// Copyright 2017 The Dawn Authors
//
// Licensed 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
//
//     http://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.

#include "dawn_native/metal/BufferMTL.h"

#include "common/Math.h"
#include "dawn_native/CommandBuffer.h"
#include "dawn_native/metal/CommandRecordingContext.h"
#include "dawn_native/metal/DeviceMTL.h"

#include <limits>

namespace dawn_native { namespace metal {
    // The size of uniform buffer and storage buffer need to be aligned to 16 bytes which is the
    // largest alignment of supported data types
    static constexpr uint32_t kMinUniformOrStorageBufferAlignment = 16u;

    // The maximum buffer size if querying the maximum buffer size or recommended working set size
    // is not available. This is a somewhat arbitrary limit of 1 GiB.
    static constexpr uint32_t kMaxBufferSizeFallback = 1024u * 1024u * 1024u;

    // static
    ResultOrError<Ref<Buffer>> Buffer::Create(Device* device, const BufferDescriptor* descriptor) {
        Ref<Buffer> buffer = AcquireRef(new Buffer(device, descriptor));
        DAWN_TRY(buffer->Initialize(descriptor->mappedAtCreation));
        return std::move(buffer);
    }

    MaybeError Buffer::Initialize(bool mappedAtCreation) {
        MTLResourceOptions storageMode;
        if (GetUsage() & kMappableBufferUsages) {
            storageMode = MTLResourceStorageModeShared;
        } else {
            storageMode = MTLResourceStorageModePrivate;
        }

        uint32_t alignment = 1;
#ifdef DAWN_PLATFORM_MACOS
        // [MTLBlitCommandEncoder fillBuffer] requires the size to be a multiple of 4 on MacOS.
        alignment = 4;
#endif

        // Metal validation layer requires the size of uniform buffer and storage buffer to be no
        // less than the size of the buffer block defined in shader, and the overall size of the
        // buffer must be aligned to the largest alignment of its members.
        if (GetUsage() &
            (wgpu::BufferUsage::Uniform | wgpu::BufferUsage::Storage | kInternalStorageBuffer)) {
            ASSERT(IsAligned(kMinUniformOrStorageBufferAlignment, alignment));
            alignment = kMinUniformOrStorageBufferAlignment;
        }

        // The vertex pulling transform requires at least 4 bytes in the buffer.
        // 0-sized vertex buffer bindings are allowed, so we always need an additional 4 bytes
        // after the end.
        NSUInteger extraBytes = 0u;
        if ((GetUsage() & wgpu::BufferUsage::Vertex) != 0) {
            extraBytes = 4u;
        }

        if (GetSize() > std::numeric_limits<NSUInteger>::max() - extraBytes) {
            return DAWN_OUT_OF_MEMORY_ERROR("Buffer allocation is too large");
        }
        NSUInteger currentSize =
            std::max(static_cast<NSUInteger>(GetSize()) + extraBytes, NSUInteger(4));

        if (currentSize > std::numeric_limits<NSUInteger>::max() - alignment) {
            // Alignment would overlow.
            return DAWN_OUT_OF_MEMORY_ERROR("Buffer allocation is too large");
        }
        currentSize = Align(currentSize, alignment);

        if (@available(iOS 12, macOS 10.14, *)) {
            NSUInteger maxBufferSize = [ToBackend(GetDevice())->GetMTLDevice() maxBufferLength];
            if (currentSize > maxBufferSize) {
                return DAWN_OUT_OF_MEMORY_ERROR("Buffer allocation is too large");
            }
#if defined(DAWN_PLATFORM_MACOS)
        } else if (@available(macOS 10.12, *)) {
            // |maxBufferLength| isn't always available on older systems. If available, use
            // |recommendedMaxWorkingSetSize| instead. We can probably allocate more than this,
            // but don't have a way to discover a better limit. MoltenVK also uses this heuristic.
            uint64_t maxWorkingSetSize =
                [ToBackend(GetDevice())->GetMTLDevice() recommendedMaxWorkingSetSize];
            if (currentSize > maxWorkingSetSize) {
                return DAWN_OUT_OF_MEMORY_ERROR("Buffer allocation is too large");
            }
#endif
        } else if (currentSize > kMaxBufferSizeFallback) {
            return DAWN_OUT_OF_MEMORY_ERROR("Buffer allocation is too large");
        }

        mAllocatedSize = currentSize;
        mMtlBuffer.Acquire([ToBackend(GetDevice())->GetMTLDevice()
            newBufferWithLength:currentSize
                        options:storageMode]);
        if (mMtlBuffer == nullptr) {
            return DAWN_OUT_OF_MEMORY_ERROR("Buffer allocation failed");
        }

        // The buffers with mappedAtCreation == true will be initialized in
        // BufferBase::MapAtCreation().
        if (GetDevice()->IsToggleEnabled(Toggle::NonzeroClearResourcesOnCreationForTesting) &&
            !mappedAtCreation) {
            CommandRecordingContext* commandContext =
                ToBackend(GetDevice())->GetPendingCommandContext();
            ClearBuffer(commandContext, uint8_t(1u));
        }

        // Initialize the padding bytes to zero.
        if (GetDevice()->IsToggleEnabled(Toggle::LazyClearResourceOnFirstUse) &&
            !mappedAtCreation) {
            uint32_t paddingBytes = GetAllocatedSize() - GetSize();
            if (paddingBytes > 0) {
                uint32_t clearSize = Align(paddingBytes, 4);
                uint64_t clearOffset = GetAllocatedSize() - clearSize;

                CommandRecordingContext* commandContext =
                    ToBackend(GetDevice())->GetPendingCommandContext();
                ClearBuffer(commandContext, 0, clearOffset, clearSize);
            }
        }
        return {};
    }

    Buffer::~Buffer() {
        DestroyInternal();
    }

    id<MTLBuffer> Buffer::GetMTLBuffer() const {
        return mMtlBuffer.Get();
    }

    bool Buffer::IsCPUWritableAtCreation() const {
        // TODO(enga): Handle CPU-visible memory on UMA
        return GetUsage() & kMappableBufferUsages;
    }

    MaybeError Buffer::MapAtCreationImpl() {
        return {};
    }

    MaybeError Buffer::MapAsyncImpl(wgpu::MapMode mode, size_t offset, size_t size) {
        CommandRecordingContext* commandContext =
            ToBackend(GetDevice())->GetPendingCommandContext();
        EnsureDataInitialized(commandContext);

        return {};
    }

    void* Buffer::GetMappedPointerImpl() {
        return [*mMtlBuffer contents];
    }

    void Buffer::UnmapImpl() {
        // Nothing to do, Metal StorageModeShared buffers are always mapped.
    }

    void Buffer::DestroyImpl() {
        mMtlBuffer = nullptr;
    }

    void Buffer::EnsureDataInitialized(CommandRecordingContext* commandContext) {
        if (IsDataInitialized() ||
            !GetDevice()->IsToggleEnabled(Toggle::LazyClearResourceOnFirstUse)) {
            return;
        }

        InitializeToZero(commandContext);
    }

    void Buffer::EnsureDataInitializedAsDestination(CommandRecordingContext* commandContext,
                                                    uint64_t offset,
                                                    uint64_t size) {
        if (IsDataInitialized() ||
            !GetDevice()->IsToggleEnabled(Toggle::LazyClearResourceOnFirstUse)) {
            return;
        }

        if (IsFullBufferRange(offset, size)) {
            SetIsDataInitialized();
        } else {
            InitializeToZero(commandContext);
        }
    }

    void Buffer::EnsureDataInitializedAsDestination(CommandRecordingContext* commandContext,
                                                    const CopyTextureToBufferCmd* copy) {
        if (IsDataInitialized() ||
            !GetDevice()->IsToggleEnabled(Toggle::LazyClearResourceOnFirstUse)) {
            return;
        }

        if (IsFullBufferOverwrittenInTextureToBufferCopy(copy)) {
            SetIsDataInitialized();
        } else {
            InitializeToZero(commandContext);
        }
    }

    void Buffer::InitializeToZero(CommandRecordingContext* commandContext) {
        ASSERT(GetDevice()->IsToggleEnabled(Toggle::LazyClearResourceOnFirstUse));
        ASSERT(!IsDataInitialized());

        ClearBuffer(commandContext, uint8_t(0u));

        SetIsDataInitialized();
        GetDevice()->IncrementLazyClearCountForTesting();
    }

    void Buffer::ClearBuffer(CommandRecordingContext* commandContext,
                             uint8_t clearValue,
                             uint64_t offset,
                             uint64_t size) {
        ASSERT(commandContext != nullptr);
        size = size > 0 ? size : GetAllocatedSize();
        ASSERT(size > 0);
        [commandContext->EnsureBlit() fillBuffer:mMtlBuffer.Get()
                                           range:NSMakeRange(offset, size)
                                           value:clearValue];
    }

}}  // namespace dawn_native::metal