// Copyright 2019 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

namespace torque_internal {
// Unsafe is a marker that we require to be passed when calling internal APIs
// that might lead to unsoundness when used incorrectly. Unsafe markers should
// therefore not be instantiated anywhere outside of this namespace.
struct Unsafe {}

// Size of a type in memory (on the heap). For class types, this is the size
// of the pointer, not of the instance.
intrinsic %SizeOf<T: type>(): constexpr int31;

struct Reference<T: type> {
  const object: HeapObject;
  const offset: intptr;
  unsafeMarker: Unsafe;
}
type ConstReference<T: type> extends Reference<T>;
type MutableReference<T: type> extends ConstReference<T>;

namespace unsafe {
macro NewReference<T: type>(object: HeapObject, offset: intptr):&T {
  return %RawDownCast<&T>(
      Reference<T>{object: object, offset: offset, unsafeMarker: Unsafe {}});
}
}  // namespace unsafe

struct Slice<T: type> {
  macro TryAtIndex(index: intptr):&T labels OutOfBounds {
    if (Convert<uintptr>(index) < Convert<uintptr>(this.length)) {
      return unsafe::NewReference<T>(
          this.object, this.offset + index * %SizeOf<T>());
    } else {
      goto OutOfBounds;
    }
  }

  macro AtIndex(index: intptr):&T {
    return this.TryAtIndex(index) otherwise unreachable;
  }

  macro AtIndex(index: uintptr):&T {
    return this.TryAtIndex(Convert<intptr>(index)) otherwise unreachable;
  }

  macro AtIndex(index: constexpr int31):&T {
    const i: intptr = Convert<intptr>(index);
    return this.TryAtIndex(i) otherwise unreachable;
  }

  macro AtIndex(index: Smi):&T {
    const i: intptr = Convert<intptr>(index);
    return this.TryAtIndex(i) otherwise unreachable;
  }

  macro Iterator(): SliceIterator<T> {
    const end = this.offset + this.length * %SizeOf<T>();
    return SliceIterator<T>{
      object: this.object,
      start: this.offset,
      end: end,
      unsafeMarker: Unsafe {}
    };
  }
  macro Iterator(startIndex: intptr, endIndex: intptr): SliceIterator<T> {
    check(
        Convert<uintptr>(endIndex) <= Convert<uintptr>(this.length) &&
        Convert<uintptr>(startIndex) <= Convert<uintptr>(endIndex));
    const start = this.offset + startIndex * %SizeOf<T>();
    const end = this.offset + endIndex * %SizeOf<T>();
    return SliceIterator<T>{
      object: this.object,
      start,
      end,
      unsafeMarker: Unsafe {}
    };
  }

  const object: HeapObject;
  const offset: intptr;
  const length: intptr;
  unsafeMarker: Unsafe;
}

macro UnsafeNewSlice<T: type>(
    object: HeapObject, offset: intptr, length: intptr): Slice<T> {
  return Slice<T>{
    object: object,
    offset: offset,
    length: length,
    unsafeMarker: Unsafe {}
  };
}

struct SliceIterator<T: type> {
  macro Empty(): bool {
    return this.start == this.end;
  }

  macro Next(): T labels NoMore {
    return * this.NextReference() otherwise NoMore;
  }

  macro NextReference():&T labels NoMore {
    if (this.Empty()) {
      goto NoMore;
    } else {
      const result = unsafe::NewReference<T>(this.object, this.start);
      this.start += %SizeOf<T>();
      return result;
    }
  }

  object: HeapObject;
  start: intptr;
  end: intptr;
  unsafeMarker: Unsafe;
}

macro AddIndexedFieldSizeToObjectSize(
    baseSize: intptr, arrayLength: intptr, fieldSize: constexpr int32): intptr {
  const arrayLength = Convert<int32>(arrayLength);
  const byteLength = TryInt32Mul(arrayLength, fieldSize)
      otherwise unreachable;
  return TryIntPtrAdd(baseSize, Convert<intptr>(byteLength))
      otherwise unreachable;
}

macro AlignTagged(x: intptr): intptr {
  // Round up to a multiple of kTaggedSize.
  return (x + kObjectAlignmentMask) & ~kObjectAlignmentMask;
}

macro IsTaggedAligned(x: intptr): bool {
  return (x & kObjectAlignmentMask) == 0;
}

