# Membership Contributions - Technical Architecture

**Project:** Mila - Membership Management System  
**Feature:** Membership Contribution Management  
**Version:** 1.0  
**Last Updated:** 2025-11-27  
**Status:** Architecture Design - Ready for Implementation

---

## Purpose

This document defines the technical architecture for the Membership Contributions system. It focuses on architectural decisions, patterns, module structure, and integration points **without** concrete implementation details.

**Related Documents:**
- [contributions-overview.md](./contributions-overview.md) - Business logic and requirements
- [database-schema-readme.md](./database-schema-readme.md) - Database documentation
- [database_schema.dbml](./database_schema.dbml) - Database schema definition

---

## Table of Contents

1. [Architecture Principles](#architecture-principles)
2. [Domain Structure](#domain-structure)
3. [Data Architecture](#data-architecture)
4. [Business Logic Architecture](#business-logic-architecture)
5. [Integration Points](#integration-points)
6. [Acceptance Criteria](#acceptance-criteria)
7. [Testing Strategy](#testing-strategy)
8. [Security Considerations](#security-considerations)
9. [Performance Considerations](#performance-considerations)

---

## Architecture Principles

### Core Design Decisions

1. **Single Responsibility:**
   - Each module has one clear responsibility
   - Period generation separated from status management
   - Calendar logic isolated in dedicated module

2. **No Redundancy:**
   - No `period_end` field (calculated from `period_start` + `interval`)
   - No `interval_type` field (read from `contribution_type.interval`)
   - Eliminates data inconsistencies

3. **Immutability Where Important:**
   - `contribution_type.interval` cannot be changed after creation
   - Prevents complex migration scenarios
   - Enforced via Ash change validation

4. **Historical Accuracy:**
   - `amount` stored per period for audit trail
   - Enables tracking of contribution changes over time
   - Old periods retain original amounts

5. **Calendar-Based Periods:**
   - All periods aligned to calendar boundaries
   - Simplifies date calculations
   - Predictable period generation

---

## Domain Structure

### Ash Domain: `Mv.Contributions`

**Purpose:** Encapsulates all contribution-related resources and logic

**Resources:**
- `ContributionType` - Contribution type definitions (admin-managed)
- `ContributionPeriod` - Individual contribution periods per member

**Extensions:**
- Member resource extended with contribution fields

### Module Organization

```
lib/
├── contributions/
│   ├── contributions.ex              # Ash domain definition
│   ├── contribution_type.ex          # ContributionType resource
│   ├── contribution_period.ex        # ContributionPeriod resource
│   └── changes/
│       ├── prevent_interval_change.ex       # Validates interval immutability
│       ├── set_contribution_start_date.ex   # Auto-sets start date
│       └── validate_same_interval.ex        # Validates interval match on type change
├── mv/
│   └── contributions/
│       ├── period_generator.ex              # Period generation algorithm
│       └── calendar_periods.ex              # Calendar period calculations
└── membership/
    └── member.ex                     # Extended with contribution relationships
```

### Separation of Concerns

**Domain Layer (Ash Resources):**
- Data validation
- Relationship management
- Policy enforcement
- Action definitions

**Business Logic Layer (`Mv.Contributions`):**
- Period generation algorithm
- Calendar calculations
- Date boundary handling
- Status transitions

**UI Layer (LiveView):**
- User interaction
- Display logic
- Authorization checks
- Form handling

---

## Data Architecture

### Database Schema Extensions

**See:** [database-schema-readme.md](./database-schema-readme.md) and [database_schema.dbml](./database_schema.dbml) for complete schema documentation.

### New Tables

1. **`contribution_types`**
   - Purpose: Define contribution types with fixed intervals
   - Key Constraint: `interval` field immutable after creation
   - Relationships: has_many members, has_many contribution_periods

2. **`contribution_periods`**
   - Purpose: Individual contribution periods for members
   - Key Design: NO `period_end` or `interval_type` fields (calculated)
   - Relationships: belongs_to member, belongs_to contribution_type
   - Composite uniqueness: One period per member per period_start

### Member Table Extensions

**Fields Added:**
- `contribution_type_id` (FK, NOT NULL with default from settings)
- `contribution_start_date` (Date, nullable)

**Existing Fields Used:**
- `joined_at` - For calculating contribution start
- `left_at` - For limiting period generation

### Settings Integration

**Global Settings:**
- `contributions.include_joining_period` (Boolean)
- `contributions.default_contribution_type_id` (UUID)

**Storage:** Existing settings mechanism (TBD: dedicated table or configuration resource)

### Foreign Key Behaviors

| Relationship | On Delete | Rationale |
|--------------|-----------|-----------|
| `contribution_periods.member_id → members.id` | CASCADE | Remove periods when member deleted |
| `contribution_periods.contribution_type_id → contribution_types.id` | RESTRICT | Prevent type deletion if periods exist |
| `members.contribution_type_id → contribution_types.id` | RESTRICT | Prevent type deletion if assigned to members |

---

## Business Logic Architecture

### Period Generation System

**Component:** `Mv.Contributions.PeriodGenerator`

**Responsibilities:**
- Calculate which periods should exist for a member
- Generate missing periods
- Respect contribution_start_date and left_at boundaries
- Skip existing periods (idempotent)

**Triggers:**
1. Member contribution type assigned (via Ash change)
2. Member created with contribution type (via Ash change)
3. Scheduled job runs (daily/weekly cron)
4. Admin manual regeneration (UI action)

**Algorithm Steps:**
1. Retrieve member with contribution_type and dates
2. Determine first period start (based on contribution_start_date)
3. Calculate all period starts from first to today (or left_at)
4. Query existing periods for member
5. Generate missing periods with current contribution_type.amount
6. Insert new periods (batch operation)

**Edge Case Handling:**
- If contribution_start_date is NULL: Calculate from joined_at + global setting
- If left_at is set: Stop generation at left_at
- If contribution_type changes: Handled separately by regeneration logic

### Calendar Period Calculations

**Component:** `Mv.Contributions.CalendarPeriods`

**Responsibilities:**
- Calculate period boundaries based on interval type
- Determine current period
- Determine last completed period
- Calculate period_end from period_start + interval

**Functions (high-level):**
- `calculate_period_start/3` - Given date and interval, find period start
- `calculate_period_end/2` - Given period_start and interval, calculate end
- `next_period_start/2` - Given period_start and interval, find next
- `is_current_period?/2` - Check if period contains today
- `is_last_completed_period?/2` - Check if period just ended

**Interval Logic:**
- **Monthly:** Start = 1st of month, End = last day of month
- **Quarterly:** Start = 1st of quarter (Jan/Apr/Jul/Oct), End = last day of quarter
- **Half-yearly:** Start = 1st of half (Jan/Jul), End = last day of half
- **Yearly:** Start = Jan 1st, End = Dec 31st

### Status Management

**Component:** Ash actions on `ContributionPeriod`

**Status Transitions:**
- Simple state machine: unpaid ↔ paid ↔ suspended
- No complex validation (all transitions allowed)
- Permissions checked via Ash policies

**Actions Required:**
- `mark_as_paid` - Set status to :paid
- `mark_as_suspended` - Set status to :suspended  
- `mark_as_unpaid` - Set status to :unpaid (error correction)

**Bulk Operations:**
- `bulk_mark_as_paid` - Mark multiple periods as paid (efficiency)

### Contribution Type Change Handling

**Component:** Ash change on `Member.contribution_type_id`

**Validation:**
- Check if new type has same interval as old type
- If different: Reject change (MVP constraint)
- If same: Allow change

**Side Effects on Allowed Change:**
1. Keep all existing periods unchanged
2. Find future unpaid periods
3. Delete future unpaid periods
4. Regenerate periods with new contribution_type_id and amount

**Implementation Pattern:**
- Use Ash change module to validate
- Use after_action hook to trigger regeneration
- Use transaction to ensure atomicity

