/*
 * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Format.h>
#include <AK/LexicalPath.h>
#include <LibCore/ArgsParser.h>
#include <LibCore/DirIterator.h>
#include <LibCore/File.h>
#include <sched.h>
#include <sys/stat.h>

static int perform_copy(const String& source, const String& destination);
static void report_error(String message);
static void report_warning(String message);

int main(int argc, char** argv)
{
    String operation;
    String source;
    String destination;

    Core::ArgsParser args_parser;
    args_parser.add_positional_argument(operation, "Operation", "operation", Core::ArgsParser::Required::Yes);
    args_parser.add_positional_argument(source, "Source", "source", Core::ArgsParser::Required::Yes);
    args_parser.add_positional_argument(destination, "Destination", "destination", Core::ArgsParser::Required::Yes);
    args_parser.parse(argc, argv);

    if (operation == "Copy")
        return perform_copy(source, destination);

    report_warning(String::formatted("Unknown operation '{}'", operation));
    return 0;
}

struct WorkItem {
    enum class Type {
        CreateDirectory,
        CopyFile,
    };
    Type type;
    String source;
    String destination;
    off_t size;
};

static void report_error(String message)
{
    outln("ERROR {}", message);
}

static void report_warning(String message)
{
    outln("WARN {}", message);
}

static bool collect_work_items(const String& source, const String& destination, Vector<WorkItem>& items)
{
    struct stat st = {};
    if (stat(source.characters(), &st) < 0) {
        auto original_errno = errno;
        report_error(String::formatted("stat: {}", strerror(original_errno)));
        return false;
    }

    if (!S_ISDIR(st.st_mode)) {
        // It's a file.
        items.append(WorkItem {
            .type = WorkItem::Type::CopyFile,
            .source = source,
            .destination = String::formatted("{}/{}", destination, LexicalPath::basename(source)),
            .size = st.st_size,
        });
        return true;
    }

    // It's a directory.
    items.append(WorkItem {
        .type = WorkItem::Type::CreateDirectory,
        .source = {},
        .destination = String::formatted("{}/{}", destination, LexicalPath::basename(source)),
        .size = 0,
    });

    Core::DirIterator dt(source, Core::DirIterator::SkipParentAndBaseDir);
    while (dt.has_next()) {
        auto name = dt.next_path();
        if (!collect_work_items(
                String::formatted("{}/{}", source, name),
                String::formatted("{}/{}", destination, LexicalPath::basename(source)),
                items)) {
            return false;
        }
    }

    return true;
}

int perform_copy(const String& source, const String& destination)
{
    Vector<WorkItem> items;

    if (!collect_work_items(source, destination, items))
        return 1;

    off_t total_bytes_to_copy = 0;
    for (auto& item : items)
        total_bytes_to_copy += item.size;

    off_t bytes_copied_so_far = 0;

    for (size_t i = 0; i < items.size(); ++i) {
        auto& item = items[i];
        off_t item_done = 0;
        auto print_progress = [&] {
            outln("PROGRESS {} {} {} {} {} {} {}", i, items.size(), bytes_copied_so_far, total_bytes_to_copy, item_done, item.size, item.source);
        };
        if (item.type == WorkItem::Type::CreateDirectory) {
            outln("MKDIR {}", item.destination);
            if (mkdir(item.destination.characters(), 0755) < 0 && errno != EEXIST) {
                auto original_errno = errno;
                report_error(String::formatted("mkdir: {}", strerror(original_errno)));
                return 1;
            }
            continue;
        }
        VERIFY(item.type == WorkItem::Type::CopyFile);
        auto source_file_or_error = Core::File::open(item.source, Core::OpenMode::ReadOnly);
        if (source_file_or_error.is_error()) {
            report_warning(String::formatted("Failed to open {} for reading: {}", item.source, source_file_or_error.error()));
            return 1;
        }
        auto destination_file_or_error = Core::File::open(item.destination, (Core::OpenMode)(Core::OpenMode::WriteOnly | Core::OpenMode::Truncate));
        if (destination_file_or_error.is_error()) {
            report_warning(String::formatted("Failed to open {} for write: {}", item.destination, destination_file_or_error.error()));
            return 1;
        }
        auto& source_file = *source_file_or_error.value();
        auto& destination_file = *destination_file_or_error.value();

        while (true) {
            print_progress();
            auto buffer = source_file.read(65536);
            if (buffer.is_empty())
                break;
            if (!destination_file.write(buffer)) {
                report_warning(String::formatted("Failed to write to destination file: {}", destination_file.error_string()));
                return 1;
            }
            item_done += buffer.size();
            bytes_copied_so_far += buffer.size();
            print_progress();
            // FIXME: Remove this once the kernel is smart enough to schedule other threads
            //        while we're doing heavy I/O. Right now, copying a large file will totally
            //        starve the rest of the system.
            sched_yield();
        }
        print_progress();
    }

    outln("FINISH");
    return 0;
}