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package io.getquill.sources

import scala.reflect.macros.whitebox.Context
import io.getquill.ast._
import io.getquill.util.Messages._

trait EncodingMacro {
  val c: Context

  import c.universe._

  sealed trait Value
  case class OptionValue(value: Value) extends Value
  case class SimpleValue(ast: Ast, encoding: c.Tree, optionEncoding: c.Tree) extends Value
  case class CaseClassValue(tpe: c.Type, params: List[List[Value]]) extends Value

  protected def encoding[T](ast: Ast, inferEncoding: Type => Option[Tree])(implicit t: WeakTypeTag[T]): Value =
    encoding(ast, t.tpe, inferEncoding)

  private def encoding(ast: Ast, typ: Type, inferEncoding: Type => Option[Tree]): Value =
    (inferEncoding(typ), inferEncoding(optionType(c.WeakTypeTag(typ))), ast) match {
      case (_, _, ast) if (typ <:< c.weakTypeOf[Option[Any]]) =>
        OptionValue(encoding(ast, typ.typeArgs.head, inferEncoding))
      case (Some(encoding), Some(optionEncoding), ast) =>
        SimpleValue(ast, encoding, optionEncoding)
      case (None, _, ast) if (typ.typeSymbol.asClass.isCaseClass) =>
        caseClassValue(typ, ast, inferEncoding)
      case other =>
        c.fail(s"Source doesn't know how to decode '$ast: $typ'")
    }

  private def optionType[T](implicit t: WeakTypeTag[T]) =
    c.weakTypeOf[Option[T]]

  private def caseClassValue(typ: Type, ast: Ast, inferEncoding: Type => Option[Tree]) =
    CaseClassValue(typ, valuesForCaseClass(typ, ast, inferEncoding))

  private def valuesForCaseClass(typ: Type, ast: Ast, inferEncoding: Type => Option[Tree]) =
    valuesForConstructor(typ, caseClassConstructor(typ), ast, inferEncoding)

  private def valuesForConstructor(typ: Type, constructor: MethodSymbol, ast: Ast, inferEncoding: Type => Option[Tree]) =
    constructor.paramLists.map(_.map {
      param =>
        val paramType = param.typeSignature.asSeenFrom(typ, typ.typeSymbol)
        encoding(Property(ast, param.name.decodedName.toString), paramType, inferEncoding)
    })

  private def caseClassConstructor(t: Type) =
    t.members.collect {
      case m: MethodSymbol if (m.isPrimaryConstructor) => m
    }.headOption.get // a case class always has a primary constructor
}