import React, { useState, useEffect } from 'react';

interface Document {
  name: string;
  url: string;
}

interface Signer {
  name: string;
  email: string;
}

interface Signature {
  name: string;
  image: string;
}

interface DocumentSigningProps {
  document: Document;
  signer: Signer;
  signature: Signature;
}

const DocumentSigning: React.FC<DocumentSigningProps> = ({
  document,
  signer,
  signature,
}) => {
  const [uploadedDocument, setUploadedDocument] = useState<Document | null>(
    null
  );
  const [signingLink, setSigningLink] = useState<string | null>(null);
  const [signatureImage, setSignatureImage] = useState<string | null>(null);
  const [signaturePlacement, setSignaturePlacement] = useState<boolean>(false);
  const [confirmationEmail, setConfirmationEmail] = useState<boolean>(false);
  const [signatureValidated, setSignatureValidated] = useState<boolean>(false);
  const [signedDocument, setSignedDocument] = useState<Document | null>(null);
  const [customInstructions, setCustomInstructions] = useState<string | null>(
    null
  );
  const [linkExpired, setLinkExpired] = useState<boolean>(false);

  // Function to handle document upload
  const handleDocumentUpload = (file: File) => {
    // Code to upload document to server and set uploadedDocument state
    setUploadedDocument({
      name: file.name,
      url: 'https://example.com/document.pdf',
    });
  };

  // Function to generate unique signing link
  const generateSigningLink = () => {
    // Code to generate unique link and set signingLink state
    setSigningLink('https://example.com/signing-link');
  };

  // Function to handle sending link to signer's email
  const sendLinkToSigner = () => {
    // Code to send email to signer with signing link
    setConfirmationEmail(true);
  };

  // Function to handle signature capture
  const handleSignatureCapture = (image: string) => {
    // Code to capture signature and set signatureImage state
    setSignatureImage(image);
  };

  // Function to handle document preview
  const handleDocumentPreview = () => {
    // Code to display signed document in preview mode
    setSignedDocument({
      name: document.name,
      url: 'https://example.com/signed-document.pdf',
    });
  };

  // Function to save signature for future use
  const saveSignature = () => {
    // Code to save signature and set signature state
    setSignatureImage('https://example.com/signature.png');
  };

  // Function to handle signature placement confirmation
  const confirmSignaturePlacement = () => {
    // Code to confirm signature placement and set signaturePlacement state
    setSignaturePlacement(true);
  };

  // Function to send confirmation email to sender
  const sendConfirmationEmail = () => {
    // Code to send email to sender confirming document has been signed
    setConfirmationEmail(true);
  };

  // Function to validate signature
  const validateSignature = () => {
    // Code to validate signature and set signatureValidated state
    setSignatureValidated(true);
  };

  // Function to handle document download
  const handleDocumentDownload = () => {
    // Code to download signed document to device
    setSignedDocument({
      name: document.name,
      url: 'https://example.com/signed-document.pdf',
    });
  };

  // Function to handle custom signing instructions
  const handleCustomInstructions = (instructions: string) => {
    // Code to set custom instructions state
    setCustomInstructions(instructions);
  };

  // Function to handle link expiration
  const handleLinkExpiration = () => {
    // Code to set linkExpired state
    setLinkExpired(true);
  };

  // UseEffect hook to handle mobile responsive design
  useEffect(() => {
    // Code to check if user is accessing page on a mobile device and adjust layout accordingly
  }, []);

  // UseEffect hook to handle API integration
  useEffect(() => {
    // Code to integrate document signing API into application
  }, []);

  // UseEffect hook to handle drag-and-drop document upload
  useEffect(() => {
    // Code to handle drag-and-drop functionality
  }, []);

  return (
    <div>
      {/* Document Upload */}
      <input type="file" onChange={(e) => handleDocumentUpload(e.target.files[0])} />

      {/* Generate Unique Signing Link */}
      <button onClick={generateSigningLink}>Generate Link</button>

      {/* Email Link to Signer */}
      <input type="email" value={signer.email} />
      <button onClick={sendLinkToSigner}>Send</button>

      {/* Signature Capture */}
      <SignatureCapture onCapture={handleSignatureCapture} />

      {/* Document Preview */}
      <button onClick={handleDocumentPreview}>Preview</button>

      {/* Save Signature */}
      <button onClick={saveSignature}>Save Signature</button>

      {/* Confirm Signature Placement */}
      <button onClick={confirmSignaturePlacement}>Confirm</button>

      {/* Email Confirmation to Sender */}
      <button onClick={sendConfirmationEmail}>Send Confirmation</button>

      {/* Signature Validation */}
      <button onClick={validateSignature}>Validate Signature</button>

      {/* Document Download */}
      <button onClick={handleDocumentDownload}>Download</button>

      {/* Mobile Responsive Design */}
      {/* Code to handle mobile responsive design */}

      {/* API for Document Management */}
      {/* Code to integrate document signing API into application */}

      {/* Drag-and-Drop Document Upload */}
      {/* Code to handle drag-and-drop functionality */}

      {/* Custom Signing Instructions */}
      <input type="text" onChange={(e) => handleCustomInstructions(e.target.value)} />

      {/* Link Expiration */}
      {/* Code to handle link expiration */}
    </div>
  );
};

export default DocumentSigning;
```