use io;

use sector;
use errors;

def mbr_lba: size = 0;

export type nombr = !void;

export type mbr = struct {
	@offset(0) bootstrap: [440]u8,
	@offset(440) udid: u32,
	@offset(444) reserved: u16,
	@offset(446) entries: [4]mbr_entry,
	@offset(510) magic: u16,
};

export type mbr_entry = struct {
	@offset(0) attributes: u8,
	@offset(4) part_type: u8,
	@offset(8) lba_begin: u32,
	@offset(12) lba_end: u32, 
};

export fn validate(self: *mbr) bool = {
	if (self.magic != 0xaa55) {
		return false;
	};

	return true;
};

// Gets a handle to the MBR of a partition.
// Return value is returned to user. Resource should be freed with mbr::finish.
export fn from(fd: io::file) (*mbr | nombr | errors::error) = {
	const self = io::mmap(null, sector::length, io::prot::READ | io::prot::WRITE, io::mflags::SHARED, fd, sector::lba(mbr_lba))!: *mbr;
	
	if (!validate(self)) {
		io::munmap(self, sector::length)?;
		return nombr;
	};
	
	return self;
};

// Frees the resources associated with the MBR partition.
// User revokes ownership.
export fn finish(self: *mbr) (void | errors::error) = {
	io::munmap(self, sector::length)?;
};