/* NSC -- new Scala compiler
 * Copyright 2005-2011 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala.reflect
package api

import scala.reflect.base.TreeCreator

trait Exprs { self: Universe =>

  /** An expression tree tagged with its type */
  trait Expr[+T] extends Equals with Serializable {
    val mirror: Mirror
    def in[U <: Universe with Singleton](otherMirror: MirrorOf[U]): U # Expr[T]

    def tree: Tree
    def staticTpe: Type
    def actualTpe: Type

    def splice: T
    val value: T

    /** case class accessories */
    override def canEqual(x: Any) = x.isInstanceOf[Expr[_]]
    override def equals(x: Any) = x.isInstanceOf[Expr[_]] && this.mirror == x.asInstanceOf[Expr[_]].mirror && this.tree == x.asInstanceOf[Expr[_]].tree
    override def hashCode = mirror.hashCode * 31 + tree.hashCode
    override def toString = "Expr["+staticTpe+"]("+tree+")"
  }

  object Expr {
    def apply[T: TypeTag](mirror: MirrorOf[self.type], treec: TreeCreator): Expr[T] = new ExprImpl[T](mirror.asInstanceOf[Mirror], treec)
    def unapply[T](expr: Expr[T]): Option[Tree] = Some(expr.tree)
  }

  private class ExprImpl[+T: TypeTag](val mirror: Mirror, val treec: TreeCreator) extends Expr[T] {
    def in[U <: Universe with Singleton](otherMirror: MirrorOf[U]): U # Expr[T] = {
      val otherMirror1 = otherMirror.asInstanceOf[MirrorOf[otherMirror.universe.type]]
      val tag1 = (implicitly[TypeTag[T]] in otherMirror).asInstanceOf[otherMirror.universe.TypeTag[T]]
      otherMirror.universe.Expr[T](otherMirror1, treec)(tag1)
    }

    lazy val tree: Tree = treec[Exprs.this.type](mirror)
      // [Eugene++] this is important
      // !!! remove when we have improved type inference for singletons
      // search for .type] to find other instances
    lazy val staticTpe: Type = implicitly[TypeTag[T]].tpe
    def actualTpe: Type = tree.tpe

    def splice: T = throw new UnsupportedOperationException("""
      |the function you're calling has not been spliced by the compiler.
      |this means there is a cross-stage evaluation involved, and it needs to be invoked explicitly.
      |if you're sure this is not an oversight, add scala-compiler.jar to the classpath,
      |import `scala.tools.reflect.Eval` and call `<your expr>.eval` instead.""".trim.stripMargin)
    lazy val value: T = throw new UnsupportedOperationException("""
      |the value you're calling is only meant to be used in cross-stage path-dependent types.
      |if you want to splice the underlying expression, use `<your expr>.splice`.
      |if you want to get a value of the underlying expression, add scala-compiler.jar to the classpath,
      |import `scala.tools.reflect.Eval` and call `<your expr>.eval` instead.""".trim.stripMargin)
  }
}