package xsbt

import scala.tools.nsc.Global
import scala.tools.nsc.symtab.Flags

/**
 * Collection of hacks that make it possible for the compiler interface
 * to stay source compatible with Scala compiler 2.9, 2.10 and 2.11.
 *
 * One common technique used in `Compat` class is use of implicit conversions to deal
 * with methods that got renamed or moved between different Scala compiler versions.
 *
 * Let's pick a specific example. In Scala 2.9 and 2.10 there was a method called `toplevelClass`
 * defined on `Symbol`. In 2.10 that method has been deprecated and `enclosingTopLevelClass`
 * method has been introduce as a replacement. In Scala 2.11 the old `toplevelClass` method has
 * been removed. How can we pick the right version based on availability of those two methods?
 *
 * We define an implicit conversion from Symbol to a class that contains both method definitions:
 *
 *   implicit def symbolCompat(sym: Symbol): SymbolCompat = new SymbolCompat(sym)
 *   class SymbolCompat(sym: Symbol) {
 *     def enclosingTopLevelClass: Symbol = sym.toplevelClass
 *     def toplevelClass: Symbol =
 *       throw new RuntimeException("For source compatibility only: should not get here.")
 *   }
 *
 * We assume that client code (code in compiler interface) should always call `enclosingTopLevelClass`
 * method. If we compile that code against 2.11 it will just directly link against method provided by
 * Symbol. However, if we compile against 2.9 or 2.10 `enclosingTopLevelClass` won't be found so the
 * implicit conversion defined above will kick in. That conversion will provide `enclosingTopLevelClass`
 * that simply forwards to the old `toplevelClass` method that is available in 2.9 and 2.10 so that
 * method will be called in the end. There's one twist: since `enclosingTopLevelClass` forwards to
 * `toplevelClass` which doesn't exist in 2.11! Therefore, we need to also define `toplevelClass`
 * that will be provided by an implicit conversion as well. However, we should never reach that method
 * at runtime if either `enclosingTopLevelClass` or `toplevelClass` is available on Symbol so this
 * is purely source compatibility stub.
 *
 * The technique described above is used in several places below.
 *
 */
abstract class Compat
{
	val global: Global
	import global._
	val LocalChild = global.tpnme.LOCAL_CHILD
	val Nullary = global.NullaryMethodType
	val ScalaObjectClass = definitions.ScalaObjectClass

	private[this] final class MiscCompat
	{
		// in 2.9, nme.LOCALCHILD was renamed to tpnme.LOCAL_CHILD
		def tpnme = nme
		def LOCAL_CHILD = nme.LOCALCHILD
		def LOCALCHILD = sourceCompatibilityOnly

		// in 2.10, ScalaObject was removed
		def ScalaObjectClass = definitions.ObjectClass

		def NullaryMethodType = NullaryMethodTpe

		def MACRO = DummyValue

		// in 2.10, sym.moduleSuffix exists, but genJVM.moduleSuffix(Symbol) does not
		def moduleSuffix(sym: Symbol): String = sourceCompatibilityOnly
		// in 2.11 genJVM does not exist
		def genJVM = this
	}
	// in 2.9, NullaryMethodType was added to Type
	object NullaryMethodTpe {
		def unapply(t: Type): Option[Type] = None
	}

	protected implicit def symbolCompat(sym: Symbol): SymbolCompat = new SymbolCompat(sym)
	protected final class SymbolCompat(sym: Symbol) {
		// before 2.10, sym.moduleSuffix doesn't exist, but genJVM.moduleSuffix does
		def moduleSuffix = global.genJVM.moduleSuffix(sym)

		def enclosingTopLevelClass: Symbol = sym.toplevelClass
		def toplevelClass: Symbol = sourceCompatibilityOnly
	}


	val DummyValue = 0
	def hasMacro(s: Symbol): Boolean =
	{
		val MACRO = Flags.MACRO // will be DummyValue for versions before 2.10
		MACRO != DummyValue && s.hasFlag(MACRO)
	}
	def moduleSuffix(s: Symbol): String = s.moduleSuffix

	private[this] def sourceCompatibilityOnly: Nothing = throw new RuntimeException("For source compatibility only: should not get here.")

	private[this] final implicit def miscCompat(n: AnyRef): MiscCompat = new MiscCompat
}