// Copyright 2020 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/wire/ChunkedCommandHandler.h"

#include <algorithm>
#include <cstring>
#include <utility>

#include "dawn/common/Alloc.h"

namespace dawn::wire {

ChunkedCommandHandler::~ChunkedCommandHandler() = default;

const volatile char* ChunkedCommandHandler::HandleCommands(const volatile char* commands,
                                                           size_t size) {
    if (mChunkedCommandRemainingSize > 0) {
        // If there is a chunked command in flight, append the command data.
        // We append at most |mChunkedCommandRemainingSize| which is enough to finish the
        // in-flight chunked command, and then pass the rest along to a second call to
        // |HandleCommandsImpl|.
        size_t chunkSize = std::min(size, mChunkedCommandRemainingSize);

        memcpy(mChunkedCommandData.get() + mChunkedCommandPutOffset,
               const_cast<const char*>(commands), chunkSize);
        mChunkedCommandPutOffset += chunkSize;
        mChunkedCommandRemainingSize -= chunkSize;

        commands += chunkSize;
        size -= chunkSize;

        if (mChunkedCommandRemainingSize == 0) {
            // Once the chunked command is complete, pass the data to the command handler
            // implemenation.
            auto chunkedCommandData = std::move(mChunkedCommandData);
            if (HandleCommandsImpl(chunkedCommandData.get(), mChunkedCommandPutOffset) == nullptr) {
                // |HandleCommandsImpl| returns nullptr on error. Forward any errors
                // out.
                return nullptr;
            }
        }
    }

    return HandleCommandsImpl(commands, size);
}

ChunkedCommandHandler::ChunkedCommandsResult ChunkedCommandHandler::BeginChunkedCommandData(
    const volatile char* commands,
    size_t commandSize,
    size_t initialSize) {
    ASSERT(!mChunkedCommandData);

    // Reserve space for all the command data we're expecting, and copy the initial data
    // to the start of the memory.
    mChunkedCommandData.reset(AllocNoThrow<char>(commandSize));
    if (!mChunkedCommandData) {
        return ChunkedCommandsResult::Error;
    }

    memcpy(mChunkedCommandData.get(), const_cast<const char*>(commands), initialSize);
    mChunkedCommandPutOffset = initialSize;
    mChunkedCommandRemainingSize = commandSize - initialSize;

    return ChunkedCommandsResult::Consumed;
}

}  // namespace dawn::wire