---

## Integration Points

### Member Resource Integration

**Extension Points:**
1. Add fields via migration
2. Add relationships (belongs_to, has_many)
3. Add calculations (current_period_status, overdue_count)
4. Add changes (auto-set contribution_start_date, validate interval)

**Backward Compatibility:**
- New fields nullable or with defaults
- Existing members get default contribution type from settings
- No breaking changes to existing member functionality

### Settings System Integration

**Requirements:**
- Store two global settings
- Provide UI for admin to modify
- Default values if not set
- Validation (e.g., default_contribution_type_id must exist)

**Access Pattern:**
- Read settings during period generation
- Read settings during member creation
- Write settings only via admin UI

### Permission System Integration

**See:** [roles-and-permissions-architecture.md](./roles-and-permissions-architecture.md)

**Required Permissions:**
- `ContributionType.create/update/destroy` - Admin only
- `ContributionType.read` - Admin, Treasurer, Board
- `ContributionPeriod.update` (status changes) - Admin, Treasurer
- `ContributionPeriod.read` - Admin, Treasurer, Board, Own member

**Policy Patterns:**
- Use existing HasPermission check
- Leverage existing roles (Admin, Kassenwart)
- Member can read own periods (linked via member_id)

### LiveView Integration

**New LiveViews Required:**
1. ContributionType index/form (admin)
2. ContributionPeriod table component (member detail view)
3. Settings form section (admin)
4. Member list column (contribution status)

**Existing LiveViews to Extend:**
- Member detail view: Add contributions section
- Member list view: Add status column
- Settings page: Add contributions section

**Authorization Helpers:**
- Use existing `can?/3` helper for UI conditionals
- Check permissions before showing actions

---

## Acceptance Criteria

### ContributionType Resource

**AC-CT-1:** Admin can create contribution type with name, amount, interval, description  
**AC-CT-2:** Interval field is immutable after creation (validation error on change attempt)  
**AC-CT-3:** Admin can update name, amount, description (but not interval)  
**AC-CT-4:** Cannot delete contribution type if assigned to members  
**AC-CT-5:** Cannot delete contribution type if periods exist referencing it  
**AC-CT-6:** Interval must be one of: monthly, quarterly, half_yearly, yearly

### ContributionPeriod Resource

**AC-CP-1:** Period has period_start, status, amount, notes, member_id, contribution_type_id  
**AC-CP-2:** Period_end is calculated, not stored  
**AC-CP-3:** Status defaults to :unpaid  
**AC-CP-4:** One period per member per period_start (uniqueness constraint)  
**AC-CP-5:** Amount is set at generation time from contribution_type.amount  
**AC-CP-6:** Periods cascade delete when member deleted  
**AC-CP-7:** Admin/Treasurer can change status  
**AC-CP-8:** Member can read own periods

### Member Extensions

**AC-M-1:** Member has contribution_type_id field (NOT NULL with default)  
**AC-M-2:** Member has contribution_start_date field (nullable)  
**AC-M-3:** New members get default contribution type from global setting  
**AC-M-4:** contribution_start_date auto-set based on joined_at and global setting  
**AC-M-5:** Admin can manually override contribution_start_date  
**AC-M-6:** Cannot change to contribution type with different interval (MVP)

### Period Generation

**AC-PG-1:** Periods generated when member gets contribution type  
**AC-PG-2:** Periods generated when member created (via change hook)  
**AC-PG-3:** Scheduled job generates missing periods daily  
**AC-PG-4:** Generation respects contribution_start_date  
**AC-PG-5:** Generation stops at left_at if member exited  
**AC-PG-6:** Generation is idempotent (skips existing periods)  
**AC-PG-7:** Periods align to calendar boundaries (1st of month/quarter/half/year)  
**AC-PG-8:** Amount comes from contribution_type at generation time

