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use core::mem::size_of;
use bitflags::bitflags;

bitflags! {
    pub struct RegionFlags: u16 {
        const IN_USE = 1;
    }
}

#[derive(Debug)]
pub struct Region {
    pub size: usize,
    pub data: usize,
    pub padding_start: usize,
    pub padding_end: usize,
    pub flags: RegionFlags,
    pub next: usize,
}

impl Region {
    pub fn new(addr: usize, size: usize) -> Region {
        assert!(size >= Self::min_size());

        Region {
            size: size - size_of::<Self>(),
            data: addr + size_of::<Self>(),
            padding_start: 0,
            padding_end: 0,
            flags: RegionFlags::empty(),
            next: 0,
        }
    }

    pub fn new_with_padding(addr: usize, size: usize, padding_start: usize, padding_end: usize) -> Region {
        let mut region = Region::new(addr, size);
        region.padding_start = padding_start;
        region.padding_end = padding_end;

        region
    }

    pub fn min_size() -> usize {
        size_of::<Self>() + (size_of::<usize>() * 2)
    }

    pub fn next(&self) -> Option<&mut Region> {
        if self.next == 0 {
            return None;
        }

        unsafe { Some(&mut *(self.next as *mut Region)) }
    }

    pub fn get_used(&self) -> bool {
        self.flags.contains(RegionFlags::IN_USE)
    }

    pub fn set_used(&mut self, used: bool) {
        self.flags.set(RegionFlags::IN_USE, used);
    }

    pub fn size(&self) -> usize {
        self.padding_start + self.size + self.padding_end
    }

    pub unsafe fn data_ptr(&self) -> *mut u8 {
        (self.data + self.padding_start) as *mut u8
    }
}