mod block_device;
mod cached_inode;
mod disk;

use std::collections::HashMap;
use clap::Parser;
use fuser::{
    Filesystem, KernelConfig, MountOption, ReplyAttr, ReplyData, ReplyDirectory, ReplyEmpty,
    ReplyEntry, ReplyLseek, ReplyWrite, Request, TimeOrNow,
};
use log::debug;
use std::ffi::OsStr;
use std::sync::Arc;
use std::time::{Duration, SystemTime, UNIX_EPOCH};

use crate::cached_inode::CachedInode;
use crate::disk::data_block::{Block, DoubleIndirectBlock, IndirectBlock, TripleIndirectBlock};
use crate::disk::inode::InodeMode;
use block_device::{memory_disk::MemoryDisk, BlockDevice, BLOCK_SIZE};
use disk::bitmap::Bitmap;
use disk::inode::{Inode, INODE_SIZE};
use libc::{c_int, ENOENT, ENOSPC, ENOSYS};
use users::{get_current_gid, get_current_uid};

#[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,

    cached_inode: HashMap<usize, CachedInode>,
    cache: [[u8; 4096]; 8192],
}

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!("data_bitmap_block_number: {}", data_bitmap_block_number);
        debug!("inode_bitmap_block_number: {}", inode_bitmap_block_number);
        debug!("inode_block_number:  {}", inode_block_number);
        debug!("data_block_number:  {}", data_block_number);
        debug!(
            "sum:  {}",
            1 + data_bitmap_block_number
                + inode_bitmap_block_number
                + inode_block_number
                + data_block_number
        );

        let data_bitmap = Bitmap::new(1, data_bitmap_block_number, device.clone());
        let 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,
            cached_inode: HashMap::new(),
            cache: [[0; 4096]; 8192],
        };

        let _ = fs.data_bitmap.allocate().unwrap(); // data block 0 is not usable
        let _ = fs.inode_bitmap.allocate().unwrap(); // inode block 0 is not usable
        let root_inode_index = fs.inode_bitmap.allocate().unwrap(); // Inode starts from 1
        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(
                0o755,
                get_current_uid(),
                get_current_gid(),
                Self::time_now(),
                0,
                0,
                0,
                0,
            ),
        );

        fs
    }

    fn time_now() -> u32 {
        SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .expect("How can current time be earlier than UNIX_EPOCH?")
            .as_secs() as u32
    }

    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_index: usize) -> (usize, usize) {
        let block_number =
            inode_index / INODE_PER_BLOCK + 1 + self.inode_bitmap.length + self.data_bitmap.length;
        let block_offset = inode_index % INODE_PER_BLOCK * INODE_SIZE;
        (block_number, block_offset)
    }

    pub fn create_inode(
        &mut self,
        permissions: u16,
        mode: InodeMode,
        uid: u32,
        gid: u32,
        flags: u32,
    ) -> Option<usize> {
        self.inode_bitmap.allocate().map(|inode_index| {
            let inode = CachedInode {
                inode: Inode::make_inode(
                    permissions,
                    mode,
                    uid,
                    gid,
                    Self::time_now(),
                    flags,
                    0,
                    0,
                    0,
                ),
                index: inode_index,
                dirty: false,
            };
            self.cached_inode.insert(inode_index, inode);
            inode_index
        })
    }

    /// 得有一个 Inode Cache 数据结构!
    pub fn read_inode(
        &mut self,
        index: usize,
    ) -> bool {
        if self.cached_inode.contains_key(&index) {
            return true;
        } // 已经在 Inode Cache 里了, 返回 true
        if self.inode_bitmap.query(index) {
            let (block, offset) = self.locate_inode(index);
            let inode = CachedInode {
                inode: self.fetch_inode(block, offset),
                index,
                dirty: false,
            };
            self.cached_inode.insert(index, inode);
            return true;
        } // 没有在 Inode Cache 里, 但是是有效 inode, 可以读到 Cache 里, 返回 true
        false // 都没有, 返回 false.
    }

    pub fn write_back_inode(
        &mut self,
        index: usize,
    ) -> bool {
        if let Some(cached_inode) = self.cached_inode.get_mut(&index) {
            if cached_inode.dirty {
                let (block, offset) = self.locate_inode(cached_inode.index);
                self.put_inode(block, offset, &cached_inode.inode);
                cached_inode.dirty = false;
            }
            true // Inode 在 Cache 中, 如果 dirty 则写回, 如果不脏不用管, 都返回写回成功.
        } else {
            false // Inode 没有在 Cache 中, 返回失败.
        }
    }

