### Configure Hardhat for HashKey Chain Testnet

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Developer-QuickStart

This snippet demonstrates how to modify the `hardhat.config.ts` file to add the HashKey Chain Testnet network configuration, including its RPC URL, chain ID, and account setup using an environment variable for the private key.

```TypeScript
const config: HardhatUserConfig = {
  networks: {
    hashkeyTestnet: {
      url: "https://testnet.hsk.xyz" || "",
      accounts:
        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
      chainId: 133
    }
  }
};
```

--------------------------------

### Install viem Library

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/KYC

Installs the `viem` library, a lightweight Ethereum JavaScript library, required for interacting with the HashKey Chain. This command should be run in a Node.js environment.

```JavaScript
npm install viem
```

--------------------------------

### Set up ethers.js Provider for HashKey Chain Testnet

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Developer-QuickStart

This code demonstrates how to initialize an `ethers.js` `JsonRpcProvider` to establish a connection with the HashKey Chain Testnet, using its designated RPC URL for interacting with the blockchain.

```JavaScript
import { ethers } from "ethers"

const provider = new ethers.providers.JsonRpcProvider("https://testnet.hsk.xyz")
```

--------------------------------

### Deploy with Foundry to HashKey Chain Testnet

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Developer-QuickStart

This command illustrates how to use Foundry's `forge create` command to deploy a smart contract to the HashKey Chain Testnet, specifying the RPC URL and chain ID directly in the command line arguments.

```Shell
forge create ... --rpc-url=https://testnet.hsk.xyz --chain-id 133
```

--------------------------------

### Configure Truffle for HashKey Chain Testnet

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Developer-QuickStart

This snippet shows how to configure the `truffle.js` file to connect to the HashKey Chain Testnet. It uses `HDWalletProvider` to manage the private key and specifies the network ID and RPC URL for deployment.

```JavaScript
const HDWalletProvider = require("@truffle/hdwallet-provider")

module.exports = {
  networks: {
    hashkeyTestnet: {
      provider: () =>
        new HDWalletProvider(process.env.PRIVATE_KEY, "https://testnet.hsk.xyz"),
      network_id: 133
    }
  }
}
```

--------------------------------

### Install Graph Protocol Dependencies

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Subgraph

Install the necessary Node.js packages for Graph Protocol development, including Graph CLI for command-line operations and Graph TypeScript for type definitions.

```Shell
npm install -g @graphprotocol/graph-cli
npm install @graphprotocol/graph-ts
```

--------------------------------

### Oracle Provider Selection Guide

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Oracle

A comparative guide to different oracle providers (SUPRA, APRO, Ethereum Global, Chainlink), detailing their update mechanisms, best use cases, and unique features. This table assists developers in selecting the most suitable oracle for their specific application requirements on HashKey Chain.

```APIDOC
Oracle Selection Guide:
- Provider: SUPRA
  Update Mechanism: Pull-based
  Best For: Applications requiring on-demand data
  Unique Features: High throughput consensus algorithm (DORA)
- Provider: APRO
  Update Mechanism: Push-based
  Best For: DeFi protocols needing real-time updates
  Unique Features: Threshold-based updates reducing gas costs
- Provider: Ethereum Global
  Update Mechanism: Verify Proxy
  Best For: Cross-chain applications
  Unique Features: Multi-chain compatibility
- Provider: Chainlink
  Update Mechanism: Streams
  Best For: Mission-critical applications
  Unique Features: Industry-standard security and reliability
```

--------------------------------

### HashKey Chain Testnet and Ethereum Sepolia Network Configuration

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Developer-QuickStart

This section provides essential network configuration details for both HashKey Chain Testnet and Ethereum Sepolia, including RPC URLs, Chain IDs, Currency Symbols, and Block Explorer URLs, necessary for setting up development tools.

```APIDOC
Network Configuration:
  HashKey Chain Testnet:
    Network Name: HashKey Chain Testnet
    RPC URL: https://testnet.hsk.xyz
    Chain ID: 133
    Currency Symbol: HSK
    Block Explorer URL: https://testnet-explorer.hsk.xyz
  Ethereum Sepolia:
    Network Name: Ethereum Sepolia
    RPC URL: https://rpc2.sepolia.org
    Chain ID: 11155111
    Currency Symbol: ETH
    Block Explorer URL: https://sepolia.etherscan.io
```

--------------------------------

### Constructing Block Explorer Links for dApps

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Explorer

This example demonstrates how to programmatically construct URLs to specific transactions on BlockScout and contract addresses on OKLink. Developers can use these links to improve user experience and transparency by providing direct access to on-chain data from their dApp UIs.

```javascript
// Example: Constructing a link to a transaction on BlockScout
const txHash = "0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef";
const blockscoutUrl = `https://explorer.hsk.xyz/tx/${txHash}`;

// Example: Constructing a link to a contract on OKLink
const contractAddress = "0xabcdef1234567890abcdef1234567890abcdef1234";
const oklinkUrl = `https://www.oklink.com/zh-hans/hashkey/address/${contractAddress}`;
```

--------------------------------

### Clone HashKey Chain Fullnode Sync Repository

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/RPC-Node-Provider

This command clones the `fullnode-sync` repository from GitHub, which contains the necessary files for setting up a HashKey Chain full node. After cloning, it changes the current directory into the newly created `fullnode-sync` directory to prepare for further setup steps.

```Shell
git clone https://github.com/HashKeyChain/fullnode-sync
cd fullnode-sync
```

