feat: feature flag first commit (#14)

Author: dieppa

feature-flags/.gitignore

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+.gradle/
+build/
+!gradle/wrapper/gradle-wrapper.jar
+.idea/
+*.iml
+*.ipr
+*.iws
+out/
+.settings/
+.classpath
+.project
+bin/

feature-flags/.sdkmanrc

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+java=21-tem

feature-flags/Dockerfile

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+FROM gradle:8-jdk21 AS build
+WORKDIR /app
+COPY . .
+RUN gradle bootJar --no-daemon
+
+FROM eclipse-temurin:21-jre
+WORKDIR /app
+COPY --from=build /app/build/libs/*.jar app.jar
+ENTRYPOINT ["java", "-jar", "app.jar"]

feature-flags/README.md

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+# Feature Flags with Flamingock + Spring Boot + PostgreSQL
+
+A working example that builds a feature-flag service from scratch using [Flamingock](https://www.flamingock.io) to manage database schema evolution, Spring Boot for the REST API, and PostgreSQL as the backing store.
+
+## Prerequisites
+
+- Java 21 (use `sdk env` if you have [SDKMAN](https://sdkman.io/) installed)
+- Docker & Docker Compose
+
+## Quick Start
+
+```bash
+docker compose up --build
+```
+
+That's it. Postgres starts first (health-checked), then the app boots, Flamingock runs the migrations, and the API is live at `http://localhost:8080`.
+
+### Running locally (without Docker for the app)
+
+```bash
+# Start only Postgres
+docker compose up db -d
+
+# Run the app
+./gradlew bootRun
+```
+
+## API
+
+### Create a flag
+
+```bash
+curl -s -X POST localhost:8080/flags \
+  -H "Content-Type: application/json" \
+  -d '{"name":"dark-mode","description":"Dark mode UI"}'
+```
+
+### List all flags
+
+```bash
+curl -s localhost:8080/flags
+```
+
+### Update a flag (enable + set rollout %)
+
+```bash
+curl -s -X PUT localhost:8080/flags/dark-mode \
+  -H "Content-Type: application/json" \
+  -d '{"enabled":true,"rolloutPercentage":30}'
+```
+
+### Evaluate a flag for a user
+
+```bash
+curl -s "localhost:8080/flags/evaluate/dark-mode?userId=user-42"
+```
+
+Evaluation is deterministic — the same `userId` always lands in the same rollout bucket (SHA-256 hash).
+
+### Add a targeting rule
+
+```bash
+curl -s -X POST localhost:8080/flags/dark-mode/rules \
+  -H "Content-Type: application/json" \
+  -d '{"attribute":"plan","operator":"equals","value":"pro"}'
+```
+
+### Evaluate with attributes
+
+```bash
+curl -s "localhost:8080/flags/evaluate/dark-mode?userId=user-999&plan=pro"
+```
+
+When a targeting rule matches, the flag is enabled regardless of rollout percentage.
+
+### List rules for a flag
+
+```bash
+curl -s localhost:8080/flags/dark-mode/rules
+```
+
+## How Flamingock manages the schema
+
+Instead of `ddl-auto` or hand-written SQL scripts, Flamingock applies versioned, auditable changes at startup:
+
+| Change | What it does |
+|--------|-------------|
+| `_0001__CreateFlagsTable` | Creates the `feature_flags` table |
+| `_0002__AddRolloutPercentage` | Adds the `rollout_percentage` column |
+| `_0003__CreateTargetingRules` | Creates the `targeting_rules` table + index |
+
+Each change targets the `postgres-flags` SQL target system and receives a `java.sql.Connection` automatically. Flamingock tracks execution in its audit store so changes run exactly once, even across restarts.
+
+## Targeting rule operators
+
+| Operator | Behaviour |
+|----------|-----------|
+| `equals` | Exact string match |
+| `contains` | Substring match |
+| `in` | Comma-separated list membership |
+| `starts_with` | Prefix match |
+
+## Project structure
+
+```
+feature-flags/
+├── docker-compose.yml
+├── Dockerfile
+├── build.gradle
+├── settings.gradle
+└── src/main/java/com/example/flags/
+    ├── FeatureFlagApplication.java      # @EnableFlamingock entry point
+    ├── config/FlamingockConfig.java      # SqlTargetSystem + audit store beans
+    ├── changes/                          # Flamingock migrations
+    ├── model/                            # JPA entities
+    ├── repository/                       # Spring Data repositories
+    ├── service/EvaluationService.java    # Flag evaluation logic
+    └── controller/FlagController.java    # REST API
+```

feature-flags/build.gradle

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+plugins {
+    id 'java'
+    id 'org.springframework.boot' version '3.2.0'
+    id 'io.spring.dependency-management' version '1.1.4'
+    id 'io.flamingock' version '1.0.0'
+}
+
+flamingock {
+    community()
+    springboot()
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+repositories {
+    mavenLocal()
+    mavenCentral()
+}
+
+group = 'com.example'
+version = '1.0-SNAPSHOT'
+
+dependencies {
+    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
+    implementation 'org.springframework.boot:spring-boot-starter-web'
+    runtimeOnly 'org.postgresql:postgresql'
+}
+
+tasks.withType(JavaCompile).configureEach {
+    options.compilerArgs.add('-parameters')
+}

feature-flags/docker-compose.yml

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+volumes:
+  pgdata:
+
+services:
+  db:
+    image: postgres:16
+    environment:
+      POSTGRES_DB: flags
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+    ports:
+      - "5432:5432"
+    volumes:
+      - pgdata:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 5s
+      timeout: 5s
+      retries: 5
+
+  app:
+    build: .
+    ports:
+      - "8080:8080"
+    environment:
+      SPRING_DATASOURCE_URL: jdbc:postgresql://db:5432/flags
+      SPRING_DATASOURCE_USERNAME: postgres
+      SPRING_DATASOURCE_PASSWORD: postgres
+    depends_on:
+      db:
+        condition: service_healthy

feature-flags/gradle/wrapper/gradle-wrapper.jar

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+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-bin.zip
+networkTimeout=10000
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists