class FileUpload extends HTMLElement {
  connectedCallback() {
    this.attachShadow({ mode: 'open' });
    this.shadowRoot.innerHTML = `
      <style>
        .file-upload-container {
          display: flex;
          flex-direction: column;
          gap: 0.5rem;
          margin-bottom: 1rem;
        }
        .drop-area {
          border: 2px dashed #d1d5db;
          border-radius: 0.5rem;
          padding: 1rem;
          text-align: center;
          cursor: pointer;
          transition: all 0.2s;
        }
        .drop-area:hover, .drop-area.highlight {
          border-color: #7c3aed;
          background-color: #f5f3ff;
        }
        .file-input {
          display: none;
        }
        .file-info {
          font-size: 0.875rem;
          color: #6b7280;
          margin-top: 0.5rem;
        }
      </style>
      <div class="file-upload-container">
        <label for="file-upload" class="drop-area" id="drop-area">
          <p>Click to select or drag & drop a text file</p>
          <input type="file" id="file-upload" class="file-input" accept=".txt">
        </label>
        <div class="file-info" id="file-info">No file selected</div>
      </div>
    `;

    const dropArea = this.shadowRoot.getElementById('drop-area');
    const fileInput = this.shadowRoot.getElementById('file-upload');
    const fileInfo = this.shadowRoot.getElementById('file-info');

    ['dragenter', 'dragover', 'dragleave', 'drop'].forEach(eventName => {
      dropArea.addEventListener(eventName, preventDefaults, false);
    });

    ['dragenter', 'dragover'].forEach(eventName => {
      dropArea.addEventListener(eventName, highlight, false);
    });

    ['dragleave', 'drop'].forEach(eventName => {
      dropArea.addEventListener(eventName, unhighlight, false);
    });

    dropArea.addEventListener('drop', handleDrop, false);
    fileInput.addEventListener('change', handleFiles, false);

    function preventDefaults(e) {
      e.preventDefault();
      e.stopPropagation();
    }

    function highlight() {
      dropArea.classList.add('highlight');
    }

    function unhighlight() {
      dropArea.classList.remove('highlight');
    }

    function handleDrop(e) {
      const dt = e.dataTransfer;
      const files = dt.files;
      fileInput.files = files;
      handleFiles({ target: fileInput });
    }

    function handleFiles(e) {
      const file = e.target.files[0];
      if (file) {
        fileInfo.textContent = `Selected: ${file.name} (${(file.size / 1024).toFixed(1)} KB)`;
        const reader = new FileReader();
        reader.onload = function(e) {
          const textarea = document.getElementById('dataset');
          textarea.value = e.target.result;
        };
        reader.readAsText(file);
      } else {
        fileInfo.textContent = 'No file selected';
      }
    }
  }
}

customElements.define('file-upload', FileUpload);