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/* Magnolia, version 0.7.1. Copyright 2018 Jon Pretty, Propensive Ltd.
*
* The primary distribution site is: http://co.ntextu.al/
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the
* License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
* either express or implied. See the License for the specific language governing permissions
* and limitations under the License.
*/
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] = (s: String) => s
/** decodes ints */
implicit val int: Decoder[Int] = _.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] = value => {
val (_, 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] = param => {
val (name, _) = parse(param)
val subtype = ctx.subtypes.find(_.typeName.full == 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).toList
(label, value)
}
(name, parts(value.substring(end + 1, value.length - 1)).map(keyValue).toMap)
}
}
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