fix enrollment, invoice, payment and financila aid

app/Models/FinancialAidEstimateModel.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace App\Models;
+
+use InvalidArgumentException;
+
+/**
+ * PHP port of app/Controllers/financial_aid_formula.py
+ */
+class FinancialAidEstimateModel
+{
+    private const FEDERAL_POVERTY_BASE = 15960.0;
+    private const FEDERAL_POVERTY_STEP = 5680.0;
+    private const MASSACHUSETTS_COST_FACTOR = 1.05757;
+    private const PROTECTED_INCOME_MULTIPLIER = 2.0;
+    private const DISCRETIONARY_CONTRIBUTION_RATE = 0.10;
+
+    public function estimatedAid(float $totalBalance, int $householdSize, float $householdIncome): float
+    {
+        if ($householdSize < 1) {
+            throw new InvalidArgumentException('household_size must be at least 1');
+        }
+        if ($totalBalance < 0 || $householdIncome < 0) {
+            throw new InvalidArgumentException('balance and income cannot be negative');
+        }
+
+        $federalPovertyLevel = self::FEDERAL_POVERTY_BASE + (self::FEDERAL_POVERTY_STEP * ($householdSize - 1));
+        $adjustedNeedThreshold = $federalPovertyLevel * self::MASSACHUSETTS_COST_FACTOR;
+        $protectedIncome = self::PROTECTED_INCOME_MULTIPLIER * $adjustedNeedThreshold;
+        $discretionaryIncome = max(0.0, $householdIncome - $protectedIncome);
+        $expectedContribution = self::DISCRETIONARY_CONTRIBUTION_RATE * $discretionaryIncome;
+        $estimated = $totalBalance - $expectedContribution;
+
+        return round(max(0.0, min($totalBalance, $estimated)), 2);
+    }
+
+    public function finalRebate(
+        float $totalBalance,
+        int $householdSize,
+        float $householdIncome,
+        float $amountRequested
+    ): float {
+        if ($amountRequested < 0) {
+            throw new InvalidArgumentException('amount_requested cannot be negative');
+        }
+
+        $estimated = $this->estimatedAid($totalBalance, $householdSize, $householdIncome);
+
+        return min($estimated, $amountRequested, $totalBalance);
+    }
+}