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    use super::TaskContext;
    use super::{pid_alloc, KernelStack, PidHandle};
    use crate::config::TRAP_CONTEXT;
    use crate::fs::{File, Stdin, Stdout};
    use crate::mm::{MemorySet, PhysPageNum, VirtAddr, KERNEL_SPACE};
    use crate::sync::UPSafeCell;
    use crate::trap::{trap_handler, TrapContext};
    use alloc::sync::{Arc, Weak};
    use alloc::vec;
    use alloc::vec::Vec;
    use core::cell::RefMut;

    pub struct TaskControlBlock {
        // immutable
        pub pid: PidHandle,
        pub kernel_stack: KernelStack,
        // mutable
        inner: UPSafeCell<TaskControlBlockInner>,
    }

    pub struct TaskControlBlockInner {
        pub trap_cx_ppn: PhysPageNum,
        pub base_size: usize,
        pub task_cx: TaskContext,
        pub task_status: TaskStatus,
        pub memory_set: MemorySet,
        pub parent: Option<Weak<TaskControlBlock>>,
        pub children: Vec<Arc<TaskControlBlock>>,
        pub exit_code: i32,
        pub fd_table: Vec<Option<Arc<dyn File + Send + Sync>>>,
    }

    impl TaskControlBlockInner {
        pub fn get_trap_cx(&self) -> &'static mut TrapContext {
            self.trap_cx_ppn.get_mut()
        }
        pub fn get_user_token(&self) -> usize {
            self.memory_set.token()
        }
        fn get_status(&self) -> TaskStatus {
            self.task_status
        }
        pub fn is_zombie(&self) -> bool {
            self.get_status() == TaskStatus::Zombie
        }
        pub fn alloc_fd(&mut self) -> usize {
            if let Some(fd) = (0..self.fd_table.len()).find(|fd| self.fd_table[*fd].is_none()) {
                fd
            } else {
                self.fd_table.push(None);
                self.fd_table.len() - 1
            }
        }
    }

    impl TaskControlBlock {
        pub fn inner_exclusive_access(&self) -> RefMut<'_, TaskControlBlockInner> {
            self.inner.exclusive_access()
        }
        pub fn new(elf_data: &[u8]) -> Self {
            // memory_set with elf program headers/trampoline/trap context/user stack
            let (memory_set, user_sp, entry_point) = MemorySet::from_elf(elf_data);
            let trap_cx_ppn = memory_set
                .translate(VirtAddr::from(TRAP_CONTEXT).into())
                .unwrap()
                .ppn();
            // alloc a pid and a kernel stack in kernel space
            let pid_handle = pid_alloc();
            let kernel_stack = KernelStack::new(&pid_handle);
            let kernel_stack_top = kernel_stack.get_top();
            let task_control_block = Self {
                pid: pid_handle,
                kernel_stack,
                inner: unsafe {
                    UPSafeCell::new(TaskControlBlockInner {
                        trap_cx_ppn,
                        base_size: user_sp,
                        task_cx: TaskContext::goto_trap_return(kernel_stack_top),
                        task_status: TaskStatus::Ready,
                        memory_set,
                        parent: None,
                        children: Vec::new(),
                        exit_code: 0,
                        fd_table: vec![
                            // 0 -> stdin
                            Some(Arc::new(Stdin)),
                            // 1 -> stdout
                            Some(Arc::new(Stdout)),
                            // 2 -> stderr
                            Some(Arc::new(Stdout)),
                        ],
                    })
                },
            };
            // prepare TrapContext in user space
            let trap_cx = task_control_block.inner_exclusive_access().get_trap_cx();
            *trap_cx = TrapContext::app_init_context(
                entry_point,
                user_sp,
                KERNEL_SPACE.exclusive_access().token(),
                kernel_stack_top,
                trap_handler as usize,
            );
            task_control_block
        }
        pub fn exec(&self, elf_data: &[u8]) {
            // memory_set with elf program headers/trampoline/trap context/user stack
            let (memory_set, user_sp, entry_point) = MemorySet::from_elf(elf_data);
            let trap_cx_ppn = memory_set
                .translate(VirtAddr::from(TRAP_CONTEXT).into())
                .unwrap()
                .ppn();

            // **** access current TCB exclusively
            let mut inner = self.inner_exclusive_access();
            // substitute memory_set
            inner.memory_set = memory_set;
            // update trap_cx ppn
            inner.trap_cx_ppn = trap_cx_ppn;
            // initialize trap_cx
            let trap_cx = TrapContext::app_init_context(
                entry_point,
                user_sp,
                KERNEL_SPACE.exclusive_access().token(),
                self.kernel_stack.get_top(),
                trap_handler as usize,
            );
            *inner.get_trap_cx() = trap_cx;
            // **** release current PCB
        }
        pub fn fork(self: &Arc<TaskControlBlock>) -> Arc<TaskControlBlock> {
            // ---- hold parent PCB lock
            let mut parent_inner = self.inner_exclusive_access();
            // copy user space(include trap context)
            let memory_set = MemorySet::from_existed_user(&parent_inner.memory_set);
            let trap_cx_ppn = memory_set
                .translate(VirtAddr::from(TRAP_CONTEXT).into())
                .unwrap()
                .ppn();
            // alloc a pid and a kernel stack in kernel space
            let pid_handle = pid_alloc();
            let kernel_stack = KernelStack::new(&pid_handle);
            let kernel_stack_top = kernel_stack.get_top();
            // copy fd table
            let mut new_fd_table: Vec<Option<Arc<dyn File + Send + Sync>>> = Vec::new();
            for fd in parent_inner.fd_table.iter() {
                if let Some(file) = fd {
                    new_fd_table.push(Some(file.clone()));
                } else {
                    new_fd_table.push(None);
                }
            }
            let task_control_block = Arc::new(TaskControlBlock {
                pid: pid_handle,
                kernel_stack,
                inner: unsafe {
                    UPSafeCell::new(TaskControlBlockInner {
                        trap_cx_ppn,
                        base_size: parent_inner.base_size,
                        task_cx: TaskContext::goto_trap_return(kernel_stack_top),
                        task_status: TaskStatus::Ready,
                        memory_set,
                        parent: Some(Arc::downgrade(self)),
                        children: Vec::new(),
                        exit_code: 0,
                        fd_table: new_fd_table,
                    })
                },
            });
            // add child
            parent_inner.children.push(task_control_block.clone());
            // modify kernel_sp in trap_cx
            // **** access child PCB exclusively
            let trap_cx = task_control_block.inner_exclusive_access().get_trap_cx();
            trap_cx.kernel_sp = kernel_stack_top;
            // return
            task_control_block
            // **** release child PCB
            // ---- release parent PCB
        }
        pub fn getpid(&self) -> usize {
            self.pid.0
        }
    }

    #[derive(Copy, Clone, PartialEq)]
    pub enum TaskStatus {
        Ready,
        Running,
        Zombie,
    }