Enable Travis CI to auto-deploy APKs

The resulting APK of a CI build is now automatically uploaded to GitHub
for tagged revisions. They are signed with the same key that is used in
the Google Play Store. All secrets are encrypted and only visible to
Travis CI.

.travis.yml

@@ -1,4 +1,13 @@
 language: android
+
+env:
+  global:
+    # ORG_GRADLE_PROJECT_keystorePassword.
+    - secure: "TGGsl0Jdc6cKt0dHarl6/YobzOZTxtxGCSZiwDPZn2Qe2IAUb8JssvTviOkCtbXQesdjcHuvpVlG70Yz0sISxTanwJI6yRMmqAOm6mfr1bVvcaeFIXXEm1s8q8rQfHxOv0BTMxLQ2MdYkz6MteTOcn722e0NEs+lh73aSbCi0Os="
+
+    # ORG_GRADLE_PROJECT_keystoreKeyPassword.
+    - secure: "KbIFt5KMY6sMLsMtYQDbHUX8MtYQSY+6Lj9qc+jJdTAukc2qAtJLNyXKKQlG5pyoSN/F/hVBJKbmDDz2AY6ifMZkOpzVVKlN8E2MPG1BCln0BwMJactL1kLb+287oFg6tXDc6YoxImeKlpFMucy2RjeWwtZptmbsUiXT2UwhPn8="
+
 android:
   components:
     # Specify the components that are needed to build the project.
@@ -16,14 +25,39 @@ android:
     - extra-google-m2repository
     - extra-android-m2repository
 
+before_script:
+  # Decrypts the keystore (if this is not a PR build).
+  - 'if [ ${TRAVIS_SECURE_ENV_VARS} = "true" ]; then
+       openssl aes-256-cbc -d
+         -K $encrypted_d213628fe2b0_key -iv $encrypted_d213628fe2b0_iv
+         -in keystores/warmshowers.jks.enc -out "$HOME/warmshowers.jks" &&
+       export ORG_GRADLE_PROJECT_keystoreFile="$HOME/warmshowers.jks";
+     fi'
+
+  # Sets the (public) keystore settings.
+  - export ORG_GRADLE_PROJECT_keystoreKeyAlias="wsandroid"
 
 before_cache:
-  # Clean up the cache.
-  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
-  - rm -fR $HOME/.gradle/caches/*/plugin-resolution/
+  # Cleans up the cache.
+  - rm -f  "$HOME/.gradle/caches/modules-2/modules-2.lock"
+  - rm -fR "$HOME/.gradle/caches/*/plugin-resolution/"
+  - rm -f  "$HOME/warmshowers.jks"
 
 cache:
   directories:
-    - $HOME/.android/build-cache
-    - $HOME/.gradle/caches/
-    - $HOME/.gradle/wrapper/
+    - "$HOME/.android/build-cache"
+    - "$HOME/.gradle/caches/"
+    - "$HOME/.gradle/wrapper/"
+
+before_deploy:
+  - mv app/build/outputs/apk/app-release.apk wsandroid-$TRAVIS_TAG.apk
+
+deploy:
+  # Deploys the release APK for tagged revisions to GitHub.
+  provider: releases
+  api_key:
+    secure: "dIzw4tJxXLPlA7wDdcgwLop6qcAU9lPTD4Z322APx6430Pevx93o6u8H6vnNMPytbpL4kpsxQjsqe+gz3DLB5vSUmftn0UF5GrjJTxNCeSj0wxW5kgeb2iuw4UsjpoI1FOroN0FxOg+CJUoD27MRwjjl4S9NnEVYmbcj9+8O8f4="
+  file: "wsandroid-$TRAVIS_TAG.apk"
+  skip_cleanup: true
+  on:
+    tags: true

app/build.gradle

@@ -36,13 +36,6 @@ dependencies {
     testCompile 'org.json:json:20170516'
 }
 
-
-def propertiesFile = rootProject.file("local.properties")
-def properties = new Properties()
-if (propertiesFile.canRead()) {
-    properties.load(new FileInputStream(propertiesFile))
-}
-
 android {
     buildToolsVersion "26.0.0"
 
@@ -57,14 +50,14 @@ android {
         }
 
         release {
-            if (properties['keystoreFile']) {
+            if (keystoreFile) {
                 doSignRelease = true
 
-                // Set these values in local.properties
-                storeFile file(properties['keystoreFile'])
-                storePassword properties['keystorePassword']
-                keyAlias properties['keyAlias']
-                keyPassword properties['keyPassword']
+                // Set these values in local.properties.
+                storeFile file(keystoreFile)
+                storePassword keystorePassword
+                keyAlias keystoreKeyAlias
+                keyPassword keystoreKeyPassword
             }
         }
     }

build.gradle

@@ -25,6 +25,16 @@ ext {
     isPreDexEnabled = "true".equals(System.getProperty("pre-dex", "true"))
 }
 
+// Loads the local properties.
+def localPropertiesFile = rootProject.file("local.properties")
+if (localPropertiesFile.canRead()) {
+    def localProperties = new Properties()
+    localProperties.load(new FileInputStream(localPropertiesFile))
+    localProperties.stringPropertyNames().each {
+        project.ext[it] = localProperties[it]
+    }
+}
+
 task clean(type: Delete) {
     delete rootProject.buildDir
 }