--------------------------------

### Deposit ETH to WETH Contract on Sepolia using Ethers.js

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Faucet

This JavaScript example demonstrates how to interact with a Wrapped ETH (WETH) contract on the Sepolia testnet using the Ethers.js library. It shows the process of initializing a contract instance and executing the `deposit()` function to convert native ETH into WETH. The snippet includes error handling and logging for successful transactions.

```JavaScript
// Example: Depositing ETH into WETH contract on Sepolia
const wethContract = new ethers.Contract(
  "0x7b79995e5f793a07bc00c21412e50ecae098e7f9",
  wethAbi,
  signer
);

// Convert 0.1 ETH to WETH
const tx = await wethContract.deposit({ value: ethers.utils.parseEther("0.1") });
await tx.wait();
console.log("Successfully wrapped 0.1 ETH to WETH on Sepolia");
```

--------------------------------

### Start HashKey Chain Node using Docker Compose

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/RPC-Node-Provider

This command initiates the HashKey Chain node services defined in the `docker-compose.yml` file in detached mode (`-d`). It orchestrates the execution and consensus layers, bringing up all necessary containers for the node to run in the background.

```Shell
docker compose up -d
```

--------------------------------

### Retrieve Safe Information using Safe SDK

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Safe

This example demonstrates how to connect to the HashKey Chain Mainnet Safe and retrieve Safe details using the Safe SDK. It initializes `SafeApiKit` with the transaction service URL and an `ethAdapter`, then calls `getSafeInfo` to fetch information about a specific Safe address.

```TypeScript
// Example: Retrieving Safe information using Safe SDK
import { SafeApiKit, SafeFactory } from '@safe-global/api-kit'

// Connect to HashKey Chain Mainnet Safe
const safeService = new SafeApiKit({
  txServiceUrl: 'https://safe-transaction-hashkey.safe.global',
  ethAdapter: ethAdapter
})

// Retrieve Safe details
const safeInfo = await safeService.getSafeInfo(safeAddress)
```

--------------------------------

### Solidity KycDemo Contract Implementation Example

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/KYC

Provides a demonstration contract `KycDemo` that interacts with the `IKycSBT` interface. It showcases how to delegate calls to the `IKycSBT` instance for functions like checking a user's human status, retrieving their KYC information, and verifying ENS name approval.

```Solidity
contract KycDemo {
    IKycSBT public kycSBT;

    constructor(address _kycSBT) {
        kycSBT = IKycSBT(_kycSBT);
    }

    function checkHuman(address account) external view returns (bool isHuman, uint8 level) {
        return kycSBT.isHuman(account);
    }

    function getUserKycInfo(address account) external view returns (
        string memory ensName,
        IKycSBT.KycLevel level,
        IKycSBT.KycStatus status,
        uint256 createTime
    ) {
        return kycSBT.getKycInfo(account);
    }

    function checkEnsNameApproval(address user, string calldata ensName) external view returns (bool) {
        return kycSBT.isEnsNameApproved(user, ensName);
    }
}
```

--------------------------------

### Solidity Example for SUPRA Pull Oracle Integration

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Oracle

This Solidity smart contract demonstrates how to integrate with the SUPRA Pull Oracle on HashKey Chain. It defines a `SupraConsumer` contract that can query the BTC/USD price and its timestamp from the oracle by calling the `getIndexedPrice` function.

```Solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "./ISupraPullOracle.sol";

contract SupraConsumer {
    ISupraPullOracle public oracle;

    constructor(address _oracleAddress) {
        oracle = ISupraPullOracle(_oracleAddress);
    }

    function getBTCPrice() public view returns (uint256, uint256) {
        // pair_id for BTC/USD = 0
        (uint256 price, uint256 timestamp) = oracle.getIndexedPrice(0);
        return (price, timestamp);
    }
}
```

--------------------------------

### Query Subgraph Data with GraphQL

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Subgraph

Example GraphQL query to retrieve indexed data from the deployed subgraph, filtering and ordering results.

```GraphQL
{
  entities(first: 5, orderBy: timestamp, orderDirection: desc) {
    id
    count
    timestamp
  }
}
```

--------------------------------

### JavaScript: Get Address Transactions via Explorer API

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Explorer-Wallet

Demonstrates how to programmatically retrieve transaction data for a specific blockchain address using the HashKey Chain Explorer's REST API. This asynchronous function sends a GET request to the API endpoint and returns the JSON response containing transaction details.

```JavaScript
async function getAddressTransactions(address) {
  const response = await fetch(
    `https://explorer.hsk.xyz/api/v2/addresses/${address}/transactions`
  );
  return await response.json();
}
```

--------------------------------

### NFT Application Categories and Standards

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Ethereum-Applications

Details various Non-Fungible Token application categories, their examples, underlying technical standards, and integration points within the blockchain ecosystem.

```APIDOC
Category: Digital Art
Examples: Unique artworks, collectibles
Technical Standards: ERC-721, ERC-1155
Integration Points: IPFS, Layer 2 Solutions
```

```APIDOC
Category: Gaming Assets
Examples: In-game items, characters
Technical Standards: ERC-1155 multi-token standard
Integration Points: Gaming engines, EVM
```

```APIDOC
Category: Virtual Real Estate
Examples: Land in metaverse platforms
Technical Standards: Custom standards, ERC-721
Integration Points: 3D rendering, spatial interfaces
```

```APIDOC
Category: Tokenized RWAs
Examples: Real-world asset representation
Technical Standards: ERC-721 with metadata
Integration Points: Oracles, legal frameworks
```

