ExtendCaseClass.scala

package com.ncl.vacation.analytics.utils

import scala.language.experimental.macros
import scala.reflect.macros.blackbox
import scala.reflect.runtime.universe.typeOf

object ExtendCaseClass {

  def extendCaseClassImpl[T: c.WeakTypeTag](c: blackbox.Context)(additionalFields: c.Expr[Any]*): c.Expr[Any] = {
    import c.universe._

    // Extract the name of the base class
    val baseClassName = weakTypeOf[T].typeSymbol.name.toString

    // Extract fields
    val fields = weakTypeOf[T].decls.collectFirst {
      case m: MethodSymbol if m.isPrimaryConstructor => m.paramLists.headOption.getOrElse {
        c.abort(c.enclosingPosition, s"$baseClassName does not have a primary constructor with parameters.")
      }
    }.getOrElse {
      c.abort(c.enclosingPosition, s"$baseClassName does not have a primary constructor.")
    }

    val additionalFieldTrees = additionalFields.map(_.tree)

    // Generate field names and types from the original case class
    val originalFields = fields.map { sym =>
      q"val ${sym.name.toTermName}: ${sym.typeSignature}"
    }

    // Use the additional fields to create new field definitions
    // This assumes additional fields are passed as tuples of (String, Type)
    val newFields = additionalFieldTrees.map {
      case q"(${Literal(Constant(name: String))}, $tpe)" =>
        q"val ${TermName(name)}: $tpe"
    }

    val allFields = originalFields ++ newFields

    // Create a new case class with the desired name format
    val result = q"""
    case class ${TypeName(s"Extended$baseClassName")}(..$allFields)
  """

    c.Expr(result)
  }

  def extendCaseClass[T](additionalFields: Any*): Any = macro extendCaseClassImpl[T]


}


/*
lazy val macroProject = project
  .in(file("macro"))
  .settings(
    name := "macro-project",
    libraryDependencies ++= Seq(
      "org.scala-lang" % "scala-reflect" % scalaVersion.value
    )
  )

lazy val mainProject = project
  .in(file("."))
  .dependsOn(macroProject)
  .settings(
    name := "main-project"
  )


case class Person(name: String, age: Int)
extendCaseClass[Person](("address", typeOf[String]), ("phone", typeOf[Int]))
*/