"use client";

import { Search, X } from "lucide-react";
import { useEffect, useId, useRef, useState, type KeyboardEvent, type ReactNode } from "react";

type LookupProps<T> = {
  placeholder?: string;
  onSearch: (query: string) => Promise<T[]>;
  renderResult: (item: T) => ReactNode;
  onSelect: (item: T) => void;
  minChars?: number;
  id?: string;
  "aria-describedby"?: string;
  "aria-invalid"?: true;
};

// Generic async search-select used by the position lookup (hire wizard),
// manager/superior lookup (create position), and the reorg workbench.
//
// Implements the combobox contract rather than just looking like one: it was
// a plain text input with a div of clickable buttons underneath, so a
// keyboard user could type but never reach a result, and a screen reader was
// never told a list had appeared. Arrow keys move the selection, Enter takes
// it, Escape closes without also closing the surrounding dialog.
export function Lookup<T>({
  placeholder = "Suchen…",
  onSearch,
  renderResult,
  onSelect,
  minChars = 2,
  id: idProp,
  "aria-describedby": describedBy,
  "aria-invalid": invalid,
}: LookupProps<T>) {
  const generatedId = useId();
  const id = idProp ?? generatedId;
  const [query, setQuery] = useState("");
  const [results, setResults] = useState<T[]>([]);
  const [open, setOpen] = useState(false);
  const [activeIndex, setActiveIndex] = useState(0);
  // Derived from "have we finished searching for the current query yet",
  // rather than a separate state flag flipped synchronously at the top of
  // the effect below — the effect only ever sets state from the async
  // search's own completion callback now.
  const [lastSearchedQuery, setLastSearchedQuery] = useState<string | null>(null);
  const containerRef = useRef<HTMLDivElement>(null);
  const listRef = useRef<HTMLDivElement>(null);

  const tooShort = query.trim().length < minChars;
  const loading = !tooShort && lastSearchedQuery !== query.trim();

  useEffect(() => {
    if (tooShort) return;
    let cancelled = false;
    const timeout = setTimeout(() => {
      onSearch(query.trim()).then((res) => {
        if (cancelled) return;
        setResults(res);
        setActiveIndex(0);
        setOpen(true);
        setLastSearchedQuery(query.trim());
      });
    }, 200);
    return () => {
      cancelled = true;
      clearTimeout(timeout);
    };
  }, [query, minChars, onSearch, tooShort]);

  // Derived rather than reset via effect: once the query drops below
  // minChars, hide the dropdown and any stale results immediately without
  // needing a synchronous setState inside the effect above.
  const showDropdown = open && !tooShort;
  const visibleResults = tooShort ? [] : results;
  const selectable = loading ? [] : visibleResults;

  useEffect(() => {
    function onClickOutside(e: MouseEvent) {
      if (containerRef.current && !containerRef.current.contains(e.target as Node)) {
        setOpen(false);
      }
    }
    document.addEventListener("mousedown", onClickOutside);
    return () => document.removeEventListener("mousedown", onClickOutside);
  }, []);

  useEffect(() => {
    if (!showDropdown) return;
    listRef.current?.querySelector('[data-active="true"]')?.scrollIntoView({ block: "nearest" });
  }, [activeIndex, showDropdown]);

  function reset() {
    setQuery("");
    setResults([]);
    setOpen(false);
    setActiveIndex(0);
  }

  function choose(item: T) {
    onSelect(item);
    reset();
  }

  function onKeyDown(e: KeyboardEvent<HTMLInputElement>) {
    if (e.key === "ArrowDown" || e.key === "ArrowUp") {
      if (selectable.length === 0) return;
      e.preventDefault();
      const delta = e.key === "ArrowDown" ? 1 : -1;
      setActiveIndex((i) => (i + delta + selectable.length) % selectable.length);
    } else if (e.key === "Enter") {
      if (showDropdown && selectable[activeIndex]) {
        e.preventDefault();
        choose(selectable[activeIndex]);
      }
    } else if (e.key === "Escape") {
      if (showDropdown) {
        // Without this the Escape also reaches Modal/SlideOver and closes
        // the whole dialog behind the dropdown.
        e.stopPropagation();
        setOpen(false);
      }
    }
  }

  const listId = `${id}-listbox`;

  return (
    <div ref={containerRef} className="relative">
      <div className="flex items-center gap-2 rounded border border-border bg-white px-3 py-2 focus-within:outline-2 focus-within:outline-offset-1 focus-within:outline-brand-500">
        <Search className="h-4 w-4 shrink-0 text-ink-muted" aria-hidden />
        <input
          id={id}
          role="combobox"
          aria-expanded={showDropdown}
          aria-controls={listId}
          aria-activedescendant={showDropdown && selectable[activeIndex] ? `${id}-option-${activeIndex}` : undefined}
          aria-autocomplete="list"
          aria-describedby={describedBy}
          aria-invalid={invalid}
          autoComplete="off"
          value={query}
          onChange={(e) => setQuery(e.target.value)}
          onKeyDown={onKeyDown}
          placeholder={placeholder}
          className="w-full text-sm outline-none placeholder:text-ink-muted"
        />
        {query && (
          <button type="button" onClick={reset} aria-label="Zurücksetzen" className="rounded p-0.5 hover:bg-surface">
            <X className="h-4 w-4 text-ink-muted" />
          </button>
        )}
      </div>
      {/* Announces "Suche…" / result count without stealing focus. */}
      <span aria-live="polite" className="sr-only">
        {showDropdown ? (loading ? "Suche läuft" : `${visibleResults.length} Treffer`) : ""}
      </span>
      {showDropdown && (
        <div
          ref={listRef}
          id={listId}
          role="listbox"
          className="absolute z-20 mt-1 max-h-64 w-full overflow-y-auto rounded border border-border bg-white shadow-[var(--shadow-card-hover)]"
        >
          {loading && <div className="px-3 py-2 text-sm text-ink-muted">Suche…</div>}
          {!loading && visibleResults.length === 0 && <div className="px-3 py-2 text-sm text-ink-muted">Keine Treffer</div>}
          {!loading &&
            visibleResults.map((item, i) => (
              <button
                key={i}
                id={`${id}-option-${i}`}
                role="option"
                aria-selected={i === activeIndex}
                data-active={i === activeIndex}
                type="button"
                // Mouse down would blur the input and close the list before
                // the click landed.
                onMouseDown={(e) => e.preventDefault()}
                onMouseEnter={() => setActiveIndex(i)}
                onClick={() => choose(item)}
                className={`block w-full px-3 py-2 text-left text-sm ${i === activeIndex ? "bg-brand-100" : "hover:bg-surface"}`}
              >
                {renderResult(item)}
              </button>
            ))}
        </div>
      )}
    </div>
  );
}
