mod block_device;
mod disk;

use clap::Parser;
use fuser::{Filesystem, MountOption, ReplyAttr, ReplyData, ReplyDirectory, ReplyEntry, Request};
use std::ffi::OsStr;
use std::sync::Arc;
use std::time::Duration;
use log::debug;

use block_device::{memory_disk::MemoryDisk, BlockDevice, BLOCK_SIZE};
use disk::bitmap::Bitmap;
use disk::inode::{Inode, INODE_SIZE};
use libc::ENOENT;

#[derive(Parser, Debug)]
#[command(author, version, about)]
struct Args {
    mount_point: Option<String>,
    #[arg(long)]
    auto_unmount: bool,
    #[arg(long)]
    allow_root: bool,
}

const TTL: Duration = Duration::from_secs(1);
const INODE_PER_BLOCK: usize = BLOCK_SIZE / INODE_SIZE;

/// The design of MyFS is rather simple:
/// +-------------------+
/// | Super Block       |
/// +-------------------+
/// | Inode Bitmap      |
/// +-------------------+
/// | ...               |
/// +-------------------+
/// | Data Block Bitmap |
/// +-------------------+
/// | ...               |
/// +-------------------+
/// | Inode Block       |
/// +-------------------+
/// | ...               |
/// +-------------------+
/// | Data Block        |
/// +-------------------+
/// With each block 4KiB, each Inode entry 128B

#[repr(C)]
struct MyFS {
    device: Arc<dyn BlockDevice>,
    data_bitmap: Bitmap,
    inode_bitmap: Bitmap,
    inode_start_block: usize,
    data_start_block: usize,
}

impl MyFS {
    fn new(device: Arc<dyn BlockDevice>, total_block_number: usize) -> Self {
        let max_inode_number: usize = 16384; // TODO: remove hard-coded magic number
        let inode_block_number = max_inode_number / INODE_PER_BLOCK; // == 128
        let inode_bitmap_block_number = (inode_block_number + BLOCK_SIZE - 1) / BLOCK_SIZE;

        let blocks_remaining =
            total_block_number - inode_block_number - inode_bitmap_block_number - 1;
        // let number of data blocks be x, the remaining block number be C,
        // the corresponding data bitmap length should be ceil(x / BLK_SIZE),
        // thus we have BLK_SIZE * (C-1) / (BLK_SIZE+1) <= x <= BLK_SIZE * C / (BLK_SIZE+1)
        // the difference of the two bounds is less than 1,
        // meaning only 1 integer could be in between.
        // Thus we have x = floor(BLK_SIZE * C / (BLK_SIZE + 1))
        let data_block_number = BLOCK_SIZE * blocks_remaining / (BLOCK_SIZE + 1);
        let data_bitmap_block_number = blocks_remaining - data_block_number;
        debug!("dbbn: {}", data_bitmap_block_number);
        debug!("ibbn: {}", inode_bitmap_block_number);
        debug!("ibn:  {}", inode_block_number);
        debug!("dbn:  {}", data_block_number);
        debug!("sum:  {}", 1 + data_bitmap_block_number + inode_bitmap_block_number + inode_block_number + data_block_number);

        let mut data_bitmap = Bitmap::new(1, data_bitmap_block_number, device.clone());
        let mut inode_bitmap = Bitmap::new(
            data_bitmap_block_number + 1,
            inode_bitmap_block_number,
            device.clone(),
        );
        let mut fs = Self {
            device,
            data_bitmap,
            inode_bitmap,
            inode_start_block: data_bitmap_block_number + inode_bitmap_block_number + 1,
            data_start_block: data_bitmap_block_number
                + inode_bitmap_block_number
                + inode_block_number
                + 1,
        };

        let _ = fs.inode_bitmap.allocate(); // Inode starts from 1
        let root_inode_index = fs.inode_bitmap.allocate();
        assert_eq!(root_inode_index, 1);
        let (root_inode_block, root_inode_offset) = fs.locate_inode(root_inode_index);
        fs.put_inode(root_inode_block, root_inode_offset, Inode::directory());

        fs
    }

    // pub fn allocate_inode(&mut self) -> usize {
    //     self.inode_bitmap.allocate()
    // }

    pub fn inode_active(&self, inode: usize) -> bool {
        self.inode_bitmap.query(inode)
    }

