package h4

import scala.language.experimental.macros
import scala.reflect.macros.blackbox.Context

abstract class Expression
case class Var(name: String) extends Expression
case class Number(num: Double) extends Expression
case class BinOp(operator: String, left: Expression, right: Expression) extends Expression


class ExpressionImplicitsImpl(val c: Context) {
  import c.universe._

  def getExpr(tree: Tree): Tree = {
    return tree match {
      case Ident(TermName(name)) => q"""Var(${name})"""
      case Literal(Constant(name: Int)) => q"""Number($name)"""
      case Literal(Constant(name: Double)) => q"""Number($name)"""
      case Apply(Select(left, operator), List(right)) => q"""BinOp(${operator.toString()}, ${getExpr(left)}, ${getExpr(right)})"""
      case _ => throw new UnsupportedOperationException()
    }
  }

  def expr(exprTree: c.Expr[AnyRef]): c.Expr[Expression] = {
    val e = exprTree.tree match {
      case Function(params, tree) => getExpr(tree)
      case _ => throw new Exception("Not supported.")
    }
    return c.Expr[Expression](e)
  }
}

object ExpressionImplicits {
  def expr(exprTree: AnyRef): Expression = macro ExpressionImplicitsImpl.expr
}