/**
 * Vela Payroll Engine — Australia Tax Jurisdiction
 *
 * Based on ATO 2025-26 tax year (1 July 2025 – 30 June 2026)
 * Source: https://www.ato.gov.au/rates/individual-income-tax-rates
 *
 * PAYG Withholding — Resident taxpayers
 * ┌──────────────────────────────────┬─────────────────────────────┐
 * │ Taxable Income                   │ Tax on this income          │
 * ├──────────────────────────────────┼─────────────────────────────┤
 * │ $0 – $18,200                     │ Nil                         │
 * │ $18,201 – $45,000                │ 16c for each $1 over $18,200│
 * │ $45,001 – $135,000               │ $4,288 + 30c per $1 over    │
 * │                                  │ $45,000                     │
 * │ $135,001 – $190,000              │ $31,288 + 37c per $1 over   │
 * │                                  │ $135,000                    │
 * │ $190,001 and over                │ $51,638 + 45c per $1 over   │
 * │                                  │ $190,000                    │
 * └──────────────────────────────────┴─────────────────────────────┘
 *
 * Medicare Levy: 2% of taxable income (applies to most taxpayers)
 * Medicare Levy Surcharge: Not included in MVP (requires private health insurance check)
 *
 * Superannuation Guarantee: 11.5% of ordinary time earnings
 * (effective 1 July 2025, increasing from 11.0%)
 * Source: https://www.ato.gov.au/rates/key-superannuation-rates-and-previous-year-rates
 *
 * Note: Low Income Tax Offset (LITO) and Low and Middle Income
 * Tax Offset (LMITO) are NOT included in MVP — these would require
 * rebate calculations.
 */

import {
  TaxJurisdiction,
  TaxBracket,
  DeductionLineItem,
  EmployerContribution,
  progressiveTaxCalc,
  round2,
} from "../types";

// ── 2025-26 Tax Brackets (ATO Stage 3 tax cuts — as legislated) ──
const TAX_BRACKETS: TaxBracket[] = [
  { min: 0, max: 18_200, rate: 0.0 },
  { min: 18_200, max: 45_000, rate: 0.16 },
  { min: 45_000, max: 135_000, rate: 0.30 },
  { min: 135_000, max: 190_000, rate: 0.37 },
  { min: 190_000, max: null, rate: 0.45 },
];

const MEDICARE_LEVY_RATE = 0.02;
const SUPER_GUARANTEE_RATE = 0.115; // 11.5% from 1 July 2025

export class AustraliaTax implements TaxJurisdiction {
  readonly name = "Australia";
  readonly countryCode = "AU";
  readonly currency = "AUD";

  calculate(grossAnnual: number): {
    deductions: DeductionLineItem[];
    employerContributions: EmployerContribution[];
  } {
    // 1. PAYG Income Tax
    const incomeTax = progressiveTaxCalc(grossAnnual, TAX_BRACKETS);

    // 2. Medicare Levy (2% of gross)
    const medicareLevy = round2(grossAnnual * MEDICARE_LEVY_RATE);

    // 3. Total employee deductions
    const totalTax = round2(incomeTax + medicareLevy);

    const deductions: DeductionLineItem[] = [
      {
        name: "PAYG Income Tax",
        amount: round2(incomeTax),
        type: "tax",
        description: "ATO PAYG withholding (2025-26 brackets)",
      },
      {
        name: "Medicare Levy",
        amount: medicareLevy,
        type: "levy",
        description: "2% of taxable income",
      },
    ];

    // 4. Employer Superannuation Guarantee (NOT deducted from employee pay)
    const superContribution = round2(grossAnnual * SUPER_GUARANTEE_RATE);

    const employerContributions: EmployerContribution[] = [
      {
        name: "Superannuation Guarantee",
        amount: superContribution,
        description: "11.5% of ordinary time earnings (2025-26)",
      },
    ];

    return { deductions, employerContributions };
  }
}