Add list of env variables to documentation

Issue: #1121

project/EnvConfig.scala

@@ -0,0 +1,75 @@
+import sbt._
+import com.typesafe.config._
+
+import scala.annotation.tailrec
+import scala.jdk.CollectionConverters._
+import java.util.{Map => JMap}
+
+object EnvConfig {
+  def serializeTo(cfg: Config, out: File): Unit =
+    IO.write(out, serialize(cfg))
+
+  def serialize(cfg: Config): String = {
+    val buffer = new StringBuilder
+    buffer.append("#### Server Configuration ####\n")
+    for (
+      entry <- cfg.entrySet().asScala.toList.sortBy(_.getKey)
+      if isValidKey("docspell.server", entry)
+    ) append(buffer, entry.getKey, entry.getValue)
+
+    buffer.append("\n#### JOEX Configuration ####\n")
+    for (
+      entry <- cfg.entrySet().asScala.toList.sortBy(_.getKey)
+      if isValidKey("docspell.joex", entry)
+    ) append(buffer, entry.getKey, entry.getValue)
+
+    buffer.toString().trim
+  }
+
+  private def append(buffer: StringBuilder, key: String, value: ConfigValue): Unit = {
+    if (value.origin().comments().asScala.nonEmpty) {
+      buffer.append("\n")
+    }
+    value
+      .origin()
+      .comments()
+      .forEach(c => buffer.append("# ").append(c).append("\n"))
+    buffer.append(keyToEnv(key)).append("=").append(value.render()).append("\n")
+  }
+
+  def isValidKey(prefix: String, entry: JMap.Entry[String, ConfigValue]): Boolean =
+    entry.getKey
+      .startsWith(prefix) && entry.getValue.valueType() != ConfigValueType.LIST
+
+  def makeConfig(files: List[File]): Config =
+    files
+      .foldLeft(ConfigFactory.empty()) { (cfg, file) =>
+        val cf = ConfigFactory.parseFile(file)
+        cfg.withFallback(cf)
+      }
+      .withFallback(ConfigFactory.defaultOverrides(getClass.getClassLoader))
+      .resolve()
+
+  def makeConfig(file: File, files: File*): Config =
+    makeConfig(file :: files.toList)
+
+  def keyToEnv(k: String): String = {
+    val buffer = new StringBuilder()
+    val len = k.length
+
+    @tailrec
+    def go(current: Int): String =
+      if (current >= len) buffer.toString()
+      else {
+        k.charAt(current) match {
+          case '.' => buffer.append("_")
+          case '-' => buffer.append("__")
+          case '_' => buffer.append("___")
+          case c   => buffer.append(c.toUpper)
+        }
+        go(current + 1)
+      }
+
+    go(0)
+  }
+}

project/build.sbt

@@ -0,0 +1,2 @@
+libraryDependencies ++=
+  Seq("com.typesafe" % "config" % "1.4.1")