title === cmd.group);
    if (!group) {
      group = { title: cmd.group, items: [] };
      groups.push(group);
    }
    group.items.push(cmd);
  }
  return groups;
}

// The overlay's own two commands. `help.close` is `overlay`-scoped: it is only
// fed keys while the dialog is up.
const helpKeys = new CommandSet(defineCommands({ "help.toggle": () => toggleHelp() }));
const overlayKeys = new CommandSet(defineCommands({ "help.close": () => closeHelp() }));

let installed = false;

/** Global keybind: `?` toggles the overlay, Escape closes it. Idempotent, so a
 *  second call during a hot reload doesn't double-toggle. */
export function installHelpKeybind(): void {
  if (installed) return;
  installed = true;
  window.addEventListener("keydown", (e) => {
    if (open && overlayKeys.handle(e)) return;
    helpKeys.handle(e);
  });
}