--------------------------------

### Solidity Staking Contract Interaction

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Knowledge/pos

Illustrates a simplified conceptual Solidity interface for a staking contract, showing functions for depositing, unstaking, withdrawing, and checking validator stakes. It also includes comments on how a user might interact with such a contract, including ERC20 approval and calling the deposit function.

```Solidity
// Very simplified concept - Real staking is much more complex!
interface StakingContract {
    // Function to deposit and stake HSK tokens
    function depositAndStake(uint256 amount) external payable;

    // Function to signal intent to withdraw stake (often involves unbonding period)
    function unstake(uint256 amount) external;

    // Function for validators to withdraw unlocked stake
    function withdrawStake() external;

    // Function to check a validator's stake
    function getValidatorStake(address validator) external view returns (uint256);
}

// A user (potential validator) interacts with the staking contract:
// Assume 'hskToken' is the ERC20 contract for HSK
// Assume 'stakingContractAddress' is the address of the PoS staking contract
// 1. Approve the staking contract to spend HSK:
//    hskToken.approve(stakingContractAddress, stakeAmount);
// 2. Call the staking contract to deposit:
//    StakingContract(stakingContractAddress).depositAndStake{value: msg.value}(stakeAmount); // msg.value if native token staking
```

--------------------------------

### Web3.js Transaction Gas Estimation

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Gas-Fee-Calculation

This JavaScript example demonstrates how to use the `web3.eth.estimateGas` RPC method to predict the gas required for a transaction. It also shows how to add a safety buffer to the estimated gas limit.

```JavaScript
const gasEstimate = await web3.eth.estimateGas({
    from: myAddress,
    to: contractAddress,
    data: contractFunction.encodeABI()
});

// Add buffer for safety (e.g., 20%)
const gasLimitWithBuffer = Math.floor(gasEstimate * 1.2);
```

--------------------------------

### Resolve ENS Names and Addresses with ethers.js

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Knowledge/ens

This JavaScript example demonstrates how to use the `ethers.js` library to perform both forward ENS resolution (mapping a human-readable name like 'example.eth' to an Ethereum address) and reverse lookup (mapping an Ethereum address back to its associated ENS name). It utilizes the `Web3Provider` for interaction with the Ethereum network.

```JavaScript
// ethers.js example
const provider = new ethers.providers.Web3Provider(window.ethereum);
const address = await provider.resolveName('example.eth');
const name = await provider.lookupAddress('0x123...'); // Reverse lookup
```

--------------------------------

### Get Total Fee for KYC SBT

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/KYC

Asynchronously retrieves the total fee required for KYC verification from the `KycSBT` smart contract. This function uses the `publicClient` to call the `getTotalFee` read-only method.

```TypeScript
async function getTotalFee() {
  const fee = await publicClient.readContract({
    address: KYC_SBT_ADDRESS,
    abi: KycSBTAbi,
    functionName: 'getTotalFee',
  })
  return fee as bigint
}
```

--------------------------------

### Integrate Chainlink Price Feed in Solidity

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Oracle

This Solidity contract shows how to interact with Chainlink's AggregatorV3Interface to fetch the latest price. It takes the verifier proxy address during construction and exposes a public view function to get the current price from the oracle.

```Solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

contract ChainlinkConsumer {
    AggregatorV3Interface internal priceFeed;

    constructor(address _verifierProxy) {
        priceFeed = AggregatorV3Interface(_verifierProxy);
    }

    function getLatestPrice() public view returns (int) {
        (
            /* uint80 roundID */,
            int answer,
            /* uint startedAt */,
            /* uint timeStamp */,
            /* uint80 answeredInRound */
        ) = priceFeed.latestRoundData();
        return answer;
    }
}
```

--------------------------------

### Comparison of Ethereum Consensus Mechanisms

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Ethereum-Technology

A table comparing different blockchain consensus mechanisms, highlighting their energy usage, throughput, finality, security model, and examples, including Proof of Work (PoW), Proof of Stake (PoS), Delegated PoS (DPoS), and Proof of Authority (PoA).

```APIDOC
Mechanism: Proof of Work (PoW)
  Energy Usage: Very High
  Throughput: Low (10-15 TPS)
  Finality: Probabilistic
  Security Model: Based on computational power
  Examples: Bitcoin, Ethereum (pre-Merge), Litecoin

Mechanism: Proof of Stake (PoS)
  Energy Usage: Low
  Throughput: Medium (25-100 TPS)
  Finality: Faster, deterministic
  Security Model: Based on economic stake
  Examples: Ethereum (post-Merge), Cardano, Avalanche

Mechanism: Delegated PoS (DPoS)
  Energy Usage: Low
  Throughput: High (1000+ TPS)
  Finality: Near-instant
  Security Model: Relies on elected block producers
  Examples: EOS, Tron, BNB Chain

Mechanism: Proof of Authority (PoA)
  Energy Usage: Very Low
  Throughput: Very High
  Finality: Instant
  Security Model: Based on identity of validators
  Examples: Most testnets, sidechains
```

