diff --git a/build.gradle b/build.gradle
index da292bf..074819b 100644
--- a/build.gradle
+++ b/build.gradle
@@ -4,17 +4,13 @@ apply plugin: 'java'
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.lang.RuntimeException;
 import java.util.zip.GZIPInputStream;
 import java.util.zip.GZIPOutputStream;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-def workdir='build/unzip_boot'
-def defaultRootDir = workdir + "/root"
-String[] bins = [ "sh", "logcat", "logd", "linker", "toolbox", "toybox", "applypatch_static" ]
-String[] libs = [ "libdl.so", "libutils.so", "libc++.so", "libc.so", "libm.so", "libcutils.so", "libselinux.so", "liblog.so", "libpcre.so", "libsysutils.so", "libnl.so", "libbase.so", "libbacktrace.so", "libunwind.so" ]
-boolean gDebug=true
-
+// ----------------------------------------------------------------------------
 model {
     buildTypes {
         release
@@ -50,6 +46,26 @@ model {
     }
 }
 
+
+// ----------------------------------------------------------------------------
+//                       global
+// ----------------------------------------------------------------------------
+def workdir='build/unzip_boot'
+def defaultRootDir = workdir + "/root"
+String[] bins = [ "sh", "logcat", "logd", "linker", "toolbox", "toybox", "applypatch" ]
+String[] libs = [ "libdl.so", "libutils.so", "libc++.so", "libc.so", "libm.so", "libz.so", "libstdc++.so", "libcutils.so", "libselinux.so", "liblog.so", "libpcre.so", "libsysutils.so", "libnl.so", "libbase.so", "libbacktrace.so", "libunwind.so" ]
+boolean gDebug=true
+String activeImg = null;
+if (new File("boot.img").exists()) {
+    activeImg = "boot.img";
+} else if (new File("recovery.img").exists()) {
+    activeImg = "recovery.img";
+}
+println("Active image target: " + activeImg);
+
+// ----------------------------------------------------------------------------
+//                       tasks
+// ----------------------------------------------------------------------------
 task unpack_bootimg(type: Exec, dependsOn: 'abootimgExecutable') {
     doFirst {
         def rootdir = new File(workdir)
@@ -60,7 +76,7 @@ task unpack_bootimg(type: Exec, dependsOn: 'abootimgExecutable') {
     }
     workingDir '.'
     executable 'build/exe/abootimg/abootimg'
-    args = ['-x', 'boot.img', workdir+'/bootimg.cfg', workdir+'/kernel', workdir+'/ramdisk.img.gz']
+    args = ['-x', activeImg, workdir+'/bootimg.cfg', workdir+'/kernel', workdir+'/ramdisk.img.gz']
 }
 
 task unpack_ramdisk_gz << {
@@ -82,8 +98,9 @@ task unpack_cpio(type: Exec, dependsOn: unpack_ramdisk_gz) {
 }
 
 task unpack(type: Delete, dependsOn: unpack_cpio) {
-  delete workdir + "/ramdisk.img.gz"
-  delete workdir + "/ramdisk.img"
+    description "extract boot.img or recovery.img"
+    delete workdir + "/ramdisk.img.gz"
+    delete workdir + "/ramdisk.img"
 }
 
 task pack_ramdisk_and_gz { Task task ->
@@ -123,10 +140,7 @@ task pack_clear(type: Exec, dependsOn: [pack_ramdisk_and_gz, 'mkbootimgExecutabl
         '--ramdisk', workdir + "/ramdisk.img.gz",
         '--cmdline', theCmdLine,
         '--base', theBaseAddr,
-        '--output', 'boot.img.clear']
-}
-if (!new File(workdir + "/bootimg.cfg").exists()) {
-    pack_clear.enabled = false;
+        '--output', activeImg + '.clear']
 }
 
 void unGnuzipFile(String compressedFile, String decompressedFile) throws IOException {
@@ -226,7 +240,7 @@ task pack(type: JavaExec, dependsOn: [pack_clear, 'boot_signer:jar']) {
     main = 'com.android.verity.BootSignature'
     classpath = files("boot_signer/build/libs/boot_signer.jar")
     maxHeapSize '512m'
-    args '/boot','boot.img.clear', 'security/verity.pk8', 'security/verity.x509.pem', 'boot.img.signed'
+    args '/boot', activeImg + '.clear', 'security/verity.pk8', 'security/verity.x509.pem', activeImg + '.signed'
 }
 
 task _setup(type: Copy) {
@@ -271,12 +285,20 @@ void RunFunc(String inCmd, String inWorkdir = null) {
 }
 
 void updateBootImage() {
-    String flashTarget = "/dev/block/by-name/" + System.getProperty("img", "boot")
+    String flashTarget = null;
+    switch (activeImg) {
+        case "boot.img":
+            flashTarget = "/dev/block/by-name/boot";
+            break;
+        case "recovery.img":
+            flashTarget = "/dev/block/by-name/recovery";
+            break;
+    }
     Run("adb root")
-    Run("adb push boot.img.signed /cache/")
-    List<String> cmd2 = ["adb", "shell", "dd if=/cache/boot.img.signed of=" + flashTarget];
+    Run("adb push " + activeImg + ".signed /cache/")
+    List<String> cmd2 = ["adb", "shell", "dd if=/cache/" + activeImg + ".signed of=" + flashTarget];
     Run(cmd2)
-    cmd2 = ["adb", "shell", "rm -f /cache/boot.img.signed"];
+    cmd2 = ["adb", "shell", "rm -f /cache/" + activeImg + ".signed"];
     Run(cmd2)
 }
 
@@ -312,7 +334,7 @@ void updateLinks(String inWorkdir) {
 }
 
 task debug(dependsOn: ['addSystemBin', 'addSystemLib']) {
-    description "add debug tools into recovery rootfs"
+    description "add debug tools into recovery rootfs from ANDROID_PRODUCT_OUT"
     doLast {
         updateLinks(workdir);
     }
@@ -342,3 +364,18 @@ boolean inTargetList(String file, String[] inArray) {
     }
     return false;
 }
+
+// ----------------------------------------------------------------------------
+//                      post configs
+// ----------------------------------------------------------------------------
+if (null == activeImg) {
+    pack.enabled = false
+    unpack.enabled = false
+    unpack_cpio.enabled = false
+    unpack_bootimg.enabled = false
+    unpack_ramdisk_gz.enabled = false
+}
+
+if (!new File(workdir + "/bootimg.cfg").exists()) {
+    pack_clear.enabled = false;
+}