Part 2: Memahami Smart Contract SimpleVibeRaffle

"Smart contract itu tidak seseram yang kamu kira - mari kita bedah bareng!" 🔍

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🎯 Tujuan Part Ini

Setelah menyelesaikan part ini, kamu akan:

• ✅ Paham struktur dasar smart contract Solidity
• ✅ Mengerti setiap baris kode SimpleVibeRaffle
• ✅ Tahu cara compile contract di Remix
• ✅ Bisa deploy contract ke Base Sepolia testnet
• ✅ Memahami bagaimana contract interact dengan USDC token (ERC-20)

Durasi: 15 menit (saat workshop)

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📖 Intro: Apa Itu Smart Contract?

Definisi Sederhana

Smart Contract = Kode yang berjalan di blockchain & tidak bisa diubah.

Analogi:

Smart Contract = Mesin Vending Otomatis

Mesin Vending:
1. Kamu masukkan uang
2. Pilih barang
3. Mesin otomatis kasih barang
4. Tidak ada penjual yang bisa curang

Smart Contract:
1. Kamu kirim ETH ke contract
2. Panggil fungsi (misal: join game)
3. Contract otomatis execute logic
4. Tidak ada yang bisa ubah aturan

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Karakteristik Smart Contract

Sifat	Penjelasan	Analogi
Immutable	Tidak bisa diubah setelah deploy	Seperti kontrak yang sudah ditandatangani
Deterministic	Input sama = output sama (selalu!)	Seperti kalkulator (2+2 selalu 4)
Trustless	Tidak perlu percaya orang, percaya kode	Mesin ATM (tidak butuh teller)
Transparent	Semua orang bisa lihat kodenya	Open source code
Autonomous	Jalan sendiri tanpa intervensi	Autopilot

---

Bahasa Pemrograman: Solidity

Solidity adalah bahasa untuk menulis smart contract di Ethereum.

Fun Facts:

• 🎂 Dibuat tahun 2014 (masih muda!)
• 👨‍💻 Syntax mirip JavaScript & C++
• 📝 File extension: .sol
• ⚡ Compile jadi bytecode (EVM = Ethereum Virtual Machine)

Contoh Kode Sederhana:

contract Hello {
    string public message = "GM!";
}

Itu aja udah smart contract! 🎉

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🎲 SimpleVibeRaffle: Overview

Apa yang Dilakukan Contract Ini?

SimpleVibeRaffle adalah game undian on-chain dengan fitur:

1. Join Game GRATIS - Tidak perlu deposit untuk join!
2. USDC Prize Pool - Hadiah menggunakan USDC token (bukan ETH)
3. Dual Registration - Self-register atau admin add manual
4. Pick Winner - Owner bisa pilih pemenang random
5. Auto Transfer USDC - Hadiah otomatis terkirim ke pemenang

---

Alur Game

┌──────────────────────────────────────────────────┐
│                                                   │
│  1. OWNER DEPLOY CONTRACT                        │
│     → Set USDC address (Base Sepolia)            │
│     → Fund prize pool dengan USDC                │
│                                                   │
│  2. PLAYERS JOIN GAME (2 Cara)                   │
│     A. Self-Register:                            │
│        → Connect wallet                          │
│        → Panggil joinGame() - GRATIS!            │
│     B. Admin Register:                           │
│        → Admin panggil addPlayer(address)        │
│        → Untuk registrasi offline/manual         │
│                                                   │
│  3. OWNER PICK WINNER                            │
│     → Panggil pickWinner()                       │
│     → Contract random pilih 1 player             │
│                                                   │
│  4. AUTO TRANSFER USDC                           │
│     → Seluruh prize pool USDC terkirim otomatis  │
│     → Winner dapat USDC di wallet!               │
│                                                   │
└──────────────────────────────────────────────────┘

---

💻 Full Source Code

SimpleVibeRaffle.sol

Copy kode ini ke Remix nanti:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.30;

/**
 * @title IERC20
 * @notice Interface untuk USDC token
 */
interface IERC20 {
    function approve(address spender, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function transfer(address to, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
    function balanceOf(address account) external view returns (uint256);
}

/**
 * @title SimpleVibeRaffle
 * @notice Smart contract untuk raffle game dengan USDC prize pool
 * @dev Educational purpose - NOT production ready!
 */
contract SimpleVibeRaffle {
    // ============================================
    // STATE VARIABLES
    // ============================================

    address public owner;           // Address yang deploy contract
    address[] public players;       // Array semua peserta
    bool public gameOpen;           // Status game (open/closed)
    address public lastWinner;      // Address pemenang terakhir
    uint256 public lastPrize;       // Hadiah terakhir yang diberikan
    uint256 public totalGamesPlayed; // Total game yang sudah dimainkan

    IERC20 public usdcToken;        // USDC token contract

    // ============================================
    // EVENTS
    // ============================================

    event PlayerJoined(address indexed player);
    event PlayersAddedByAdmin(address[] players, address indexed admin);
    event WinnerPicked(address indexed winner, uint256 prize);
    event PrizeFunded(address indexed funder, uint256 amount);
    event GameReset(address indexed admin, uint256 timestamp);

    // ============================================
    // CONSTRUCTOR
    // ============================================

    /**
     * @dev Constructor dipanggil saat deploy
     * @param _usdcAddress Address USDC token di Base Sepolia
     */
    constructor(address _usdcAddress) {
        owner = msg.sender;
        gameOpen = true;
        usdcToken = IERC20(_usdcAddress);
        totalGamesPlayed = 0;
    }

    // ============================================
    // MODIFIERS
    // ============================================

    /**
     * @dev Modifier untuk restrict fungsi hanya untuk owner
     */
    modifier onlyOwner() {
        require(msg.sender == owner, "Not owner");
        _;
    }