--------------------------------

### Solidity Slashing Mechanism Event

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Knowledge/pos

Demonstrates a conceptual Solidity contract for a slashing mechanism. It defines an event `ValidatorSlashed` and a `reportMisbehavior` function, which includes logic for verifying evidence, calculating penalties, decreasing validator stake, and emitting the slashing event.

```Solidity
// Solidity event that might be emitted by a slashing mechanism contract
contract SlashingMechanism {
    event ValidatorSlashed(address indexed validator, uint256 amountSlashed, bytes reason);

    function reportMisbehavior(address validator, bytes memory evidence) public {
        // ... Complex logic to verify evidence ...
        if (isMalicious(evidence)) {
            uint256 stakedAmount = getValidatorStake(validator);
            uint256 penalty = calculatePenalty(stakedAmount, evidence);

            // ... Logic to burn or redistribute slashed funds ...
            decreaseValidatorStake(validator, penalty);

            emit ValidatorSlashed(validator, penalty, evidence);
        }
    }
    // ... other functions ...
}
```

--------------------------------

### Ethereum EVM Operation Gas Costs

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Gas-Fee-Calculation

This table lists the gas costs for various common operations within the Ethereum Virtual Machine (EVM), providing examples like arithmetic, storage, and contract calls. These costs are fundamental for understanding transaction execution expenses.

```APIDOC
| Operation | Gas Cost | Description |
| --- | --- | --- |
| `ADD`, `SUB` | 3 | Simple arithmetic |
| `MUL`, `DIV` | 5 | More complex arithmetic |
| `SSTORE` (0→1) | 20,000 | Storing a new value in state |
| `SSTORE` (modify) | 5,000 | Modifying an existing state value |
| `CALL` | 700+ | Calling another contract |
| `CREATE` | 32,000+ | Creating a new contract |
```

--------------------------------

### Import viem and Contract Dependencies

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/KYC

Imports necessary modules from `viem` for client creation and account management, along with the HashKey Chain testnet configuration and the `KycSBTAbi` for contract interactions. This sets up the basic environment for frontend integration.

```TypeScript
import { createPublicClient, createWalletClient, http, type Address, type WalletClient } from 'viem'
import { privateKeyToAccount } from 'viem/accounts'
import { hashkeyTestnet } from 'viem/chains'
import { KYC_SBT_ADDRESS } from '@/config/contracts'
import KycSBTAbi from '@/abis/KycSBT.json'
```

--------------------------------

### Deploy Subgraph to Hosted Service

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Subgraph

Deploy the prepared subgraph project to the Graph hosted service, making it available for indexing and querying.

```Shell
graph deploy --product hosted-service <GITHUB_USER>/<SUBGRAPH_NAME>
```

--------------------------------

### Initialize New Subgraph Project for HashKey Chain

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Subgraph

Initialize a new subgraph project using the Graph CLI, configured for the HashKey Chain network and set up to index events from a specified contract.

```Shell
graph init --product hosted-service \
  --from-example \
  --protocol ethereum \
  --network hashkeychain \
  --contract-name YourContract \
  --index-events
```

--------------------------------

### HashKey Chain Mainnet Node Configuration (.env)

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/RPC-Node-Provider

This configuration template defines the environment variables required for running a HashKey Chain Mainnet node. It specifies Docker images for Geth and Op-Node, the L1 RPC URL and kind, static P2P bootnodes, the rollup configuration URL, and the sequencer HTTP endpoint. Users must replace placeholders like `<L1_RPC_URL>` with their actual Ethereum mainnet endpoints.

```Shell
# geth image
GETH_IMAGE=us-docker.pkg.dev/oplabs-tools-artifacts/images/op-geth:v1.101503.3
# l1 rpc url
# node image
NODE_IMAGE=us-docker.pkg.dev/oplabs-tools-artifacts/images/op-node:v1.13.1
L1_RPC=<L1_RPC_URL>
# l1 rpc kind(standard/basic/quicknode/alchemy/erigon)
# https://docs.optimism.io/builders/node-operators/tutorials/node-from-docker
L1_RPC_KIND=standard
# node libp2p bootnodes
P2P_STATIC="/dns/hashkey-mainnet-bootnodes.altlayer.network/tcp/31112/p2p/16Uiu2HAm1UX8Lx4XKnHXncKCw5Q4r6jsajKDEukHk9S9NXuroVKY,/dns/hashkey-mainnet-bootnodes.altlayer.network/tcp/31114/p2p/16Uiu2HAm2PzcWR3pgBkCSUC8Co6WsKHhyyxJysQqzeZpHoX2RaAf,/dns/hashkey-mainnet-bootnodes.altlayer.network/tcp/31116/p2p/16Uiu2HAm6s2pY65dcXi8zM4EfD7oCP4o64C6a8XbxwgLU1q6WAUe,/dns/hashkey-mainnet-bootnodes.altlayer.network/tcp/31118/p2p/16Uiu2HAmQEAZhJTPSdrJpH2NqZ5X368XPXGq68XxL1r8wQamdbwQ"
# rollup config file url link
ROLLUP_CONFIG_URL="https://operator-public.s3.us-west-2.amazonaws.com/hashkeychain/mainnet/rollup.json"
# tx forward endpoint
SEQUENCER_HTTP=https://mainnet.hsk.xyz
```

--------------------------------

### Configure HashKey Chain Network in Wallet

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Explorer-Wallet

Instructions and network parameters for adding the HashKey Chain mainnet to a compatible cryptocurrency wallet like MetaMask, enabling interaction with the network.

```Configuration
Network Name: HashKey Chain
RPC URL: https://hsk-mainnet.hashkey.com
Chain ID: 1719
Currency Symbol: HSK
Block Explorer URL: https://explorer.hsk.xyz
```

