use port_block_device::BlockDevice;
use super::io::{read_block, write_block, read_u32, write_u32, read_u16, write_u16};

pub struct BlockGroupDescriptor {
    pub block_bitmap: u32,
    pub inode_bitmap: u32,
    pub inode_table: u32,
    pub free_blocks_count: u16,
    pub free_inodes_count: u16,
}

impl BlockGroupDescriptor {
    pub fn read<B: BlockDevice>(device: &mut B, gdt_block: u32, bg: u32, spb: usize) -> Option<Self> {
        let mut buf = [0u8; 4096];
        if !read_block(device, gdt_block as u64, spb, &mut buf) { return None; }
        let off = (bg as usize) * 32;
        if off + 32 > buf.len() { return None; }
        Some(Self {
            block_bitmap: read_u32(&buf, off),
            inode_bitmap: read_u32(&buf, off + 4),
            inode_table: read_u32(&buf, off + 8),
            free_blocks_count: read_u16(&buf, off + 12),
            free_inodes_count: read_u16(&buf, off + 14),
        })
    }

    pub fn write_back<B: BlockDevice>(&self, device: &mut B, gdt_block: u32, bg: u32, spb: usize) -> bool {
        let mut buf = [0u8; 4096];
        if !read_block(device, gdt_block as u64, spb, &mut buf) { return false; }
        let off = (bg as usize) * 32;
        if off + 32 > buf.len() { return false; }
        write_u32(&mut buf, off, self.block_bitmap);
        write_u32(&mut buf, off + 4, self.inode_bitmap);
        write_u32(&mut buf, off + 8, self.inode_table);
        write_u16(&mut buf, off + 12, self.free_blocks_count);
        write_u16(&mut buf, off + 14, self.free_inodes_count);
        write_block(device, gdt_block as u64, spb, &buf)
    }
}