// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

// TODO(https://dartbug.com/44621): Remove this copy when package:ffi can be
// rolled. We need to wait until the `Allocator` interface has rolled into
// Flutter.

import 'dart:ffi';
import 'dart:io';

final DynamicLibrary stdlib = Platform.isWindows
    ? DynamicLibrary.open('kernel32.dll')
    : DynamicLibrary.process();

typedef PosixCallocNative = Pointer Function(IntPtr num, IntPtr size);
typedef PosixCalloc = Pointer Function(int num, int size);
final PosixCalloc posixCalloc =
    stdlib.lookupFunction<PosixCallocNative, PosixCalloc>('calloc');

typedef PosixFreeNative = Void Function(Pointer);
typedef PosixFree = void Function(Pointer);
final PosixFree posixFree =
    stdlib.lookupFunction<PosixFreeNative, PosixFree>('free');

typedef WinGetProcessHeapFn = Pointer Function();
final WinGetProcessHeapFn winGetProcessHeap = stdlib
    .lookupFunction<WinGetProcessHeapFn, WinGetProcessHeapFn>('GetProcessHeap');
final Pointer processHeap = winGetProcessHeap();

typedef WinHeapAllocNative = Pointer Function(Pointer, Uint32, IntPtr);
typedef WinHeapAlloc = Pointer Function(Pointer, int, int);
final WinHeapAlloc winHeapAlloc =
    stdlib.lookupFunction<WinHeapAllocNative, WinHeapAlloc>('HeapAlloc');

typedef WinHeapFreeNative = Int32 Function(
    Pointer heap, Uint32 flags, Pointer memory);
typedef WinHeapFree = int Function(Pointer heap, int flags, Pointer memory);
final WinHeapFree winHeapFree =
    stdlib.lookupFunction<WinHeapFreeNative, WinHeapFree>('HeapFree');

const int HEAP_ZERO_MEMORY = 8;

/// Manages memory on the native heap.
///
/// Initializes newly allocated memory to zero.
///
/// For POSIX-based systems, this uses `calloc` and `free`. On Windows, it uses
/// `HeapAlloc` with [HEAP_ZERO_MEMORY] and `HeapFree` against the default
/// public heap.
class _CallocAllocator implements Allocator {
  const _CallocAllocator();

  /// Allocates [byteCount] bytes of zero-initialized of memory on the native
  /// heap.
  ///
  /// For POSIX-based systems, this uses `calloc`. On Windows, it uses
  /// `HeapAlloc` against the default public heap.
  ///
  /// Throws an [ArgumentError] if the number of bytes or alignment cannot be
  /// satisfied.
  // TODO: Stop ignoring alignment if it's large, for example for SSE data.
  @override
  Pointer<T> allocate<T extends NativeType>(int byteCount, {int alignment}) {
    Pointer<T> result;
    if (Platform.isWindows) {
      result = winHeapAlloc(processHeap, /*flags=*/ HEAP_ZERO_MEMORY, byteCount)
          .cast();
    } else {
      result = posixCalloc(byteCount, 1).cast();
    }
    if (result.address == 0) {
      throw ArgumentError('Could not allocate $byteCount bytes.');
    }
    return result;
  }

  /// Releases memory allocated on the native heap.
  ///
  /// For POSIX-based systems, this uses `free`. On Windows, it uses `HeapFree`
  /// against the default public heap. It may only be used against pointers
  /// allocated in a manner equivalent to [allocate].
  ///
  /// Throws an [ArgumentError] if the memory pointed to by [pointer] cannot be
  /// freed.
  ///
  // TODO(dartbug.com/36855): Once we have a ffi.Bool type we can use it instead
  // of testing the return integer to be non-zero.
  @override
  void free(Pointer pointer) {
    if (Platform.isWindows) {
      if (winHeapFree(processHeap, /*flags=*/ 0, pointer) == 0) {
        throw ArgumentError('Could not free $pointer.');
      }
    } else {
      posixFree(pointer);
    }
  }
}

/// Manages memory on the native heap.
///
/// Initializes newly allocated memory to zero. Use [malloc] for unintialized
/// memory allocation.
///
/// For POSIX-based systems, this uses `calloc` and `free`. On Windows, it uses
/// `HeapAlloc` with [HEAP_ZERO_MEMORY] and `HeapFree` against the default
/// public heap.
const Allocator calloc = _CallocAllocator();