# Rewrite Architecture Decisions

**Status:**
- proposed: 2026-07-07
- accepted: 2026-07-07
- rejected: -
- superseded: partially on 2026-07-07 — the "no managed nginx/TLS" part is revised by ADR 0005 (opt-in managed nginx/TLS container for hosts without a reverse proxy)

**Decision [accepted, nginx part revised by ADR 0005]:** JSON-file persistence behind a repository interface, server-rendered UI with JSON polling, no managed nginx/TLS by default — deployment via systemd user unit behind the host's reverse proxy.

## Context and Problem Statement

The rewrite of `legacy/werkator` (bash) as a Kotlin/Spring application (see `docs/plan/`) required several cross-cutting architecture decisions.
They were proposed in `docs/plan/README.md`, validated step by step during implementation, and are summarized here as one record.

### Technical Background

The legacy script kept all state in TSV/HTML files, patched its web UI with regex rewrites, and managed its own nginx+certbot Docker container.
Its two structural defects — build status not observable during a build, and a web UI that could get stuck loading forever — had to be fixed by design, not by patching.

## Considered Options

* Database persistence (SQLite) vs. JSON files behind a repository interface
* SPA frontend or server push (WebSocket/SSE) vs. server-rendered HTML with JSON polling
* Managed nginx/Let's Encrypt container vs. documented deployment behind an existing reverse proxy

### Persistence: JSON files behind `BuildResultRepository`

Build results are persisted as a JSON file under `.git/werkator/`, accessed only through the `BuildResultRepository` interface.

#### Advantages

- No database dependency, no schema migrations; state stays inspectable with a text editor, like legacy.
- The volume is tiny (retention prunes per branch), so file rewrites are cheap.
- The interface keeps a later switch to SQLite possible without touching callers.

#### Disadvantages

- No queries or transactions; concurrent writers must be serialized in-process.

### Web UI: server-rendered Thymeleaf plus JSON polling

Pages render the full state server-side; one hand-written JavaScript file polls JSON endpoints and re-renders table bodies.

#### Advantages

- No SPA framework and no frontend build pipeline.
- Fixes the legacy stuck-spinner defect by design: every fetch has a timeout and an explicit error badge, and status transitions are event-driven and observable while a build runs.
- Pages stay useful without JavaScript (initial render is complete).

#### Disadvantages

- Updates are only as fresh as the polling interval; no server push.

### Deployment: no managed nginx, systemd user unit instead

nginx/Let's Encrypt container management was not ported; `init --systemd` generates a user unit running `java -jar werkator.jar server`, and `docs/deployment.md` documents the reverse-proxy setup with the host's certbot.

#### Advantages

- Removes the largest and most brittle legacy subsystem (container lifecycle, certificate renewal, config templating).
- Hosts usually already run a web server with TLS; one `server` block suffices.
- The generated unit replaces the legacy self-copy/self-update machinery with plain jar deployment.

#### Disadvantages

- HTTPS setup is a manual, host-specific step outside werkator's control.

## Decision Outcome

All three proposals from the plan were confirmed during implementation and are in force:

- JSON-file persistence behind `BuildResultRepository` (steps 01, 05, 06).
- Server-rendered HTML with polling JSON endpoints and explicit error states (steps 07–09).
- No nginx management; systemd user unit plus reverse-proxy documentation (step 12).

Related, previously decided in the same spirit: external systems are accessed by shelling out to the `git` and `docker` CLIs instead of SDK dependencies (steps 02, 11).