### Calendar Logic

**AC-CL-1:** Monthly periods: 1st to last day of month  
**AC-CL-2:** Quarterly periods: 1st of Jan/Apr/Jul/Oct to last day of quarter  
**AC-CL-3:** Half-yearly periods: 1st of Jan/Jul to last day of half  
**AC-CL-4:** Yearly periods: Jan 1 to Dec 31  
**AC-CL-5:** Period_end calculated correctly for all interval types  
**AC-CL-6:** Current period determined correctly based on today's date  
**AC-CL-7:** Last completed period determined correctly

### Contribution Type Change

**AC-TC-1:** Can change to type with same interval  
**AC-TC-2:** Cannot change to type with different interval (error message)  
**AC-TC-3:** On allowed change: future unpaid periods regenerated  
**AC-TC-4:** On allowed change: paid/suspended periods unchanged  
**AC-TC-5:** On allowed change: amount updated to new type's amount  
**AC-TC-6:** Change is atomic (transaction)

### Settings

**AC-S-1:** Global setting: include_joining_period (boolean, default true)  
**AC-S-2:** Global setting: default_contribution_type_id (UUID, required)  
**AC-S-3:** Admin can modify settings via UI  
**AC-S-4:** Settings validated (e.g., default type must exist)  
**AC-S-5:** Settings applied to new members immediately

### UI - Member List

**AC-UI-ML-1:** New column shows contribution status  
**AC-UI-ML-2:** Default: Shows last completed period status  
**AC-UI-ML-3:** Optional: Toggle to show current period status  
**AC-UI-ML-4:** Color coding: green (paid), red (unpaid), gray (suspended)  
**AC-UI-ML-5:** Filter: Unpaid in last period  
**AC-UI-ML-6:** Filter: Unpaid in current period

### UI - Member Detail

**AC-UI-MD-1:** Contributions section shows all periods  
**AC-UI-MD-2:** Table columns: Period, Interval, Amount, Status, Actions  
**AC-UI-MD-3:** Checkbox per period for bulk marking  
**AC-UI-MD-4:** "Mark selected as paid" button  
**AC-UI-MD-5:** Dropdown to change contribution type (same interval only)  
**AC-UI-MD-6:** Warning if different interval selected  
**AC-UI-MD-7:** Only show actions if user has permission

### UI - Contribution Types Admin

**AC-UI-CTA-1:** List all contribution types  
**AC-UI-CTA-2:** Show: Name, Amount, Interval, Member count  
**AC-UI-CTA-3:** Create new contribution type form  
**AC-UI-CTA-4:** Edit form: Name, Amount, Description editable  
**AC-UI-CTA-5:** Edit form: Interval grayed out (not editable)  
**AC-UI-CTA-6:** Warning on amount change (explain impact)  
**AC-UI-CTA-7:** Cannot delete if members assigned  
**AC-UI-CTA-8:** Only admin can access

### UI - Settings Admin

**AC-UI-SA-1:** Contributions section in settings  
**AC-UI-SA-2:** Dropdown to select default contribution type  
**AC-UI-SA-3:** Checkbox: Include joining period  
**AC-UI-SA-4:** Explanatory text with examples  
**AC-UI-SA-5:** Save button with validation

---

## Testing Strategy

### Unit Testing

**Period Generator Tests:**
- Correct period_start calculation for all interval types
- Correct period count from start to end date
- Respects contribution_start_date boundary
- Respects left_at boundary
- Skips existing periods (idempotent)
- Handles edge dates (year boundaries, leap years)

**Calendar Periods Tests:**
- Period boundaries correct for all intervals
- Period_end calculation correct
- Current period detection
- Last completed period detection
- Next period calculation

**Validation Tests:**
- Interval immutability enforced
- Same interval validation on type change
- Status transitions allowed
- Uniqueness constraints enforced

### Integration Testing

**Period Generation Flow:**
- Member creation triggers generation
- Type assignment triggers generation
- Type change regenerates future periods
- Scheduled job generates missing periods
- Left member stops generation

**Status Management Flow:**
- Mark single period as paid
- Bulk mark multiple periods
- Status transitions work
- Permissions enforced