--------------------------------

### Blockchain Explorer API Access

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Explorer-Wallet

Comparison of API access methods provided by HashKey Chain Explorer and OKLink Explorer, detailing the types of APIs available for each platform.

```APIDOC
HashKey Chain Explorer:
  API Access: REST, GraphQL, RPC
```

```APIDOC
OKLink Explorer:
  API Access: REST API
```

--------------------------------

### HashKey Chain Explorer API Overview

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Explorer-Wallet

Overview of the various API types offered by HashKey Chain Explorer for programmatic access to blockchain data, including REST, GraphQL, and RPC APIs.

```APIDOC
HashKey Chain Explorer APIs:
  - REST API:
    Description: Basic data retrieval
    Example Endpoint: GET /api/v2/addresses/{address}/transactions
  - GraphQL:
    Description: Complex queries
  - RPC API:
    Description: Node-like interaction
```

--------------------------------

### Configure HashKey Chain Testnet Geth Node Environment Variables

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/RPC-Node-Provider

Provides environment variables for setting up a Geth node on the HashKey Chain Testnet. This includes Geth and Node image versions, L1 RPC details, P2P bootnodes, rollup config, sequencer endpoint, Geth bootnodes, genesis file, sync/GC modes, and API endpoints.

```shell
# geth image
GETH_IMAGE=us-docker.pkg.dev/oplabs-tools-artifacts/images/op-geth:v1.101503.4
# l1 rpc url
# node image
NODE_IMAGE=us-docker.pkg.dev/oplabs-tools-artifacts/images/op-node:v1.13.2
L1_RPC=https://ethereum-sepolia-rpc.publicnode.com
# l1 rpc kind(standard/basic/quicknode/alchemy/erigon)
# https://docs.optimism.io/builders/node-operators/tutorials/node-from-docker
L1_RPC_KIND=standard
# node libp2p bootnodes
P2P_STATIC='/dns/testnet-bootnodes.hsk.xyz/tcp/31301/p2p/16Uiu2HAm2tAbwcFYMnXNvVmhacKbE1gz1oMbdrxpUNEUrTBp1fvZ,/dns/testnet-bootnodes.hsk.xyz/tcp/32343/p2p/16Uiu2HAmDKkBkmQNBRe1yXZPtRkJUWmafLgmj6Y84w2AUa3Qgp6N'
# rollup config file url link
ROLLUP_CONFIG_URL="https://hashkeychain.s3.ap-southeast-1.amazonaws.com/testnet/rollup.json"
# tx forward endpoint
SEQUENCER_HTTP=https://testnet.hsk.xyz
# op-l2 geth bootnodes
GETH_STATICNODES='[
    "enode://f26759caecdec0ae9d04f523a4ae6a7c562e47f89289f9a520c56f97da9c64cf386441df7f2e992b153a66e8988dcbd3280064db700002e9c14140913004cc52@testnet-bootnodes.hsk.xyz:31289",
    "enode://72c77ff6d8dac333d283ac2a2522452045bc292d156e4cb4c14d3ef804db77d0c11f7a0bacd507d7eaaa371a7b32cb47369c799620d245630ee137a58d19e893@testnet-bootnodes.hsk.xyz:30109"
]'
# genesis file url link
GENESIS_URL="https://hashkeychain.s3.ap-southeast-1.amazonaws.com/testnet/genesis.json"
# sync mode(full or snap)
SYNC_MODE=full
# gc mode(archive or full)
GC_MODE=archive
# geth http api
HTTP_API="web3,eth,net,engine"
# geth ws api
WS_API="web3,eth,net,engine"
# plasma enabled(true or false)
PLASMA_ENABLED=false
# plasma da server url
PLASMA_DA_SERVER=
# beacon url
L1_BEACON="<BEACON_URL>"
```

--------------------------------

### Configure HashKey Chain Mainnet Geth Node Environment Variables

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/RPC-Node-Provider

Defines essential environment variables for setting up a Geth node on the HashKey Chain Mainnet. This includes bootnode lists, genesis file URL, synchronization and garbage collection modes, and HTTP/WS API endpoints.

```shell
GETH_STATICNODES='[
    "enode://e3d83751cba1f5fd806a73e9701baaa93eb729474eb6c246050e76f9cde32915d4904e1fa12be4196ad7296aba61d4ffebfb7a9c5eeff2b9578e0d7a55cc5ed5@hashkey-mainnet-bootnodes.altlayer.network:31111",
    "enode://b3714bf5e75760fcbb4de393b75bbcf046be7aa6fb47bd928c4ad6405717a5e67cb01a31dc820ce6b51cfb6c8268ec6c1166fdb2a66f9c92ea67f2fdfdf130fc@hashkey-mainnet-bootnodes.altlayer.network:31113",
    "enode://6ad0903b679bed251393813042f2452f55ec4e6f120347d412c203072e58bb2e3c1d68247eba25a89b920995bed3b043819d49577a8c1fe4f1c0d762d7d6763a@hashkey-mainnet-bootnodes.altlayer.network:31115",
    "enode://17162151981152707b855e1e67ab9027dcad7af7a2dbcfa40352c6940f1a977f490b2522986736a8c20327abd5f50afd39f23031b3b103d99c0c03c4449bd172@hashkey-mainnet-bootnodes.altlayer.network:31117",

]'

GENESIS_URL="https://operator-public.s3.us-west-2.amazonaws.com/hashkeychain/mainnet/genesis.json"
SYNC_MODE=full
GC_MODE=archive

HTTP_API="web3,eth,net,engine"

WS_API="web3,eth,net,engine"

ALTDA_ENABLED=
ALTDA_DA_SERVER=
L1_BEACON=<BEACON_URL>
```

