Program.cs

using System;
using IndiaKit.Dates;
using IndiaKit.Gst;
using IndiaKit.Identifiers;
using IndiaKit.Money;

Console.OutputEncoding = System.Text.Encoding.UTF8;

// Identifiers: precise reasons, not just true/false
Console.WriteLine(Gstin.Check("27AAPFU0939F1ZV"));          // Valid
Console.WriteLine(Gstin.Check("27AAPFU0939F1ZX"));          // Invalid check digit: expected 'V', got 'X'. Check for a typo.

var gstin = Gstin.Parse("27 aapfu 0939f 1zv");
Console.WriteLine($"{gstin} -> {gstin.State.Name}, PAN {gstin.Pan} ({gstin.Pan.HolderType})");

Console.WriteLine(Aadhaar.Mask("2341 2341 2346"));          // XXXX XXXX 2346
Console.WriteLine(IndianMobile.ToE164("098765 43210"));     // +919876543210
Console.WriteLine(Ifsc.BankCode("HDFC0001234"));            // HDFC

// Money: Indian grouping, compact and in words
Console.WriteLine(Rupees.Format(12345678.9m));              // ₹1,23,45,678.90
Console.WriteLine(Rupees.FormatCompact(4_250_000m));        // ₹42.5 L
Console.WriteLine(Rupees.ToWords(118000m));                 // Rupees One Lakh Eighteen Thousand Only

// GST: place of supply decides CGST+SGST or IGST
var interState = GstCalculator.IsInterState(supplierStateCode: "27", placeOfSupplyStateCode: gstin.StateCode);
Console.WriteLine(GstCalculator.Calculate(100_000m, 18m, interState));
Console.WriteLine(GstCalculator.FromInclusive(1180m, 18m, interState: true));

// Financial years
var fy = FinancialYear.For(new DateTime(2026, 10, 12));
Console.WriteLine($"{fy} | {fy.AssessmentYear.ToAssessmentYearString()} | Q{FinancialYear.QuarterOf(new DateTime(2026, 10, 12))} | invoice prefix INV/{fy.ToShortString()}/");