Fixes smallrye#274. Added interceptor to activate a Configuration Pro…

…file.

doc/modules/ROOT/pages/interceptors/interceptors.adoc

@@ -41,6 +41,7 @@ interceptors are registered with the same priority, then their execution order m
 SmallRye Config provides the following built-in Interceptors:
 
 * <<expression-interceptor>>
+* <<profile-interceptor>>
 
 [[expression-interceptor]]
 === ExpressionConfigSourceInterceptor
@@ -68,3 +69,23 @@ If an expression cannot be expanded and no default is supplied a `NoSuchElementE
 
 The `ExpressionConfigSourceInterceptor` is not registered by default. You need to register it via the ServiceLoader
 mechanism with your application.
+
+[[profile-interceptor]]
+=== ProfileConfigSourceInterceptor
+
+The `ProfileConfigSourceInterceptor` allows you to have multiple configurations with the same name and select them via
+a profile property.
+
+To be able to set properties with the same name, you need to prefix each property with `%` followed by the profile name
+and a dot:
+
+[source,properties]
+----
+my.prop=1234
+%dev.my.prop=5678
+----
+
+Lookup is always done using the `my.prop` property name. If you want to use the profile `dev`, you need to set the
+configuration `smallrye.config.profile=dev` into any valid ConfigSource.
+
+Only one profile can be active in any given time.

implementation/src/main/java/io/smallrye/config/ConfigSourceInterceptor.java

@@ -2,6 +2,8 @@
 
 import java.io.Serializable;
 
+import org.eclipse.microprofile.config.Config;
+
 /**
  * The ConfigSourceInterceptor allows you to intercept the resolution of a configuration key name before the
  * configuration value is resolved by the Config.
@@ -18,6 +20,15 @@
  * order may be non deterministic.
  */
 public interface ConfigSourceInterceptor extends Serializable {
+    /**
+     * This method initializes the interceptor, with access to the current Config object. This allows to
+     * configure the interceptor using configurations retrieved from the Config.
+     *
+     * @param config the current {@code Config} associated to the interceptor.
+     */
+    default void initialize(Config config) {
+    }
+
     /**
      * Single method to intercept the resolution of a configuration key. Calling
      * {@link ConfigSourceInterceptorContext#proceed(String)} will proceed executing the interceptor chain. The chain

implementation/src/main/java/io/smallrye/config/ProfileConfigSourceInterceptor.java

@@ -0,0 +1,39 @@
+package io.smallrye.config;
+
+import javax.annotation.Priority;
+
+import org.eclipse.microprofile.config.Config;
+
+@Priority(600)
+public class ProfileConfigSourceInterceptor implements ConfigSourceInterceptor {
+    public static final String SMALLRYE_PROFILE = "smallrye.config.profile";
+
+    private String profile;
+
+    public ProfileConfigSourceInterceptor() {
+
+    }
+
+    public ProfileConfigSourceInterceptor(final String profile) {
+        this.profile = profile;
+    }
+
+    @Override
+    public void initialize(final Config config) {
+        if (profile == null) {
+            profile = config.getOptionalValue(SMALLRYE_PROFILE, String.class).orElse(null);
+        }
+    }
+
+    @Override
+    public ConfigValue getValue(final ConfigSourceInterceptorContext context, final String name) {
+        if (profile != null) {
+            final ConfigValue profileValue = context.proceed("%" + profile + "." + name);
+            if (profileValue != null) {
+                return profileValue;
+            }
+        }
+
+        return context.proceed(name);
+    }
+}

implementation/src/main/java/io/smallrye/config/SmallRyeConfig.java

@@ -71,16 +71,19 @@ public int compare(ConfigSource o1, ConfigSource o2) {
 
     SmallRyeConfig(SmallRyeConfigBuilder builder) {
         this.configSourcesRef = buildConfigSources(builder);
-        this.interceptorChain = buildInterceptorChain(builder);
         this.converters = buildConverters(builder);
+
+        final List<ConfigSourceInterceptor> interceptors = buildInterceptors(builder);
+        this.interceptorChain = buildInterceptorChain(interceptors);
+        initInterceptors(interceptors);
     }
 