    // ============================================
    // FUNCTIONS - OWNER ONLY
    // ============================================

    /**
     * @notice Owner bisa tambah prize pool dengan USDC
     * @dev Owner harus approve USDC dulu sebelum panggil fungsi ini
     * @param amount Jumlah USDC yang ditambahkan (dalam unit USDC)
     */
    function fundPrize(uint256 amount) external onlyOwner {
        uint256 amountInDecimals = amount * 10**6; // Convert to 6 decimals
        require(
            usdcToken.transferFrom(msg.sender, address(this), amountInDecimals),
            "USDC transfer failed"
        );

        emit PrizeFunded(msg.sender, amountInDecimals);
    }

    /**
     * @notice Admin bisa add player manual dari backend (single)
     * @dev Untuk registrasi offline atau manual registration
     * @param playerAddress Address player yang ingin ditambahkan
     */
    function addPlayer(address playerAddress) external onlyOwner {
        require(gameOpen, "Game is closed");
        require(playerAddress != address(0), "Invalid address");

        // Tambahkan address ke array players
        players.push(playerAddress);

        // Emit event untuk single player
        address[] memory singlePlayer = new address[](1);
        singlePlayer[0] = playerAddress;
        emit PlayersAddedByAdmin(singlePlayer, msg.sender);
    }

    /**
     * @notice Admin bisa add multiple players sekaligus (batch)
     * @dev Untuk batch registration, lebih gas efficient
     * @param playerAddresses Array of player addresses yang ingin ditambahkan
     */
    function addPlayersBatch(address[] calldata playerAddresses) external onlyOwner {
        require(gameOpen, "Game is closed");
        require(playerAddresses.length > 0, "Empty array");
        require(playerAddresses.length <= 100, "Too many players at once"); // Limit untuk gas

        for (uint256 i = 0; i < playerAddresses.length; i++) {
            require(playerAddresses[i] != address(0), "Invalid address in batch");
            players.push(playerAddresses[i]);
        }

        // Emit event untuk batch
        emit PlayersAddedByAdmin(playerAddresses, msg.sender);
    }

    /**
     * @notice Pilih pemenang secara random
     * @dev PERINGATAN: Random ini tidak aman untuk production!
     */
    function pickWinner() external onlyOwner {
        require(gameOpen, "Game already closed");
        require(players.length > 0, "No players joined");

        // Tutup game agar tidak ada yang bisa join lagi
        gameOpen = false;

        // Generate random number (SIMPLE, NOT SECURE!)
        uint256 random = uint256(
            keccak256(
                abi.encodePacked(
                    block.timestamp,    // Waktu block saat ini
                    msg.sender,         // Address owner
                    players.length,     // Jumlah players
                    blockhash(block.number - 1) // Hash block sebelumnya
                )
            )
        );

        // Pilih index pemenang
        uint256 winnerIndex = random % players.length;
        address winner = players[winnerIndex];

        // Ambil seluruh saldo USDC contract
        uint256 prize = usdcToken.balanceOf(address(this));

        // Simpan data pemenang
        lastWinner = winner;
        lastPrize = prize;
        totalGamesPlayed++;

        // Transfer USDC ke pemenang
        require(usdcToken.transfer(winner, prize), "USDC transfer to winner failed");

        // Emit event
        emit WinnerPicked(winner, prize);
    }

    /**
     * @notice Reset game untuk mulai raffle baru
     * @dev Hapus semua players dan buka game lagi
     */
    function resetGame() external onlyOwner {
        require(!gameOpen, "Game is still open, pick winner first");

        // Reset array players
        delete players;

        // Buka game lagi
        gameOpen = true;

        // Emit event
        emit GameReset(msg.sender, block.timestamp);
    }

    /**
     * @notice Emergency reset - bisa dipanggil kapan saja
     * @dev Gunakan hanya jika ada masalah atau ingin cancel game
     */
    function emergencyReset() external onlyOwner {
        // Reset array players
        delete players;

        // Buka game lagi
        gameOpen = true;

        // Emit event
        emit GameReset(msg.sender, block.timestamp);
    }

    // ============================================
    // FUNCTIONS - PUBLIC
    // ============================================

    /**
     * @notice Join game raffle - GRATIS!
     * @dev Siapa saja bisa panggil, tidak perlu deposit
     */
    function joinGame() external {
        require(gameOpen, "Game is closed");

        // Tambahkan address ke array players
        players.push(msg.sender);

        // Emit event
        emit PlayerJoined(msg.sender);
    }

    /**
     * @notice Lihat semua players yang sudah join
     * @return Array of player addresses
     */
    function getPlayers() external view returns (address[] memory) {
        return players;
    }

    /**
     * @notice Lihat jumlah players
     * @return Total number of players
     */
    function getPlayerCount() external view returns (uint256) {
        return players.length;
    }

    /**
     * @notice Lihat total prize pool dalam USDC
     * @return Prize amount (6 decimals)
     */
    function getPrizePool() external view returns (uint256) {
        return usdcToken.balanceOf(address(this));
    }

    /**
     * @notice Lihat informasi pemenang terakhir
     * @return winner Address pemenang terakhir
     * @return prize Jumlah hadiah terakhir
     */
    function getLastWinner() external view returns (address winner, uint256 prize) {
        return (lastWinner, lastPrize);
    }

    /**
     * @notice Lihat total game yang sudah dimainkan
     * @return Total games played
     */
    function getTotalGamesPlayed() external view returns (uint256) {
        return totalGamesPlayed;
    }
}

Total: ~240 baris (dengan comments & interface!) Tanpa comments: ~120 baris clean code

Key Features & Updates:

