Retrieving Changed Files from the encoded bucket

scripts/src/java/org/oppia/android/scripts/ci/RetrieveChangedFiles.kt

@@ -0,0 +1,50 @@
+package org.oppia.android.scripts.ci
+
+import org.oppia.android.scripts.common.ProtoStringEncoder.Companion.mergeFromCompressedBase64
+import org.oppia.android.scripts.proto.ChangedFilesBucket
+import java.io.File
+import kotlin.system.exitProcess
+
+/**
+ * The main entrypoint for retrieving the list of changed files from a particular encoded Base64
+ * bucket. This is used to parse the output from compute_changed_files.
+ *
+ * Usage:
+ *   bazel run //scripts:retrieve_changed_files -- \\
+ *     <encoded_proto_in_base64> <path_to_bucket_name_output_file> \\
+ *     <path_to_file_list_output_file>
+ *
+ * Arguments:
+ * - encoded_proto_in_base64: the compressed & Base64-encoded [ChangedFilesBucket] proto computed
+ *     by compute_changed_files.
+ * - path_to_bucket_name_output_file: path to the file where the file bucket name corresponding to
+ *     this bucket should be printed.
+ * - path_to_file_list_output_file: path to the file where the list of changed files
+ *     corresponding to this bucket should be printed.
+ *
+ * Example:
+ *   bazel run //scripts:retrieve_changed_files -- $CHANGED_FILES_BUCKETS_BASE64_ENCODED_PROTO \\
+ *     $(pwd)/file_bucket_name $(pwd)/changed_files
+ */
+fun main(args: Array<String>) {
+  if (args.size < 3) {
+    println(
+      "Usage: bazel run //scripts:retrieve_changed_files --" +
+        " <encoded_proto_in_base64> <path_to_bucket_name_output_file>" +
+        " <path_to_file_list_output_file>"
+    )
+    exitProcess(1)
+  }
+
+  val protoBase64 = args[0]
+  val bucketNameOutputFile = File(args[1])
+  val fileListOutputFile = File(args[2])
+  val changedFilesBucket =
+    ChangedFilesBucket.getDefaultInstance().mergeFromCompressedBase64(protoBase64)
+  bucketNameOutputFile.printWriter().use { writer ->
+    writer.println(changedFilesBucket.cacheBucketName)
+  }
+  fileListOutputFile.printWriter().use { writer ->
+    writer.println(changedFilesBucket.changedFilesList.joinToString(separator = " "))
+  }
+}