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    use super::File;
    use crate::drivers::BLOCK_DEVICE;
    use crate::mm::UserBuffer;
    use crate::sync::UPSafeCell;
    use alloc::sync::Arc;
    use alloc::vec::Vec;
    use bitflags::*;
    use easy_fs::{EasyFileSystem, Inode};
    use lazy_static::*;

    pub struct OSInode {
        readable: bool,
        writable: bool,
        inner: UPSafeCell<OSInodeInner>,
    }

    pub struct OSInodeInner {
        offset: usize,
        inode: Arc<Inode>,
    }

    impl OSInode {
        pub fn new(readable: bool, writable: bool, inode: Arc<Inode>) -> Self {
            Self {
                readable,
                writable,
                inner: unsafe { UPSafeCell::new(OSInodeInner { offset: 0, inode }) },
            }
        }
        pub fn read_all(&self) -> Vec<u8> {
            let mut inner = self.inner.exclusive_access();
            let mut buffer = [0u8; 512];
            let mut v: Vec<u8> = Vec::new();
            loop {
                let len = inner.inode.read_at(inner.offset, &mut buffer);
                if len == 0 {
                    break;
                }
                inner.offset += len;
                v.extend_from_slice(&buffer[..len]);
            }
            v
        }
    }

    lazy_static! {
        pub static ref ROOT_INODE: Arc<Inode> = {
            let efs = EasyFileSystem::open(BLOCK_DEVICE.clone());
            Arc::new(EasyFileSystem::root_inode(&efs))
        };
    }

    pub fn list_apps() {
        println!("/**** APPS ****");
        for app in ROOT_INODE.ls() {
            println!("{}", app);
        }
        println!("**************/")
    }

    bitflags! {
        pub struct OpenFlags: u32 {
            const RDONLY = 0;
            const WRONLY = 1 << 0;
            const RDWR = 1 << 1;
            const CREATE = 1 << 9;
            const TRUNC = 1 << 10;
        }
    }

    impl OpenFlags {
        /// Do not check validity for simplicity
        /// Return (readable, writable)
        pub fn read_write(&self) -> (bool, bool) {
            if self.is_empty() {
                (true, false)
            } else if self.contains(Self::WRONLY) {
                (false, true)
            } else {
                (true, true)
            }
        }
    }

    pub fn open_file(name: &str, flags: OpenFlags) -> Option<Arc<OSInode>> {
        let (readable, writable) = flags.read_write();
        if flags.contains(OpenFlags::CREATE) {
            if let Some(inode) = ROOT_INODE.find(name) {
                // clear size
                inode.clear();
                Some(Arc::new(OSInode::new(readable, writable, inode)))
            } else {
                // create file
                ROOT_INODE
                    .create(name)
                    .map(|inode| Arc::new(OSInode::new(readable, writable, inode)))
            }
        } else {
            ROOT_INODE.find(name).map(|inode| {
                if flags.contains(OpenFlags::TRUNC) {
                    inode.clear();
                }
                Arc::new(OSInode::new(readable, writable, inode))
            })
        }
    }

    impl File for OSInode {
        fn readable(&self) -> bool {
            self.readable
        }
        fn writable(&self) -> bool {
            self.writable
        }
        fn read(&self, mut buf: UserBuffer) -> usize {
            let mut inner = self.inner.exclusive_access();
            let mut total_read_size = 0usize;
            for slice in buf.buffers.iter_mut() {
                let read_size = inner.inode.read_at(inner.offset, *slice);
                if read_size == 0 {
                    break;
                }
                inner.offset += read_size;
                total_read_size += read_size;
            }
            total_read_size
        }
        fn write(&self, buf: UserBuffer) -> usize {
            let mut inner = self.inner.exclusive_access();
            let mut total_write_size = 0usize;
            for slice in buf.buffers.iter() {
                let write_size = inner.inode.write_at(inner.offset, *slice);
                assert_eq!(write_size, slice.len());
                inner.offset += write_size;
                total_write_size += write_size;
            }
            total_write_size
        }
    }