    // TODO: 实现一个 LRU 的 cache 机制, 不要每次都开 buffer
    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());
    }

    pub fn write_inode(&mut self, inode_index: usize, inode: &Inode) -> bool {
        if self.inode_active(inode_index) {
            let (block, offset) = self.locate_inode(inode_index);
            self.put_inode(block, offset, inode);
            true
        } else {
            false
        }
    }

    pub fn get_inode(&self, inode_index: usize) -> Option<Inode> {
        if self.inode_active(inode_index) {
            let (block, offset) = self.locate_inode(inode_index);
            Some(self.fetch_inode(block, offset))
        } else {
            None
        }
    }

    /// 为 Inode 分配新 block, 返回 block 的编号
    pub fn allocate_block(&mut self, inode: &mut Inode) -> Option<u32> {
        /// 从 direct block 里面尝试分配
        for index in inode.direct.iter_mut() {
            /// 如果这个位置没被分配, 分配一个 index 塞进去
            if self.data_bitmap.query(*index as usize) == false {
                let block_index = self.data_bitmap.allocate() as u32;
                *index = block_index;
                inode.n_blocks += 1;
                // TODO 标记 inode 所在 block 为脏
                return Some(block_index);
            }
        }

        /// 如果这个 indirect block 还未分配, 分配一个
        if self.data_bitmap.query(inode.single_indirect as usize) == false {
            // TODO 标记 inode 所在 block 为脏
            inode.single_indirect = self.data_bitmap.allocate() as u32;
        }
        if let Some(block_index) = self.allocate_in_indirect(inode.single_indirect) {
            // TODO 标记 inode 所在 block 为脏
            inode.n_blocks += 1;
            return Some(block_index);
        }

        /// 如果 double indirect block 还未分配, 分配一个
        if self.data_bitmap.query(inode.double_indirect as usize) == false {
            // TODO 标记 inode 所在 block 为脏
            inode.double_indirect = self.data_bitmap.allocate() as u32;
        }
        if let Some(block_index) = self.alloc_in_double_indirect(inode.double_indirect) {
            // TODO 标记 inode 所在 block 为脏
            inode.n_blocks += 1;
            return Some(block_index);
        }

        /// 如果 triple indirect block 还未分配, 分配一个
        if self.data_bitmap.query(inode.triple_indirect as usize) == false {
            // TODO 标记 inode 所在 block 为脏
            inode.triple_indirect = self.data_bitmap.allocate() as u32;
        }
        if let Some(block_index) = self.alloc_in_triple_indirect(inode.triple_indirect) {
            // TODO 标记 inode 所在 block 为脏
            inode.n_blocks += 1;
            return Some(block_index);
        }

        /// 到这里说明真没空间了
        None
    }

    fn allocate_in_indirect(&mut self, indirect_entry: u32) -> Option<u32> {
        // 取出 single indirect block, 尝试在里面分配
        let indirect = self.fetch_block::<IndirectBlock>(*indirect_entry);
        for entry in indirect.entries.iter_mut() {
            // 如果这个位置没被分配, 分配一个 index 塞进去
            if self.data_bitmap.query(*entry as usize) == false {
                let block_index = self.data_bitmap.allocate() as u32;
                *entry = block_index;
                // TODO 标记 single indirect 为脏
                return Some(block_index);
            }
        }
        None
    }

    fn alloc_in_double_indirect(&mut self, double_indirect_entry: u32) -> Option<u32> {
        let double_indirect = self.fetch_block::<DoubleIndirectBlock>(double_indirect_entry);
        for indirect_entry in double_indirect.indirect.iter_mut() {
            if self.data_bitmap.query(*indirect_entry as usize) == false {
                // TODO 标记 double indirect 为脏
                *indirect_entry = self.data_bitmap.allocate() as u32;
            }
            if let Some(block_index) = self.allocate_in_indirect(*indirect_entry) {
                return Some(block_index);
            }
        }
        None
    }

    fn alloc_in_triple_indirect(&mut self, triple_indirect_entry: u32) -> Option<u32> {
        let triple_indirect = self.fetch_block::<TripleIndirectBlock>(triple_indirect_entry);
        for double_indirect_entry in triple_indirect.double_indirect.iter_mut() {
            if self.data_bitmap.query(*double_indirect_entry as usize) == false {
                // TODO 标记 triple indirect 为脏
                *double_indirect_entry = self.data_bitmap.allocate() as u32;
            }
            if let Some(block_index) = self.alloc_in_double_indirect(*double_indirect_entry) {
                return Some(block_index);
            }
        }
        None
    }

