Cache find baseline for an hour (#369)

The previous implementation required fetching the remote list of
releases before determining if the task was cacheable or not. This
caused rate limiting issues on GitHub (while this was in theory
the right thing to do).

To workaround limits, we're replacing the JSON input with a
timestamp corresponding to the current hour, so we'd fetch at most
once per hour.

src/main/java/io/micronaut/build/compat/FindBaselineTask.java

@@ -21,12 +21,15 @@
 import org.gradle.api.file.RegularFileProperty;
 import org.gradle.api.provider.Property;
 import org.gradle.api.provider.Provider;
+import org.gradle.api.provider.ProviderFactory;
 import org.gradle.api.tasks.CacheableTask;
 import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.Internal;
 import org.gradle.api.tasks.OutputFile;
 import org.gradle.api.tasks.TaskAction;
 import org.jetbrains.annotations.NotNull;
 
+import javax.inject.Inject;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.net.HttpURLConnection;
@@ -44,17 +47,32 @@
 
 @CacheableTask
 public abstract class FindBaselineTask extends DefaultTask {
+
+    public static final int CACHE_IN_SECONDS = 3600;
+
     @Input
     public abstract Property<String> getGithubSlug();
 
     @Input
     public abstract Property<String> getCurrentVersion();
 
     @Input
+    protected Provider<Long> getTimestamp() {
+        return getProviders().provider(() -> {
+            long seconds = System.currentTimeMillis() / 1000;
+            long base = seconds / CACHE_IN_SECONDS;
+            return base * CACHE_IN_SECONDS;
+        });
+    }
+
+    @Internal
     protected Provider<byte[]> getJson() {
         return getGithubSlug().map(this::fetchReleasesFromGitHub);
     }
 
+    @Inject
+    protected abstract ProviderFactory getProviders();
+
     private byte[] fetchReleasesFromGitHub(String slug) {
         String releasesUrl = "https://api.github.com/repos/" + normalizeSlug(slug) + "/releases";
         try {