import { useState, useRef, useEffect, useCallback } from 'react';

interface Props {
  value: string;
  onChange: (value: string) => void;
  suggestions: string[];
  placeholder?: string;
  className?: string;
  onKeyDown?: (e: React.KeyboardEvent) => void;
}

export default function AutocompleteInput({ value, onChange, suggestions, placeholder, className, onKeyDown }: Props) {
  const [open, setOpen] = useState(false);
  const [highlightIdx, setHighlightIdx] = useState(-1);
  const inputRef = useRef<HTMLInputElement>(null);
  const listRef = useRef<HTMLUListElement>(null);

  const filtered = value
    ? suggestions.filter(s => s.toLowerCase().includes(value.toLowerCase()))
    : suggestions;

  const handleSelect = useCallback((val: string) => {
    onChange(val);
    setOpen(false);
    setHighlightIdx(-1);
  }, [onChange]);

  const handleKeyDown = (e: React.KeyboardEvent) => {
    if (!open || filtered.length === 0) {
      // Tab with no dropdown: accept what's typed, let focus move naturally
      onKeyDown?.(e);
      return;
    }

    if (e.key === 'ArrowDown') {
      e.preventDefault();
      setHighlightIdx(i => Math.min(i + 1, filtered.length - 1));
    } else if (e.key === 'ArrowUp') {
      e.preventDefault();
      setHighlightIdx(i => Math.max(i - 1, 0));
    } else if (e.key === 'Enter' && highlightIdx >= 0) {
      e.preventDefault();
      handleSelect(filtered[highlightIdx]);
    } else if (e.key === 'Tab' && highlightIdx >= 0) {
      // Tab accepts highlighted suggestion
      handleSelect(filtered[highlightIdx]);
      // Don't prevent default — let focus move to next field
    } else if (e.key === 'Tab' && filtered.length > 0 && value) {
      // Tab with text typed: accept first match
      handleSelect(filtered[0]);
    } else if (e.key === 'Escape') {
      setOpen(false);
      setHighlightIdx(-1);
    } else {
      onKeyDown?.(e);
    }
  };

  useEffect(() => {
    if (highlightIdx >= 0 && listRef.current) {
      const el = listRef.current.children[highlightIdx] as HTMLElement;
      el?.scrollIntoView({ block: 'nearest' });
    }
  }, [highlightIdx]);

  return (
    <div className="relative">
      <input
        ref={inputRef}
        type="text"
        value={value}
        onChange={e => {
          onChange(e.target.value);
          setOpen(true);
          setHighlightIdx(-1);
        }}
        onFocus={() => setOpen(true)}
        onBlur={() => {
          // Delay to allow click on dropdown items
          setTimeout(() => setOpen(false), 150);
        }}
        onKeyDown={handleKeyDown}
        placeholder={placeholder}
        className={className}
        autoComplete="off"
      />
      {open && filtered.length > 0 && (
        <ul
          ref={listRef}
          className="absolute z-50 left-0 min-w-full w-max top-full mt-1 bg-white dark:bg-gray-800 border border-gray-200 dark:border-gray-700 rounded-md shadow-lg max-h-40 overflow-y-auto text-sm"
        >
          {filtered.slice(0, 10).map((item, idx) => (
            <li
              key={item}
              className={`px-3 py-1.5 cursor-pointer ${idx === highlightIdx ? 'bg-gray-100 dark:bg-gray-700 text-gray-900 dark:text-gray-100' : 'text-gray-700 dark:text-gray-300 hover:bg-gray-50 dark:hover:bg-gray-700'}`}
              onMouseDown={() => handleSelect(item)}
              onMouseEnter={() => setHighlightIdx(idx)}
            >
              {item}
            </li>
          ))}
        </ul>
      )}
    </div>
  );
}