• ✅ Menggunakan USDC (ERC-20 token) untuk prize pool
• ✅ Network: Base Sepolia (bukan Ethereum Sepolia)
• ✅ Join game tetap GRATIS (no deposit required)
• ✅ Interface IERC20 untuk interact dengan USDC contract
• ✅ NEW: Batch player registration (addPlayersBatch())
• ✅ NEW: Game reset functionality (resetGame(), emergencyReset())
• ✅ NEW: Winner history tracking (lastWinner, lastPrize, totalGamesPlayed)
• ✅ NEW: Enhanced random dengan blockhash
• ✅ NEW: View functions untuk lihat history (getLastWinner(), getTotalGamesPlayed())

---

🔍 Bedah Kode: Baris per Baris

1. License & Pragma

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.30;

Penjelasan:

• SPDX-License-Identifier = Lisensi kode (MIT = open source)
• pragma solidity ^0.8.30 = Versi compiler yang dipakai
  • ^0.8.30 = Versi 0.8.30 atau lebih baru (tapi di bawah 0.9.0)
  • Version update untuk fitur dan optimizations terbaru

Analogi:

Seperti di file HTML:
<!DOCTYPE html>  ← Tentukan versi

---

2. State Variables

address public owner;
address[] public players;
bool public gameOpen;
address public lastWinner;
uint256 public lastPrize;
uint256 public totalGamesPlayed;

Penjelasan:

Variable	Type	Fungsi
owner	address	Alamat yang deploy contract (owner)
players	address[]	Array (list) semua peserta
gameOpen	bool	Status game (true/false)
lastWinner	address	Address pemenang terakhir (history)
lastPrize	uint256	Jumlah hadiah terakhir dalam USDC (6 decimals)
totalGamesPlayed	uint256	Counter total game yang sudah selesai

Keyword public:

• Auto-generate fungsi getter
• Siapa saja bisa baca (tapi tidak bisa ubah langsung!)

Contoh:

address public owner;

// Otomatis ada fungsi:
function owner() public view returns (address) {
    return owner;
}

---

3. Events

event PlayerJoined(address indexed player);
event PlayersAddedByAdmin(address[] players, address indexed admin);
event WinnerPicked(address indexed winner, uint256 prize);
event PrizeFunded(address indexed funder, uint256 amount);
event GameReset(address indexed admin, uint256 timestamp);

Apa itu Event?

Event = Log yang tersimpan di blockchain.

Fungsi:

• 📝 Recording aktivitas (audit trail)
• 🔔 Notifikasi untuk frontend (via WebSocket)
• 🔍 Mudah di-search (kalau pakai indexed)

Event Breakdown:

Event	Purpose	Indexed Parameters
PlayerJoined	Player join sendiri via joinGame()	player
PlayersAddedByAdmin	Admin add player(s) manual	admin
WinnerPicked	Pemenang terpilih dan prize terkirim	winner
PrizeFunded	Owner top-up prize pool	funder
GameReset	Game direset untuk round baru	admin

Analogi:

Event = Mutasi rekening bank

Setiap transaksi tercatat:
- Tanggal
- Jenis transaksi
- Jumlah
- Dari/ke siapa

Keyword indexed:

• Maksimal 3 parameter bisa indexed
• Indexed = bisa di-filter saat query
• Contoh: Cari semua event di mana player = 0x123...

Note: PlayersAddedByAdmin menggunakan array untuk support batch operations

---

4. Constructor

constructor(address _usdcAddress) {
    owner = msg.sender;
    gameOpen = true;
    usdcToken = IERC20(_usdcAddress);
    totalGamesPlayed = 0;
}

Apa itu Constructor?

Constructor = Fungsi yang jalan HANYA SAAT DEPLOY.

Karakteristik:

• Jalan 1x saja (saat contract dibuat)
• Tidak bisa dipanggil lagi
• Biasa untuk setup awal

Parameter _usdcAddress:

• Address USDC token contract di Base Sepolia
• Value: 0x036CbD53842c5426634e7929541eC2318f3dCF7e
• Contract menyimpan address ini untuk interact dengan USDC

Initialization:

• owner = msg.sender - Deployer menjadi owner
• gameOpen = true - Game langsung open
• usdcToken = IERC20(_usdcAddress) - Set USDC interface
• totalGamesPlayed = 0 - Counter dimulai dari 0 (NEW!)

msg.sender:

• Global variable
• Address yang kirim transaksi
• Di constructor, msg.sender = deployer (becomes owner)

usdcToken = IERC20(_usdcAddress):

• Inisialisasi interface IERC20 dengan address USDC
• Setelah ini, contract bisa call USDC functions (transfer, balanceOf, dll)

Contoh Deploy:

Kamu deploy contract dengan parameter:
_usdcAddress = 0x036CbD53842c5426634e7929541eC2318f3dCF7e

→ constructor() jalan
→ owner = address kamu
→ gameOpen = true
→ usdcToken = USDC contract interface
→ totalGamesPlayed = 0
→ Prize pool = 0 (owner perlu fund manual)

---

5. Modifier

modifier onlyOwner() {
    require(msg.sender == owner, "Not owner");
    _;
}

Apa itu Modifier?

Modifier = Reusable guard/check untuk fungsi.

Struktur:

• require(kondisi, "error message") = Check condition
• _ = Placeholder untuk kode fungsi yang pakai modifier

Flow:

function pickWinner() onlyOwner {
    // 1. Cek modifier dulu
    //    require(msg.sender == owner)
    // 2. Kalau pass, jalankan function body
    //    ...
}

Kenapa Pakai Modifier?