--------------------------------

### Core DeFi Primitives on Ethereum

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Ethereum-Applications

Overview of fundamental Decentralized Finance applications on Ethereum, detailing their purpose, key technologies, and technical implementation, including integration with HashKey Chain.

```APIDOC
Application: Decentralized Exchanges (DEXs)
Description: Platforms enabling peer-to-peer trading without intermediaries
Key Technology: Smart Contracts, Automated Market Makers
Technical Implementation: ERC-20 tokens, EVM
```

```APIDOC
Application: Lending Protocols
Description: Platforms for borrowing and lending crypto assets
Key Technology: Collateralization mechanisms, Interest rate models
Technical Implementation: Smart Contracts, Oracles
```

```APIDOC
Application: Yield Aggregators
Description: Services optimizing returns across multiple protocols
Key Technology: Smart contract composability
Technical Implementation: Ethereum Dev Tech
```

```APIDOC
Application: Stablecoins
Description: Cryptocurrencies with stable value pegged to fiat
Key Technology: Collateralization or algorithmic stability
Technical Implementation: ERC-20, DeFi
```

--------------------------------

### Ethereum Virtual Machine (EVM) Overview

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Ethereum-Technology

An explanation of the Ethereum Virtual Machine (EVM), which serves as the runtime environment for smart contracts on the Ethereum blockchain, providing a sandboxed execution context.

```APIDOC
The EVM is the runtime environment for smart contracts in Ethereum, providing a sandboxed execution context.
```

--------------------------------

### Authenticate Graph CLI with Hosted Service

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Subgraph

Authenticate your Graph CLI with the hosted service using your access token, enabling deployment of subgraphs.

```Shell
graph auth --product hosted-service <YOUR_ACCESS_TOKEN>
```

--------------------------------

### Initialize Public and Wallet Clients

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/KYC

Initializes `publicClient` for read-only operations and `walletClient` for write operations on the HashKey Chain testnet. Both clients are configured with the `hashkeyTestnet` chain and an HTTP transport.

```TypeScript
// Public client for read operations
const publicClient = createPublicClient({
  chain: hashkeyTestnet,
  transport: http('https://hk-testnet.rpc.alt.technology')
})

// Wallet client for write operations
const walletClient = createWalletClient({
  account,
  chain: hashkeyTestnet,
  transport: http('https://hk-testnet.rpc.alt.technology')
})
```

--------------------------------

### Integrate APRO Price Feed in Solidity

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Oracle

This Solidity contract demonstrates how to consume price data from the APROPriceFeed. It initializes with the price feed's address during construction and provides a public view function to retrieve the latest price and its corresponding timestamp.

```Solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@apro/contracts/APROPriceFeed.sol";

contract APROConsumer {
    APROPriceFeed public priceFeed;

    constructor(address _priceFeedAddress) {
        priceFeed = APROPriceFeed(_priceFeedAddress);
    }

    function getLatestPrice() public view returns (int256, uint256) {
        (
            /*uint80 roundID*/,
            int256 price,
            /*uint startedAt*/,
            uint256 timestamp,
            /*uint80 answeredInRound*/
        ) = priceFeed.latestRoundData();

        return (price, timestamp);
    }
}
```

--------------------------------

### Configure Subgraph Manifest (subgraph.yaml)

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Subgraph

Configure the subgraph manifest file, defining data sources, contract ABIs, event handlers, and the mapping file for processing blockchain events.

```YAML
specVersion: 0.0.4
schema:
  file: ./schema.graphql
dataSources:
  - kind: ethereum
    name: YourContract
    network: hashkeychain
    source:
      address: "0x..."
      abi: YourContract
      startBlock: 1
    mapping:
      kind: ethereum/events
      apiVersion: 0.0.6
      language: wasm/assemblyscript
      entities:
        - Entity
      abis:
        - name: YourContract
          file: ./abis/YourContract.json
      eventHandlers:
        - event: YourEvent(indexed address,uint256)
          handler: handleYourEvent
      file: ./src/mapping.ts
```

