# Technical Architecture

See the [Diagrams page](https://docs.emb.digital/books/rev-spain/page/diagrams) for the deployment diagram. See the [Functional Overview](https://docs.emb.digital/books/rev-spain/page/functional-overview) for goals, context, and users.

## 1. Building Block View

REV Spain is a monolith. Main internal modules:

- **Intake module** — claimant onboarding and document/data submission entry point
- **Extraction engine** — parses ITA and RNT documents (fixed-structure official Spanish government PDFs) using direct PDF text extraction (no OCR, since layout is standardized)
- **Unified.to adapter** — alternative ingestion path fetching employee/salary data directly from client HR/payroll systems
- **Project & employee allocation module** — gathers project information and maps employees to projects
- **Eligibility rules engine** — evaluates R&D tax credit eligibility criteria
- **Report generator** — produces both financial and technical claim reports
- **Access control** — role-based access for claimants, reviewers, and admins

## 2. Deployment View

### Stack

- Frontend: Vue.js 3 SPA
- Backend: Node.js / Express API
- Data & document storage: MongoDB, including GridFS for document storage (no separate object storage service)

### Topology

- **VM 1** — runs the full application stack via Docker Compose (frontend, API, MongoDB)
- **VM 2** — reverse proxy handling the domain name and TLS termination, forwarding to VM 1

This is a single-server deployment: no horizontal scaling or failover across app instances currently exists.

## 3. Risks & Technical Debt

- **Single point of failure** — the entire application stack (including the database) runs on one VM; no redundancy or failover.
- **No documented scaling path** — current architecture sits in tension with quality goals like fast data gathering and claims centralization at higher volume.
- **Shared storage engine** — MongoDB serves both transactional data and GridFS document storage; document I/O could contend with regular query load as usage grows.
- **External dependency** — the Unified.to ingestion path introduces availability dependency on a third party for one of the two data-gathering flows.
- **PII handling** — sensitive employee/salary data is processed directly by the core system in both ingestion paths; encryption, access control, and retention policies should be explicitly reviewed and documented.