Tanpa Modifier (Repetitive):

function pickWinner() {
    require(msg.sender == owner, "Not owner");
    // ... logic
}

function fundPrize() {
    require(msg.sender == owner, "Not owner");
    // ... logic
}

Dengan Modifier (DRY - Don't Repeat Yourself):

function pickWinner() onlyOwner {
    // ... logic
}

function fundPrize() onlyOwner {
    // ... logic
}

Lebih clean! ✨

---

6. Function: fundPrize()

function fundPrize(uint256 amount) external onlyOwner {
    uint256 amountInDecimals = amount * 10**6;
    require(
        usdcToken.transferFrom(msg.sender, address(this), amountInDecimals),
        "USDC transfer failed"
    );
    emit PrizeFunded(msg.sender, amountInDecimals);
}

Penjelasan:

Keyword	Artinya
external	Hanya bisa dipanggil dari luar contract
onlyOwner	Hanya owner yang bisa panggil
amount	Parameter: jumlah USDC (dalam unit, bukan decimals)

Flow Fungsi:

1. Convert amount ke decimals: USDC punya 6 decimals, jadi 10 USDC = 10,000,000
2. Transfer USDC: Pakai transferFrom() untuk ambil USDC dari owner ke contract
3. Emit event: Log berapa USDC yang di-fund

⚠️ PENTING: Butuh Approval Dulu!

Sebelum call fundPrize(), owner HARUS approve USDC contract dulu:

// Di USDC contract:
approve(contractAddress, 1000 * 10**6) // Approve 1000 USDC

Kenapa perlu approve?

• ERC-20 security mechanism
• Contract tidak bisa ambil token tanpa izin
• Owner explicitly approve berapa max yang boleh di-transfer

Contoh:

1. Owner approve USDC: 1000 USDC
2. Owner call fundPrize(10) → Transfer 10 USDC
3. Prize pool sekarang: 10 USDC
4. Allowance tersisa: 990 USDC

---

7. Function: joinGame()

function joinGame() external {
    require(gameOpen, "Game is closed");
    players.push(msg.sender);
    emit PlayerJoined(msg.sender);
}

Penjelasan Baris per Baris:

Line 1: require(gameOpen, "Game is closed")

• Check apakah game masih open
• Kalau gameOpen == false, revert dengan error

Line 2: players.push(msg.sender)

• Tambahkan address pemanggil ke array players
• push() = append ke akhir array

Line 3: emit PlayerJoined(msg.sender)

• Emit event untuk log

Flow:

User A panggil joinGame()
→ Check: gameOpen? ✅ true
→ players = [addressA]
→ Emit event: PlayerJoined(addressA)

User B panggil joinGame()
→ Check: gameOpen? ✅ true
→ players = [addressA, addressB]
→ Emit event: PlayerJoined(addressB)

Catatan Penting:

• Fungsi ini GRATIS (tidak pakai payable)
• Satu address bisa join berkali-kali
  • joinGame() 3x = 3 entries = peluang 3x lebih besar!

---

8. Function: pickWinner()

Ini adalah jantung dari contract! Mari kita bedah detail.

function pickWinner() external onlyOwner {
    require(gameOpen, "Game already closed");
    require(players.length > 0, "No players joined");

    gameOpen = false;

    uint256 random = uint256(
        keccak256(
            abi.encodePacked(
                block.timestamp,
                msg.sender,
                players.length
            )
        )
    );

    uint256 winnerIndex = random % players.length;
    address winner = players[winnerIndex];

    uint256 prize = address(this).balance;

    (bool success, ) = winner.call{value: prize}("");
    require(success, "Transfer failed");

    emit WinnerPicked(winner, prize);
}

Mari bedah step by step:

---

Step 1: Validation

require(gameOpen, "Game already closed");
require(players.length > 0, "No players joined");

Check:

1. Game masih open?
2. Ada minimal 1 player?

Kalau salah satu false → transaksi revert.

---

Step 2: Close Game

gameOpen = false;

Kenapa?

• Agar tidak ada yang bisa joinGame() lagi setelah winner dipilih
• Prevent manipulation

---

Step 3: Generate Random Number

uint256 random = uint256(
    keccak256(
        abi.encodePacked(
            block.timestamp,    // Waktu block saat ini
            msg.sender,         // Address owner
            players.length      // Jumlah players
        )
    )
);

Breakdown:

1. abi.encodePacked(...) = Gabungkan 4 nilai jadi bytes (update: +blockhash)
2. keccak256(...) = Hash bytes tersebut (SHA-3)
3. uint256(...) = Convert hash jadi angka

Komponen Random:

• block.timestamp = Timestamp block (selalu beda tiap block)
• msg.sender = Address owner (constant)
• players.length = Jumlah players (beda tiap game)
• blockhash(block.number - 1) = Hash dari block sebelumnya (NEW!)

⚠️ PERINGATAN PENTING:

Ini BUKAN random yang aman!

Kenapa tidak aman?

• Miner bisa manipulasi block.timestamp (±15 detik)
• msg.sender & players.length bisa diprediksi
• Untuk uang beneran, bisa di-exploit!

Solusi untuk production:

• Gunakan Chainlink VRF (Verifiable Random Function)
• VRF = Random yang benar-benar tidak bisa di-manipulate

Tapi untuk workshop & testnet? Ini cukup! ✅

---

Step 4: Pick Winner

uint256 winnerIndex = random % players.length;
address winner = players[winnerIndex];

Penjelasan:

% = Modulo (sisa bagi)

Contoh:

players.length = 5 (5 players)
random = 123456789

winnerIndex = 123456789 % 5 = 4

players = [A, B, C, D, E]
           0  1  2  3  4
                      ↑
                   winner = E

Kenapa pakai modulo?

• Memastikan index selalu valid (0 sampai length-1)
• Distribusi merata

---

Step 5: Get Prize Amount

uint256 prize = usdcToken.balanceOf(address(this));

Penjelasan:

• usdcToken = Interface IERC20 yang pointing ke USDC contract
• .balanceOf(address(this)) = Check saldo USDC yang dimiliki contract ini
• address(this) = Address contract SimpleVibeRaffle
• prize = Seluruh saldo USDC contract

Contoh:

Contract USDC balance: 10,000,000 (dalam 6 decimals)
→ prize = 10,000,000 = 10 USDC (seluruhnya untuk pemenang!)