--------------------------------

### Interacting with an L1 Bridge Contract for Asset Deposits

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Knowledge/layer-2

This snippet provides a simplified Solidity interface for an L1 bridge contract, detailing the 'depositERC20' function used to send tokens from L1 to L2 and the 'DepositInitiated' event. It also includes conceptual JavaScript code demonstrating how to approve tokens and call the 'depositERC20' function on the L1 bridge using a library like ethers.js, illustrating the client-side interaction for initiating an L2 deposit.

```Solidity
// Highly simplified L1 bridge contract interface (e.g., for depositing to an L2)
interface L1Bridge {
    // User calls this on L1 to send tokens to their address on L2
    // The contract locks the L1 tokens and emits an event L2 can listen for
    function depositERC20(
        address l1Token, // Address of the token contract on L1
        address l2Token, // Address of the corresponding token contract on L2
        address recipient, // Who gets the tokens on L2
        uint256 amount,
        bytes calldata data // Optional extra data for L2 message
    ) external payable; // Payable if depositing native ETH

    // Event signaling a deposit has occurred for L2 bridge to process
    event DepositInitiated(
        address indexed l1Token,
        address indexed l2Token,
        address indexed from,
        address to,
        uint256 amount,
        bytes data
    );

    // Withdrawals are usually initiated on L2 and finalized on L1 after a delay/proof
    // function finalizeWithdrawal(...) external; // Complex process involving L2 state roots/proofs
}
```

```JavaScript
// Example Interaction (Conceptual JS using ethers.js or similar)
// const l1BridgeContract = new ethers.Contract(L1_BRIDGE_ADDRESS, L1BridgeABI, signer);
// const l1TokenContract = new ethers.Contract(L1_TOKEN_ADDRESS, ERC20ABI, signer);

// // 1. Approve the bridge to spend L1 tokens
// await l1TokenContract.approve(L1_BRIDGE_ADDRESS, depositAmount);

// // 2. Call the deposit function on the L1 bridge
// await l1BridgeContract.depositERC20(
//     L1_TOKEN_ADDRESS,
//     L2_TOKEN_ADDRESS, // The representation of the token on the L2
//     USER_ADDRESS,     // User's address (often the same on L1/L2)
//     depositAmount,
//     '0x'              // Empty extra data
// );

// The L2 network's bridge component will then detect the DepositInitiated event
// and credit the user's account on the L2 side.
```

--------------------------------

### HashKey Chain Mainnet Connection Details

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/network-info

Provides essential network parameters for connecting to the HashKey Chain Mainnet, including Network Name, RPC Endpoint, ChainID, Native Token, and Explorer URL.

```APIDOC
Network Name: HashKey Chain
RPC Endpiont: https://mainnet.hsk.xyz
ChainID: 177
Native Token: HSK
Explorer: https://explorer.hsk.xyz
```

--------------------------------

### Basic ERC-20 Token Implementation in Solidity

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Knowledge/erc20

Provides a foundational Solidity contract demonstrating the implementation of a basic ERC-20 token, including state variables, constructor, and the `balanceOf` and `transfer` functions.

```Solidity
contract ERC20Token {
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;

    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    constructor(string memory _name, string memory _symbol, uint8 _decimals, uint256 _initialSupply) {
        name = _name;
        symbol = _symbol;
        decimals = _decimals;
        totalSupply = _initialSupply;
        _balances[msg.sender] = _initialSupply;
    }

    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) public returns (bool) {
        require(_balances[msg.sender] >= amount, "Insufficient balance");

        _balances[msg.sender] -= amount;
        _balances[recipient] += amount;

        emit Transfer(msg.sender, recipient, amount);
        return true;
    }

    // Additional functions for approve, transferFrom, allowance, etc.
}
```

--------------------------------

### Ethereum Smart Contract Languages Overview

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Ethereum-Technology

A table detailing various smart contract languages used on Ethereum, including their features, learning curve, maturity, and best use cases. Languages covered are Solidity, Vyper, Fe, and Yul.

```APIDOC
Language: Solidity
  Features: Static typing, inheritance, libraries
  Learning Curve: Moderate
  Maturity: High
  Best For: Most applications

Language: Vyper
  Features: Python-like, no recursion, bounded loops
  Learning Curve: Moderate
  Maturity: Medium
  Best For: Security-critical contracts

Language: Fe
  Features: Rust-inspired, type safety
  Learning Curve: Steep
  Maturity: Low (emerging)
  Best For: Experimental projects

Language: Yul
  Features: Low-level intermediate language
  Learning Curve: Very steep
  Maturity: Medium
  Best For: Gas optimization
```

--------------------------------

### HashKey Chain Testnet Connection Details

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/network-info

Provides essential network parameters for connecting to the HashKey Chain Testnet, including Network Name, RPC Endpoint, ChainID, Native Token, and Explorer URL.

```APIDOC
Network Name: HashKey Chain Testnet
RPC Endpiont: https://testnet.hsk.xyz
ChainID: 133
Native Token: HSK
Explorer: https://testnet-explorer.hsk.xyz
```

--------------------------------

### APRO Oracle Price Feed Details

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Oracle

This section details the APRO price feeds available on HashKey Testnet and Mainnet, including currency pairs, configurable deviation thresholds, heartbeat intervals, and their respective contract addresses for real-time data delivery.

```APIDOC
HashKey Testnet Price Feeds:
| Pair     | Deviation | Heartbeat | Contract Address                         |
|----------|-----------|-----------|------------------------------------------|
| BTC/USD  | 0.5%      | 4h        | `0x64697A6Abb508079687465FA9EF99D2Da955D791` |
| USDT/USD | 0.5%      | 4h        | `0xC45D520D18A465Ec23eE99A58Dc4cB96b357E744` |
| USDC/USD | 0.1%      | 24h       | `0xCdB10dC9dB30B6ef2a63aB4460263655808fAE27` |

HashKey Mainnet Price Feeds:
| Pair     | Deviation | Heartbeat | Contract Address                         |
|----------|-----------|-----------|------------------------------------------|
| BTC/USD  | 0.5%      | 1h        | `0x204ED500ab56A2E19B051561258E3A45c850360F` |
| HSK/USD  | 0.5%      | 1h        | `0x86CE42c1b714149Dc3A7b169EF67b5F78A224b` |
| USDT/USD | 0.1%      | 24h       | `0x823d7f90f7A3498DB6595886b6B5dC95E6B0B7f3` |
| USDC/USD | 0.1%      | 24h       | `0x244Ce344df8837c9d938867E2Ffbf0E4B0169B56` |
```

