このページは英語からの機械翻訳を使用しており、誤りや不明瞭な表現が含まれている可能性があります。最も正確な情報については、オリジナルの英語版をご覧ください。頻繁な更新のため、一部のコンテンツはオリジナルの英語になっている可能性があります。Crowdinでの取り組みに参加して、このページの翻訳改善にご協力ください。 (Crowdin translation page, Contributing guide)

Integrating a Next.js frontend application with smart contract

In the previous steps, you successfully built and deployed the smart contract to a localhost. Now, it's time to interact with it from the frontend. The frontend uses Next.js, integrates Semaphore for privacy features and the Mini Dapp SDK for authentication.

Setup & Installation

Having already cloned the project repo inclusive of Next.js frontend, the next thing you want to do is to create a .env file in the root directory by using the command below:


touch .env

Note: Ensure you are in the root directory before running the command above.

Inside the .env file you just created, add the following:


SURVEY_FACTORY_V1_CONTRACT_ADDRESS=[factory address]
NEXT_PUBLIC_SURVEY_FACTORY_V1_CONTRACT_ADDRESS=[factory address]
NODE_URL=http://localhost:8545

備考

Make sure to Replace SURVEY_FACTORY_V1_CONTRACT_ADDRESS and NEXT_PUBLIC_SURVEY_FACTORY_V1_CONTRACT_ADDRESS with the contract address you deployed to localhost earlier in this tutorial.

Now lets take a look at the core functionalities of the app:

Survey Management

1. Creating Survey

Interface Definition:

The SurveyInfo interface standardizes how survey data is handled across the application, ensuring consistency in data types and structure.


// types/index.ts
export interface SurveyInfo {
  title: string;          // Survey's display title
  desc: string;          // Detailed survey description
  id: string;           // Unique identifier (contract address)
  remaining: number;    // Number of responses still needed
  reward: string;       // Per-response reward amount
  respondents: number;  // Current number of participants
  daysleft: number;    // Time until expiration
  finished: boolean;   // Survey completion status
}

Implementation and Usage

A. Data Fetching: This layer manages the communication between the smart contracts and the application, converting raw blockchain data into the SurveyInfo format.


// backend/survey.tsx
export const getSurvey = async (address: string): Promise<SurveyInfo> => {
  const survey = getSurveyV1(address);
  const info = await survey.surveyInfo();
  return decodeSurveyInfo(info, address);
};
// Decode contract data to SurveyInfo
const decodeSurveyInfo = (info: any[], contractAddr: string): SurveyInfo => {
  return {
    title: info[0],
    desc: info[1],
    id: contractAddr,
    remaining: remainedSurvey(info[4], info[5]),
    reward: ethers.formatEther(info[3]),
    respondents: info[5],
    daysleft: daysLeft(info[7]),
    finished: info[10]
  };
};
// Helper functions
const remainedSurvey = (targetNumber: number, respondents: number) => {
  return targetNumber - respondents;
};
const daysLeft = (duration: bigint) => {
  const now = BigInt(Math.floor(Date.now() / 1000));
  return Number(duration - now) / 86400; // Convert to days
};

B. Display components: This React component handles the visual representation of survey data, including status indicators, progress tracking, and other interactive elements.


// components/SurveyCard.tsx
interface SurveyCardProps extends SurveyInfo {}
export default function SurveyCard({
  id,
  title,
  desc,
  reward,
  remaining,
  respondents,
  daysleft,
  finished,
}: SurveyCardProps) {
  return (
    <div className="flex flex-col rounded-lg bg-violet-400">
      {/* Status Badge */}
      {finished ? (
        <div className="bg-red-400 rounded-2xl">
          <span>Finished</span>
        </div>
      ) : (
        <div className="bg-lime-400 rounded-2xl">
          <span>In Progress</span>
        </div>
      )}
      {/* Time Remaining */}
      {!finished && (
        daysleft < 1 ? (
          <div className="bg-amber-600 rounded-2xl">
            <span>{`h-${Math.floor(daysleft * 24)}`}</span>
          </div>
        ) : (
          <div className="bg-teal-500 rounded-2xl">
            <span>D-{Math.floor(daysleft)}</span>
          </div>
        )
      )}
      {/* Reward Display */}
      <span className="text-white">
        <span className="font-bold">{reward}</span> KAIA
      </span>
      {/* Survey Details */}
      <div className="px-5 pt-2">
        <h1 className="text-xl font-bold">
          {title.length > 20 ? title.substring(0, 20) + "..." : title}
        </h1>
        <p className="text-white mt-1 break-words">
          {desc.length > 65 ? desc.substring(0, 65) + "..." : desc}
        </p>
      </div>
      {/* Statistics */}
      <div className="flex justify-start">
        <div className="flex flex-col mr-8">
          <span>Remains</span>
          <span className="font-bold">{remaining}</span>
        </div>
        <div className="flex flex-col">
          <span>Respondents</span>
          <span className="font-bold">{respondents}</span>
        </div>
      </div>
    </div>
  );
}

C. Survey Listing: Handles the organization and display of survey collections, featuring sections like Hot Topics and Ending Soon to improve user navigation.


