add feature flags to jinjava config

src/main/java/com/hubspot/jinjava/JinjavaConfig.java

@@ -23,6 +23,8 @@
 import com.hubspot.jinjava.el.JinjavaObjectUnwrapper;
 import com.hubspot.jinjava.el.JinjavaProcessors;
 import com.hubspot.jinjava.el.ObjectUnwrapper;
+import com.hubspot.jinjava.features.FeatureConfig;
+import com.hubspot.jinjava.features.Features;
 import com.hubspot.jinjava.interpret.Context;
 import com.hubspot.jinjava.interpret.Context.Library;
 import com.hubspot.jinjava.interpret.InterpreterFactory;
@@ -80,6 +82,8 @@ public class JinjavaConfig {
   private final boolean enablePreciseDivideFilter;
   private final ObjectMapper objectMapper;
 
+  private final Features features;
+
   private final ObjectUnwrapper objectUnwrapper;
   private final JinjavaProcessors processors;
 
@@ -140,6 +144,7 @@ private JinjavaConfig(Builder builder) {
     objectMapper = setupObjectMapper(builder.objectMapper);
     objectUnwrapper = builder.objectUnwrapper;
     processors = builder.processors;
+    features = new Features(builder.featureConfig);
   }
 
   private ObjectMapper setupObjectMapper(@Nullable ObjectMapper objectMapper) {
@@ -288,6 +293,10 @@ public DateTimeProvider getDateTimeProvider() {
     return dateTimeProvider;
   }
 
+  public Features getFeatures() {
+    return features;
+  }
+
   public static class Builder {
     private Charset charset = StandardCharsets.UTF_8;
     private Locale locale = Locale.ENGLISH;
@@ -322,6 +331,7 @@ public static class Builder {
 
     private ObjectUnwrapper objectUnwrapper = new JinjavaObjectUnwrapper();
     private JinjavaProcessors processors = JinjavaProcessors.newBuilder().build();
+    private FeatureConfig featureConfig = FeatureConfig.newBuilder().build();
 
     private Builder() {}
 
@@ -508,6 +518,11 @@ public Builder withProcessors(JinjavaProcessors jinjavaProcessors) {
       return this;
     }
 
+    public Builder withFeatureConfig(FeatureConfig featureConfig) {
+      this.featureConfig = featureConfig;
+      return this;
+    }
+
     public JinjavaConfig build() {
       return new JinjavaConfig(this);
     }

src/main/java/com/hubspot/jinjava/features/DateTimeFeatureActivationStrategy.java

@@ -0,0 +1,25 @@
+package com.hubspot.jinjava.features;
+
+import com.hubspot.jinjava.interpret.Context;
+import java.time.LocalDateTime;
+
+public class DateTimeFeatureActivationStrategy implements FeatureActivationStrategy {
+  private final LocalDateTime activateAt;
+
+  public static DateTimeFeatureActivationStrategy of(LocalDateTime activateAt) {
+    return new DateTimeFeatureActivationStrategy(activateAt);
+  }
+
+  private DateTimeFeatureActivationStrategy(LocalDateTime activateAt) {
+    this.activateAt = activateAt;
+  }
+
+  @Override
+  public boolean isActive(Context context) {
+    return LocalDateTime.now().isAfter(activateAt);
+  }
+
+  public LocalDateTime getActivateAt() {
+    return activateAt;
+  }
+}

src/main/java/com/hubspot/jinjava/features/FeatureActivationStrategy.java

@@ -0,0 +1,7 @@
+package com.hubspot.jinjava.features;
+
+import com.hubspot.jinjava.interpret.Context;
+
+public interface FeatureActivationStrategy {
+  boolean isActive(Context context);
+}

src/main/java/com/hubspot/jinjava/features/FeatureConfig.java

@@ -0,0 +1,34 @@
+package com.hubspot.jinjava.features;
+
+import com.google.common.collect.ImmutableMap;
+import java.util.HashMap;
+import java.util.Map;
+
+public class FeatureConfig {
+  Map<String, FeatureActivationStrategy> features;
+
+  private FeatureConfig(Map<String, FeatureActivationStrategy> features) {
+    this.features = ImmutableMap.copyOf(features);
+  }
+
+  public FeatureActivationStrategy getFeature(String name) {
+    return features.getOrDefault(name, FeatureStrategies.INACTIVE);
+  }
+
+  public static FeatureConfig.Builder newBuilder() {
+    return new Builder();
+  }
+
+  public static class Builder {
+    private final Map<String, FeatureActivationStrategy> features = new HashMap<>();
+
+    public Builder add(String name, FeatureActivationStrategy strategy) {
+      features.put(name, strategy);
+      return this;
+    }
+
+    public FeatureConfig build() {
+      return new FeatureConfig(features);
+    }
+  }
+}

