import { AL_MASK, MAX_SIZE_32 } from "./allocator";

/**
 * The common runtime object header prepended to all managed objects. Has a size of 16 bytes in
 * WASM32 and contains a classId (e.g. for instanceof checks), the allocation size (e.g. for
 * .byteLength and .length computation) and additional reserved fields to be used by GC. If no
 * GC is present, the HEADER is cut into half excluding the reserved fields, as indicated by
 * HEADER_SIZE.
*/
@unmanaged export class HEADER {
  /** Unique id of the respective class or a magic value if not yet registered.*/
  classId: u32;
  /** Size of the allocated payload. */
  payloadSize: u32;
  /** Reserved field for use by GC. Only present if GC is. */
  reserved1: usize; // itcm: tagged next
  /** Reserved field for use by GC. Only present if GC is. */
  reserved2: usize; // itcm: prev
}

/** Common runtime header size. */
// @ts-ignore: decorator
@lazy
export const HEADER_SIZE: usize = isDefined(__ref_collect)
  ? (offsetof<HEADER>(           ) + AL_MASK) & ~AL_MASK  // full header if GC is present
  : (offsetof<HEADER>("reserved1") + AL_MASK) & ~AL_MASK; // half header if GC is absent

/** Common runtime header magic. Used to assert registered/unregistered status. */
// @ts-ignore: decorator
@lazy
export const HEADER_MAGIC: u32 = 0xA55E4B17;

/** Maximum byte length of any buffer-like object. */
// @ts-ignore
@lazy
export const MAX_BYTELENGTH: i32 = MAX_SIZE_32 - HEADER_SIZE;

/** Adjusts an allocation to actual block size. Primarily targets TLSF. */
export function adjust(payloadSize: usize): usize {
  // round up to power of 2, e.g. with HEADER_SIZE=8:
  // 0            -> 2^3  = 8
  // 1..8         -> 2^4  = 16
  // 9..24        -> 2^5  = 32
  // ...
  // MAX_LENGTH   -> 2^30 = 0x40000000 (MAX_SIZE_32)
  return <usize>1 << <usize>(<u32>32 - clz<u32>(payloadSize + HEADER_SIZE - 1));
}

/** Allocates the memory necessary to represent a managed object of the specified size. */
// @ts-ignore: decorator
@unsafe
export function allocate(payloadSize: usize): usize {
  var header = changetype<HEADER>(memory.allocate(adjust(payloadSize)));
  header.classId = HEADER_MAGIC;
  header.payloadSize = payloadSize;
  if (isDefined(__ref_collect)) {
    header.reserved1 = 0;
    header.reserved2 = 0;
  }
  return changetype<usize>(header) + HEADER_SIZE;
}

/** Reallocates the memory of a managed object that turned out to be too small or too large. */
// @ts-ignore: decorator
@unsafe
export function reallocate(ref: usize, newPayloadSize: usize): usize {
  // Background: When managed objects are allocated these aren't immediately registered with GC
  // but can be used as scratch objects while unregistered. This is useful in situations where
  // the object must be reallocated multiple times because its final size isn't known beforehand,
  // e.g. in Array#filter, with only the final object making it into GC'ed userland.
  var header = changetype<HEADER>(ref - HEADER_SIZE);
  var payloadSize = header.payloadSize;
  if (payloadSize < newPayloadSize) {
    let newAdjustedSize = adjust(newPayloadSize);
    if (select(adjust(payloadSize), 0, ref > HEAP_BASE) < newAdjustedSize) {
      // move if the allocation isn't large enough or not a heap object
      let newHeader = changetype<HEADER>(memory.allocate(newAdjustedSize));
      newHeader.classId = header.classId;
      if (isDefined(__ref_collect)) {
        newHeader.reserved1 = 0;
        newHeader.reserved2 = 0;
      }
      let newRef = changetype<usize>(newHeader) + HEADER_SIZE;
      memory.copy(newRef, ref, payloadSize);
      memory.fill(newRef + payloadSize, 0, newPayloadSize - payloadSize);
      if (header.classId == HEADER_MAGIC) {
        // free right away if not registered yet
        assert(ref > HEAP_BASE); // static objects aren't scratch objects
        memory.free(changetype<usize>(header));
      } else if (isDefined(__ref_collect)) {
        // if previously registered, register again
        // @ts-ignore: stub
        __ref_register(ref);
      }
      header = newHeader;
      ref = newRef;
    } else {
      // otherwise just clear additional memory within this block
      memory.fill(ref + payloadSize, 0, newPayloadSize - payloadSize);
    }
  } else {
    // if the size is the same or less, just update the header accordingly.
    // unused space is cleared when grown, so no need to do this here.
  }
  header.payloadSize = newPayloadSize;
  return ref;
}

/** Discards the memory of a managed object that hasn't been registered yet. */
// @ts-ignore: decorator
@unsafe
export function discard(ref: usize): void {
  if (!ASC_NO_ASSERT) {
    assert(ref > HEAP_BASE); // must be a heap object
    let header = changetype<HEADER>(ref - HEADER_SIZE);
    assert(header.classId == HEADER_MAGIC);
    memory.free(changetype<usize>(header));
  } else {
    memory.free(changetype<usize>(ref - HEADER_SIZE));
  }
}

/** Registers a managed object of the kind represented by the specified runtime id. */
// @ts-ignore: decorator
@unsafe
export function register(ref: usize, id: u32): usize {
  if (!ASC_NO_ASSERT) {
    assert(ref > HEAP_BASE); // must be a heap object
    let header = changetype<HEADER>(ref - HEADER_SIZE);
    assert(header.classId == HEADER_MAGIC);
    header.classId = id;
  } else {
    changetype<HEADER>(ref - HEADER_SIZE).classId = id;
  }
  if (isDefined(__ref_register)) __ref_register(ref);
  return ref;
}

/** Allocates and registers, but doesn't initialize the data of, a new `Array` of the specified length and element alignment. */
// @ts-ignore: decorator
@unsafe
export function newArray(length: i32, alignLog2: usize, id: u32, data: usize = 0): usize {
  // TODO: This API isn't great, but the compiler requires it for array literals anyway,
  // that is when an array literal is encountered and its data is static, this function is
  // called and the static buffer provided as `data`. This function can also be used to
  // create typed arrays in that `Array` also implements `ArrayBufferView` but has an
  // additional `.length_` property that remains unused overhead for typed arrays.
  var array = newObject(offsetof<i32[]>(), id);
  var bufferSize = <u32>length << alignLog2;
  var buffer = newArrayBuffer(bufferSize);
  changetype<ArrayBufferView>(array).data = changetype<ArrayBuffer>(buffer); // links
  changetype<ArrayBufferView>(array).dataStart = buffer;
  changetype<ArrayBufferView>(array).dataLength = bufferSize;
  store<i32>(changetype<usize>(array), length, offsetof<i32[]>("length_"));
  if (data) memory.copy(buffer, data, <usize>bufferSize);
  return array;
}