/*
    * Copyright 2021 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty5.buffer.api.unsafe;
  
  import io.netty5.buffer.api.AllocationType;
  import io.netty5.buffer.api.AllocatorControl;
  import io.netty5.buffer.api.Buffer;
  import io.netty5.buffer.api.Drop;
  import io.netty5.buffer.api.MemoryManager;
  import io.netty5.buffer.api.StandardAllocationTypes;
  import io.netty5.buffer.api.internal.ArcDrop;
  import io.netty5.buffer.api.internal.Statics;
  import io.netty5.buffer.api.internal.WrappingAllocation;
  import io.netty5.util.internal.PlatformDependent;
  import io.netty5.util.internal.SystemPropertyUtil;
  
  import java.lang.ref.Cleaner;
  import java.util.function.Function;
  
  import static io.netty5.buffer.api.internal.Statics.convert;
  
  /**
   * This memory manager produces and manages {@link Buffer} instances that are using {@code Unsafe} to allocate and
   * access memory.
   * <p>
   * Memory managers are normally not used directly.
   * Instead, you likely want to use the {@link io.netty5.buffer.api.DefaultBufferAllocators}, or the static methods on
   * {@link io.netty5.buffer.api.BufferAllocator}.
   */
  public final class UnsafeMemoryManager implements MemoryManager {
      private static final boolean FREE_IMMEDIATELY = SystemPropertyUtil.getBoolean(
              "io.netty5.buffer.api.unsafe.UnsafeMemoryManager.freeDirectMemoryImmediately", true);
  
      public UnsafeMemoryManager() {
          if (!PlatformDependent.hasUnsafe()) {
              UnsupportedOperationException notSupported = new UnsupportedOperationException("Unsafe is not available.");
              notSupported.addSuppressed(PlatformDependent.getUnsafeUnavailabilityCause());
              throw notSupported;
          }
          if (!PlatformDependent.hasDirectBufferNoCleanerConstructor()) {
              throw new UnsupportedOperationException("DirectByteBuffer internal constructor is not available.");
          }
      }
  
      @Override
      public Buffer allocateShared(AllocatorControl control, long size,
                                   Function<Drop<Buffer>, Drop<Buffer>> dropDecorator,
                                   AllocationType allocationType) {
          final Object base;
          final long address;
          final UnsafeMemory memory;
          final int size32 = Math.toIntExact(size);
          Cleaner cleaner = Statics.CLEANER;
          Drop<Buffer> drop = Statics.NO_OP_DROP;
          if (allocationType == StandardAllocationTypes.OFF_HEAP) {
              base = null;
              address = PlatformDependent.allocateMemory(size);
              Statics.MEM_USAGE_NATIVE.add(size);
              PlatformDependent.setMemory(address, size, (byte) 0);
              memory = new UnsafeMemory(base, address, size32);
              FreeAddress freeAddress = new FreeAddress(address, size32);
              if (FREE_IMMEDIATELY) {
                  drop = ArcDrop.wrap(freeAddress);
              } else {
                  cleaner.register(memory, freeAddress);
              }
          } else if (allocationType == StandardAllocationTypes.ON_HEAP) {
              base = PlatformDependent.allocateUninitializedArray(size32);
              address = PlatformDependent.byteArrayBaseOffset();
              memory = new UnsafeMemory(base, address, size32);
          } else if (allocationType instanceof WrappingAllocation) {
              base = ((WrappingAllocation) allocationType).getArray();
              address = PlatformDependent.byteArrayBaseOffset();
              memory = new UnsafeMemory(base, address, size32);
          } else {
              throw new IllegalArgumentException("Unknown allocation type: " + allocationType);
          }
          return createBuffer(memory, size32, control, dropDecorator.apply(drop));
      }
  
      @Override
      public Buffer allocateConstChild(Buffer readOnlyConstParent) {
          UnsafeBuffer buf = (UnsafeBuffer) readOnlyConstParent;
          return buf.newConstChild();
      }
  
     @Override
     public Object unwrapRecoverableMemory(Buffer buf) {
         return ((UnsafeBuffer) buf).recover();
     }
 
     @Override
     public Buffer recoverMemory(AllocatorControl allocatorControl, Object recoverableMemory, Drop<Buffer> drop) {
         UnsafeMemory memory = (UnsafeMemory) recoverableMemory;
         int size = memory.size;
         return createBuffer(memory, size, allocatorControl, drop);
     }
 
     private static UnsafeBuffer createBuffer(UnsafeMemory memory, int size, AllocatorControl allocatorControl,
                                              Drop<Buffer> drop) {
         Drop<UnsafeBuffer> concreteDrop = convert(drop);
         UnsafeBuffer unsafeBuffer = new UnsafeBuffer(memory, 0, size, allocatorControl, concreteDrop);
         concreteDrop.attach(unsafeBuffer);
         return unsafeBuffer;
     }
 
     @Override
     public Object sliceMemory(Object memory, int offset, int length) {
         return ((UnsafeMemory) memory).slice(offset, length);
     }
 
     @Override
     public void clearMemory(Object memory) {
         ((UnsafeMemory) memory).clearMemory();
     }
 
     @Override
     public String implementationName() {
         return "Unsafe";
     }
 }