//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

protocol CVarArg {
  func encode() -> Word[]
}

#if arch(x86_64)
let _x86_64CountGPRegisters = 6
let _x86_64CountSSERegisters = 8
let _x86_64SSERegisterWords = 2
let _x86_64RegisterSaveWords = _x86_64CountGPRegisters + _x86_64CountSSERegisters * _x86_64SSERegisterWords
#endif

func withVaList<R>(args: CVarArg[], f: (CVaListPointer)->R) -> R {
  var builder = VaListBuilder()
  for a in args {
    builder.append(a)
  }
  return withVaList(builder, f)
}

func withVaList<R>(builder: VaListBuilder, f: (CVaListPointer)->R) -> R {
  let result = f(builder.va_list())
  _fixLifetime(builder)
  return result
}

func getVaList(args: CVarArg[]) -> CVaListPointer {
  var builder = VaListBuilder()
  for a in args {
    builder.append(a)
  }
  // FIXME: Use some Swift equivalent of NS_RETURNS_INNER_POINTER if we get one.
  Builtin.retain(builder)
  Builtin.autorelease(builder)
  return builder.va_list()
}

func encodeBitsAsWords<T: CVarArg>(x: T) -> Word[] {
  var result = Word[](count: (sizeof(T.self) + sizeof(Word.self) - 1) / sizeof(Word.self), value: 0)
  var tmp = x
  c_memcpy(dest: UnsafePointer(result.elementStorage),
           src: UnsafePointer(Builtin.addressof(&tmp)),
           size: UInt(sizeof(T.self)))
  return result
}

// CVarArg conformances for the integer types.  Everything smaller
// than a CInt must be promoted to CInt or CUnsignedInt before
// encoding.

// Signed types
extension Int : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

extension Int64 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

extension Int32 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

extension Int16 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(CInt(self))
  }
}

extension Int8 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(CInt(self))
  }
}

// Unsigned types
extension UInt : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

extension UInt64 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

extension UInt32 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

extension UInt16 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(CUnsignedInt(self))
  }
}

extension UInt8 : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(CUnsignedInt(self))
  }
}

extension COpaquePointer : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

extension Float : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(Double(self))
  }
}

extension Double : CVarArg {
  func encode() -> Word[] {
    return encodeBitsAsWords(self)
  }
}

#if !arch(x86_64)

@final
class VaListBuilder {
  
  func append(arg: CVarArg) {
    for x in arg.encode() {
      storage.append(x)
    }
  }
  
  func va_list() -> CVaListPointer {
    return CVaListPointer(fromUnsafePointer: UnsafePointer<Void>(storage.elementStorage))
  }

  var storage = Word[]()
}

#else

@final
class VaListBuilder {

  struct Header {
    var gp_offset = CUnsignedInt(0)
    var fp_offset = CUnsignedInt(_x86_64CountGPRegisters * strideof(Word.self))
    var overflow_arg_area: UnsafePointer<Word> = UnsafePointer<Word>.null()
    var reg_save_area: UnsafePointer<Word> = UnsafePointer<Word>.null()
  }
  
  init() {
    // prepare the register save area
    storage = Array(count: _x86_64RegisterSaveWords, value: 0)
  }

  func append(arg: CVarArg) {
    var encoded = arg.encode()
    
    if ((arg as Float) || (arg as Double))
    && sseRegistersUsed < _x86_64CountSSERegisters {
      var startIndex = _x86_64CountGPRegisters
           + (sseRegistersUsed * _x86_64SSERegisterWords)
      for w in encoded {
        storage[startIndex] = w
        ++startIndex
      }
      ++sseRegistersUsed
    }
    else if encoded.count == 1 && gpRegistersUsed < _x86_64CountGPRegisters {
      storage[gpRegistersUsed++] = encoded[0]
    }
    else {
      for w in encoded {
        storage.append(w)
      }
    }
  }

  func va_list() -> CVaListPointer {
    header.reg_save_area = storage.elementStorage
    header.overflow_arg_area = storage.elementStorage + _x86_64RegisterSaveWords
    return CVaListPointer(
             fromUnsafePointer: UnsafePointer<Void>(
               Builtin.addressof(&self.header)))
  }

  var gpRegistersUsed = 0
  var sseRegistersUsed = 0

  @final  // Property must be final since it is used by Builtin.addressof.
  var header = Header()
  var storage: Word[]
}

#endif