---

Step 6: Save Winner History (NEW!)

lastWinner = winner;
lastPrize = prize;
totalGamesPlayed++;

Penjelasan:

Contract sekarang menyimpan history pemenang!

State Variables Updated:

• lastWinner = Address pemenang yang baru terpilih
• lastPrize = Jumlah USDC yang dimenangkan
• totalGamesPlayed = Increment counter (game ke berapa)

Benefit:

• 📊 Bisa lihat siapa pemenang terakhir
• 📈 Track berapa game sudah dimainkan
• 🔍 Transparency dan accountability

Use Case:

Game 1: Winner A dapat 10 USDC
Game 2: Winner B dapat 5 USDC
Game 3: Winner C dapat 15 USDC

Setelah Game 3:
- lastWinner = C
- lastPrize = 15 USDC
- totalGamesPlayed = 3

---

Step 7: Transfer USDC to Winner

require(usdcToken.transfer(winner, prize), "USDC transfer to winner failed");

Ini adalah bagian yang paling keren! 💸

Penjelasan:

usdcToken.transfer(winner, prize) = Transfer USDC ke winner

Breakdown:

• usdcToken.transfer() = Call fungsi transfer di USDC contract
• winner = Address pemenang yang dipilih
• prize = Jumlah USDC (seluruh balance contract)
• Returns bool = true kalau sukses, false kalau gagal

Kenapa pakai .transfer() untuk ERC-20?

Pattern	Use Case
Native ETH: .call{value}("")	Transfer ETH (native token)
ERC-20 Token: .transfer()	Transfer token seperti USDC, DAI, dll

Perbedaan ETH vs USDC:

ETH (native):
contract.call{value: 1 ether}("")  // Direct transfer

USDC (ERC-20):
usdcToken.transfer(address, amount)  // Call USDC contract function

require(..., "USDC transfer to winner failed"):

• Kalau transfer return false, revert seluruh transaksi
• Winner pasti dapat USDC atau tidak ada yang terjadi
• Atomic execution = all or nothing!

---

Step 8: Emit Event

emit WinnerPicked(winner, prize);

Log:

• Siapa pemenang
• Berapa hadiahnya

Event ini bisa dilihat di BaseScan! 🎉

---

9. New Functions: Batch Operations & Reset (NEW!)

Contract sekarang punya fungsi-fungsi tambahan untuk flexibility!

addPlayersBatch() - Batch Registration

function addPlayersBatch(address[] calldata playerAddresses) external onlyOwner {
    require(gameOpen, "Game is closed");
    require(playerAddresses.length > 0, "Empty array");
    require(playerAddresses.length <= 100, "Too many players at once");

    for (uint256 i = 0; i < playerAddresses.length; i++) {
        require(playerAddresses[i] != address(0), "Invalid address in batch");
        players.push(playerAddresses[i]);
    }

    emit PlayersAddedByAdmin(playerAddresses, msg.sender);
}

Purpose:

• Add MULTIPLE players sekaligus (batch)
• Lebih gas-efficient daripada call addPlayer() berkali-kali
• Max 100 players per batch (limit untuk prevent out-of-gas)

Use Case:

Offline event dengan 50 peserta
→ Admin tinggal call addPlayersBatch([addr1, addr2, ..., addr50])
→ Lebih murah daripada 50x addPlayer() calls!

---

resetGame() - Normal Reset

function resetGame() external onlyOwner {
    require(!gameOpen, "Game is still open, pick winner first");
    delete players;
    gameOpen = true;
    emit GameReset(msg.sender, block.timestamp);
}

Purpose:

• Reset game setelah winner dipilih
• Hapus semua players, buka game lagi
• HARUS pick winner dulu (safety check)

Flow:

1. pickWinner() → gameOpen = false
2. resetGame() → delete players, gameOpen = true
3. Siap untuk round baru!

---

emergencyReset() - Force Reset

function emergencyReset() external onlyOwner {
    delete players;
    gameOpen = true;
    emit GameReset(msg.sender, block.timestamp);
}

Purpose:

• Reset paksa TANPA pick winner
• Untuk emergency situations
• Misal: ada bug, salah konfigurasi, atau ingin cancel game

⚠️ Use with Caution:

• Akan hapus semua players tanpa memberikan hadiah
• Only use jika memang perlu!

---

10. New View Functions: History Tracking (NEW!)

getLastWinner() - Lihat Pemenang Terakhir

function getLastWinner() external view returns (address winner, uint256 prize) {
    return (lastWinner, lastPrize);
}

Returns:

• winner: Address pemenang terakhir
• prize: Jumlah USDC yang dimenangkan (6 decimals)

Use Case:

Di frontend: "Last Winner: 0x123...abc won 10 USDC"

---

getTotalGamesPlayed() - Total Games

function getTotalGamesPlayed() external view returns (uint256) {
    return totalGamesPlayed;
}

Returns:

• Total number of games yang sudah selesai

Use Case:

Stats dashboard: "Total Games Played: 15"

---

11. Original View Functions

function getPlayers() external view returns (address[] memory) {
    return players;
}

function getPlayerCount() external view returns (uint256) {
    return players.length;
}

function getPrizePool() external view returns (uint256) {
    return usdcToken.balanceOf(address(this));
}

Apa itu view function?

• Read-only (tidak ubah state)
• Gratis (tidak perlu gas kalau dipanggil dari luar blockchain)
• Tidak bisa kirim transaksi

Fungsi:

• getPlayers() = Lihat semua player addresses
• getPlayerCount() = Lihat jumlah players
• getPrizePool() = Lihat total hadiah

Kapan pakai view?