     @Deprecated
     protected SmallRyeConfig(List<ConfigSource> configSources, Map<Type, Converter<?>> converters) {
         this.configSourcesRef = new AtomicReference<>(Collections.unmodifiableList(configSources));
         this.converters = new ConcurrentHashMap<>(Converters.ALL_CONVERTERS);
         this.converters.putAll(converters);
-        this.interceptorChain = buildInterceptorChain(new SmallRyeConfigBuilder());
+        this.interceptorChain = buildInterceptorChain(new ArrayList<>());
     }
 
     private AtomicReference<List<ConfigSource>> buildConfigSources(final SmallRyeConfigBuilder builder) {
@@ -124,7 +127,7 @@ private Map<Type, Converter<?>> buildConverters(final SmallRyeConfigBuilder buil
         return converters;
     }
 
-    private ConfigSourceInterceptorContext buildInterceptorChain(final SmallRyeConfigBuilder builder) {
+    private List<ConfigSourceInterceptor> buildInterceptors(final SmallRyeConfigBuilder builder) {
         final List<ConfigSourceInterceptor> interceptors = new ArrayList<>(builder.getInterceptors());
         if (builder.isAddDiscoveredInterceptors()) {
             interceptors.addAll(builder.discoverInterceptors());
@@ -139,6 +142,10 @@ private ConfigSourceInterceptorContext buildInterceptorChain(final SmallRyeConfi
             return Integer.compare(p2, p1);
         });
 
+        return interceptors;
+    }
+
+    private ConfigSourceInterceptorContext buildInterceptorChain(final List<ConfigSourceInterceptor> interceptors) {
         SmallRyeConfigSourceInterceptorContext current = new SmallRyeConfigSourceInterceptorContext(
                 (ConfigSourceInterceptor) (context, name) -> {
                     for (ConfigSource configSource : getConfigSources()) {
@@ -170,6 +177,12 @@ private ConfigSourceInterceptorContext buildInterceptorChain(final SmallRyeConfi
         return current;
     }
 
+    private void initInterceptors(final List<ConfigSourceInterceptor> interceptors) {
+        for (ConfigSourceInterceptor interceptor : interceptors) {
+            interceptor.initialize(this);
+        }
+    }
+
     // no @Override
     public <T, C extends Collection<T>> C getValues(String name, Class<T> itemClass, IntFunction<C> collectionFactory) {
         return getValues(name, getConverter(itemClass), collectionFactory);

implementation/src/test/java/io/smallrye/config/ProfileConfigSourceInterceptorTest.java

@@ -0,0 +1,48 @@
+package io.smallrye.config;
+
+import static io.smallrye.config.ProfileConfigSourceInterceptor.SMALLRYE_PROFILE;
+import static org.junit.Assert.assertEquals;
+
+import org.eclipse.microprofile.config.Config;
+import org.junit.Test;
+
+public class ProfileConfigSourceInterceptorTest {
+    @Test
+    public void profile() {
+        final Config config = buildConfig("my.prop", "1", "%prof.my.prop", "2", SMALLRYE_PROFILE, "prof");
+
+        assertEquals("2", config.getValue("my.prop", String.class));
+    }
+
+    @Test
+    public void fallback() {
+        final Config config = buildConfig("my.prop", "1", SMALLRYE_PROFILE, "prof");
+
+        assertEquals("1", config.getValue("my.prop", String.class));
+    }
+
+    @Test
+    public void expressions() {
+        final Config config = buildConfig("my.prop", "1", "%prof.my.prop", "${my.prop}", SMALLRYE_PROFILE, "prof");
+
+        assertEquals("1", config.getValue("my.prop", String.class));
+    }
+
+    @Test
+    public void profileExpressions() {
+        final Config config = buildConfig("my.prop", "1",
+                "%prof.my.prop", "${%prof.my.prop.profile}",
+                "%prof.my.prop.profile", "2",
+                SMALLRYE_PROFILE, "prof");
+
+        assertEquals("2", config.getValue("my.prop", String.class));
+    }
+
+    private static Config buildConfig(String... keyValues) {
+        return new SmallRyeConfigBuilder()
+                .addDefaultSources()
+                .withSources(KeyValuesConfigSource.config(keyValues))
+                .withInterceptors(new ProfileConfigSourceInterceptor(), new ExpressionConfigSourceInterceptor())
+                .build();
+    }
+}