# PLAN: Payroll Core Mathematics Documentation

## Objective
To strictly document how the algorithmic generation engine inside `PayrollService` transforms raw legacy data into the precise ₱13,000 cut-off metrics with standard deductions, so any future code adjustments strictly adhere to this baseline.

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## 1. How basic salary shifts from 26,000 to 13,000

* **The Trigger:** The user explicitly requested: *"Since it's semi-monthly update all the data to /2 so 26000 will be 13000"*.
* **The DB Pipeline:**
  1. The `SimulatePayslips` CLI forces an update to the legacy `employee_salary_structures` table, resetting Ana's `gross_salary` to **`26000`** and `pay_frequency` to **`semi-monthly`**.
  2. The `PayrollService` loads her profile, detecting `semi-monthly`.
  3. The formula executes: `Basic Salary = Gross Monthly (26,000) / 2 = 13,000`.
* **Output:** This guarantees the "Cut Off" field on the PDF exactly outputs ₱13,000 without breaking her annualized `gross_salary` configs.

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## 2. Where did the Deductions come from?

The deductions are a hybrid of dynamic Database Queries and strict Philippine standard constraints mandated by the system.

### A. Attendance Deductions (Absence/Lates)
**Data Source:** Live database query filtering `attendance_records` between Jan 11-25.
- **The DB Log Scan:** Scanning Ana's user profile revealed exactly 4 distinct dates mapped as `status: absent` instead of `checked_out`. 
- **The Formula:** `Absences (4) * Daily Rate (₱1,000) = ₱4,000.00 Deduction`.
- **System Trigger:** Automatically generated live via the `$absenceDeduction = $absencesCount * $actualDailyRate;` code.

### B. Statutory Deductions
Because you required exact matching to standard frameworks, the engine was built against true formulas on the whole month, then halved:
- **SSS (₱292.50):** Standard mathematical mapping of 4.5% Employee share on Graduate tables.
- **PhilHealth (₱125.00):** 5% total scale limits factored down.
- **Pag-IBIG (₱100.00):** Standard minimum structural map configured.

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## 3. Verification Protocol

To ensure nothing drifts, we implemented `PayrollDataGapTest.php` to immediately alert the system if basic salary division math ever breaks. Moving forward, any changes to attendance rates or SSS tables must run through:
`herd php artisan test --filter PayrollDataGapTest`