    // TODO: 实现一个 LRU 的 cache 机制, 不要每次都开 buffer
    fn fetch_block<T: Block>(&self, block_index: u32) -> T {
        let mut buffer = vec![0u8; BLOCK_SIZE];
        self.device
            .read(block_index as usize, buffer.as_mut_slice());

        let block = T::default();
        let block_slice =
            unsafe { std::slice::from_raw_parts_mut(&block as *const T as *mut u8, BLOCK_SIZE) };
        block_slice.copy_from_slice(&buffer[..]);
        block
    }

    // TODO: 实现一个 LRU 的 cache 机制, 不要每次都开 buffer
    fn fetch_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::empty();
        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 init(&mut self, _req: &Request<'_>, _config: &mut KernelConfig) -> Result<(), c_int> {
        debug!("Filesystem::init called.");
        Ok(())
    }

    fn destroy(&mut self) {
        debug!("Filesystem::destroy()");
    }

    fn access(&mut self, _req: &Request<'_>, ino: u64, mask: i32, reply: ReplyEmpty) {
        debug!("Filesystem::getattr(ino: {}, mask: {})", ino, mask);
        if let Some(inode) = self.get_inode(ino as usize) {
            reply.ok()
        } else {
            reply.error(ENOENT)
        }
    }

    fn mkdir(
        &mut self,
        _req: &Request<'_>,
        parent: u64,
        name: &OsStr,
        mode: u32,
        umask: u32,
        reply: ReplyEntry,
    ) {
        debug!(
            "Filesystem::mkdir(parent: {}, name: {:?}, mode: {}, umask: {})",
            parent, name, mode, umask
        );
        if let Some(inode) = self.get_inode(parent as usize) {
        } else {
            reply.error(ENOENT);
        }
        // reply.error(ENOSPC);
    }

    fn mknod(
        &mut self,
        _req: &Request<'_>,
        parent: u64,
        name: &OsStr,
        mode: u32,
        umask: u32,
        rdev: u32,
        reply: ReplyEntry,
    ) {
        debug!(
            "Filesystem::mknod(parent: {}, name: {:?}, mode: {}, umask: {}, rdev: {})",
            parent, name, mode, umask, rdev
        );
        reply.error(ENOSPC);
    }

    fn forget(&mut self, _req: &Request<'_>, _ino: u64, _nlookup: u64) {
        debug!("Filesystem::forget()");
        todo!("This is a dumb implementation")
    }

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

    fn setattr(
        &mut self,
        _req: &Request<'_>,
        ino: u64,
        mode: Option<u32>,
        uid: Option<u32>,
        gid: Option<u32>,
        size: Option<u64>,
        _atime: Option<TimeOrNow>,
        _mtime: Option<TimeOrNow>,
        _ctime: Option<SystemTime>,
        fh: Option<u64>,
        _crtime: Option<SystemTime>,
        _chgtime: Option<SystemTime>,
        _bkuptime: Option<SystemTime>,
        flags: Option<u32>,
        reply: ReplyAttr,
    ) {
        debug!(
            "Filesystem::setattr(ino: {:#x?}, mode: {:?}, uid: {:?}, \
            gid: {:?}, size: {:?}, fh: {:?}, flags: {:?})",
            ino, mode, uid, gid, size, fh, flags
        );
        reply.error(ENOSYS);
    }

    fn readlink(&mut self, _req: &Request<'_>, ino: u64, reply: ReplyData) {
        debug!("[Not Implemented] readlink(ino: {})", ino);
        reply.error(ENOSYS);
    }

    fn lseek(
        &mut self,
        _req: &Request<'_>,
        ino: u64,
        fh: u64,
        offset: i64,
        whence: i32,
        reply: ReplyLseek,
    ) {
        debug!(
            "lseek(ino: {:#x?}, fh: {}, offset: {}, whence: {})",
            ino, fh, offset, whence
        );
        reply.error(ENOSYS);
    }

    fn copy_file_range(
        &mut self,
        _req: &Request<'_>,
        ino_in: u64,
        fh_in: u64,
        offset_in: i64,
        ino_out: u64,
        fh_out: u64,
        offset_out: i64,
        len: u64,
        flags: u32,
        reply: ReplyWrite,
    ) {
        debug!(
            "copy_file_range(ino_in: {:#x?}, fh_in: {}, \
            offset_in: {}, ino_out: {:#x?}, fh_out: {}, offset_out: {}, \
            len: {}, flags: {})",
            ino_in, fh_in, offset_in, ino_out, fh_out, offset_out, len, flags
        );
        reply.error(ENOSYS);
    }

    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 let Some(inode) = self.get_inode(parent) {
            // debug!("{:?}", inode);
        }
        // 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 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 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();
}