Apply SDK vars simplification

apply plugin: 'com.android.library'

def _ext = rootProject.ext

def _reactNativeVersion = _ext.has('reactNative') ? _ext.reactNative : '+'

def _compileSdkVersion = _ext.has('compileSdkVersion') ? _ext.compileSdkVersion : 27

def _buildToolsVersion = _ext.has('buildToolsVersion') ? _ext.buildToolsVersion : '27.0.3'

def _minSdkVersion = _ext.has('minSdkVersion') ? _ext.minSdkVersion : 16

def _targetSdkVersion = _ext.has('targetSdkVersion') ? _ext.targetSdkVersion : 27

def safeExtGet(prop, fallback) {

    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback

}

android {

    compileSdkVersion _compileSdkVersion

    buildToolsVersion _buildToolsVersion

    compileSdkVersion safeExtGet('compileSdkVersion', 27)

    buildToolsVersion safeExtGet('buildToolsVersion', '27.0.3')

    defaultConfig {

        minSdkVersion _minSdkVersion

        targetSdkVersion _targetSdkVersion

        minSdkVersion safeExtGet('minSdkVersion', 16)

        targetSdkVersion safeExtGet('targetSdkVersion', 27)

        versionCode 1

        versionName "1.0"

    }

dependencies {

    //noinspection GradleDynamicVersion

    provided "com.facebook.react:react-native:${_reactNativeVersion}"

    provided "com.facebook.react:react-native:${safeExtGet('reactNativeVersion', '+')}"

    compile 'com.google.android.exoplayer:exoplayer:2.7.3'

    compile('com.google.android.exoplayer:extension-okhttp:2.7.3') {

        exclude group: 'com.squareup.okhttp3', module: 'okhttp'