// The web client's command registry (#148). One entry per command — a stable
// id, a plain-language label, the key chord it answers to, and a `run()` — so
// there is exactly one list of what the client can do. The `?` overlay renders
// from it (`help.ts`), and every keybinding is dispatched through it; a command
// added here is bound and documented in the same edit.
//
// Keys are canonical strings, the same spelling the TUI's `InputKey::canonical`
// produces (`ctrl-shift-h`, `enter`, `esc`, `n`, `N`) and chords are those
// joined by a space (`ctrl-a ctrl-k`). Matching the TUI's spelling is what lets
// docs/COMMAND-BAR.md describe one key model for both clients.

/** Where a command's keys are listened for. `global` is the window, `list` the
 *  sidebar's session tree, `pane` the attached terminal, `overlay` the help
 *  dialog while it is up. */
export type CommandScope = "global" | "list" | "pane" | "overlay";

export interface CommandSpec {
  /** Stable identifier. Never rendered; safe to bind config and tests to. */
  id: string;
  /** Plain-language label — what the `?` overlay and (later) the command bar
   *  show. */
  label: string;
  /** Help-overlay section. Groups render in the order they first appear here. */
  group: string;
  /** Canonical chords that run it. The first is the one shown to the operator;
   *  the rest are aliases (`j` and `down`). */
  keys: string[];
  scope: CommandScope;
}

export interface Command extends CommandSpec {
  run: () => void;
}

/** Leader used when the daemon does not name one — an older daemon, or an
 *  unreachable `/api/info`. Mirrors the TUI's `[tui].leader` default. `ctrl-a`
 *  is select-all in a browser, so a set that owns the leader
 *  `preventDefault`s it. */
export const DEFAULT_LEADER = "ctrl-a";

/** Every command the web client has, for one leader. The single list: labels,
 *  chords and grouping live here and nowhere else. Chords behind the leader are
 *  built from it (#159), so the configured leader — served on `/api/info` as
 *  `leader` — is what the overlay renders and the sets dispatch. */
export function commandSpecs(leader: string = DEFAULT_LEADER): readonly CommandSpec[] {
  return SPECS.map(({ leaderKeys, ...spec }) =>
    leaderKeys ? { ...spec, keys: leaderKeys(leader) } : spec,
  );
}

/** A spec whose chords are fixed, or a spec that builds them from the leader. */
type SpecSource = CommandSpec & { leaderKeys?: (leader: string) => string[] };

const SPECS: readonly SpecSource[] = [
  {
    id: "spawn.open",
    label: "Open the spawn form",
    group: "Sessions",
    keys: ["n"],
    scope: "global",
  },
  {
    id: "spawn.fastForward",
    label: "Spawn a session with every default resolved",
    group: "Sessions",
    keys: ["N"],
    scope: "global",
  },
  {
    id: "bar.open",
    label: "Open the command bar",
    group: "Sessions",
    keys: ["ctrl-k"],
    scope: "global",
  },
  {
    id: "pane.literalCtrlK",
    label: "Send a literal Ctrl-K to the pane",
    group: "Pane",
    keys: [`${DEFAULT_LEADER} ctrl-k`],
    leaderKeys: (leader) => [`${leader} ctrl-k`],
    scope: "global",
  },
  {
    id: "pane.literalLeader",
    label: "Send a literal leader key to the pane",
    group: "Pane",
    keys: [`${DEFAULT_LEADER} ${DEFAULT_LEADER}`],
    leaderKeys: (leader) => [`${leader} ${leader}`],
    scope: "global",
  },
  {
    id: "focus.toggle",
    label: "Move the keyboard between the session list and the pane",
    group: "Session list",
    keys: [`${DEFAULT_LEADER} h`],
    leaderKeys: (leader) => [`${leader} h`],
    scope: "global",
  },
  {
    id: "list.next",
    label: "Highlight the next session",
    group: "Session list",
    keys: ["j", "down"],
    scope: "list",
  },
  {
    id: "list.prev",
    label: "Highlight the previous session",
    group: "Session list",
    keys: ["k", "up"],
    scope: "list",
  },
  {
    id: "list.activate",
    label: "Open the highlighted session, or expand a folder",
    group: "Session list",
    keys: ["enter"],
    scope: "list",
  },
  {
    id: "list.toggleFolder",
    label: "Collapse or expand the highlighted folder",
    group: "Session list",
    keys: ["c"],
    scope: "list",
  },
  {
    id: "list.rename",
    label: "Rename the highlighted session",
    group: "Session list",
    keys: ["r"],
    scope: "list",
  },
  {
    id: "list.kill",
    label: "Kill the highlighted session",
    group: "Session list",
    keys: ["x"],
    scope: "list",
  },
  {
    id: "list.focusPane",
    label: "Send the keyboard to the pane",
    group: "Session list",
    keys: ["tab"],
    scope: "list",
  },
  {
    id: "help.toggle",
    label: "Show or hide this help",
    group: "Help",
    keys: ["?"],
    scope: "global",
  },
  {
    id: "help.close",
    label: "Close the help overlay or an open menu",
    group: "Help",
    keys: ["esc"],
    scope: "overlay",
  },
  {
    id: "debug.toggleHud",
    label: "Toggle the debug HUD",
    group: "Debug",
    keys: ["ctrl-shift-d"],
    scope: "global",
  },
];

