import csv
import io
import re

PAN_RE = re.compile(r"^[A-Z]{5}[0-9]{4}[A-Z]$")
GSTIN_RE = re.compile(r"^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z][1-9A-Z]Z[0-9A-Z]$")
TAN_RE = re.compile(r"^[A-Z]{4}[0-9]{5}[A-Z]$")
MOBILE_RE = re.compile(r"^[6-9][0-9]{9}$")
PIN_RE = re.compile(r"^[0-9]{6}$")

def normalize_text(value):
    if value is None:
        return None
    text = str(value).strip()
    return text or None

def normalize_upper(value):
    value = normalize_text(value)
    return value.upper() if value else None

def build_csv(rows, headers):
    output = io.StringIO()
    writer = csv.writer(output)
    writer.writerow(headers)
    for row in rows:
        writer.writerow(row)
    return output.getvalue()