    /// 输入 inode 编号, 返回它对应的 block number 和 block 内 offset
    pub fn locate_inode(&self, inode: usize) -> (usize, usize) {
        let block_number =
            inode / INODE_PER_BLOCK + 1 + self.inode_bitmap.length + self.data_bitmap.length;
        let block_offset = inode % INODE_PER_BLOCK * INODE_SIZE;
        (block_number, block_offset)
    }

    // TODO: 实现一个 LRU 的 cache 机制, 不要每次都开 buffer
    pub fn put_inode(&mut self, block: usize, offset: usize, inode: Inode) {
        let mut buffer = vec![0u8; BLOCK_SIZE];
        self.device.read(block, buffer.as_mut_slice());

        let inode_raw = &inode as *const Inode as *const u8;
        let inode_slice = unsafe { std::slice::from_raw_parts(inode_raw, INODE_SIZE) };
        buffer[offset..offset + INODE_SIZE].copy_from_slice(inode_slice);

        self.device.write(block, buffer.as_slice());
    }

    // TODO: 实现一个 LRU 的 cache 机制, 不要每次都开 buffer
    pub fn get_inode(&self, block: usize, offset: usize) -> Inode {
        let mut buffer = vec![0u8; BLOCK_SIZE];
        self.device.read(block, buffer.as_mut_slice());

        let inode = Inode::file();
        let inode_slice = unsafe {
            std::slice::from_raw_parts_mut(&inode as *const Inode as *mut u8, INODE_SIZE)
        };
        inode_slice.copy_from_slice(&buffer[offset..offset + INODE_SIZE]);
        inode
    }
}

impl Filesystem for MyFS {
    fn lookup(&mut self, _req: &Request<'_>, parent: u64, name: &OsStr, reply: ReplyEntry) {
        debug!(
            "Filesystem::lookup called with parent {} name {}",
            parent,
            name.to_str().unwrap()
        );
        let parent = parent as usize;
        if self.inode_active(parent) {
            let (block, offset) = self.locate_inode(parent);
            let inode = self.get_inode(block, offset);
            debug!("{:?}", inode);
        }
        reply.error(ENOENT);
    }

    fn getattr(&mut self, _req: &Request<'_>, ino: u64, reply: ReplyAttr) {
        debug!("Filesystem::getattr called with ino {}", ino);
        let ino = ino as usize;
        if self.inode_active(ino) {
            let (block, offset) = self.locate_inode(ino);
            let inode = self.get_inode(block, offset);
            debug!("{:?}", inode);
        }
        reply.error(ENOENT);
    }

    fn read(
        &mut self,
        _req: &Request<'_>,
        ino: u64,
        _fh: u64,
        offset: i64,
        _size: u32,
        _flags: i32,
        _lock_owner: Option<u64>,
        reply: ReplyData,
    ) {
        todo!()
    }

    fn readdir(
        &mut self,
        _req: &Request<'_>,
        ino: u64,
        _fh: u64,
        offset: i64,
        mut reply: ReplyDirectory,
    ) {
        todo!()
    }
}

fn main() {
    env_logger::init();
    let args = Args::parse();
    let mount_point = args.mount_point.unwrap();
    // let mut options = vec![
    //     MountOption::RO,
    //     MountOption::FSName("hello".to_string()),
    // ];
    // if args.allow_root {
    //     options.push(MountOption::AutoUnmount);
    // }
    // if args.allow_root {
    //     options.push(MountOption::AllowRoot);
    // }
    let options = vec![
        MountOption::RO,
        MountOption::FSName("hello".to_string()),
        MountOption::AutoUnmount,
        MountOption::AllowRoot,
    ];
    let mem_disk = Arc::new(MemoryDisk::new());
    let filesystem = MyFS::new(mem_disk, 16384);

    fuser::mount2(filesystem, mount_point, &options).unwrap();
}