/** The command list under the default leader. Iteration order everywhere else
 *  (the help overlay, the bar) comes from here. */
export const COMMAND_SPECS: readonly CommandSpec[] = commandSpecs();

/** Attach handlers to specs, by id. Throws on an unknown id, so a typo is a
 *  test failure rather than a key that silently does nothing. `leader` picks
 *  the chords behind the leader; omit it for a set that has none. */
export function defineCommands(
  handlers: Record<string, () => void>,
  leader: string = DEFAULT_LEADER,
): Command[] {
  const byId = new Map(commandSpecs(leader).map((s) => [s.id, s]));
  return Object.entries(handlers).map(([id, run]) => {
    const spec = byId.get(id);
    if (!spec) throw new Error(`unknown command id: ${id}`);
    return { ...spec, run };
  });
}

// ---- what the help overlay renders ----

const published = new Map<string, Command>();

/** Record commands as bound. Re-registering an id replaces it, so a second
 *  sidebar (tests, hot reload) doesn't duplicate rows in the overlay. */
export function publishCommands(cmds: Command[]): void {
  for (const c of cmds) published.set(c.id, c);
}

/** Every bound command, in `COMMAND_SPECS` order. */
export function publishedCommands(): Command[] {
  return COMMAND_SPECS.map((s) => published.get(s.id)).filter((c): c is Command => c !== undefined);
}

// ---- key canonicalisation ----

const NAMED: Record<string, string> = {
  Escape: "esc",
  Enter: "enter",
  Tab: "tab",
  Backspace: "backspace",
  ArrowUp: "up",
  ArrowDown: "down",
  ArrowLeft: "left",
  ArrowRight: "right",
  Home: "home",
  End: "end",
  PageUp: "pageup",
  PageDown: "pagedown",
  Delete: "delete",
  " ": "space",
};

/** The canonical string for one keydown. Mirrors the TUI's
 *  `InputKey::canonical`: modifier prefixes in ctrl/alt/shift order, then the
 *  key. A shifted character already spells itself (`N`, `?`), so `shift-` is
 *  only written when another modifier is present and the char was folded to
 *  lower case. */
export function canonicalizeKey(e: KeyboardEvent): string | null {
  if (!e.key) return null;
  // Modifier keys pressed alone are never a binding.
  if (e.key === "Control" || e.key === "Alt" || e.key === "Shift" || e.key === "Meta") return null;
  const named = NAMED[e.key];
  if (named === "tab" && e.shiftKey) return "backtab";
  let out = "";
  if (e.ctrlKey) out += "ctrl-";
  if (e.altKey) out += "alt-";
  if (e.metaKey) out += "meta-";
  if (named) {
    if (e.shiftKey) out += "shift-";
    return out + named;
  }
  if (e.key.length === 1) {
    if (out === "") return e.key;
    if (e.shiftKey) out += "shift-";
    return out + e.key.toLowerCase();
  }
  if (e.shiftKey) out += "shift-";
  return out + e.key.toLowerCase();
}

/** The raw control byte for a canonical `ctrl-<letter>` chord — `ctrl-a` is
 *  `0x01` — mirroring the TUI's `encode_key`. Built from the chord string
 *  itself so a different leader sends its own byte, not a hardcoded one. */
export function controlByte(chord: string): string {
  const m = /^ctrl-([a-z])$/.exec(chord);
  if (!m) throw new Error(`not a plain ctrl chord: ${chord}`);
  return String.fromCharCode(m[1].charCodeAt(0) - 96);
}

const MOD_PREFIX = /^(ctrl|alt|meta|shift)-/;

/** True when a chord carries a modifier or more than one key. Plain single-key
 *  chords are the ones that stay deaf inside form fields. */
function isChorded(chord: string): boolean {
  return chord.includes(" ") || MOD_PREFIX.test(chord);
}

/** True when the event target swallows plain keystrokes — a form field, or the
 *  hidden textarea xterm types into. Every plain single-key binding is deaf in
 *  the same places. */
export function isTypingTarget(target: EventTarget | null): boolean {
  const el = target as HTMLElement | null;
  if (!el || typeof el.tagName !== "string") return false;
  return (
    el.tagName === "INPUT" ||
    el.tagName === "TEXTAREA" ||
    el.tagName === "SELECT" ||
    el.isContentEditable
  );
}

/** xterm's offscreen textarea. It is a typing target like any other, but it is
 *  also where the leader has to work — a pane is exactly where the operator
 *  needs the escape hatch (docs/COMMAND-BAR.md). */
export function isTerminalTextarea(target: EventTarget | null): boolean {
  const el = target as HTMLElement | null;
  return !!el && typeof el.className === "string" && el.classList?.contains("xterm-helper-textarea");
}