--------------------------------

### Ethereum Smart Contract Development Frameworks

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Ethereum-Technology

A list of popular development frameworks for Ethereum smart contracts, outlining their key features and benefits. This includes Hardhat, Foundry, and Truffle, which aid in testing, deployment, and task automation.

```APIDOC
Framework: Hardhat
  Description: JavaScript-based development environment
  Features: Built-in testing, deployment, and task automation; Extensive plugin ecosystem

Framework: Foundry
  Description: Rust-based, fast testing framework
  Features: Built-in fuzzing capabilities; Direct use of Solidity for tests

Framework: Truffle
  Description: Pioneering development suite
  Features: Integrated testing, asset pipeline; Mature ecosystem and documentation
```

--------------------------------

### Monitor HashKey Chain Node Logs

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/RPC-Node-Provider

This command displays the real-time logs from the Docker Compose services, allowing you to monitor the node's activity, synchronization progress, and any potential errors. The `-f` flag ensures that the logs are streamed continuously to the console.

```Shell
docker compose logs -f
```

--------------------------------

### HashKey Chain Network Parameters for Wallet Configuration

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/Wallet

Details required to manually add HashKey Chain to EVM-compatible wallets like OKX Wallet, MetaMask, TokenPocket, and ImToken. These parameters define how the wallet connects to the HashKey Chain network.

```APIDOC
Network Parameters:
  Network Name: HashKey Chain
  RPC URL: https://mainnet.hsk.xyz
  Chain ID: 177
  Currency Symbol: HSK
  Block Explorer URL: https://explorer.hsk.xyz
```

--------------------------------

### KYC System Emitted Events Reference

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Build-on-HashKey-Chain/Tools/KYC

Lists the various events emitted by the HashKey Chain KYC system. These events provide crucial insights into state changes and actions within the smart contracts, enabling off-chain monitoring, indexing, and building responsive applications.

```APIDOC
Events:
  KycRequested: When a user requests KYC verification
  KycLevelUpdated: When a user's KYC level is updated
  KycStatusUpdated: When a user's KYC status changes
  KycRevoked: When a user's KYC is revoked
  KycRestored: When a revoked KYC is restored
  AddressApproved: When an address is approved for a specific KYC level
  EnsNameApproved: When an ENS name is approved for a user
```

--------------------------------

### Simulating Blockchain Proof-of-Work Mining in Python

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Knowledge/pow

This Python code snippet demonstrates a simplified proof-of-work mining process. It defines a BlockHeader class to encapsulate block metadata and hash calculation. The main loop iteratively increments a nonce, recalculates the block's hash, and checks if the hash meets a predefined difficulty target, simulating the core mechanism of finding a valid block in a blockchain.

```Python
import hashlib
import time

class BlockHeader:
    def __init__(self, previous_hash, merkle_root, timestamp, difficulty_target):
        self.previous_hash = previous_hash
        self.merkle_root = merkle_root
        self.timestamp = timestamp
        self.difficulty_target = difficulty_target # A numerical representation of the target
        self.nonce = 0

    def calculate_hash(self):
        header_string = str(self.previous_hash) + \
                        str(self.merkle_root) + \
                        str(self.timestamp) + \
                        str(self.difficulty_target) + \
                        str(self.nonce)
        # In real blockchains, often double-hashed or using specific serialization
        return hashlib.sha256(header_string.encode()).hexdigest()

# --- Simplified Mining Loop ---
# Assume previous_hash, merkle_root are available
# Target represented conceptually as needing 'n' leading zeros
target_prefix = "0000" # Example: target needs 4 leading zeros
difficulty_target_value = int(target_prefix + "F" * (64 - len(target_prefix)), 16) # Conceptual numeric target

block_header = BlockHeader("prev_hash_abc", "merkle_xyz", int(time.time()), difficulty_target_value)

start_time = time.time()
while True:
    current_hash = block_header.calculate_hash()
    # Convert hex hash to integer for comparison
    hash_value_int = int(current_hash, 16)

    if hash_value_int < difficulty_target_value: # Check if hash meets the target
        print(f"Found valid hash! Nonce: {block_header.nonce}")
        print(f"Hash: {current_hash}")
        print(f"Time taken: {time.time() - start_time:.2f} seconds")
        # Broadcast the block with this nonce
        break
    else:
        block_header.nonce += 1 # Increment nonce and try again
        if block_header.nonce % 100000 == 0: # Print progress periodically
             print(f"Trying nonce {block_header.nonce}...")
```

--------------------------------

### Legacy Ethereum Transaction Structure and Fee Calculation

Source: https://docs.hsk.xyz/docs/About-HashKey-Chain/Learn/Ethereum-More/Gas-Fee-Calculation

A simplified representation of the legacy Ethereum transaction structure, showing fields like `nonce`, `gasPrice`, `gasLimit`, `to`, `value`, and `data`. It also includes the basic fee calculation based on `gasUsed` and `gasPrice`.

```Solidity
// Legacy transaction structure (simplified)
struct LegacyTransaction {
    uint nonce;
    uint gasPrice;     // User-specified gas price in wei
    uint gasLimit;     // Maximum gas user is willing to pay
    address to;
    uint value;
    bytes data;
    // v, r, s signature values
}

// Fee calculation
uint transactionFee = gasUsed * gasPrice;
```