// app/[locale]/square/surveys/page.tsx
export default async function SurveysPage() {
  const data = await getAllSurveyV1s();
  // Sort and filter surveys
  const hotTopics = data
    .sort((a, b) => b.respondents - a.respondents)
    .slice(0, 10);
  const endingSoon = data
    .filter((survey) => survey.daysleft < 2);
  return (
    <div className="flex flex-col mt-5">
      {/* Hot Topics Section */}
      {hotTopics.length > 0 && (
        <div>
          <h1 className="text-3xl font-bold">Hot Topics</h1>
          <div className="flex overflow-x-scroll">
            {hotTopics.map((survey) => (
              <SurveyCard key={survey.id} {...survey} />
            ))}
          </div>
        </div>
      )}
      {/* Ending Soon Section */}
      {endingSoon.length > 0 && (
        <div>
          <h1 className="text-3xl font-bold">Ending Soon</h1>
          <div className="flex overflow-x-scroll">
            {endingSoon.map((survey) => (
              <SurveyCard key={survey.id} {...survey} />
            ))}
          </div>
        </div>
      )}
    </div>
  );
}

2. Answering Survey

A. Interface Definition: The Answer interface provides a standardized format for survey responses, including both the answer data and privacy-related proof information.


// types/index.ts
interface Answer {
  respondent: string;           // Wallet address of respondent
  answers: number[];           // Array of selected answer indices
  merkleTreeDepth: number;     // Depth of merkle tree for proof
  merkleTreeRoot: string;      // Root of merkle tree
  nullifier: string;          // Unique identifier to prevent double submission
  points: number[];          // Proof points for zero-knowledge verification
}

B. Submission Function: This function manages the interaction with the smart contract, including transaction creation and confirmation.


// browser/survey.tsx
export const submitAnswer = async (
  surveyAddress: string,
  provider: Web3Provider,
  answer: Answer
) => {
  const signer = await provider.getSigner(0);
// Get contract instance
  const survey = getSurveyV1(surveyAddress, signer);
  try {
// Submit transaction
    const tx = await survey.submitAnswer(answer, { gasLimit: 5000000 });
// Wait for confirmation
    const receipt = await tx.wait();
    return receipt;
  } catch (e: any) {
    console.log("error", e);
    return e.message;
  }
};

C. Display components: The frontend component manages form data collection, validates user input, interacts with Web3 providers, and handles the submission process while providing appropriate user feedback.


// Component for submitting answers
export default function SubmitAnswerForm({
  id,
  questions,
}: {
  id: string;
  questions: Question[];
}) {
  const { provider, identity, account } = useWeb3();
  const router = useRouter();
  const handleSubmit = async (e: React.FormEvent) => {
    e.preventDefault();
    
    try {
      // 1. Validate prerequisites
      if (!provider || !account) {
        alert("Please connect wallet first!");
        return;
      }
      if (!identity) {
        alert("You need to login with LINE first!");
        return;
      }
      // 2. Collect form data
      const formData = new FormData(e.target as HTMLFormElement);
      const answers = Array.from(formData.values()).map(val => 
        parseInt(val as string)
      );
      // 3. Generate proof
      const group = new Group(members);
      const proof = await generateProof(
        identity,
        group,
        new Uint8Array(answers),
        groupId
      );
      // 4. Prepare answer object
      const answer = {
        respondent: account,
        answers,
        merkleTreeDepth: proof.merkleTreeDepth,
        merkleTreeRoot: proof.merkleTreeRoot,
        nullifier: proof.nullifier,
        points: proof.points
      };
      // 5. Submit answer
      const receipt = await submitAnswer(id, provider, answer);
      // 6. Handle success
      if (receipt.status) {
        alert("Successfully submitted!");
        router.push(`/square/surveys/${id}`);
      }
    } catch (error) {
      // Handle specific error cases
      if (error.code === 'INSUFFICIENT_FUNDS') {
        alert("Insufficient funds for transaction");
      } else if (error.code === 'ALREADY_SUBMITTED') {
        alert("You have already submitted an answer");
      } else {
        alert("Failed to submit: " + error.message);
      }
    }
  };
  return (
    <form onSubmit={handleSubmit}>
      {/* Form fields */}
    </form>
  );
}

LINE LIFF Authentication

Provides secure user authentication and access to LINE user profiles while ensuring the application runs properly in the LINE environment.