• ✅ Baca data
• ❌ Ubah data (pakai function biasa)

---

🛠️ Compile Contract di Remix

Step-by-Step Compile

1. Buat File Baru

• Buka Remix: https://remix.ethereum.org
• Klik icon "File Explorer" 📁
• Klik kanan folder contracts
• Pilih "New File"
• Nama: SimpleVibeRaffle.sol

2. Copy-Paste Kode

• Copy kode SimpleVibeRaffle dari section sebelumnya
• Paste ke file yang baru dibuat

3. Compile

• Klik icon "Solidity Compiler" 📊 di sidebar kiri
• Compiler version: Pilih 0.8.20 atau lebih baru
• Auto compile: ON (recommended)
• Klik "Compile SimpleVibeRaffle.sol"

4. Check Hasil

Kalau sukses, akan ada:

✅ Compilation successful

Contract artifacts:
- SimpleVibeRaffle

5. Lihat Details (Opsional)

Klik "Compilation Details" untuk lihat:

• ABI (Application Binary Interface) - Seperti API contract
• Bytecode - Kode yang di-deploy ke blockchain
• Gas estimates - Estimasi biaya setiap fungsi

---

Troubleshooting Compile Errors

Error: Version mismatch

Error: Source file requires different compiler version

Solusi:

• Check pragma solidity ^0.8.20 di kode
• Set compiler version yang sesuai di Remix

---

Error: Syntax error

ParserError: Expected ';' but got ')'

Solusi:

• Check syntax (titik koma, kurung, dll)
• Pastikan copy-paste kode complete (tidak terpotong)

---

🚀 Deploy Contract ke Base Sepolia

Persiapan

Pastikan:

• ✅ Contract sudah compiled tanpa error
• ✅ MetaMask connected ke Remix
• ✅ Network di MetaMask = Base Sepolia
• ✅ Punya ETH Base Sepolia (minimal 0.01 untuk gas)
• ✅ Punya USDC Base Sepolia untuk prize pool

---

Step-by-Step Deploy

1. Buka Deploy Tab

• Klik icon "Deploy & Run Transactions" 🚀

2. Pilih Environment

Environment: Injected Provider - MetaMask

3. Verify Connection

Check di Remix:

Account: 0x1234...5678 (your address)
Balance: 0.01 ETH (your balance)
Network: Base Sepolia (84532)

IMPORTANT: Pastikan network adalah Base Sepolia (84532), bukan Ethereum Sepolia!

4. Set Constructor Parameters

Contract ini butuh 1 parameter saat deploy:

Di field "Deploy" ada input untuk constructor:

_USDCADDRESS: 0x036CbD53842c5426634e7929541eC2318f3dCF7e

Penjelasan:

• _usdcAddress = Address USDC token di Base Sepolia
• Copy-paste: 0x036CbD53842c5426634e7929541eC2318f3dCF7e

5. Deploy!

• Contract dropdown: Pilih SimpleVibeRaffle
• Input parameter: Paste USDC address
• Klik tombol "Deploy" (warna orange)

6. Confirm di MetaMask

MetaMask akan popup:

Contract Deployment
Network: Base Sepolia
Gas fee: ~0.0005 ETH

[Reject] [Confirm]

Klik Confirm

7. Tunggu Mining

Remix akan show:

[pending] Waiting for transaction to be mined...

Tunggu ~5-10 detik (Base lebih cepat dari Ethereum!).

8. Success! 🎉

Terminal akan show:

✅ Contract deployed at: 0xABC...123
Gas used: 450000
Transaction hash: 0xdef...456

---

Verify Deployment

Di Remix:

Check section "Deployed Contracts":

📦 SimpleVibeRaffle at 0xABC...123

Functions:
- owner
- gameOpen
- joinGame
- pickWinner
- getPlayers
- ...

---

Di BaseScan:

1. Copy contract address: 0xABC...123

2. Buka: https://sepolia.basescan.org

3. Paste address di search bar

4. Akan lihat:

Contract: 0xABC...123
Balance: 0 ETH (normal, prize dalam USDC)
Creator: 0x1234...5678 (you)
Creation Tx: 0xdef...456

5. Klik tab "Contract" → Harusnya ada bytecode

---

Test Fungsi Read:

Di Remix, klik button:

• owner → Harusnya return address kamu
• gameOpen → Harusnya return true
• usdcToken → Harusnya return 0x036CbD53842c5426634e7929541eC2318f3dCF7e
• getPlayerCount → Harusnya return 0 (belum ada yang join)
• getPrizePool → Harusnya return 0 (belum fund prize)

Kalau semua berfungsi = Deploy sukses! ✅

---

💰 Fund Prize Pool dengan USDC

Sekarang contract sudah deployed, tapi prize pool masih 0 USDC!

Owner perlu fund prize pool agar ada hadiah untuk pemenang.

⚠️ PENTING: Kenapa Perlu Approve?

Masalah: Contract SimpleVibeRaffle ingin mengambil USDC dari wallet kamu, tapi USDC contract belum kasih izin!

Solusi: Kamu harus approve USDC contract dulu, agar SimpleVibeRaffle boleh ambil USDC dari wallet kamu.

Analogi:

Seperti kasih kartu akses:

Tanpa Approve:
- Contract: "Saya mau ambil 10 USDC dari wallet owner"
- USDC: "Tidak bisa! Kamu tidak punya izin!" ❌

Dengan Approve:
- Owner: "USDC, izinkan contract ambil max 1000 USDC"
- USDC: "OK, izin tercatat!" ✅
- Contract: "Ambil 10 USDC"
- USDC: "Boleh! (1000-10=990 tersisa)" ✅

---

Step 1: Load USDC Contract di Remix

USDC sudah deployed di Base Sepolia, kita cuma perlu connect ke contract tersebut.

