/**
 * Vela Payroll Engine — Core Calculation Engine
 *
 * The engine orchestrates the calculation flow:
 * 1. Accept PayrollInput (salary/hourly + frequency + jurisdiction)
 * 2. Derive gross annual from hourly if needed
 * 3. Ask the jurisdiction plugin for deductions and contributions
 * 4. Build and return a complete PayslipCalculation
 *
 * The engine is jurisdiction-agnostic — it delegates all tax
 * calculations to the injected TaxJurisdiction plugin.
 * This means new countries can be added without touching this code.
 */

import {
  PayslipCalculation,
  PayrollInput,
  DeductionLineItem,
  EmployerContribution,
  toPeriod,
  round2,
} from "./types";

export class PayrollEngine {
  /**
   * Calculate a complete payslip.
   */
  calculate(input: PayrollInput): PayslipCalculation {
    const jurisdiction = input.jurisdiction;

    // 1. Derive gross annual from hourly rate if provided
    let grossAnnual = input.grossAnnual ?? 0;
    if (input.hourlyRate && input.hoursPerWeek) {
      grossAnnual = input.hourlyRate * input.hoursPerWeek * 52;
    }

    grossAnnual = round2(grossAnnual);

    // 2. Ask the jurisdiction plugin for deductions & contributions
    const { deductions, employerContributions } = jurisdiction.calculate(grossAnnual);

    // 3. Calculate totals
    const totalDeductions = round2(
      deductions.reduce((sum, d) => sum + d.amount, 0)
    );
    const totalEmployerContributions = round2(
      employerContributions.reduce((sum, c) => sum + c.amount, 0)
    );

    // 4. Per-period amounts
    const grossPay = toPeriod(grossAnnual, input.payFrequency);
    const netPay = toPeriod(grossAnnual - totalDeductions, input.payFrequency);
    const totalEmployerCost = toPeriod(
      grossAnnual + totalEmployerContributions,
      input.payFrequency
    );

    // 5. Build result
    return {
      jurisdiction: jurisdiction.name,
      jurisdictionCode: jurisdiction.countryCode,
      payPeriod: input.payFrequency,
      grossAnnual,
      grossPay: round2(grossPay),

      deductions,
      totalDeductions,

      employerContributions,
      totalEmployerContributions,

      netPay: round2(netPay),
      totalEmployerCost: round2(totalEmployerCost),

      // Annual summary
      annualTax: round2(totalDeductions),
      annualTotalDeductions: totalDeductions,
      annualEmployerContributions: totalEmployerContributions,
      annualNetPay: round2(grossAnnual - totalDeductions),
    };
  }
}