---
phase: 03-postgresql-support
plan: "02"
subsystem: wiring
tags: [postgresql, sqlite, database, docker-compose, branching]
dependency_graph:
  requires: [03-01]
  provides: [DATABASE_URL branching, postgres docker profile, NewTestPostgresServer]
  affects: [cmd/diunwebhook/main.go, compose.yml, compose.dev.yml, pkg/diunwebhook/diunwebhook.go]
tech_stack:
  added: []
  patterns: [DATABASE_URL env var branching, Docker Compose profiles, build-tagged test helpers]
key_files:
  created:
    - pkg/diunwebhook/postgres_test.go
  modified:
    - cmd/diunwebhook/main.go
    - pkg/diunwebhook/diunwebhook.go
    - compose.yml
    - compose.dev.yml
decisions:
  - "DATABASE_URL present activates PostgreSQL path; absent falls back to SQLite with DB_PATH"
  - "postgres Docker service uses profiles: [postgres] so default compose up remains SQLite-only"
  - "UNIQUE detection uses strings.ToLower for case-insensitive matching across SQLite and PostgreSQL"
  - "Build tag //go:build postgres gates postgres_test.go so standard test runs have no pgx dependency"
metrics:
  duration: "~2 minutes"
  completed: "2026-03-24T08:13:21Z"
  tasks_completed: 2
  files_changed: 5
---

# Phase 03 Plan 02: Wire PostgreSQL Support and Deployment Infrastructure Summary

DATABASE_URL branching in main.go routes to PostgresStore or SQLiteStore at startup; Docker Compose postgres profile enables optional PostgreSQL; build-tagged test helper and cross-dialect UNIQUE detection complete the integration.

## What Was Built

### Updated main.go (cmd/diunwebhook/main.go)
- `DATABASE_URL` env var check: when set, opens pgx connection, runs `RunPostgresMigrations`, creates `NewPostgresStore`, logs `"Using PostgreSQL database"`
- When absent: existing SQLite path using `RunSQLiteMigrations` (renamed in Plan 01), `NewSQLiteStore`, logs `"Using SQLite database at {path}"`
- Blank import `_ "github.com/jackc/pgx/v5/stdlib"` registers the `"pgx"` driver name
- All route wiring and graceful shutdown logic unchanged

### Cross-dialect UNIQUE detection (pkg/diunwebhook/diunwebhook.go)
- `TagsHandler` now uses `strings.Contains(strings.ToLower(err.Error()), "unique")` for 409 Conflict detection
- SQLite errors: `UNIQUE constraint failed: tags.name` (uppercase UNIQUE)
- PostgreSQL errors: `duplicate key value violates unique constraint "tags_name_key"` (lowercase unique)
- Both backends now return 409 correctly

### Docker Compose postgres profiles
- `compose.yml`: postgres service added with `profiles: [postgres]`, healthcheck via `pg_isready`, `DATABASE_URL` env var in app service, conditional `depends_on` with `required: false`, `postgres-data` volume
- `compose.dev.yml`: same postgres service with port 5432 exposed on host for direct psql access during development
- Default `docker compose up` (no profile) unchanged — SQLite only, no new services start

### Build-tagged test helper (pkg/diunwebhook/postgres_test.go)
- `//go:build postgres` tag — only compiled with `go test -tags postgres`
- `NewTestPostgresServer()` constructs a `*Server` backed by PostgreSQL using `TEST_DATABASE_URL` env var (defaults to `postgres://diun:diun@localhost:5432/diundashboard_test?sslmode=disable`)
- Calls `RunPostgresMigrations` and `NewPostgresStore` — mirrors the production startup path

## Decisions Made

| Decision | Rationale |
|----------|-----------|
| DATABASE_URL presence-check (not a separate DB_DRIVER var) | Simpler UX; empty string = SQLite, any value = PostgreSQL |
| profiles: [postgres] in compose files | Standard Docker Compose pattern for optional services; default deploy unchanged |
| required: false in depends_on | App can start without postgres service (SQLite fallback); Docker Compose v2.20+ required |
| //go:build postgres tag on test helper | Prevents pgx import at test time for standard `go test ./...` runs; explicit opt-in |
| strings.ToLower for UNIQUE check | SQLite and PostgreSQL use different cases in constraint error messages |

## Deviations from Plan

None — plan executed exactly as written. The `export_test.go` rename (RunMigrations -> RunSQLiteMigrations) was already completed as a deviation in Plan 01, as noted in the objective.

## Verification Results

- `go build ./...` exits 0
- `go test -count=1 ./pkg/diunwebhook/` passes (all 20+ SQLite tests, postgres_test.go skipped)
- `docker compose config` validates without errors
- `docker compose --profile postgres config` shows postgres service
- `grep -c "DATABASE_URL" cmd/diunwebhook/main.go` returns 1
- `grep "strings.ToLower" pkg/diunwebhook/diunwebhook.go` shows case-insensitive UNIQUE check

## Known Stubs

None — this plan wires implementation code, no UI stubs.

## Self-Check: PASSED