1. Pastikan Interface IERC20 Ada

Check apakah interface IERC20 sudah ada di file SimpleVibeRaffle.sol.

Kalau belum, pastikan ada interface ini di atas contract:

interface IERC20 {
    function approve(address spender, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function transfer(address to, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
    function balanceOf(address account) external view returns (uint256);
}

2. Compile Interface

• Klik "Solidity Compiler" 📊
• Pastikan SimpleVibeRaffle.sol sudah compiled
• Interface IERC20 otomatis ikut compiled ✅

3. Load USDC Contract (JANGAN Deploy!)

Di tab "Deploy & Run Transactions" 🚀:

1. Di Contract dropdown, pilih:

   IERC20 - SimpleVibeRaffle.sol

   (Bukan SimpleVibeRaffle, tapi IERC20 interface!)

2. Scroll ke bawah, cari field "At Address"

3. Paste USDC contract address:

   0x036CbD53842c5426634e7929541eC2318f3dCF7e

4. Klik tombol "At Address" (warna pink/merah muda)

5. USDC Contract akan muncul di "Deployed Contracts":

   📦 IERC20 at 0x036C...CF7e
   
   Functions:
   🔵 allowance
   🔵 balanceOf
   🟠 approve
   🟠 transfer

Catatan Penting:

• ❌ JANGAN klik "Deploy" - ini akan deploy contract baru!
• ✅ Gunakan "At Address" - ini connect ke contract yang sudah ada!

---

Step 2: Check USDC Balance (Opsional)

Verify kamu punya USDC:

1. Klik function balanceOf (blue button)

2. Input:

   account: 0x296f...C86 (paste address wallet kamu)

3. Klik "call"

4. Harusnya return angka > 0 (misal: 10000000 = 10 USDC)

Kalau balance = 0:

• Kamu perlu minta USDC testnet dulu
• Circle USDC Faucet: https://faucet.circle.com/
• Pilih network: Base Sepolia
• Paste address wallet kamu
• Atau untuk workshop, instructor akan kasih

---

Step 3: Approve USDC ke Contract

Ini adalah step WAJIB sebelum fundPrize!

Di IERC20 contract (yang baru kamu load):

1. Expand function approve (orange button 🟠)

2. Input parameters:

   spender: 0x0d247121788afC6F510B3fCE0a672D74947125de
   (Paste address SimpleVibeRaffle contract kamu)
   
   amount: 1000000000
   (1000 USDC dalam 6 decimals)

   Penjelasan amount:

   • USDC punya 6 decimals
   • 1 USDC = 1,000,000 (1 juta)
   • 1000 USDC = 1,000,000,000 (1 miliar)
   • Approve 1000 USDC sekaligus biar tidak perlu approve terus-terusan

3. Klik "transact"

4. MetaMask akan popup:

   Token Approval
   
   Allow SimpleVibeRaffle to spend your USDC?
   Amount: 1000 USDC
   
   Network: Base Sepolia
   Gas fee: ~0.0001 ETH
   
   [Reject] [Confirm]

5. Klik "Confirm"

6. Tunggu transaksi success (~5-10 detik)

7. Terminal Remix akan show:

   ✅ Transaction confirmed
   Status: Success
   Function: approve

Selamat! USDC sudah di-approve! ✅

---

Step 4: Verify Approval (Opsional)

Double-check approval berhasil:

1. Klik function allowance (blue button)

2. Input:

   owner: 0x296f...C86 (address wallet kamu)
   spender: 0x0d24...25de (address SimpleVibeRaffle contract)

3. Klik "call"

4. Harusnya return:

   1000000000

Kalau return angka tersebut = Approval berhasil! ✅

---

Step 5: Fund Prize Pool

Sekarang kamu bisa fund prize pool!

Kembali ke SimpleVibeRaffle contract:

1. Expand function fundPrize (orange button 🟠)

2. Input:

   amount: 10
   (Akan jadi 10 USDC, karena di contract dikali 10^6)

3. Klik "transact"

4. MetaMask popup:

   Contract Interaction
   
   Function: fundPrize
   Network: Base Sepolia
   Gas fee: ~0.0002 ETH
   
   [Reject] [Confirm]

5. Klik "Confirm"

6. Tunggu success!

7. Terminal akan show:

   ✅ Transaction confirmed
   Status: Success
   Event: PrizeFunded(funder, 10000000)

Prize pool sudah terisi! 🎉

---

Step 6: Verify Prize Pool

Check prize pool sudah masuk:

1. Klik function getPrizePool (blue button)

2. Harusnya return:

   10000000
   (10 USDC dalam 6 decimals)

Kalau angka tersebut muncul = Fund prize berhasil! ✅

---

Troubleshooting Fund Prize

Error: "ERC20: transfer amount exceeds allowance"

Solusi:

• Kamu belum approve atau approve amount terlalu kecil
• Ulangi Step 3 (approve USDC)
• Pastikan approve amount >= amount yang mau di-fund

---

Error: "ERC20: transfer amount exceeds balance"

Solusi:

• USDC balance kamu tidak cukup
• Check balance dengan balanceOf()
• Minta USDC dari faucet atau swap di testnet

---

Approval Sudah Habis

Kalau sudah fund beberapa kali dan allowance habis:

Contoh:
Approve: 1000 USDC
Fund 1: -10 USDC (sisa 990)
Fund 2: -10 USDC (sisa 980)
...
Fund 100: -10 USDC (sisa 0) ❌ Error!

Solusi: Approve lagi!

