use crate::block_device::{BlockDevice, BLOCK_SIZE};
use std::sync::Arc;

pub struct Bitmap {
    pub starting_block: usize,
    pub length: usize,
    pub device: Arc<dyn BlockDevice>,
    pub data: Vec<u8>,
    pub dirty_blocks: Vec<usize>,
}

impl Bitmap {
    pub fn new(starting_block: usize, length: usize, device: Arc<dyn BlockDevice>) -> Self {
        Self {
            starting_block,
            length,
            device,
            data: vec![0u8; length * BLOCK_SIZE],
            dirty_blocks: Vec::new(),
        }
    }
    pub fn allocate(&mut self) -> Option<usize> {
        for (i, byte) in self.data.iter_mut().enumerate() {
            let leading_ones = byte.leading_ones();
            if leading_ones != 8 {
                *byte |= (1 << (7 - leading_ones)) as u8;
                self.dirty_blocks.push(i / BLOCK_SIZE);
                return Some(i * 8 + leading_ones as usize);
            }
        }
        None
        // panic!("No more space for allocation!")
    }

    pub fn query(&self, index: usize) -> bool {
        if index == 0 {
            false
        } else {
            self.data[index / 8] & ((1 << (7 - index % 8)) as u8) != 0
        }
    }

    fn write_back(&mut self) {
        for block_index_offset in self.dirty_blocks.iter() {
            let buffer_front_index = BLOCK_SIZE * block_index_offset;
            let buffer_back_index = BLOCK_SIZE * (block_index_offset + 1);
            self.device.write(
                self.starting_block + block_index_offset,
                &self.data[buffer_front_index..buffer_back_index],
            );
        }
        self.dirty_blocks = Vec::new();
    }
}