// Shell-style directory autocomplete for a path <input> (NAP-329).
//
// Lists one directory at a time over the live `GET /api/dirs` endpoint, caches
// per directory, and filters the trailing path segment locally — so typing within a segment is instant and only crossing a `/`
// hits the network. Keyboard model mirrors `cd dir/sub<tab>`:
//
//   Tab    commit the highlighted entry and let focus move on; with nothing
//          highlighted, plain tab navigation
//   ↑/↓    move the highlight
//   Enter  accept the highlighted entry (and suppress form submit)
//   Esc    close the dropdown, refocus the input, and swallow the key so it
//          can't also discard a surrounding draft pane
//
// Once dismissed (Esc or blur) the popup stays closed until the operator types
// again — refocusing alone doesn't reopen it.
//
// Failures (offline daemon, permission denied) degrade to no suggestions.

import { splitPath } from "./paths.js";
import { listDir } from "./api.js";

export interface DirAutocompleteHandle {
  destroy(): void;
}

/** Most entries we render at once — a long list is unhelpful and slow. */
const MAX_VISIBLE = 60;
/** Debounce before a network fetch when the user crosses into a new directory. */
const FETCH_DEBOUNCE_MS = 90;

/** Split a path value into the directory to list and the trailing fragment
 * being typed within it. The directory keeps its trailing `/` (or is empty,
 * meaning "the daemon's home dir"). */
export function attachDirAutocomplete(input: HTMLInputElement): DirAutocompleteHandle {
  const dropdown = document.createElement("ul");
  dropdown.className = "dir-ac";
  dropdown.setAttribute("role", "listbox");
  dropdown.hidden = true;
  document.body.appendChild(dropdown);

  // `dir -> entries`. Successful listings only; errors aren't cached so a
  // transient failure can recover on the next keystroke.
  const cache = new Map<string, string[]>();
  let filtered: string[] = [];
  let highlight = -1;
  let fetchSeq = 0;
  let debounce: number | undefined;
  let open = false;
  // Set when the operator dismissed the popup (Esc, blur, outside click); a
  // refocus must not reopen it — only new typing does.
  let dismissed = false;


  function close(): void {
    if (!open) return;
    open = false;
    dropdown.hidden = true;
    dropdown.replaceChildren();
    highlight = -1;
    window.removeEventListener("scroll", reposition, true);
    window.removeEventListener("resize", reposition);
  }

  function dismiss(): void {
    dismissed = true;
    close();
  }

  function reposition(): void {
    const r = input.getBoundingClientRect();
    dropdown.style.left = `${r.left}px`;
    dropdown.style.top = `${r.bottom + 4}px`;
    dropdown.style.width = `${r.width}px`;
  }

  function render(): void {
    dropdown.replaceChildren();
    if (filtered.length === 0) {
      close();
      return;
    }
    const shown = filtered.slice(0, MAX_VISIBLE);
    shown.forEach((name, i) => {
      const li = document.createElement("li");
      li.className = "dir-ac-item" + (i === highlight ? " is-active" : "");
      li.setAttribute("role", "option");
      li.setAttribute("aria-selected", String(i === highlight));
      li.textContent = name + "/";
      // mousedown (not click) so we accept before the input's blur fires.
      li.addEventListener("mousedown", (e) => {
        e.preventDefault();
        accept(name);
      });
      dropdown.appendChild(li);
    });
    if (filtered.length > MAX_VISIBLE) {
      const more = document.createElement("li");
      more.className = "dir-ac-more";
      more.textContent = `+${filtered.length - MAX_VISIBLE} more — keep typing to narrow`;
      dropdown.appendChild(more);
    }
    if (!open) {
      open = true;
      dropdown.hidden = false;
      window.addEventListener("scroll", reposition, true);
      window.addEventListener("resize", reposition);
    }
    reposition();
  }

  function applyFilter(entries: string[], prefix: string): void {
    // A fetch can outlive the dismissal that was meant to close this popup
    // (Tab-commit re-arms a refresh, then blur dismisses 120ms later). Showing
    // it now would anchor a dropdown under an unfocused input that nothing
    // closes until the next interaction.
    if (dismissed || document.activeElement !== input) {
      close();
      return;
    }
    const lower = prefix.toLowerCase();
    filtered = entries.filter((e) => e.toLowerCase().startsWith(lower));
    highlight = filtered.length > 0 ? 0 : -1;
    render();
  }

