# Plan: Country-Driven Standard Available Hours (SAH) and FTE

**Date:** 2026-03-13
**Status:** Draft
**Depends on:** OrgUnit hierarchy, Resource model extensions

## Problem

Planarchy currently uses a flat `hoursPerDay` on allocations. The chargeability reporting model requires:

- Country-specific daily working hours (8h Germany, 9h India, variable Spain)
- Public holidays per country AND metro city
- FTE as a multiplier that reduces available hours (FTE 0.5 = 4h/day in an 8h country)
- SAH (Standard Available Hours) = net hours after deducting holidays and absences

Without SAH, FTE-based chargeability calculations cannot be accurate.

## Concepts

### Standard Available Hours (SAH)

> "Die Standard Available Hrs (SAH) bezeichnen die Netto-Arbeitszeit, also die Zeit, die nach Abzug aller Fehlzeiten tatsaechlich fuer die produktive Arbeit zur Verfuegung steht."

**Formula per resource per period:**

```
grossHoursPerDay = country.dailyWorkingHours (with Spain schedule rules)
effectiveHoursPerDay = grossHoursPerDay * resource.fte
workingDaysInPeriod = calendarDays - weekends - publicHolidays(country, metroCity)
absenceDays = vacation + illness + other absence
SAH = effectiveHoursPerDay * (workingDaysInPeriod - absenceDays)
```

### Daily Working Hours by Country

| Country | Daily Hours | Special Rules |
|---|---|---|
| Costa Rica | 8h | - |
| Germany | 8h | - |
| Hungary | 8h | - |
| India | 9h | - |
| Italy | 8h | - |
| Portugal | 8h | - |
| Spain | variable | Fridays always 6.5h; Mon-Thu 6.5h during 1 Jul - 15 Sep, otherwise 9h |
| United Kingdom | 8h | - |

### FTE Impact

- FTE is stored with at least 2 decimal places (e.g. 0.50, 0.80)
- FTE can change per month (contract changes, joiners/leavers)
- Part-time 50% in Germany: 8h * 0.50 = 4h effective daily hours
- Part-time 80% in India: 9h * 0.80 = 7.2h effective daily hours

## Schema Changes

### New: `Country` model

```prisma
model Country {
  id                String     @id @default(cuid())
  code              String     @unique       // ISO 3166-1 alpha-2 (DE, IN, ES, ...)
  name              String                   // Display name
  dailyWorkingHours Float      @default(8.0) // Base daily hours
  scheduleRules     Json?      @db.JsonB     // For Spain-style variable schedules
  createdAt         DateTime   @default(now())
  updatedAt         DateTime   @updatedAt

  metroCities       MetroCity[]
  resources         Resource[]
}
```

### New: `MetroCity` model

```prisma
model MetroCity {
  id        String   @id @default(cuid())
  name      String                        // e.g. "Munich", "Stuttgart"
  countryId String
  country   Country  @relation(fields: [countryId], references: [id])
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt

  resources Resource[]

  @@unique([countryId, name])
}
```

### Resource model extensions

```prisma
model Resource {
  // ... existing fields ...

  fte          Float     @default(1.0)   // Already exists, ensure 2+ decimals
  countryId    String?
  country      Country?  @relation(fields: [countryId], references: [id])
  metroCityId  String?
  metroCity    MetroCity? @relation(fields: [metroCityId], references: [id])
}
```

Note: Resource already has `postalCode` and `federalState` from Phase 9 (Vacation Pro).
The new `countryId` + `metroCityId` are complementary — `federalState` stays for German public holiday derivation, `countryId` drives daily hours and SAH.

## Engine: SAH Calculator

Location: `packages/engine/src/sah/calculator.ts`

```typescript
interface SAHInput {
  country: { dailyWorkingHours: number; scheduleRules?: SpainScheduleRule };
  fte: number;
  periodStart: Date;
  periodEnd: Date;
  publicHolidays: Date[];   // from country + metro city
  absenceDays: Date[];       // vacation, illness, other
}

interface SAHResult {
  grossWorkingDays: number;
  publicHolidayDays: number;
  absenceDays: number;
  netWorkingDays: number;
  effectiveHoursPerDay: number;
  standardAvailableHours: number;
}

function calculateSAH(input: SAHInput): SAHResult;
```

Spain schedule handling:

```typescript
interface SpainScheduleRule {
  type: 'spain';
  fridayHours: number;           // 6.5
  summerPeriod: { from: string; to: string }; // "07-01" to "09-15"
  summerHours: number;           // 6.5
  regularHours: number;          // 9.0
}

function getSpainDailyHours(date: Date, rule: SpainScheduleRule): number;
```

## Public Holidays

Phase 9 already has `computeEaster()` and `getPublicHolidays(year, state?)` for German states (Bavaria).
This needs extension:

- Move to a country-aware public holiday system
- Support metro city specific holidays (e.g. Munich Assumption Day)
- Seed known holidays per country from a reference table
- Admin UI to manage/override holidays per country+city

Existing Phase 9 German holiday logic becomes the "Germany" implementation within the broader system.

## FTE Monthly Tracking

The chargeability report shows FTE can vary by month per resource. Options:

1. **Simple:** Single `fte` field on Resource, changed when contract changes (current approach)
2. **Monthly:** `ResourceFTEHistory` model tracking FTE per month with effective date

Recommendation: Start with option 1 (single FTE field). Add history tracking as a follow-up if month-over-month FTE change reporting is needed. The current Resource model already has `fte`.

## UI Changes

### Admin: Country + Metro City Management

- `/admin/countries` page
- CRUD for countries with daily working hours and schedule rules
- Nested metro city management per country
- Seed data for the 8 known countries + their metro cities

### Resource: Country + Metro City Assignment

- `ResourceModal.tsx` gets Country dropdown (required) and Metro City dropdown (filtered by country)
- Auto-suggest metro city based on existing `postalCode` where possible

### Dashboard/Reports: SAH Display

- Resource detail page shows SAH for current period
- Chargeability report uses SAH as the denominator

## Migration

1. Create Country + MetroCity tables with seed data
2. Backfill existing resources: derive country from `federalState` (Germany) or leave null
3. Admin assigns countries to remaining resources

## Dependencies

- Public holiday system must be extended to all countries (not just German states)
- Vacation/absence system (Phase 9) feeds into SAH absence deduction
- Chargeability report (separate plan) consumes SAH as primary metric

## Acceptance Criteria

- [ ] Country model with daily working hours and optional schedule rules
- [ ] Metro City model linked to Country
- [ ] Resource linked to Country + Metro City
- [ ] SAH calculator in engine: `calculateSAH()` pure function
- [ ] Spain variable schedule correctly handled
- [ ] FTE reduces effective daily hours: `effectiveHours = dailyHours * fte`
- [ ] Public holidays extended beyond Germany to all 8 countries
- [ ] Admin UI for Country + Metro City CRUD
- [ ] Resource modal with Country + Metro City selection
- [ ] Seed data for all 8 countries and their metro cities
