Read config from environment variables

The application configuration should be read from command line options
as well as from environment variables. The priority: cmd-line over env
over defaults.

Change-Id: I785fd1fbaf66f3eab84a162f037153f1688ed791
Issue-ID: DCAEGEN2-748
Signed-off-by: Piotr Jaszczyk <piotr.jaszczyk@nokia.com>

3 files changed, 26 insertions, 3 deletions

diff --git a/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/arrow/core.kt b/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/arrow/core.kt
index 844d18d8..2d538b72 100644
--- a/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/arrow/core.kt
+++ b/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/arrow/core.kt
@@ -20,8 +20,12 @@
 package org.onap.dcae.collectors.veshv.utils.arrow
 
 import arrow.core.Either
+import arrow.core.None
 import arrow.core.Option
+import arrow.core.Some
 import arrow.core.identity
+import arrow.syntax.collections.firstOption
+import java.util.*
 import java.util.concurrent.atomic.AtomicReference
 
 /**
@@ -32,3 +36,11 @@ import java.util.concurrent.atomic.AtomicReference
 fun <A> Either<A, A>.flatten() = fold(::identity, ::identity)
 
 fun <A> AtomicReference<A>.getOption() = Option.fromNullable(get())
+
+fun <A> Option.Companion.fromNullablesChain(firstValue: A?, vararg nextValues: () -> A?): Option<A> =
+        if (firstValue != null)
+            Option.just(firstValue)
+        else nextValues.asSequence()
+                .map { it() }
+                .filter { it != null }
+                .firstOption()
diff --git a/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/ArgBasedConfiguration.kt b/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/ArgBasedConfiguration.kt
index 16634889..1ebe4e48 100644
--- a/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/ArgBasedConfiguration.kt
+++ b/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/ArgBasedConfiguration.kt
@@ -27,6 +27,7 @@ import arrow.core.getOrElse
 import org.apache.commons.cli.CommandLine
 import org.apache.commons.cli.CommandLineParser
 import org.apache.commons.cli.Options
+import org.onap.dcae.collectors.veshv.utils.arrow.fromNullablesChain
 import java.io.File
 import java.nio.file.Path
 import java.nio.file.Paths
@@ -77,6 +78,7 @@ abstract class ArgBasedConfiguration<T>(private val parser: CommandLineParser) {
 
     protected fun stringPathToPath(path: String): Path = Paths.get(File(path).toURI())
 
-    private fun CommandLine.optionValue(cmdLineOpt: CommandLineOption): Option<String> =
-            Option.fromNullable(getOptionValue(cmdLineOpt.option.opt))
+    private fun CommandLine.optionValue(cmdLineOpt: CommandLineOption) = Option.fromNullablesChain(
+            getOptionValue(cmdLineOpt.option.opt),
+            { System.getenv(cmdLineOpt.environmentVariableName()) })
 }
diff --git a/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/CommandLineOption.kt b/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/CommandLineOption.kt
index 836a05df..3a154db2 100644
--- a/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/CommandLineOption.kt
+++ b/hv-collector-utils/src/main/kotlin/org/onap/dcae/collectors/veshv/utils/commandline/CommandLineOption.kt
@@ -117,5 +117,14 @@ enum class CommandLineOption(val option: Option) {
             .longOpt("dummy")
             .desc("If present will start in dummy mode (dummy external services)")
             .build()
-    ),
+    );
+
+    fun environmentVariableName(prefix: String = DEFAULT_ENV_PREFIX): String =
+            option.longOpt.toUpperCase().replace('-', '_').let { mainPart ->
+                "${prefix}_${mainPart}"
+            }
+
+    companion object {
+        private const val DEFAULT_ENV_PREFIX = "VESHV"
+    }
 }