"use client";

import { useEffect, useRef, useState } from "react";
import { CONTROL_CLASS } from "./Field";

type CountryPickerProps = {
  value: string;
  onChange: (value: string) => void;
  countries: string[];
  placeholder?: string;
  id?: string;
  "aria-describedby"?: string;
  "aria-invalid"?: true;
};

const MAX_VISIBLE = 50;

// Searchable text combobox constrained to a fixed list (UN member states)
// rather than a Lookup-style "selected card" — a country is a single text
// value, not an object with its own detail fields.
//
// Carries the full combobox contract: without role/aria-expanded/
// aria-activedescendant a screen reader announces a plain text box and never
// mentions that a list appeared, and without the key handling the list is
// reachable by mouse only.
export function CountryPicker({
  value,
  onChange,
  countries,
  placeholder = "Land suchen…",
  id,
  "aria-describedby": describedBy,
  "aria-invalid": invalid,
}: CountryPickerProps) {
  const [query, setQuery] = useState(value);
  const [prevValue, setPrevValue] = useState(value);
  const [open, setOpen] = useState(false);
  const [activeIndex, setActiveIndex] = useState(0);
  const containerRef = useRef<HTMLDivElement>(null);
  const listRef = useRef<HTMLDivElement>(null);

  // Re-sync the local draft text when `value` changes externally (e.g. the
  // surrounding form loads a different employee). Adjusting state directly
  // during render — rather than in an effect — avoids an extra render pass
  // and the synchronous setState-in-effect this used to do.
  if (value !== prevValue) {
    setPrevValue(value);
    setQuery(value);
  }

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

  const filtered = (query.trim() ? countries.filter((c) => c.toLowerCase().includes(query.trim().toLowerCase())) : countries).slice(
    0,
    MAX_VISIBLE
  );
  const listId = id ? `${id}-listbox` : undefined;
  const activeId = id && filtered[activeIndex] ? `${id}-option-${activeIndex}` : undefined;

  function commit(country: string) {
    onChange(country);
    setQuery(country);
    setOpen(false);
  }

  // Keeps the highlighted row inside the scroll container as it moves.
  useEffect(() => {
    if (!open) return;
    listRef.current?.querySelector('[data-active="true"]')?.scrollIntoView({ block: "nearest" });
  }, [activeIndex, open]);

  function onKeyDown(e: React.KeyboardEvent<HTMLInputElement>) {
    if (e.key === "ArrowDown" || e.key === "ArrowUp") {
      e.preventDefault();
      if (!open) {
        setOpen(true);
        setActiveIndex(0);
        return;
      }
      const delta = e.key === "ArrowDown" ? 1 : -1;
      setActiveIndex((i) => (filtered.length === 0 ? 0 : (i + delta + filtered.length) % filtered.length));
    } else if (e.key === "Enter") {
      if (open && filtered[activeIndex]) {
        e.preventDefault();
        commit(filtered[activeIndex]);
      }
    } else if (e.key === "Escape") {
      if (open) {
        // Stop here rather than letting it bubble — otherwise the dialog
        // containing this field closes along with the dropdown.
        e.stopPropagation();
        setOpen(false);
        setQuery(value);
      }
    }
  }

  return (
    <div ref={containerRef} className="relative">
      <input
        id={id}
        role="combobox"
        aria-expanded={open}
        aria-controls={listId}
        aria-activedescendant={open ? activeId : undefined}
        aria-autocomplete="list"
        aria-describedby={describedBy}
        aria-invalid={invalid}
        autoComplete="off"
        value={query}
        onChange={(e) => {
          setQuery(e.target.value);
          setActiveIndex(0);
          setOpen(true);
        }}
        onFocus={() => setOpen(true)}
        onKeyDown={onKeyDown}
        placeholder={placeholder}
        className={CONTROL_CLASS}
      />
      {open && (
        <div
          ref={listRef}
          id={listId}
          role="listbox"
          className="absolute z-20 mt-1 max-h-56 w-full overflow-y-auto rounded border border-border bg-white shadow-[var(--shadow-card-hover)]"
        >
          {filtered.length === 0 && <div className="px-3 py-2 text-sm text-ink-muted">Keine Treffer</div>}
          {filtered.map((c, i) => (
            <button
              key={c}
              id={id ? `${id}-option-${i}` : undefined}
              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={() => commit(c)}
              className={`block w-full px-3 py-2 text-left text-sm ${i === activeIndex ? "bg-brand-100 text-brand-700" : "hover:bg-surface"}`}
            >
              {c}
            </button>
          ))}
        </div>
      )}
    </div>
  );
}