  // Fetch (or read from cache) the listing for the directory currently implied
  // by the input, then filter by the trailing fragment.
  function refresh(): void {
    const { dir, prefix } = splitPath(input.value);
    const cached = cache.get(dir);
    if (cached) {
      applyFilter(cached, prefix);
      return;
    }
    const seq = ++fetchSeq;
    listDir(dir)
      .then((listing) => {
        cache.set(dir, listing.entries);
        if (seq !== fetchSeq) return; // a newer fetch superseded this one
        // The input may have changed while in flight; re-split before filtering.
        const cur = splitPath(input.value);
        if (cur.dir === dir) applyFilter(listing.entries, cur.prefix);
      })
      .catch(() => {
        if (seq === fetchSeq) close();
      });
  }

  function scheduleRefresh(): void {
    window.clearTimeout(debounce);
    debounce = window.setTimeout(refresh, FETCH_DEBOUNCE_MS);
  }

  // Accept `name` as the next path segment: complete it and append `/` so the
  // child directory's listing loads on the next interaction (the drill-in
  // gesture). Unlike `accept`, doesn't steal focus — Tab uses this to commit
  // and move to the next field in one gesture.
  function commit(name: string): void {
    const { dir } = splitPath(input.value);
    input.value = `${dir}${name}/`;
    // Notify other listeners (spawnForm marks the field user-edited).
    input.dispatchEvent(new Event("input", { bubbles: true }));
  }

  function accept(name: string): void {
    commit(name);
    input.focus();
  }

  function onInput(): void {
    dismissed = false;
    scheduleRefresh();
  }

  function onFocus(): void {
    if (dismissed) return;
    refresh();
  }

  function onKeydown(e: KeyboardEvent): void {
    if (e.key === "Escape") {
      if (open) {
        e.preventDefault();
        // Swallow the key: an Escape that bubbles would also discard the
        // draft pane hosting this form.
        e.stopPropagation();
        dismiss();
        input.focus();
      }
      return;
    }
    if (e.key === "Tab") {
      if (!open || highlight < 0 || highlight >= filtered.length) return; // plain tab navigation
      commit(filtered[highlight]); // no preventDefault — focus moves to the next field
      return;
    }
    if (!open) return;
    if (e.key === "ArrowDown") {
      e.preventDefault();
      highlight = Math.min(highlight + 1, filtered.length - 1);
      render();
    } else if (e.key === "ArrowUp") {
      e.preventDefault();
      highlight = Math.max(highlight - 1, 0);
      render();
    } else if (e.key === "Enter") {
      if (highlight >= 0 && highlight < filtered.length) {
        e.preventDefault(); // accept the entry instead of submitting the form
        accept(filtered[highlight]);
      }
    }
  }

  function onBlur(): void {
    // Delay so a dropdown mousedown can complete first.
    window.setTimeout(dismiss, 120);
  }

  input.addEventListener("input", onInput);
  input.addEventListener("focus", onFocus);
  input.addEventListener("keydown", onKeydown);
  input.addEventListener("blur", onBlur);

  return {
    destroy() {
      window.clearTimeout(debounce);
      close();
      input.removeEventListener("input", onInput);
      input.removeEventListener("focus", onFocus);
      input.removeEventListener("keydown", onKeydown);
      input.removeEventListener("blur", onBlur);
      dropdown.remove();
    },
  };
}