import { createWalletClient, http, keccak256, toHex } from 'viem';
import { baseSepolia, base } from 'viem/chains';
import { privateKeyToAccount } from 'viem/accounts';
import { writeFileSync, readFileSync, existsSync } from 'node:fs';

// ── Config ─────────────────────────────────────────────

const AUDIT_CONTRACT = process.env.SPENDOS_AUDIT_CONTRACT ?? '0x37a66d3404aDCaf0a558189a338bCeaD3a06A5Ee';
const DEPLOYER_KEY = process.env.DEPLOYER_PRIVATE_KEY ?? '';
const CHAIN = process.env.SPENDOS_CHAIN === 'mainnet' ? base : baseSepolia;
const RPC_URL = process.env.SPENDOS_RPC_URL ?? (process.env.SPENDOS_CHAIN === 'mainnet'
  ? 'https://mainnet.base.org'
  : 'https://sepolia.base.org');
const AUDIT_FILE = './audit.json';

const LOG_ABI = [{
  name: 'log',
  type: 'function',
  inputs: [
    { name: 'delegationHash', type: 'bytes32' },
    { name: 'action', type: 'string' },
    { name: 'details', type: 'string' },
    { name: 'amount', type: 'uint256' },
  ],
  outputs: [],
  stateMutability: 'nonpayable',
}] as const;

// ── Types ──────────────────────────────────────────────

interface AuditEntry {
  timestamp: string;
  action: string;
  delegationId: string;
  details: string;
  amount: number;
  txHash?: string;
}

// ── In-Memory + File Store ─────────────────────────────

const entries: AuditEntry[] = [];

function persist(): void {
  writeFileSync(AUDIT_FILE, JSON.stringify(entries, null, 2));
}

// Load existing entries on startup
if (existsSync(AUDIT_FILE)) {
  try {
    const content = readFileSync(AUDIT_FILE, 'utf-8').trim();
    if (content.startsWith('[')) {
      entries.push(...JSON.parse(content));
    } else if (content) {
      // Legacy line-delimited format
      entries.push(...content.split('\n').map(l => JSON.parse(l)));
    }
  } catch { /* start fresh */ }
}

export function getAuditLog(): AuditEntry[] {
  return [...entries].reverse();
}

// ── Nonce Queue ────────────────────────────────────────

const txQueue: Array<() => Promise<void>> = [];
let processing = false;

async function drainQueue(): Promise<void> {
  if (processing) return;
  processing = true;
  while (txQueue.length > 0) {
    const fn = txQueue.shift()!;
    try { await fn(); } catch (e) { console.error('[Audit] Queue tx failed:', e); }
  }
  processing = false;
}

// ── Public API ─────────────────────────────────────────

const ONCHAIN_ACTIONS = new Set(['approved', 'rejected', 'revoked', 'expired']);

export async function logAuditEvent(
  action: string,
  delegationId: string,
  details: string,
  amount: number,
): Promise<string | null> {
  const entry: AuditEntry = {
    timestamp: new Date().toISOString(),
    action,
    delegationId,
    details,
    amount,
  };

  // Add to in-memory store immediately (dashboard sees it right away)
  entries.push(entry);
  persist();

  // Only governance events go on-chain
  if (!AUDIT_CONTRACT || !DEPLOYER_KEY || !ONCHAIN_ACTIONS.has(action)) {
    console.log(`[Audit] Local: ${action} — ${details}`);
    return null;
  }

  // Queue on-chain tx (updates entry.txHash when complete)
  return new Promise((resolve) => {
    txQueue.push(async () => {
      try {
        const hash = await sendOnChainLog(delegationId, action, details, amount);
        if (hash) {
          entry.txHash = hash;
          persist(); // Re-persist with txHash
        }
        resolve(hash);
      } catch {
        resolve(null);
      }
    });
    drainQueue();
  });
}

// ── On-Chain Sender ────────────────────────────────────

// Track nonce to avoid "replacement transaction underpriced"
let currentNonce: number | null = null;

async function sendOnChainLog(
  delegationId: string, action: string, details: string, amount: number
): Promise<string | null> {
  try {
    const account = privateKeyToAccount(DEPLOYER_KEY as `0x${string}`);
    const client = createWalletClient({
      account,
      chain: CHAIN,
      transport: http(RPC_URL),
    });

    // Get or increment nonce
    if (currentNonce === null) {
      const { createPublicClient } = await import('viem');
      const pub = createPublicClient({ chain: CHAIN, transport: http(RPC_URL) });
      currentNonce = await pub.getTransactionCount({ address: account.address });
    }
    const nonce = currentNonce++;

    const hash = await client.writeContract({
      address: AUDIT_CONTRACT as `0x${string}`,
      abi: LOG_ABI,
      functionName: 'log',
      args: [keccak256(toHex(delegationId)), action, details, BigInt(Math.round(amount * 1e6))],
      nonce,
    });

    console.log(`[Audit] On-chain: ${action} — tx: ${hash}`);
    return hash;
  } catch (err) {
    // Reset nonce on failure so next tx refetches from chain
    currentNonce = null;
    console.error(`[Audit] On-chain failed (${action} for ${delegationId}): ${err}`);
    return null;
  }
}