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use axdriver::prelude::*;

const BLOCK_SIZE: usize = 512;

/// A disk device with a cursor.
pub struct Disk {
    block_id: u64,
    offset: usize,
    dev: AxBlockDevice,
}

impl Disk {
    /// Create a new disk.
    pub fn new(dev: AxBlockDevice) -> Self {
        assert_eq!(BLOCK_SIZE, dev.block_size());
        Self {
            block_id: 0,
            offset: 0,
            dev,
        }
    }

    /// Get the size of the disk.
    pub fn size(&self) -> u64 {
        self.dev.num_blocks() * BLOCK_SIZE as u64
    }

    /// Get the position of the cursor.
    pub fn position(&self) -> u64 {
        self.block_id * BLOCK_SIZE as u64 + self.offset as u64
    }

    /// Set the position of the cursor.
    pub fn set_position(&mut self, pos: u64) {
        self.block_id = pos / BLOCK_SIZE as u64;
        self.offset = pos as usize % BLOCK_SIZE;
    }

    /// Read within one block, returns the number of bytes read.
    pub fn read_one(&mut self, buf: &mut [u8]) -> DevResult<usize> {
        let read_size = if self.offset == 0 && buf.len() >= BLOCK_SIZE {
            // whole block
            self.dev
                .read_block(self.block_id, &mut buf[0..BLOCK_SIZE])?;
            self.block_id += 1;
            BLOCK_SIZE
        } else {
            // partial block
            let mut data = [0u8; BLOCK_SIZE];
            let start = self.offset;
            let count = buf.len().min(BLOCK_SIZE - self.offset);

            self.dev.read_block(self.block_id, &mut data)?;
            buf[..count].copy_from_slice(&data[start..start + count]);

            self.offset += count;
            if self.offset >= BLOCK_SIZE {
                self.block_id += 1;
                self.offset -= BLOCK_SIZE;
            }
            count
        };
        Ok(read_size)
    }

    /// Write within one block, returns the number of bytes written.
    pub fn write_one(&mut self, buf: &[u8]) -> DevResult<usize> {
        let write_size = if self.offset == 0 && buf.len() >= BLOCK_SIZE {
            // whole block
            self.dev.write_block(self.block_id, &buf[0..BLOCK_SIZE])?;
            self.block_id += 1;
            BLOCK_SIZE
        } else {
            // partial block
            let mut data = [0u8; BLOCK_SIZE];
            let start = self.offset;
            let count = buf.len().min(BLOCK_SIZE - self.offset);

            self.dev.read_block(self.block_id, &mut data)?;
            data[start..start + count].copy_from_slice(&buf[..count]);
            self.dev.write_block(self.block_id, &data)?;

            self.offset += count;
            if self.offset >= BLOCK_SIZE {
                self.block_id += 1;
                self.offset -= BLOCK_SIZE;
            }
            count
        };
        Ok(write_size)
    }
}