import { useId, useRef, useState } from 'react';

const MAX_FILES = 20;
const MAX_SIZE_MB = 250;
const MAX_SIZE_BYTES = MAX_SIZE_MB * 1024 * 1024;

const formatSize = (bytes) => {
  if (bytes < 1024 * 1024) return (bytes / 1024).toFixed(1) + ' KB';
  return (bytes / (1024 * 1024)).toFixed(1) + ' MB';
};

export default function FileAttachment({ files, onChange }) {
  const inputId = useId();
  const [errors, setErrors] = useState([]);
  const [dragging, setDragging] = useState(false);
  const dragCounter = useRef(0);

  const processFiles = (incoming) => {
    const combined = [...files, ...incoming];
    const errs = [];
    if (combined.length > MAX_FILES) errs.push(`Maximum ${MAX_FILES} files allowed.`);
    incoming.filter(f => f.size > MAX_SIZE_BYTES).forEach(f => errs.push(`"${f.name}" exceeds ${MAX_SIZE_MB} MB limit.`));
    if (errs.length > 0) { setErrors(errs); return; }
    setErrors([]);
    onChange(combined);
  };

  const handleChange = (e) => {
    processFiles(Array.from(e.target.files));
    e.target.value = '';
  };

  const handleDragEnter = (e) => {
    e.preventDefault();
    dragCounter.current++;
    setDragging(true);
  };

  const handleDragLeave = (e) => {
    e.preventDefault();
    dragCounter.current--;
    if (dragCounter.current === 0) setDragging(false);
  };

  const handleDragOver = (e) => {
    e.preventDefault();
  };

  const handleDrop = (e) => {
    e.preventDefault();
    dragCounter.current = 0;
    setDragging(false);
    const dropped = Array.from(e.dataTransfer.files);
    if (dropped.length > 0) processFiles(dropped);
  };

  const remove = (index) => {
    setErrors([]);
    onChange(files.filter((_, i) => i !== index));
  };

  return (
    <div className="form-group">
      <div style={{ fontSize: 11, fontWeight: 500, textTransform: 'uppercase', letterSpacing: 0.8, color: 'var(--text-secondary)', marginBottom: 6 }}>
        Attach Files
        <span style={{ fontWeight: 400, color: 'var(--text-muted)', marginLeft: 6, textTransform: 'none', letterSpacing: 0 }}>
          Up to {MAX_FILES} files · Max {MAX_SIZE_MB} MB each · Any file type
        </span>
      </div>

      <div
        onDragEnter={handleDragEnter}
        onDragLeave={handleDragLeave}
        onDragOver={handleDragOver}
        onDrop={handleDrop}
        style={{
          border: `2px dashed ${dragging ? 'var(--accent)' : files.length > 0 ? 'var(--accent)' : 'var(--border)'}`,
          borderRadius: 8, padding: '16px', textAlign: 'center',
          background: dragging ? 'color-mix(in srgb, var(--accent) 8%, var(--bg))' : 'transparent',
          transition: 'all 160ms', cursor: 'pointer',
        }}
      >
        <input type="file" multiple onChange={handleChange} style={{ display: 'none' }} id={inputId} />
        <label htmlFor={inputId} style={{ cursor: 'pointer', textTransform: 'none', letterSpacing: 'normal', fontWeight: 400 }}>
          <div style={{ fontSize: 20, marginBottom: 4 }}>{dragging ? '📂' : '📎'}</div>
          <div style={{ fontSize: 13, color: 'var(--text-primary)' }}>
            {dragging
              ? 'Drop files here'
              : files.length > 0
                ? `${files.length} file${files.length !== 1 ? 's' : ''} attached — click or drag to add more`
                : 'Click or drag files here'}
          </div>
          <div style={{ fontSize: 12, color: 'var(--text-secondary)', marginTop: 2 }}>Any file type accepted</div>
        </label>
      </div>

      {errors.length > 0 && errors.map((err, i) => (
        <div key={i} style={{ fontSize: 12, color: 'var(--danger)', marginTop: 6 }}>⚠ {err}</div>
      ))}

      {files.length > 0 && (
        <div style={{ marginTop: 8, display: 'flex', flexDirection: 'column', gap: 6 }}>
          {files.map((file, i) => (
            <div key={i} style={{
              display: 'flex', alignItems: 'center', justifyContent: 'space-between',
              padding: '7px 12px', background: 'var(--card-bg)', borderRadius: 4, border: 'var(--card-border)',
            }}>
              <div style={{ display: 'flex', alignItems: 'center', gap: 8 }}>
                <span>📄</span>
                <div>
                  <div style={{ fontSize: 13, fontWeight: 400 }}>{file.name}</div>
                  <div style={{ fontSize: 11, color: 'var(--text-muted)' }}>{formatSize(file.size)}</div>
                </div>
              </div>
              <button type="button" onClick={() => remove(i)}
                style={{ background: 'none', border: 'none', cursor: 'pointer', color: 'var(--danger)', fontSize: 16, padding: '0 4px' }}>
                ✕
              </button>
            </div>
          ))}
          <div style={{ fontSize: 11, color: 'var(--text-muted)', textAlign: 'right' }}>
            {files.length}/{MAX_FILES} files
          </div>
        </div>
      )}
    </div>
  );
}