async function sha256(message) {
    const msgBuffer = new TextEncoder().encode(message);
    const hashBuffer = await crypto.subtle.digest('SHA-256', msgBuffer);
    const hashArray = Array.from(new Uint8Array(hashBuffer));
    const hashHex = hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
    return hashHex;
}

async function startPoW() {
    document.getElementById('status').innerText = "Starting PoW...";

    // Fetch challenge from the server
    const response = await fetch('/get-challenge');
    const challenge = await response.json();
    const { nonce, difficulty } = challenge;

    let solution = 0;
    let hash = '';

    // Brute-force to find a solution
    while (true) {
        hash = await sha256(nonce + solution);
        if (hash.startsWith('0'.repeat(difficulty))) {
            break;
        }
        solution++;
    }

    document.getElementById('status').innerText = `Solution found: ${solution} (Hash: ${hash})`;

    // Send the solution back to the server for verification
    const verifyResponse = await fetch('/verify', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json',
        },
        body: JSON.stringify({ nonce, solution: solution.toString(), difficulty })
    });

    if (verifyResponse.status === 200) {
        document.getElementById('status').innerText += " - Verified!";
    } else {
        document.getElementById('status').innerText += " - Verification failed!";
    }
}

document.getElementById('start-pow').addEventListener('click', startPoW);