[extern] memcmp = fn [cc(c)] (a: &u8, b: &u8, byte_count: u64) s32;

string_no_match = #integer_max(u64);

c_string_length = fn (c_string: &u8) u64
{
    >it = c_string;

    while (it.&)
    {
        it = it + 1;
    }

    return #int_from_pointer(it) - #int_from_pointer(c_string);
}

c_string_to_slice = fn (c_string: &u8) []u8
{
    >length = c_string_length(c_string);
    return c_string[0..length];
}

string_equal = fn(a: []u8, b: []u8) u1
{
    >result: #ReturnType() = 0;

    if (a.length == b.length)
    {
        result = memcmp(a.pointer, b.pointer, a.length) == 0;
    }

    return result;
}

string_last_character = fn(string: []u8, character: u8) u64
{
    >i = string.length;

    while (i > 0)
    {
        i -= 1;

        if (string[i] == character)
        {
            return i;
        }
    }

    return string_no_match;
}

OS_Linux_PROT = bits u32
{
    read: u1,
    write: u1,
    execute: u1,
    sem: u1,
    _: u28,
}

OS_Linux_MAP_Type = enum u4
{
    shared = 0x1,
    private = 0x2,
    shared_validate = 0x3,
}

OS_Linux_MAP = bits u32
{
    type: OS_Linux_MAP_Type,
    fixed: u1,
    anonymous: u1,
    bit_32: u1,
    _: u1,
    grows_down: u1,
    _: u2,
    deny_write: u1,
    executable: u1,
    locked: u1,
    no_reserve: u1,
    populate: u1,
    non_block: u1,
    stack: u1,
    huge_tlb: u1,
    sync: u1,
    fixed_noreplace: u1,
    _: u5,
    uninitialized: u1,
    _: u5,
}

[extern] mmap = fn [cc(c)] (address: u64, size: u64, protection: OS_Linux_PROT, map: OS_Linux_MAP, file_descriptor: s32, offset: s64) &u8;
[extern] mprotect = fn [cc(c)] (address: u64, size: u64, protection: OS_Linux_PROT) s32;

OS_ProtectionFlags = bits
{
    read: u1,
    write: u1,
    execute: u1,
}

OS_MapFlags = bits
{
    private: u1,
    anonymous: u1,
    no_reserve: u1,
    populate: u1,
}

os_linux_protection_flags = fn(map_flags: OS_ProtectionFlags) OS_Linux_PROT
{
    return {
        .read = map_flags.read,
        .write = map_flags.write,
        .execute = map_flags.execute,
        zero,
    };
}

os_linux_map_flags = fn(map_flags: OS_MapFlags) OS_Linux_MAP
{
    return {
        .type = #select(map_flags.private, .private, .shared),
        .anonymous = map_flags.anonymous,
        .no_reserve = map_flags.no_reserve,
        .populate = map_flags.populate,
        zero,
    };
}

os_reserve = fn (base: u64, size: u64, protection: OS_ProtectionFlags, map: OS_MapFlags) &u8
{
    >protection_flags = os_linux_protection_flags(protection);
    >map_flags = os_linux_map_flags(map);
    >address = mmap(base, size, protection_flags, map_flags, -1, 0);
    if (#int_from_pointer(address) == #integer_max(u64))
    {
        unreachable;
    }

    return address;
}

os_commit = fn (address: u64, size: u64, protection: OS_ProtectionFlags) void
{
    >protection_flags = os_linux_protection_flags(protection);
    >result = mprotect(address, size, protection_flags);
    if (result != 0)
    {
        unreachable;
    }
}

Arena = struct
{
    reserved_size: u64,
    position: u64,
    os_position: u64,
    granularity: u64,
    reserved: [32]u8,
}

minimum_position: u64 = #byte_size(Arena);

ArenaInitialization = struct
{
    reserved_size: u64,
    granularity: u64,
    initial_size: u64,
}

arena_initialize = fn (initialization: ArenaInitialization) &Arena
{
    >protection_flags: OS_ProtectionFlags = {
        .read = 1,
        .write = 1,
        zero,
    };

    >map_flags: OS_MapFlags = {
        .private = 1,
        .anonymous = 1,
        .no_reserve = 1,
        .populate = 0,
    };

    >arena: &Arena = #pointer_cast(os_reserve(0, initialization.reserved_size, protection_flags, map_flags));
    os_commit(#int_from_pointer(arena), initialization.initial_size, {
        .read = 1,
        .write = 1,
        zero,
    });

    arena.& = {
        .reserved_size = initialization.reserved_size,
        .position = minimum_position,
        .os_position = initialization.initial_size,
        .granularity = initialization.granularity,
        zero,
    };

    return arena;
}

arena_initialize_default = fn (initial_size: u64) &Arena
{
    return arena_initialize({
        .reserved_size = 4 * 1024 * 1024 * 1024,
        .granularity = 4 * 1024,
        .initial_size = initial_size,
    });
}

GlobalState = struct
{
    arena: &Arena,
}

global_state: GlobalState = undefined;

global_state_initialize = fn () void
{
    global_state = {
        .arena = arena_initialize_default(2 * 1024 * 1024),
    };
}

[export] main = fn [cc(c)] (argument_count: u32, argv: &&u8) s32
{
    if (argument_count != 2)
    {
        return 1;
    }

    >relative_file_path_pointer = argv[1];
    if (!relative_file_path_pointer)
    {
        return 1;
    }

    >relative_file_path = c_string_to_slice(relative_file_path_pointer);

    if (relative_file_path.length < 5)
    {
        return 1;
    }

    >extension_start = string_last_character(relative_file_path, '.');
    if (extension_start == string_no_match)
    {
        return 1;
    }

    if (!string_equal(relative_file_path[extension_start..], ".bbb"))
    {
        return 1;
    }

    global_state_initialize();
    return 0;
}