LIFF Initialization


// context/LiffProvider.tsx
export const LiffProvider: React.FC<{ children: React.ReactNode }> = ({
  children,
}) => {
  const [liffObject, setLiffObject] = useState<typeof liff | null>(null);
  const [liffError, setLiffError] = useState(null);
  useEffect(() => {
    // Check if running in LINE environment
    if (liff.isInClient()) {
      liff
        .init({ 
          liffId: process.env.NEXT_PUBLIC_LIFF_ID as string 
        })
        .then(() => {
          console.log("LIFF initialization succeeded");
          setLiffObject(liff);
        })
        .catch((error: any) => {
          console.error("LIFF initialization failed:", error);
          setLiffError(error.toString());
        });
    }
  }, []);
  return (
    <LiffContext.Provider value={{ liffObject, liffError }}>
      {children}
    </LiffContext.Provider>
  );
};

Login Implementation


// components/buttons/LineLoginBtn.tsx
export default function LineLoginBtn() {
  const { liffObject } = useLiff();
  const loginRequest = async () => {
    if (!liffObject) {
      return;
    }
    const login = await liffObject.login();
    if (!login) {
      return;
    }
  };
  return (
    <button
      onClick={() => {
        loginRequest();
      }}
    >
      LINE Login
    </button>
  );
}

Web3 Integration

Handles wallet connection, account management, and blockchain interactions while maintaining state across the application.

Web3 Provider Setup


// context/Web3Provider.tsx
export const Web3Provider: React.FC<{ children: React.ReactNode }> = ({
  children,
}) => {
  const [provider, setProvider] = useState<Web3Provider | null>(null);
  const [account, setAccount] = useState<string | null>(null);
  const [isConnected, setIsConnected] = useState<boolean>(false);
  const { liffObject, dappPortalSDK } = useLiff();
  // Initialize from session storage
  useEffect(() => {
    const storedAccount = sessionStorage.getItem(WALLET_ACCOUNT_KEY);
    const storedIsConnected = sessionStorage.getItem(WALLET_IS_CONNECTED_KEY);
    
    if (storedAccount) {
      setAccount(storedAccount);
    }
    if (storedIsConnected) {
      setIsConnected(true);
    }
  }, []);
  // Persist state changes
  useEffect(() => {
    if (account) {
      sessionStorage.setItem(WALLET_ACCOUNT_KEY, account);
    } else {
      sessionStorage.removeItem(WALLET_ACCOUNT_KEY);
    }
  }, [account]);
  return (
    <Web3Context.Provider value={{ provider, account, isConnected }}>
      {children}
    </Web3Context.Provider>
  );
};

Wallet Connection


const connectWallet = async () => {
  try {
    // 1. Get wallet provider from Mini Dapp SDK
    const provider = dappPortalSDK?.getWalletProvider();
    // 2. Create Web3 provider instance
  const web3Provider = new w3(provider);
    // 3. Request account access
    const accounts = await web3Provider.send("kaia_requestAccounts", []);
    
    // 4. Get payment provider for transactions
    const pProvider = dappPortalSDK?.getPaymentProvider();
     setPProvider(pProvider as PaymentProvider);
    // 5. Create identity if necessary
    if (
      provider &&
      liffObject &&
      (provider.getWalletType() === WalletType.Liff ||
        provider.getWalletType() === WalletType.Web) &&
      liffObject.isLoggedIn()
    ) {
      const identity = await createIdentity(
        web3Provider,
        accounts[0],
        liffObject
      );
      setIdentity(identity);
    }
    // 6. Update state
    setProvider(web3Provider);
    setAccount(accounts[0]);
    setIsConnected(true);
    
  } catch (error) {
    console.error("Wallet connection error:", error);
    throw error;
  }
};

Friend Invitation System

The platform incorporates LINE's social features to enable users to invite friends through a seamless sharing experience. This is implemented through the LIFF ShareTargetPicker, which provides a native LINE interface for friend selection.