/** True where the command bar's own keys must stay out of the way: a real form
 *  field, and not the pane. `ctrl-k` is intercepted ahead of xterm
 *  (docs/COMMAND-BAR.md, "Opening"), so a focused terminal opens the bar, while
 *  the spawn form's inputs keep their own Ctrl-K. */
export function isBarTypingTarget(target: EventTarget | null): boolean {
  return isTypingTarget(target) && !isTerminalTextarea(target);
}

// ---- display ----

const CAPS: Record<string, string> = {
  ctrl: "Ctrl",
  alt: "Alt",
  meta: "Meta",
  shift: "Shift",
  esc: "Esc",
  enter: "Enter",
  tab: "Tab",
  backtab: "Shift Tab",
  backspace: "Backspace",
  up: "Up",
  down: "Down",
  left: "Left",
  right: "Right",
  home: "Home",
  end: "End",
  pageup: "PgUp",
  pagedown: "PgDn",
  delete: "Del",
  space: "Space",
};

/** Keycaps for a chord, left to right: `ctrl-shift-h` → Ctrl, Shift, H. A
 *  multi-key chord separates its keys with a `then` cap. */
export function keyCaps(chord: string): string[] {
  const caps: string[] = [];
  for (const [i, key] of chord.split(" ").entries()) {
    if (i > 0) caps.push("then");
    const parts = key.split("-");
    // A bare `-` key splits into two empties; treat it as the key itself.
    if (parts.every((p) => p === "")) {
      caps.push("-");
      continue;
    }
    const last = parts.pop() as string;
    const mods = parts.filter((p) => p !== "");
    for (const m of mods) caps.push(CAPS[m] ?? m);
    caps.push(CAPS[last] ?? (mods.length > 0 && last.length === 1 ? last.toUpperCase() : last));
  }
  return caps;
}

// ---- dispatch ----

/** How long a partial chord waits for its next key — the TUI's
 *  `chord_timeout_ms` default. */
export const DEFAULT_CHORD_TIMEOUT_MS = 1000;

export interface CommandSetOptions {
  /** Canonical leader key. A set given one holds every leader press as a
   *  pending chord, whether or not anything is bound behind it yet. */
  leader?: string | null;
  chordTimeoutMs?: number;
  /** Call `preventDefault()` on a handled key. Off for the terminal's own key
   *  handler, which swallows by returning `false` to xterm instead. */
  preventDefault?: boolean;
  /** Clock, for tests. */
  now?: () => number;
}

/** A group of commands listening on one surface. Resolves a keydown to a
 *  command the way the TUI's `ChordState` does: hold while the sequence is a
 *  strict prefix of some binding, otherwise resolve and dispatch. */
export class CommandSet {
  private readonly byChord = new Map<string, Command>();
  private readonly leader: string | null;
  private readonly timeout: number;
  private readonly preventDefault: boolean;
  private readonly now: () => number;
  private held: string[] = [];
  private lastPress = 0;

  constructor(
    readonly commands: Command[],
    opts: CommandSetOptions = {},
  ) {
    for (const c of commands) for (const k of c.keys) this.byChord.set(k, c);
    this.leader = opts.leader ?? null;
    this.timeout = opts.chordTimeoutMs ?? DEFAULT_CHORD_TIMEOUT_MS;
    this.preventDefault = opts.preventDefault ?? true;
    this.now = opts.now ?? (() => Date.now());
    publishCommands(commands);
  }

  /** Whether any binding starts with `candidate` and continues. */
  private isPrefix(candidate: string): boolean {
    const marker = `${candidate} `;
    for (const chord of this.byChord.keys()) if (chord.startsWith(marker)) return true;
    return false;
  }

  /** Feed one keydown. Returns true when the key was consumed — dispatched, or
   *  held as a partial chord. */
  handle(e: KeyboardEvent): boolean {
    const key = canonicalizeKey(e);
    if (key === null) return false;
    if (this.held.length > 0 && this.now() - this.lastPress > this.timeout) this.held = [];
    const candidate = this.held.length > 0 ? `${this.held.join(" ")} ${key}` : key;
    this.lastPress = this.now();

    // The leader is a prefix by construction, so it stops being select-all
    // before anything is bound behind it (#149 binds the first chord).
    if (this.leader !== null && this.held.length === 0 && key === this.leader) {
      if (isTypingTarget(e.target) && !isTerminalTextarea(e.target)) return false;
      this.held = [key];
      if (this.preventDefault) e.preventDefault();
      return true;
    }

    if (this.isPrefix(candidate)) {
      this.held.push(key);
      if (this.preventDefault) e.preventDefault();
      return true;
    }

    const wasChord = this.held.length > 0;
    this.held = [];
    const cmd = this.byChord.get(candidate);
    if (!cmd) {
      // A chord that resolved to nothing is still consumed: the leader took
      // the key, so it must not also fall through to a plain binding.
      return wasChord;
    }
    // Plain single-key bindings are deaf where typing happens; chorded ones are
    // not, and neither are the pane's and the overlay's, which are only fed
    // from the surface that owns them.
    if (
      !isChorded(candidate) &&
      cmd.scope !== "pane" &&
      cmd.scope !== "overlay" &&
      isTypingTarget(e.target)
    ) {
      return false;
    }
    if (this.preventDefault) e.preventDefault();
    cmd.run();
    return true;
  }
}