**Contribution Type Management:**
- Create type
- Update amount (regeneration triggered)
- Cannot update interval
- Cannot delete if in use

### LiveView Testing

**Member List:**
- Status column displays correctly
- Toggle between last/current works
- Filters work correctly
- Color coding applied

**Member Detail:**
- Periods table displays all periods
- Checkboxes work
- Bulk marking works
- Type change validation works
- Actions only shown with permission

**Admin UI:**
- Type CRUD works
- Settings save correctly
- Validations display errors
- Only authorized users can access

### Edge Case Testing

**Interval Change Attempt:**
- Error message displayed
- No data modified
- User can cancel/choose different type

**Exit with Unpaid:**
- Warning shown
- Option to suspend offered
- Exit completes correctly

**Amount Change:**
- Warning displayed
- Only future unpaid regenerated
- Historical periods unchanged

**Date Boundaries:**
- Today = period start handled
- Today = period end handled
- Leap year handled

### Performance Testing

**Period Generation:**
- Generate 10 years of monthly periods: < 100ms
- Generate for 1000 members: < 5 seconds
- Idempotent check efficient (no full scan)

**Member List Query:**
- With status column: < 200ms for 1000 members
- Filters applied efficiently
- No N+1 queries

---

## Security Considerations

### Authorization

**Permissions Required:**
- ContributionType management: Admin only
- ContributionPeriod status changes: Admin + Treasurer
- View all periods: Admin + Treasurer + Board
- View own periods: All authenticated users

**Policy Enforcement:**
- All actions protected by Ash policies
- UI shows/hides based on permissions
- Backend validates permissions (never trust UI alone)

### Data Integrity

**Validation Layers:**
1. Database constraints (NOT NULL, UNIQUE, CHECK)
2. Ash validations (business rules)
3. UI validations (user experience)

**Immutability Protection:**
- Interval change prevented at multiple layers
- Period amounts immutable (audit trail)
- Settings changes logged (future)

### Audit Trail

**Tracked Information:**
- Period status changes (who, when) - future enhancement
- Type amount changes (implicit via period amounts)
- Member type assignments (via timestamps)

---

## Performance Considerations

### Database Indexes

**Required Indexes:**
- `contribution_periods(member_id)` - For member period lookups
- `contribution_periods(contribution_type_id)` - For type queries
- `contribution_periods(status)` - For unpaid filters
- `contribution_periods(period_start)` - For date range queries
- `contribution_periods(member_id, period_start)` - Composite unique index
- `members(contribution_type_id)` - For type membership count

### Query Optimization

**Preloading:**
- Load contribution_type with periods (avoid N+1)
- Load periods when displaying member detail
- Use Ash's load for efficient preloading

**Calculated Fields:**
- period_end calculated on-demand (not stored)
- current_period_status calculated when needed
- Use Ash calculations for lazy evaluation

**Pagination:**
- Period list paginated if > 50 periods
- Member list already paginated

### Caching Strategy

**No caching needed in MVP:**
- Contribution types rarely change
- Period queries are fast
- Settings read infrequently

**Future caching if needed:**
- Cache settings in application memory
- Cache contribution types list
- Invalidate on change

### Scheduled Job Performance

**Period Generation Job:**
- Run daily or weekly (not hourly)
- Batch members (process 100 at a time)
- Skip members with no changes
- Log failures for retry

---

## Future Enhancements

### Phase 2: Interval Change Support

**Architecture Changes:**
- Add logic to handle period overlaps
- Calculate prorata amounts if needed
- More complex validation
- Migration path for existing periods

### Phase 3: Payment Details

**Architecture Changes:**
- Add PaymentTransaction resource
- Link transactions to periods
- Support multiple payments per period
- Reconciliation logic

### Phase 4: vereinfacht.digital Integration

**Architecture Changes:**
- External API client module
- Webhook handling for transactions
- Automatic matching logic
- Manual review interface

---

**End of Architecture Document**