/**
 * ⚠️ SHELVED / NOT A PRODUCTION CAPABILITY (2026-07-27) — READ FIRST:
 * Cloud-side of edge↔cloud failover for a CENTRAL-CLOUD topology. Production is standalone-per-bank
 * (no central cloud), so this is NOT a production capability. verifyPQCSignature is a PLACEHOLDER
 * accept-all and cloudLedger is in-memory. Its HTTP routes (/api/cloud/*, incl. the UNAUTHENTICATED
 * /api/cloud/sync and root /sync forged-write surface) were REMOVED 2026-07-27 as consumer-less and
 * unsafe. RETAINED as roadmap-wrong-topology reference (chaosEngine drives heartbeatMonitor). If ever
 * wired for a real topology, REBUILD with real auth + real PQC verify — NEVER the accept-all.
 * (Offline-moat reconciliation, project memory 2026-07-27.)
 */

/**
 * Cloud Core - Primary Banking Ledger Sync Handler
 * Receives offline transactions from Edge Nodes and merges them
 * 
 * Patent Reference: AEGIS-PAT-2026-001
 * Component: Primary Cloud Core (300)
 * 
 * Key Features:
 * - Idempotency: Handles retries without duplicates
 * - HLC Verification: Respects causal ordering
 * - PQC Signature Verification: ML-KEM-768 validation
 * - Audit Flagging: Older transactions flagged for review
 */

import { HLC } from './hlc';
import { logger } from './lib/logger';

const cloudLogger = logger.child('cloud-core');

export interface SyncTransaction {
  id: string;
  amount: number;
  currency: string;
  hlc_timestamp: string;  // BigInt as string
  pqc_signature: string;
  node_id: string;
  readable_timestamp?: string;
}

export interface LedgerEntry {
  id: string;
  amount: number;
  currency: string;
  hlcTimestamp: bigint;
  pqcSignature: string;
  nodeId: string;
  syncedAt: Date;
  status: 'SETTLED' | 'PENDING_AUDIT' | 'REJECTED';
  auditReason?: string;
}

export interface SyncResponse {
  acknowledged: boolean;
  hlcTimestamp: string;
  conflictResolution: 'accepted' | 'rejected' | 'merged' | 'duplicate';
  message?: string;
  auditRequired?: boolean;
}

export interface MerkleRootResponse {
  merkleRoot: string;
  transactionIds: string[];
  lastUpdated: Date;
}

// In-memory cloud ledger (would be PostgreSQL in production)
const cloudLedger: Map<string, LedgerEntry> = new Map();

// Track the latest known HLC per user/account for audit detection
const latestHLCByAccount: Map<string, bigint> = new Map();

// Cloud's own HLC for response timestamps
const cloudClock = new HLC('cloud-core-001');

/**
 * Verifies PQC signature (ML-KEM-768)
 * In production, this would use liboqs/oqspy for actual verification
 */
function verifyPQCSignature(signature: string, transactionId: string): boolean {
  // Mock verification - in 2026 production:
  // 1. Decapsulate ML-KEM-768 key from signature
  // 2. Verify HMAC of transaction data using decapsulated secret
  // 3. Check against registered edge node public keys
  
  if (!signature || signature.length < 10) {
    return false;
  }
  
  // Placeholder: Accept all properly formatted signatures
  return true;
}

/**
 * Determines if a transaction should be flagged for audit
 * based on HLC ordering and timing rules
 */
function shouldFlagForAudit(tx: SyncTransaction, existingLatest: bigint | undefined): {
  requiresAudit: boolean;
  reason?: string;
} {
  const txHLC = BigInt(tx.hlc_timestamp);
  
  // Check if transaction is "old" compared to latest known
  if (existingLatest && txHLC < existingLatest) {
    const [txPhysical] = HLC.unpack(txHLC);
    const [latestPhysical] = HLC.unpack(existingLatest);
    const ageMs = latestPhysical - txPhysical;
    
    // If more than 1 hour old, flag for audit
    if (ageMs > 3600000) {
      return {
        requiresAudit: true,
        reason: `Transaction HLC is ${Math.floor(ageMs / 60000)} minutes older than latest known`
      };
    }
  }
  
  // Check for suspicious patterns (simplified)
  if (tx.amount > 10000000) { // Over 10M UGX
    return {
      requiresAudit: true,
      reason: 'High-value transaction during offline period'
    };
  }
  
  return { requiresAudit: false };
}

/**
 * Sync Endpoint Handler
 * Receives an offline transaction from an Edge Node
 * Implements Idempotency and HLC verification
 */
export async function handleSyncTransaction(tx: SyncTransaction): Promise<SyncResponse> {
  const txId = tx.id;
  const txHLC = BigInt(tx.hlc_timestamp);
  
  // 1. Idempotency Check: Have we seen this ID before?
  if (cloudLedger.has(txId)) {
    const existing = cloudLedger.get(txId)!;
    
    // If the HLC matches, it's a duplicate retry; return OK
    if (existing.hlcTimestamp === txHLC) {
      cloudLogger.info('Duplicate sync request - acknowledging', { metadata: { txId } });
      return {
        acknowledged: true,
        hlcTimestamp: cloudClock.now().toString(),
        conflictResolution: 'duplicate',
        message: 'Transaction already synced'
      };
    } else {
      // ID exists but HLC is different - this is a conflict/error
      cloudLogger.error('Transaction ID collision with different HLC', { metadata: { txId } });
      return {
        acknowledged: false,
        hlcTimestamp: cloudClock.now().toString(),
        conflictResolution: 'rejected',
        message: 'Transaction ID collision with different HLC'
      };
    }
  }
  
