// React port of ../../dirAutocomplete.ts: shell-style directory autocomplete
// on a path <input>. Lists one directory at a time over `GET /api/dirs`,
// caches per directory, and filters the trailing path segment locally.
//
// 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); with
//          nothing highlighted, bubble to the form unprevented
//   Esc    close the dropdown, refocus the input, and stop the key from
//          bubbling — so dismissing the popup can't also close a parent modal
//
// Once dismissed (Esc or blur) the popup stays closed until the operator
// types again — refocusing alone doesn't reopen it.

import { useCallback, useEffect, useRef, useState, type InputHTMLAttributes, type Ref } from "react";
import { createPortal } from "react-dom";

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

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

export interface DirAutocompleteProps
  extends Omit<InputHTMLAttributes<HTMLInputElement>, "value" | "onChange"> {
  value: string;
  onChange(value: string): void;
  /** Access to the underlying `<input>` — e.g. to focus/select it. */
  inputRef?: Ref<HTMLInputElement>;
}

function assignRef(ref: Ref<HTMLInputElement> | undefined, el: HTMLInputElement | null): void {
  if (!ref) return;
  if (typeof ref === "function") ref(el);
  else (ref as { current: HTMLInputElement | null }).current = el;
}

export function DirAutocomplete({ value, onChange, inputRef, ...inputProps }: DirAutocompleteProps) {
  const localRef = useRef<HTMLInputElement | null>(null);
  const cache = useRef(new Map<string, string[]>());
  const fetchSeq = useRef(0);
  const debounceTimer = useRef<number | undefined>(undefined);
  const dismissedRef = useRef(false);

  const [filtered, setFiltered] = useState<string[]>([]);
  const [highlight, setHighlight] = useState(-1);
  const [open, setOpen] = useState(false);
  const [rect, setRect] = useState<{ left: number; top: number; width: number } | null>(null);

  const setInputRef = useCallback(
    (el: HTMLInputElement | null) => {
      localRef.current = el;
      assignRef(inputRef, el);
    },
    [inputRef],
  );

  const reposition = useCallback(() => {
    const el = localRef.current;
    if (!el) return;
    const r = el.getBoundingClientRect();
    setRect({ left: r.left, top: r.bottom + 4, width: r.width });
  }, []);

  const close = useCallback(() => {
    setOpen(false);
    setFiltered([]);
    setHighlight(-1);
  }, []);

  const dismiss = useCallback(() => {
    dismissedRef.current = true;
    close();
  }, [close]);

  const applyFilter = useCallback(
    (entries: string[], prefix: string) => {
      // A fetch can outlive the dismissal it was meant to serve (Tab-commit
      // re-arms a refresh, then blur dismisses 120ms later). Showing it now
      // would anchor a dropdown under an unfocused input nothing closes.
      if (dismissedRef.current || document.activeElement !== localRef.current) {
        close();
        return;
      }
      const lower = prefix.toLowerCase();
      const next = entries.filter((e) => e.toLowerCase().startsWith(lower));
      setFiltered(next);
      setHighlight(next.length > 0 ? 0 : -1);
      if (next.length === 0) {
        close();
        return;
      }
      setOpen(true);
      reposition();
    },
    [close, reposition],
  );

  const refresh = useCallback(
    (raw: string) => {
      const { dir, prefix } = splitPath(raw);
      const cached = cache.current.get(dir);
      if (cached) {
        applyFilter(cached, prefix);
        return;
      }
      const seq = ++fetchSeq.current;
      listDir(dir)
        .then((listing) => {
          cache.current.set(dir, listing.entries);
          if (seq !== fetchSeq.current) return; // a newer fetch superseded this one
          const cur = splitPath(localRef.current?.value ?? raw);
          if (cur.dir === dir) applyFilter(listing.entries, cur.prefix);
        })
        .catch(() => {
          if (seq === fetchSeq.current) close();
        });
    },
    [applyFilter, close],
  );

  const scheduleRefresh = useCallback(
    (raw: string) => {
      window.clearTimeout(debounceTimer.current);
      debounceTimer.current = window.setTimeout(() => refresh(raw), FETCH_DEBOUNCE_MS);
    },
    [refresh],
  );

  /** Complete `name` as the next path segment 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. */
  const commit = useCallback(
    (name: string) => {
      const { dir } = splitPath(value);
      onChange(`${dir}${name}/`);
    },
    [value, onChange],
  );

  const accept = useCallback(
    (name: string) => {
      commit(name);
      localRef.current?.focus();
    },
    [commit],
  );

  useEffect(() => {
    if (!open) return;
    window.addEventListener("scroll", reposition, true);
    window.addEventListener("resize", reposition);
    return () => {
      window.removeEventListener("scroll", reposition, true);
      window.removeEventListener("resize", reposition);
    };
  }, [open, reposition]);

  useEffect(() => () => window.clearTimeout(debounceTimer.current), []);

  return (
    <>
      <input
        {...inputProps}
        ref={setInputRef}
        value={value}
        autoComplete="off"
        role="combobox"
        aria-expanded={open}
        aria-autocomplete="list"
        onChange={(e) => {
          dismissedRef.current = false;
          const next = e.currentTarget.value;
          onChange(next);
          scheduleRefresh(next);
        }}
        onFocus={(e) => {
          inputProps.onFocus?.(e);
          if (dismissedRef.current) return;
          refresh(value);
        }}
        onBlur={(e) => {
          inputProps.onBlur?.(e);
          // Delay so a dropdown mousedown can complete first.
          window.setTimeout(dismiss, 120);
        }}
        onKeyDown={(e) => {
          inputProps.onKeyDown?.(e);
          if (e.defaultPrevented) return;
          if (e.key === "Escape") {
            if (open) {
              e.preventDefault();
              e.stopPropagation();
              dismiss();
              localRef.current?.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();
            setHighlight((h) => Math.min(h + 1, filtered.length - 1));
          } else if (e.key === "ArrowUp") {
            e.preventDefault();
            setHighlight((h) => Math.max(h - 1, 0));
          } else if (e.key === "Enter" && highlight >= 0 && highlight < filtered.length) {
            e.preventDefault(); // accept the entry instead of submitting the form
            accept(filtered[highlight]);
          }
        }}
      />
      {open &&
        rect &&
        createPortal(
          <ul
            role="listbox"
            className="dir-ac fixed z-modal max-h-[240px] overflow-y-auto rounded-r-2 border border-border-strong bg-surface py-sp-1 font-mono shadow-2"
            style={{ left: rect.left, top: rect.top, width: rect.width }}
          >
            {filtered.slice(0, MAX_VISIBLE).map((name, i) => (
              <li
                key={name}
                role="option"
                aria-selected={i === highlight}
                className={`cursor-pointer truncate px-sp-3 py-1 text-fs-12 text-ink ${
                  i === highlight ? "bg-accent-tint" : ""
                }`}
                onMouseDown={(e) => {
                  e.preventDefault(); // accept before the input's blur fires
                  accept(name);
                }}
              >
                {name}/
              </li>
            ))}
            {filtered.length > MAX_VISIBLE && (
              <li className="px-sp-3 py-1 text-fs-11 text-faint">
                +{filtered.length - MAX_VISIBLE} more — keep typing to narrow
              </li>
            )}
          </ul>,
          document.body,
        )}
    </>
  );
}