---

Summary: Complete Flow

┌─────────────────────────────────────────┐
│                                          │
│  1. DEPLOY SimpleVibeRaffle              │
│     ✅ Contract address: 0x0d24...      │
│                                          │
│  2. LOAD USDC Contract                   │
│     → At Address: 0x036C...             │
│     ✅ IERC20 loaded                     │
│                                          │
│  3. APPROVE USDC                         │
│     → approve(contract, 1000 USDC)      │
│     ✅ Allowance: 1000 USDC              │
│                                          │
│  4. FUND PRIZE                           │
│     → fundPrize(10)                     │
│     ✅ Prize pool: 10 USDC               │
│                                          │
│  5. READY TO PLAY!                       │
│     → Game open, prize funded           │
│     ✅ Workshop can start!               │
│                                          │
└─────────────────────────────────────────┘

Sekarang contract ready untuk workshop! 🚀

---

📊 Contract State Tracking

Memahami State Contract

State = Data yang tersimpan di contract.

Current state setelah deploy (dan fund prize):

owner: 0x1234...5678 (address kamu)
players: [] (array kosong)
gameOpen: true
lastWinner: 0x0000...0000 (belum ada winner)
lastPrize: 0 (belum ada prize diberikan)
totalGamesPlayed: 0 (belum ada game selesai)
usdcToken: 0x036CbD...CF7e (USDC contract address)

USDC Balance (bukan state variable, tapi penting):

Contract USDC balance: 10000000 (10 USDC jika sudah fund)
(Dihitung via: usdcToken.balanceOf(address(this)))

State akan berubah kalau:

• Ada yang joinGame() → players bertambah
• Owner fundPrize() → Contract USDC balance bertambah
• Owner pickWinner() → gameOpen = false, lastWinner = winner address, lastPrize = prize amount, totalGamesPlayed++, contract USDC balance = 0
• Owner resetGame() atau emergencyReset() → players = [], gameOpen = true

---

Lihat State di Remix

Variables Public:

Klik button di "Deployed Contracts":

owner (blue) → Returns address
players (blue, dengan input field untuk index) → Returns address at index
gameOpen (blue) → Returns bool

View Functions:

Klik button:

getPlayers (blue) → Returns array
getPlayerCount (blue) → Returns uint256
getPrizePool (blue) → Returns uint256

Color Code:

• 🔵 Blue = Read (view/pure) - Gratis
• 🟠 Orange = Write (state-changing) - Perlu gas
• 🔴 Red = Payable (kirim ETH) - Perlu gas + value

---

🎯 Quick Reference

Contract Functions Cheat Sheet

Owner Functions:

Function	Type	Gas	Fungsi
fundPrize(uint256)	External	Yes	Tambah prize pool dengan USDC (butuh approve dulu)
addPlayer(address)	External	Yes	Add 1 player manual dari backend
addPlayersBatch(address[])	External	Yes	Add multiple players sekaligus (NEW!)
pickWinner()	External	Yes	Pilih winner & transfer USDC, simpan history (UPDATED!)
resetGame()	External	Yes	Reset game setelah pickWinner (normal) (NEW!)
emergencyReset()	External	Yes	Force reset tanpa pickWinner (emergency) (NEW!)

Public Functions:

Function	Type	Who	Gas	Fungsi
joinGame()	External	Anyone	Yes	Join raffle - GRATIS! No deposit!

View Functions (Read-Only, No Gas):

Function	Type	Returns	Fungsi
getPlayers()	View	address[]	List semua players yang join
getPlayerCount()	View	uint256	Jumlah total players
getPrizePool()	View	uint256	Total USDC prize pool (6 decimals)
getLastWinner()	View	address, uint256	Pemenang terakhir & hadiah (NEW!)
getTotalGamesPlayed()	View	uint256	Total games yang sudah selesai (NEW!)

Public State Variables (Auto-Generated Getters):

Variable	Type	Returns	Info
owner	address	address	Address owner contract
gameOpen	bool	bool	Status game (true = open, false = closed)
lastWinner	address	address	Pemenang terakhir (NEW!)
lastPrize	uint256	uint256	Hadiah terakhir dalam USDC (NEW!)
totalGamesPlayed	uint256	uint256	Counter total games (NEW!)
usdcToken	IERC20	address	USDC contract address
players(uint256)	address[]	address	Get player by index

---

Solidity Keywords Reference

Keyword	Artinya
contract	Definisi contract
function	Definisi fungsi
modifier	Reusable guard
constructor	Fungsi deploy
public	Bisa diakses siapa saja
external	Hanya dari luar contract
view	Read-only, gratis
payable	Bisa terima ETH
require()	Assert condition
emit	Emit event/log

---

✅ Checklist: Ready for Part 3?

Sebelum lanjut, pastikan:

Understanding

• Paham struktur contract (state vars, functions, events, interface)
• Paham setiap fungsi di SimpleVibeRaffle
• Paham kenapa perlu approve USDC sebelum fundPrize
• Paham perbedaan "Deploy" vs "At Address"

Contract Deployment

• Contract sudah compiled tanpa error
• Contract sudah deployed ke Base Sepolia
• Punya contract address (copy & save!)
• Bisa lihat contract di BaseScan
• Test fungsi owner, gameOpen, usdcToken works

Prize Pool Setup

• USDC contract sudah di-load dengan "At Address"
• USDC sudah di-approve ke SimpleVibeRaffle contract
• Prize pool sudah di-fund (minimal 10 USDC)
• getPrizePool() return angka > 0
• Bisa lihat event PrizeFunded di BaseScan

---

🚀 Next: Hands-on Game!

Sekarang contract sudah deploy & ready!

Saatnya:

1. Join game dari wallet peserta
2. Pick winner
3. Celebrate! 🎉

📖 Part 3: Hands-on - Join Game & Pilih Pemenang →

---

← Part 1: Setup | Main Index | Part 3: Hands-on →

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