  // 2. PQC Signature Verification
  const isValidSignature = verifyPQCSignature(tx.pqc_signature, txId);
  if (!isValidSignature) {
    cloudLogger.error('Invalid PQC signature', { metadata: { txId } });
    return {
      acknowledged: false,
      hlcTimestamp: cloudClock.now().toString(),
      conflictResolution: 'rejected',
      message: 'Invalid Post-Quantum Signature'
    };
  }
  
  // 3. Check for Audit Requirements
  const accountKey = tx.node_id; // In production, extract account ID from tx
  const latestKnown = latestHLCByAccount.get(accountKey);
  const auditCheck = shouldFlagForAudit(tx, latestKnown);
  
  // 4. Commit to Cloud Ledger
  const entry: LedgerEntry = {
    id: txId,
    amount: tx.amount,
    currency: tx.currency,
    hlcTimestamp: txHLC,
    pqcSignature: tx.pqc_signature,
    nodeId: tx.node_id,
    syncedAt: new Date(),
    status: auditCheck.requiresAudit ? 'PENDING_AUDIT' : 'SETTLED',
    auditReason: auditCheck.reason
  };
  
  cloudLedger.set(txId, entry);
  
  // Update latest known HLC for this account
  if (!latestKnown || txHLC > latestKnown) {
    latestHLCByAccount.set(accountKey, txHLC);
  }
  
  // Update cloud clock with received timestamp
  cloudClock.receive(txHLC);
  
  cloudLogger.info('Successfully synced Sovereign TX', { metadata: { txId, status: entry.status } });
  
  return {
    acknowledged: true,
    hlcTimestamp: cloudClock.now().toString(),
    conflictResolution: auditCheck.requiresAudit ? 'merged' : 'accepted',
    message: auditCheck.requiresAudit 
      ? `Transaction flagged for audit: ${auditCheck.reason}` 
      : 'Transaction settled',
    auditRequired: auditCheck.requiresAudit
  };
}

/**
 * Heartbeat Endpoint Handler
 * Responds to edge node heartbeat pings
 */
export async function handleHeartbeat(nodeId: string, nonce: string): Promise<{
  acknowledged: boolean;
  cloudTimestamp: string;
  nonce: string;
}> {
  return {
    acknowledged: true,
    cloudTimestamp: cloudClock.now().toString(),
    nonce
  };
}

/**
 * Merkle Root Endpoint Handler
 * Returns current Merkle root for divergence detection
 */
export function getMerkleRoot(): MerkleRootResponse {
  const transactionIds = Array.from(cloudLedger.keys());
  
  // Build simple Merkle root (production would use proper crypto)
  let hash = 0;
  for (const id of transactionIds.sort()) {
    const entry = cloudLedger.get(id)!;
    const data = `${id}:${entry.hlcTimestamp}:${entry.pqcSignature}`;
    for (let i = 0; i < data.length; i++) {
      hash = ((hash << 5) - hash) + data.charCodeAt(i);
      hash = hash & hash;
    }
  }
  
  return {
    merkleRoot: '0x' + Math.abs(hash).toString(16).padStart(16, '0'),
    transactionIds,
    lastUpdated: new Date()
  };
}

/**
 * Get all ledger entries (for dashboard display)
 */
export function getLedgerEntries(): LedgerEntry[] {
  return Array.from(cloudLedger.values())
    .sort((a, b) => HLC.compare(a.hlcTimestamp, b.hlcTimestamp));
}

/**
 * Get transactions pending audit
 */
export function getPendingAuditTransactions(): LedgerEntry[] {
  return Array.from(cloudLedger.values())
    .filter(entry => entry.status === 'PENDING_AUDIT');
}

/**
 * Approve an audited transaction
 */
export function approveAuditedTransaction(txId: string): boolean {
  const entry = cloudLedger.get(txId);
  if (entry && entry.status === 'PENDING_AUDIT') {
    entry.status = 'SETTLED';
    entry.auditReason = undefined;
    return true;
  }
  return false;
}

/**
 * Reject an audited transaction
 */
export function rejectAuditedTransaction(txId: string, reason: string): boolean {
  const entry = cloudLedger.get(txId);
  if (entry) {
    entry.status = 'REJECTED';
    entry.auditReason = reason;
    return true;
  }
  return false;
}

/**
 * Get cloud ledger statistics
 */
export function getLedgerStats(): {
  totalTransactions: number;
  settledCount: number;
  pendingAuditCount: number;
  rejectedCount: number;
  totalVolume: { [currency: string]: number };
  uniqueNodes: number;
} {
  const entries = Array.from(cloudLedger.values());
  const volume: { [currency: string]: number } = {};
  const nodes = new Set<string>();
  
  for (const entry of entries) {
    volume[entry.currency] = (volume[entry.currency] || 0) + entry.amount;
    nodes.add(entry.nodeId);
  }
  
  return {
    totalTransactions: entries.length,
    settledCount: entries.filter(e => e.status === 'SETTLED').length,
    pendingAuditCount: entries.filter(e => e.status === 'PENDING_AUDIT').length,
    rejectedCount: entries.filter(e => e.status === 'REJECTED').length,
    totalVolume: volume,
    uniqueNodes: nodes.size
  };
}

/**
 * Clear ledger (for testing/demo reset)
 */
export function clearLedger(): void {
  cloudLedger.clear();
  latestHLCByAccount.clear();
  cloudLogger.info('Cloud ledger cleared');
}