// Split into inserts and updates
const insertsAndUpdates = batch.reduce((acc, po) => {
  const key = `${po.po_id}-${po.pid}`;
  if (existingPOMap.has(key)) {
    const existing = existingPOMap.get(key);
    // Check if any values are different
    const hasChanges = columnNames.some(col => {
      const newVal = po[col] ?? null;
      const oldVal = existing[col] ?? null;
      // Special handling for numbers to avoid type coercion issues
      if (typeof newVal === 'number' && typeof oldVal === 'number') {
        return Math.abs(newVal - oldVal) > 0.00001; // Allow for tiny floating point differences
      }
      // Special handling for receiving_history JSON
      if (col === 'receiving_history') {
        return JSON.stringify(newVal) !== JSON.stringify(oldVal);
      }
      return newVal !== oldVal;
    });

    if (hasChanges) {
      console.log(`PO line changed: ${key}`, {
        po_id: po.po_id,
        pid: po.pid,
        changes: columnNames.filter(col => {
          const newVal = po[col] ?? null;
          const oldVal = existing[col] ?? null;
          if (typeof newVal === 'number' && typeof oldVal === 'number') {
            return Math.abs(newVal - oldVal) > 0.00001;
          }
          if (col === 'receiving_history') {
            return JSON.stringify(newVal) !== JSON.stringify(oldVal);
          }
          return newVal !== oldVal;
        })
      });
      acc.updates.push({
        po_id: po.po_id,
        pid: po.pid,
        values: columnNames.map(col => po[col] ?? null)
      });
    }
  } else {
    console.log(`New PO line: ${key}`);
    acc.inserts.push({
      po_id: po.po_id,
      pid: po.pid,
      values: columnNames.map(col => po[col] ?? null)
    });
  }
  return acc;
}, { inserts: [], updates: [] });

// Handle inserts
if (insertsAndUpdates.inserts.length > 0) {
  const insertPlaceholders = Array(insertsAndUpdates.inserts.length).fill(placeholderGroup).join(",");
  
  const insertResult = await localConnection.query(`
    INSERT INTO purchase_orders (${columnNames.join(",")})
    VALUES ${insertPlaceholders}
  `, insertsAndUpdates.inserts.map(i => i.values).flat());
  
  recordsAdded += insertResult[0].affectedRows;
}

// Handle updates
if (insertsAndUpdates.updates.length > 0) {
  const updatePlaceholders = Array(insertsAndUpdates.updates.length).fill(placeholderGroup).join(",");
  
  const updateResult = await localConnection.query(`
    INSERT INTO purchase_orders (${columnNames.join(",")})
    VALUES ${updatePlaceholders}
    ON DUPLICATE KEY UPDATE
      ${columnNames
        .filter(col => col !== "po_id" && col !== "pid")
        .map(col => `${col} = VALUES(${col})`)
        .join(",")};
  `, insertsAndUpdates.updates.map(u => u.values).flat());
  
  // Each update affects 2 rows in affectedRows, so we divide by 2 to get actual count
  recordsUpdated += insertsAndUpdates.updates.length;
}