// Copyright 2021 Google LLC
//
// 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 <flasher/logging.hpp>
#include <flasher/ops.hpp>
#include <stdplus/exception.hpp>

#include <algorithm>
#include <cstddef>
#include <format>
#include <stdexcept>
#include <vector>

namespace flasher
{
namespace ops
{

void write(Device& dev, size_t dev_offset, Reader& reader, size_t reader_offset,
           Mutate& mut, size_t max_size, std::optional<size_t> stride_size,
           bool noread)
{
    if (dev_offset > dev.getSize())
    {
        throw std::invalid_argument(std::format(
            "Device smaller than offset, {} < {}", dev.getSize(), dev_offset));
    }
    size_t stride = stride_size ? *stride_size : dev.recommendedStride();
    if (stride == 0)
    {
        throw std::invalid_argument("Stride cannot be 0");
    }
    std::vector<std::byte> reader_buf_v(stride * 2), dev_buf_v(stride * 2);
    const std::span<std::byte> reader_buf(reader_buf_v), dev_buf(dev_buf_v);
    std::span<std::byte> reader_data, dev_data;
    bool eof = false;
    const auto next_dev_buf = [&]() {
        auto next_size = std::min(
            {stride, max_size - dev_data.size(), dev.getSize() - dev_offset});
        if (next_size == 0)
        {
            throw std::runtime_error("Device not large enough for reader");
        }
        return dev_buf.subspan(dev_data.size(), next_size);
    };
    const auto too_little_dev = [&]() {
        return dev_data.size() < stride && max_size > dev_data.size();
    };
    while (max_size > 0)
    {
        while (reader_data.size() < stride && max_size > reader_data.size() &&
               !eof)
        {
            try
            {
                auto new_reader_data = reader.readAt(
                    reader_buf.subspan(
                        reader_data.size(),
                        std::min(stride, max_size - reader_data.size())),
                    reader_offset);
                LOG(LogLevel::Info, " RF@{}#{}", dev_offset,
                    new_reader_data.size());
                mut.forward(new_reader_data, reader_offset);
                reader_data = reader_buf.subspan(0, reader_data.size() +
                                                        new_reader_data.size());
                reader_offset += new_reader_data.size();
            }
            catch (const stdplus::exception::Eof&)
            {
                eof = true;
                max_size = reader_data.size();
            }
        }
        if (noread)
        {
            if (too_little_dev())
            {
                auto erased = next_dev_buf();
                dev.mockErase(erased);
                dev_data = dev_buf.subspan(0, dev_data.size() + erased.size());
                dev_offset += erased.size();
            }
        }
        else
        {
            while (too_little_dev())
            {
                auto new_dev_data = dev.readAt(next_dev_buf(), dev_offset);
                LOG(LogLevel::Info, " RD@{}#{}", dev_offset,
                    new_dev_data.size());
                dev_data =
                    dev_buf.subspan(0, dev_data.size() + new_dev_data.size());
                dev_offset += new_dev_data.size();
            }
        }
        auto start = dev.shrinkWritePre(dev_data, reader_data);
        auto consumed = start;
        if (start == 0)
        {
            auto size = dev.shrinkWritePost(dev_data, reader_data);
            consumed = std::min(dev_data.size(), reader_data.size());
            if (size > 0)
            {
                auto written = dev.writeAt(reader_data.subspan(0, size),
                                           dev_offset - dev_data.size())
                                   .size();
                LOG(LogLevel::Info, " WD@{}#{}", dev_offset - dev_data.size(),
                    written);
                if (written != size)
                {
                    consumed = written;
                }
            }
        }
        std::memmove(reader_data.data(), reader_data.data() + consumed,
                     reader_data.size() - consumed);
        reader_data = reader_data.subspan(0, reader_data.size() - consumed);
        std::memmove(dev_data.data(), dev_data.data() + consumed,
                     dev_data.size() - consumed);
        dev_data = dev_data.subspan(0, dev_data.size() - consumed);
        max_size -= consumed;
    }
    LOG(LogLevel::Info, "\n");
}

} // namespace ops
} // namespace flasher