Set up basic CI

.drone.yml

@@ -2,9 +2,80 @@ kind: pipeline
 type: docker
 name: default
 
+services:
+  - name: postgres
+    image: docker.io/library/postgres:17.2
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+
 steps:
-- name: greeting
-  image: alpine
-  commands:
-  - echo hello
-  - echo world
+  - name: restore_cache
+    # the `plugins` user seems to be owned by the drone organization
+    image: docker.io/plugins/cache:1.9
+    pull: true
+    settings:
+      backend: "filesystem"
+      restore: true
+      cache_key: "volume"
+      archive_format: "gzip"
+      # filesystem_cache_root: "/tmp/cache"
+      mount:
+        - "_build"
+    volumes:
+      - name: cache
+        path: /tmp/cache
+
+  - name: check
+    image: docker.io/library/elixir:1.18.3-otp-27
+    depends_on:
+      - restore_cache
+    commands:
+      # Install hex package manager
+      - mix local.hex --force
+      # Fetch dependencies
+      - mix deps.get
+      # Check for compilation errors & warnings
+      - mix compile --warnings-as-errors
+      # Check formatting
+      - mix format --check-formatted
+      # Security checks
+      - mix sobelow --config
+      # Check dependencies for known vulnerabilities
+      - mix deps.audit
+      # Check for dependencies that are not maintained anymore
+      - mix hex.audit
+      # Provide hints for improving code quality
+      - mix credo
+
+  - name: wait_for_postgres
+    image: docker.io/library/postgres:17.2
+    commands:
+      # Wait for postgres to become available
+      - |
+        for i in {1..20}; do
+          if pg_isready -h postgres -u postgres; then
+            exit 0
+          else
+            true
+          fi
+          sleep 2
+        done
+        echo "Postgres did not become available, aborting"
+        exit 1
+
+  - name: test
+    image: docker.io/library/elixir:1.18.3-otp-27
+    depends_on:
+      - restore_cache
+      # - wait_for_postgres
+    environment:
+      MIX_ENV: test
+      TEST_POSTGRES_HOST: postgres
+    commands:
+      # Install hex package manager
+      - mix local.hex --force
+      # Fetch dependencies
+      - mix deps.get
+      # Run tests
+      - mix test