Provider Interface


interface LiffContextType {
  // Core authentication properties
  liffObject: any;
  liffError: any;
  
  // Social feature properties
  inviteFriends: () => void;
  encodedUID: string | null;
  loading: boolean;
}

Friend Invitation Implementation


const inviteFriends = async () => {
  // 1. Check authentication
  if (liff && !liff.isLoggedIn()) {
    liff.login();
    return;
  }
  // 2. Generate invitation code
  let encodedUID;
  try {
    const result = await fetch(
      `${process.env.NEXT_PUBLIC_API_URL}/api/invite/encode`,
      {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
        },
        body: JSON.stringify({
          idToken: liff.getAccessToken(),
        }),
      }
    );
    encodedUID = result.encodedUID;
  } catch (error) {
    alert("Error when encoding user ID");
    return;
  }
  // 3. Share with friends
  const msg = getFlexMessage(locale, encodedUID);
  if (liff.isApiAvailable("shareTargetPicker")) {
    await liff.shareTargetPicker([msg]);
  }
};

Referral System

The referral system tracks user invitations through encoded UIDs in the URL parameters.


// Referral check in LiffProvider
useEffect(() => {
  liff.init({
    liffId: process.env.NEXT_PUBLIC_LIFF_ID as string,
  }).then(() => {
    // Parse referral code if present
    if (window.location.search !== "") {
      const encodedUID = parseEncodedUID(window.location.search);
      setEncodedUID(encodedUID);
      // Handle referral logic
    }
  });
}, []);

Customizable LINE Flex Message for invitations, supporting multiple languages.


const getFlexMessage = (locale: string, encodedUID: string): LiffMessage => {
  const message = inviteMessages[locale] || inviteMessages["en"];
  return {
    type: "flex",
    altText: message.altText,
    contents: {
      type: "bubble",
      hero: {
        type: "image",
        url: "your-image-url",
        size: "full",
        aspectRatio: "20:13",
        aspectMode: "cover",
      },
      body: {
        type: "box",
        layout: "vertical",
        contents: [
          {
            type: "text",
            text: encodedUID,
            weight: "bold",
            size: "xl",
          },
          {
            type: "text",
            text: message.contentsText2,
            wrap: true,
          },
        ],
      },
      footer: {
        type: "box",
        layout: "vertical",
        contents: [
          {
            type: "button",
            style: "primary",
            action: {
              type: "uri",
              label: message.footerLabel,
              uri: `https://liff.line.me/your-liff-id?encodedUID=${encodedUID}`,
            },
          },
        ],
      },
    },
  };
};

Combined Provider Setup


export const LiffProvider: React.FC<{ children: React.ReactNode }> = ({
  children,
}) => {
  // Authentication states
  const [liffObject, setLiffObject] = useState<typeof liff | null>(null);
  const [liffError, setLiffError] = useState(null);
  
  // Social feature states
  const [encodedUID, setEncodedUID] = useState<string | null>(null);
  const [loading, setLoading] = useState(true);
  // Initialize everything
  useEffect(() => {
    initializeLIFF();
    initializeDappPortal();
    checkForReferral();
  }, []);
  return (
    <LiffContext.Provider value={{
      // Auth values
      liffObject,
      liffError,
      // Social features
      inviteFriends,
      encodedUID,
      loading
    }}>
      {children}
    </LiffContext.Provider>
  );
};

Friend Invitation Component

The platform implements a dedicated component for friend invitations, making it easily accessible within the survey interface.

Component Implementation


// components/Friends.tsx
"use client";
export default function Friends() {
  const params = useParams();
  const { liffObject, loading, inviteFriends } = useLiff();
  const locale = params.locale as keyof typeof inviteMessages;
  const messages = inviteMessages[locale] || inviteMessages.en;
  // Environment and loading checks
  if (loading) return <div></div>;
  if (liffObject && !liffObject.isInClient()) return <div></div>;
  return (
    <div className="flex flex-row items-center justify-center mb-3">
      <label htmlFor="inviteButton" className="text-xl font-bold">
        {messages.inviteMessage}
      </label>
      <button
        id="inviteButton"
        onClick={() => inviteFriends()}
        className="bg-green-500 hover:bg-green-700 text-white font-bold py-1 px-2 ml-2 rounded"
      >
        {messages.invite}
      </button>
    </div>
  );
}

