/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <AK/String.h>
#include <AK/StringBuilder.h>
#include <AK/Vector.h>
#include <LibCore/ArgsParser.h>
#include <LibCore/DirIterator.h>
#include <LibCore/File.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

static String read_var(const String& name)
{
    StringBuilder builder;
    builder.append("/proc/sys/");
    builder.append(name);
    auto path = builder.to_string();
    auto f = Core::File::construct(path);
    if (!f->open(Core::IODevice::ReadOnly)) {
        fprintf(stderr, "open: %s\n", f->error_string());
        exit(1);
    }
    const auto& b = f->read_all();
    if (f->error() < 0) {
        fprintf(stderr, "read: %s\n", f->error_string());
        exit(1);
    }
    return String((const char*)b.data(), b.size(), Chomp);
}

static void write_var(const String& name, const String& value)
{
    StringBuilder builder;
    builder.append("/proc/sys/");
    builder.append(name);
    auto path = builder.to_string();
    auto f = Core::File::construct(path);
    if (!f->open(Core::IODevice::WriteOnly)) {
        fprintf(stderr, "open: %s\n", f->error_string());
        exit(1);
    }
    f->write(value);
    if (f->error() < 0) {
        fprintf(stderr, "write: %s\n", f->error_string());
        exit(1);
    }
}

static int handle_show_all()
{
    Core::DirIterator di("/proc/sys", Core::DirIterator::SkipDots);
    if (di.has_error()) {
        fprintf(stderr, "DirIterator: %s\n", di.error_string());
        return 1;
    }

    while (di.has_next()) {
        String variable_name = di.next_path();
        printf("%s = %s\n", variable_name.characters(), read_var(variable_name).characters());
    }
    return 0;
}

static int handle_var(const String& var)
{
    String spec(var.characters(), Chomp);
    auto parts = spec.split('=');
    String variable_name = parts[0];
    bool is_write = parts.size() > 1;

    if (!is_write) {
        printf("%s = %s\n", variable_name.characters(), read_var(variable_name).characters());
        return 0;
    }

    printf("%s = %s", variable_name.characters(), read_var(variable_name).characters());
    write_var(variable_name, parts[1]);
    printf(" -> %s\n", read_var(variable_name).characters());
    return 0;
}

int main(int argc, char** argv)
{
    bool show_all = false;
    const char* var = nullptr;

    Core::ArgsParser args_parser;
    args_parser.add_option(show_all, "Show all variables", nullptr, 'a');
    args_parser.add_positional_argument(var, "Command (var[=value])", "command", Core::ArgsParser::Required::No);
    args_parser.parse(argc, argv);

    if (var == nullptr) {
        // Not supplied; assume `-a`.
        show_all = true;
    }

    if (show_all) {
        // Ignore `var`, even if it was supplied. Just like the real procps does.
        return handle_show_all();
    }

    return handle_var(var);
}