src/main/java/com/hubspot/jinjava/features/FeatureStrategies.java

@@ -0,0 +1,6 @@
+package com.hubspot.jinjava.features;
+
+public class FeatureStrategies {
+  public static final FeatureActivationStrategy INACTIVE = c -> false;
+  public static final FeatureActivationStrategy ACTIVE = c -> true;
+}

src/main/java/com/hubspot/jinjava/features/Features.java

@@ -0,0 +1,19 @@
+package com.hubspot.jinjava.features;
+
+import com.hubspot.jinjava.interpret.Context;
+
+public class Features {
+  private final FeatureConfig featureConfig;
+
+  public Features(FeatureConfig featureConfig) {
+    this.featureConfig = featureConfig;
+  }
+
+  public boolean isActive(String featureName, Context context) {
+    return getActivationStrategy(featureName).isActive(context);
+  }
+
+  public FeatureActivationStrategy getActivationStrategy(String featureName) {
+    return featureConfig.getFeature(featureName);
+  }
+}

src/test/java/com/hubspot/jinjava/FeaturesTest.java

@@ -0,0 +1,74 @@
+package com.hubspot.jinjava;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.hubspot.jinjava.features.DateTimeFeatureActivationStrategy;
+import com.hubspot.jinjava.features.FeatureConfig;
+import com.hubspot.jinjava.features.FeatureStrategies;
+import com.hubspot.jinjava.features.Features;
+import com.hubspot.jinjava.interpret.Context;
+import java.time.LocalDateTime;
+import org.junit.Before;
+import org.junit.Test;
+
+public class FeaturesTest {
+  private static final String ALWAYS_OFF = "alwaysOff";
+  private static final String ALWAYS_ON = "alwaysOn";
+  private static final String DATE_PAST = "datePast";
+  private static final String DATE_FUTURE = "dateFuture";
+  private static final String DELEGATING = "delegating";
+
+  private Features features;
+
+  private boolean delegateActive = false;
+
+  private Context context = new Context();
+
+  @Before
+  public void setUp() throws Exception {
+    features =
+      new Features(
+        FeatureConfig
+          .newBuilder()
+          .add(ALWAYS_OFF, FeatureStrategies.INACTIVE)
+          .add(ALWAYS_ON, FeatureStrategies.ACTIVE)
+          .add(DATE_PAST, DateTimeFeatureActivationStrategy.of(LocalDateTime.MIN))
+          .add(DATE_FUTURE, DateTimeFeatureActivationStrategy.of(LocalDateTime.MAX))
+          .add(DELEGATING, d -> delegateActive)
+          .build()
+      );
+  }
+
+  @Test
+  public void itHasEnabledFeature() {
+    assertThat(features.isActive(ALWAYS_ON, context)).isTrue();
+  }
+
+  @Test
+  public void itDoesNotHaveDisabledFeature() {
+    assertThat(features.isActive(ALWAYS_OFF, context)).isFalse();
+  }
+
+  @Test
+  public void itHasPastEnabledFeature() {
+    assertThat(features.isActive(DATE_PAST, context)).isTrue();
+  }
+
+  @Test
+  public void itDoesNotHaveFutureEnabledFeature() {
+    assertThat(features.isActive(DATE_FUTURE, context)).isFalse();
+  }
+
+  @Test
+  public void itUsesDelegate() {
+    delegateActive = false;
+    assertThat(features.isActive(DELEGATING, context)).isEqualTo(delegateActive);
+    delegateActive = true;
+    assertThat(features.isActive(DELEGATING, context)).isEqualTo(delegateActive);
+  }
+
+  @Test
+  public void itDefaultsToFalse() {
+    assertThat(features.isActive("unknown", context)).isFalse();
+  }
+}