Integration with Survey Page


// app/[locale]/square/surveys/page.tsx
export default async function SurveysPage({
  params,
}: {
  params: Promise<{ locale: string }>;
}) {
  const data = await getAllSurveyV1s();
  const { locale } = await params;
  // Sort surveys for different sections
  const hotTopics = data
    .sort((a, b) => b.respondents - a.respondents)
    .slice(0, 10);
  const endingSoon = data.filter((survey) => survey.daysleft < 2);
  return (
    <div className="flex flex-col mt-5">
      {/* Friend Invitation Component */}
      <Friends />
      {/* Survey Sections */}
      {hotTopics.length !== 0 && (
        // Hot Topics section
      )}
      {endingSoon.length !== 0 && (
        // Ending Soon section
      )}
      {/* All Surveys */}
      <div className="flex flex-wrap gap-5 justify-center mt-5 mb-10">
        {data.map((survey) => (
          <SurveyCard
            key={survey.id}
            {...survey}
          />
        ))}
      </div>
    </div>
  );
}

Privacy & Security: Semaphore Protocol Implementation

In decentralized survey systems, protecting user privacy while ensuring response authenticity is crucial. The Semaphore Protocol is implemented to solve several critical challenges:

Anonymous Participation: Users need to prove they're eligible to participate in surveys without revealing their identity.
Double-Submission Prevention: The system must prevent multiple submissions while maintaining anonymity.
Response Privacy: Survey answers should be confidential and untraceable to individual users.
Verifiable Authenticity: Despite anonymity, responses must be verifiably from authorized participants.

The Semaphore Protocol addresses these challenges by using zero-knowledge proofs, allowing users to prove their membership in a group and submit responses without revealing their identity. This ensures both privacy and data integrity in the survey process.

1. Identity Creation: Generates a deterministic identity using multiple factors to ensure uniqueness and security while maintaining privacy.


//.. browser/survey.tsx
export const createIdentity = async (
  web3: Web3Provider,
  address: string,
  liffObject: typeof liff
) => {
// 1. Get LINE user identity
  const idToken = liffObject.getDecodedIDToken();
  if (!idToken) {
    throw Error("Failed to get ID token");
  }
  try {
// 2. Extract unique LINE user ID
    const uid = idToken.sub;
// 3. Create deterministic message
    const msg = "hello destat" + uid + address;
    const hexMsg = ethers.hexlify(ethers.toUtf8Bytes(msg));
// 4. Get wallet signature as entropy source
    // const secret = await web3.send("kaia_signLegacy", [address, hexMsg]);
    const secret = await web3.send("personal_sign", [hexMsg, address]);
// 5. Create Semaphore identity
    return new Identity(secret);
  } catch (e) {
    console.log("error", e);
    throw Error("Failed to create identity");
  }
};

2. Group Management: Handles group membership operations and verification without revealing individual identities.

Join Group Implementation


//..backend/survey.tsx
	
export const joinGroup = async (
  surveyAddress: string,
  commitment: bigint,
  signature: ethers.SignatureLike,
  idToken: string,
  address: string
) => {
// 1. Get group contract
  const survey = getManagerConnectedSurveyV1(surveyAddress);
	
// 2. Verify LINE token
  const profile = await isValidToken(idToken);
// 3. Verify wallet ownership
  await verifyLineIdentity(profile.userId, address, signature);
// 4. Add member to group
  const tx = await survey.joinGroup(commitment);
// 5. Verify successful addition
  const receipt = await tx.wait();
  return receipt;
};

Component Structure

In this section, we will do a breakdown of the components structure. Your components folder should look like this:


buttons/
  ├── dropdown.tsx       -> Handles expandable menu navigation
  ├── LineLoginBtn.tsx   -> Manages LINE authentication flow
  └── WalletBtn.tsx     -> Handles Web3 wallet connections
common/
  ├── index.tsx      -> Exports shared components and utilities
AnswerChart.tsx       -> Displays bar chart of survey responses
AnswerPie.tsx           -> Shows circular visualization of responses
Footer.tsx                  -> Shows app footer content
Header.tsx                -> Contains app header and main navigation
ItemCard.tsx             -> Displays purchasable items with pricing
LinearChart.tsx        -> Shows linear progress indicators
Nav.tsx                      -> Provides main app navigation structure
SubmitAnswerForm  -> Handles survey response submission
SurveyCard.tsx         -> Displays survey information and status

Setup & Installation ​

Survey Management ​

1. Creating Survey ​

2. Answering Survey ​

Authentication and Social Features Integration ​

LINE LIFF Authentication ​

Web3 Integration ​

Extended Social Features ​

Friend Invitation System ​

Referral System ​

Share Message Template ​

Friend Invitation Component ​

Privacy & Security: Semaphore Protocol Implementation ​

Component Structure ​