1 files changed, 79 insertions, 0 deletions
diff --git a/examples/shared/src/main/scala/decode.scala b/examples/shared/src/main/scala/decode.scala
new file mode 100644
index 0000000..5b083bd
--- /dev/null
+++ b/examples/shared/src/main/scala/decode.scala
@@ -0,0 +1,79 @@
+package magnolia.examples
+
+import magnolia._
+import scala.language.experimental.macros
+
+/** very basic decoder for converting strings to other types */
+trait Decoder[T] { def decode(str: String): T }
+
+/** derivation object (and companion object) for [[Decoder]] instances */
+object Decoder {
+
+  /** decodes strings */
+  implicit val string: Decoder[String] = new Decoder[String] {
+    def decode(str: String): String = str
+  }
+
+  /** decodes ints */
+  implicit val int: Decoder[Int] = new Decoder[Int] { def decode(str: String): Int = str.toInt }
+
+  /** binds the Magnolia macro to this derivation object */
+  implicit def gen[T]: Decoder[T] = macro Magnolia.gen[T]
+
+  /** type constructor for new instances of the typeclass */
+  type Typeclass[T] = Decoder[T]
+
+  /** defines how new [[Decoder]]s for case classes should be constructed */
+  def combine[T](ctx: CaseClass[Decoder, T]): Decoder[T] = new Decoder[T] {
+    def decode(value: String) = {
+      val (name, values) = parse(value)
+      ctx.construct { param =>
+        param.typeclass.decode(values(param.label))
+      }
+    }
+  }
+
+  /** defines how to choose which subtype of the sealed trait to use for decoding */
+  def dispatch[T](ctx: SealedTrait[Decoder, T]): Decoder[T] = new Decoder[T] {
+    def decode(param: String) = {
+      val (name, values) = parse(param)
+      val subtype = ctx.subtypes.find(_.label == name).get
+      subtype.typeclass.decode(param)
+    }
+  }
+
+  /** very simple extractor for grabbing an entire parameter value, assuming matching parentheses */
+  private def parse(value: String): (String, Map[String, String]) = {
+    val end = value.indexOf('(')
+    val name = value.substring(0, end)
+
+    def parts(value: String,
+              idx: Int = 0,
+              depth: Int = 0,
+              collected: List[String] = List("")): List[String] = {
+      def plus(char: Char): List[String] = collected.head + char :: collected.tail
+
+      if (idx == value.length) collected
+      else
+        value(idx) match {
+          case '(' =>
+            parts(value, idx + 1, depth + 1, plus('('))
+          case ')' =>
+            if (depth == 1) plus(')')
+            else parts(value, idx + 1, depth - 1, plus(')'))
+          case ',' =>
+            if (depth == 0) parts(value, idx + 1, depth, "" :: collected)
+            else parts(value, idx + 1, depth, plus(','))
+          case char =>
+            parts(value, idx + 1, depth, plus(char))
+        }
+    }
+
+    def keyValue(str: String): (String, String) = {
+      val List(label, value) = str.split("=", 2).to[List]
+      (label, value)
+    }
+
+    (name, parts(value.substring(end + 1, value.length - 1)).map(keyValue).toMap)
+  }
+}