macro ValidAllocationSize(sizeInBytes: intptr, map: Map): bool {
  if (sizeInBytes <= 0) return false;
  if (!IsTaggedAligned(sizeInBytes)) return false;
  const instanceSizeInWords = Convert<intptr>(map.instance_size_in_words);
  return instanceSizeInWords == kVariableSizeSentinel ||
      instanceSizeInWords * kTaggedSize == sizeInBytes;
}

type UninitializedHeapObject extends HeapObject;

extern macro AllocateAllowLOS(intptr): UninitializedHeapObject;
extern macro GetInstanceTypeMap(constexpr InstanceType): Map;

macro Allocate(sizeInBytes: intptr, map: Map): UninitializedHeapObject {
  assert(ValidAllocationSize(sizeInBytes, map));
  return AllocateAllowLOS(sizeInBytes);
}

macro InitializeFieldsFromIterator<T: type, Iterator: type>(
    target: Slice<T>, originIterator: Iterator) {
  let targetIterator = target.Iterator();
  let originIterator = originIterator;
  while (true) {
    const ref:&T = targetIterator.NextReference() otherwise break;
    * ref = originIterator.Next() otherwise unreachable;
  }
}
// Dummy implementations: do not initialize for UninitializedIterator.
InitializeFieldsFromIterator<char8, UninitializedIterator>(
    _target: Slice<char8>, _originIterator: UninitializedIterator) {}
InitializeFieldsFromIterator<char16, UninitializedIterator>(
    _target: Slice<char16>, _originIterator: UninitializedIterator) {}

extern macro IsDoubleHole(HeapObject, intptr): bool;
extern macro StoreDoubleHole(HeapObject, intptr);

macro LoadFloat64OrHole(r:&float64_or_hole): float64_or_hole {
  return float64_or_hole{
    is_hole: IsDoubleHole(r.object, r.offset - kHeapObjectTag),
    value: * unsafe::NewReference<float64>(r.object, r.offset)
  };
}
macro StoreFloat64OrHole(r:&float64_or_hole, value: float64_or_hole) {
  if (value.is_hole) {
    StoreDoubleHole(r.object, r.offset - kHeapObjectTag);
  } else {
    * unsafe::NewReference<float64>(r.object, r.offset) = value.value;
  }
}

macro DownCastForTorqueClass<T : type extends HeapObject>(o: HeapObject):
    T labels CastError {
  const map = o.map;
  const minInstanceType = %MinInstanceType<T>();
  const maxInstanceType = %MaxInstanceType<T>();
  if constexpr (minInstanceType == maxInstanceType) {
    if constexpr (%ClassHasMapConstant<T>()) {
      if (map != %GetClassMapConstant<T>()) goto CastError;
    } else {
      if (map.instance_type != minInstanceType) goto CastError;
    }
  } else {
    const diff: int32 = maxInstanceType - minInstanceType;
    const offset = Convert<int32>(Convert<uint16>(map.instance_type)) -
        Convert<int32>(Convert<uint16>(
            FromConstexpr<InstanceType>(minInstanceType)));
    if (Unsigned(offset) > Unsigned(diff)) goto CastError;
  }
  return %RawDownCast<T>(o);
}

}  // namespace torque_internal

// Indicates that an array-field should not be initialized.
// For safety reasons, this is only allowed for untagged types.
struct UninitializedIterator {}

// %RawDownCast should *never* be used anywhere in Torque code except for
// in Torque-based UnsafeCast operators preceeded by an appropriate
// type assert()
intrinsic %RawDownCast<To: type, From: type>(x: From): To;
intrinsic %RawConstexprCast<To: type, From: type>(f: From): To;

intrinsic %MinInstanceType<T: type>(): constexpr InstanceType;
intrinsic %MaxInstanceType<T: type>(): constexpr InstanceType;

intrinsic %ClassHasMapConstant<T: type>(): constexpr bool;
intrinsic %GetClassMapConstant<T: type>(): Map;

struct IteratorSequence<T: type, FirstIterator: type, SecondIterator: type> {
  macro Empty(): bool {
    return this.first.Empty() && this.second.Empty();
  }

  macro Next(): T labels NoMore {
    return this.first.Next()
        otherwise return (this.second.Next() otherwise NoMore);
  }

  first: FirstIterator;
  second: SecondIterator;
}

macro IteratorSequence<T: type, FirstIterator: type, SecondIterator: type>(
    first: FirstIterator, second: SecondIterator):
    IteratorSequence<T, FirstIterator, SecondIterator> {
  return IteratorSequence<T>{first, second};
}