frontend/src/components/DropZone.jsx

import { useState, useRef } from 'react';

const ACCEPTED = '.pdf,.docx,.pptx,.txt,.md';

const fmtSize = (bytes) => {
  if (bytes < 1024) return `${bytes} B`;
  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
};

export default function DropZone({ onFile, disabled }) {
  const [dragging, setDragging] = useState(false);
  const [chosen, setChosen] = useState(null);
  const inputRef = useRef(null);

  const handleFile = (file) => {
    if (!file) return;
    setChosen(file);
    onFile(file);
  };

  const onDragOver = (e) => { e.preventDefault(); setDragging(true); };
  const onDragLeave = () => setDragging(false);
  const onDrop = (e) => {
    e.preventDefault();
    setDragging(false);
    const file = e.dataTransfer.files[0];
    if (file) handleFile(file);
  };
  const onChange = (e) => handleFile(e.target.files[0]);

  return (
    <div>
      <div
        className={`drop-zone${dragging ? ' dragging' : ''}`}
        onDragOver={onDragOver}
        onDragLeave={onDragLeave}
        onDrop={onDrop}
        style={disabled ? { pointerEvents: 'none', opacity: .5 } : {}}
      >
        <input
          ref={inputRef}
          type="file"
          accept={ACCEPTED}
          onChange={onChange}
          disabled={disabled}
          id="file-input"
        />
        <div className="drop-icon">📄</div>
        <div className="drop-title">
          {dragging ? 'Drop it here!' : 'Click or drag file here'}
        </div>
        <div className="drop-sub">PDF · DOCX · PPTX · TXT · MD</div>
      </div>

      {chosen && (
        <div className="file-chosen">
          <span className="file-chosen-icon">📎</span>
          <span className="file-chosen-name">{chosen.name}</span>
          <span className="file-chosen-size">{fmtSize(chosen.size)}</span>
        </div>
      )}
    </div>
  );
}