# GDPR Compliance and Data Archiving Strategy

**Status**: accepted

The application manages sensitive tenant files (identity cards, tax notices, payslips) and property condition photos. To comply with GDPR requirements and maintain a sustainable disk storage footprint over time, we have established a strict retention and image optimization policy.

## Decisions

### 1. Automated Server-Side Image Optimization

All uploaded photos (for property condition reports) are compressed and resized on the backend before write:

- Target resolution: maximum 1920x1080 pixels.
- Format: converted to WebP.
- Compression quality factor: 75-80%.
  This reduces average photo size from ~6.0 MB (raw smartphone camera) to ~250 KB (95.8% reduction).

### 2. GDPR Retention and Purging Cycle

- **Rejected Applicants**: Complete deletion of all submitted documents (payslips, identity documents) exactly 30 days after rejection.
- **Archived Leases**:
    - Upon lease termination, the lease transitions to an `Archived` state.
    - Personal identity documents and income proofs of the former tenants are permanently purged 3 years after lease termination (matching the 3-year French statute of limitations for residential tenancy disputes).
    - General inspection photos are purged 5 years after lease termination.
    - Basic accounting records (rent ledger, invoice amounts) are retained for 10 years to comply with commercial and tax record retention laws (Article L123-22 of the French Commercial Code).

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## Storage Projections (3-Apartment Portfolio over 10 Years)

Assuming an average lease turnover rate of 2 years (i.e., 1.5 lease cycles per year across a 3-apartment portfolio).

### Unit Data Footprints

| Data Type                      | Unoptimized Size        | Optimized Size          | Purge Trigger                  |
| :----------------------------- | :---------------------- | :---------------------- | :----------------------------- |
| **MongoDB Text Records**       | ~10 KB / year           | ~10 KB / year           | Never (10-year archive)        |
| **Tenant Personal Dossier**    | ~5.0 MB (PDF/Images)    | ~5.0 MB                 | Purged 3 years after lease end |
| **Inspection Photos (In/Out)** | ~360 MB (60 raw photos) | ~15 MB (WebP 1080p)     | Purged 5 years after lease end |
| **Invoices & Receipts / year** | ~20 MB (Raw scans)      | ~5 MB (Compressed PDFs) | Never (10-year archive)        |

### 10-Year Cumulative Footprint Comparison

#### Scenario A: Unoptimized & No Purge (Default Strategy)

- **Year 1**: 3 * (22 MB tenant docs + 360 MB photos) + 67 MB operational files = **1,213 MB (~1.2 GB)**.
- **Yearly Growth**: 67 MB (ops) + 1.5 * (22 MB tenant docs + 720 MB in/out photos) = **1,180 MB / year**.
- **Year 10 Cumulative Footprint**: **~11.8 GB** (Continuous, compounding growth).

#### Scenario B: Optimized & Purged (Our Design)

- **Year 1**: 3 * (5 MB tenant docs + 15 MB photos) + 15 MB operational files = **75 MB**.
- **Yearly Growth (Before Purges)**: 15 MB (ops) + 1.5 * (5 MB tenant docs + 30 MB in/out photos) = **67.5 MB / year**.
- **Purging Offsets**:
    - _From Year 4 onwards_: Purge of tenant dossiers of expired leases saves **7.5 MB / year** (1.5 leases * 5 MB).
    - _From Year 6 onwards_: Purge of inspection photos of expired leases saves **45.0 MB / year** (1.5 leases * 30 MB).
- **Year 10 Cumulative Footprint**: **~345 MB** (Stabilizes and plates out around 350 MB due to continuous purges).

This architecture saves over **97% of server disk space** over a 10-year lifecycle compared to a naive storage strategy, while strictly respecting French GDPR constraints.