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    use super::{frame_alloc, FrameTracker};
    use super::{PTEFlags, PageTable, PageTableEntry};
    use super::{PhysAddr, PhysPageNum, VirtAddr, VirtPageNum};
    use super::{StepByOne, VPNRange};
    use crate::config::{MEMORY_END, MMIO, PAGE_SIZE, TRAMPOLINE, TRAP_CONTEXT, USER_STACK_SIZE};
    use crate::sync::UPSafeCell;
    use alloc::collections::BTreeMap;
    use alloc::sync::Arc;
    use alloc::vec::Vec;
    use core::arch::asm;
    use lazy_static::*;
    use riscv::register::satp;

    extern "C" {
        fn stext();
        fn etext();
        fn srodata();
        fn erodata();
        fn sdata();
        fn edata();
        fn sbss_with_stack();
        fn ebss();
        fn ekernel();
        fn strampoline();
    }

    lazy_static! {
        pub static ref KERNEL_SPACE: Arc<UPSafeCell<MemorySet>> =
            Arc::new(unsafe { UPSafeCell::new(MemorySet::new_kernel()) });
    }

    pub fn kernel_token() -> usize {
        KERNEL_SPACE.exclusive_access().token()
    }

    pub struct MemorySet {
        page_table: PageTable,
        areas: Vec<MapArea>,
    }

    impl MemorySet {
        pub fn new_bare() -> Self {
            Self {
                page_table: PageTable::new(),
                areas: Vec::new(),
            }
        }
        pub fn token(&self) -> usize {
            self.page_table.token()
        }
        /// Assume that no conflicts.
        pub fn insert_framed_area(
            &mut self,
            start_va: VirtAddr,
            end_va: VirtAddr,
            permission: MapPermission,
        ) {
            self.push(
                MapArea::new(start_va, end_va, MapType::Framed, permission),
                None,
            );
        }
        pub fn remove_area_with_start_vpn(&mut self, start_vpn: VirtPageNum) {
            if let Some((idx, area)) = self
                .areas
                .iter_mut()
                .enumerate()
                .find(|(_, area)| area.vpn_range.get_start() == start_vpn)
            {
                area.unmap(&mut self.page_table);
                self.areas.remove(idx);
            }
        }
        fn push(&mut self, mut map_area: MapArea, data: Option<&[u8]>) {
            map_area.map(&mut self.page_table);
            if let Some(data) = data {
                map_area.copy_data(&mut self.page_table, data);
            }
            self.areas.push(map_area);
        }
        /// Mention that trampoline is not collected by areas.
        fn map_trampoline(&mut self) {
            self.page_table.map(
                VirtAddr::from(TRAMPOLINE).into(),
                PhysAddr::from(strampoline as usize).into(),
                PTEFlags::R | PTEFlags::X,
            );
        }
        /// Without kernel stacks.
        pub fn new_kernel() -> Self {
            let mut memory_set = Self::new_bare();
            // map trampoline
            memory_set.map_trampoline();
            // map kernel sections
            println!(".text [{:#x}, {:#x})", stext as usize, etext as usize);
            println!(".rodata [{:#x}, {:#x})", srodata as usize, erodata as usize);
            println!(".data [{:#x}, {:#x})", sdata as usize, edata as usize);
            println!(
                ".bss [{:#x}, {:#x})",
                sbss_with_stack as usize, ebss as usize
            );
            println!("mapping .text section");
            memory_set.push(
                MapArea::new(
                    (stext as usize).into(),
                    (etext as usize).into(),
                    MapType::Identical,
                    MapPermission::R | MapPermission::X,
                ),
                None,
            );
            println!("mapping .rodata section");
            memory_set.push(
                MapArea::new(
                    (srodata as usize).into(),
                    (erodata as usize).into(),
                    MapType::Identical,
                    MapPermission::R,
                ),
                None,
            );
            println!("mapping .data section");
            memory_set.push(
                MapArea::new(
                    (sdata as usize).into(),
                    (edata as usize).into(),
                    MapType::Identical,
                    MapPermission::R | MapPermission::W,
                ),
                None,
            );
            println!("mapping .bss section");
            memory_set.push(
                MapArea::new(
                    (sbss_with_stack as usize).into(),
                    (ebss as usize).into(),
                    MapType::Identical,
                    MapPermission::R | MapPermission::W,
                ),
                None,
            );
            println!("mapping physical memory");
            memory_set.push(
                MapArea::new(
                    (ekernel as usize).into(),
                    MEMORY_END.into(),
                    MapType::Identical,
                    MapPermission::R | MapPermission::W,
                ),
                None,
            );
            println!("mapping memory-mapped registers");
            for pair in MMIO {
                memory_set.push(
                    MapArea::new(
                        (*pair).0.into(),
                        ((*pair).0 + (*pair).1).into(),
                        MapType::Identical,
                        MapPermission::R | MapPermission::W,
                    ),
                    None,
                );
            }
            memory_set
        }
        /// Include sections in elf and trampoline and TrapContext and user stack,
        /// also returns user_sp and entry point.
        pub fn from_elf(elf_data: &[u8]) -> (Self, usize, usize) {
            let mut memory_set = Self::new_bare();
            // map trampoline
            memory_set.map_trampoline();
            // map program headers of elf, with U flag
            let elf = xmas_elf::ElfFile::new(elf_data).unwrap();
            let elf_header = elf.header;
            let magic = elf_header.pt1.magic;
            assert_eq!(magic, [0x7f, 0x45, 0x4c, 0x46], "invalid elf!");
            let ph_count = elf_header.pt2.ph_count();
            let mut max_end_vpn = VirtPageNum(0);
            for i in 0..ph_count {
                let ph = elf.program_header(i).unwrap();
                if ph.get_type().unwrap() == xmas_elf::program::Type::Load {
                    let start_va: VirtAddr = (ph.virtual_addr() as usize).into();
                    let end_va: VirtAddr = ((ph.virtual_addr() + ph.mem_size()) as usize).into();
                    let mut map_perm = MapPermission::U;
                    let ph_flags = ph.flags();
                    if ph_flags.is_read() {
                        map_perm |= MapPermission::R;
                    }
                    if ph_flags.is_write() {
                        map_perm |= MapPermission::W;
                    }
                    if ph_flags.is_execute() {
                        map_perm |= MapPermission::X;
                    }
                    let map_area = MapArea::new(start_va, end_va, MapType::Framed, map_perm);
                    max_end_vpn = map_area.vpn_range.get_end();
                    memory_set.push(
                        map_area,
                        Some(&elf.input[ph.offset() as usize..(ph.offset() + ph.file_size()) as usize]),
                    );
                }
            }
            // map user stack with U flags
            let max_end_va: VirtAddr = max_end_vpn.into();
            let mut user_stack_bottom: usize = max_end_va.into();
            // guard page
            user_stack_bottom += PAGE_SIZE;
            let user_stack_top = user_stack_bottom + USER_STACK_SIZE;
            memory_set.push(
                MapArea::new(
                    user_stack_bottom.into(),
                    user_stack_top.into(),
                    MapType::Framed,
                    MapPermission::R | MapPermission::W | MapPermission::U,
                ),
                None,
            );
            // map TrapContext
            memory_set.push(
                MapArea::new(
                    TRAP_CONTEXT.into(),
                    TRAMPOLINE.into(),
                    MapType::Framed,
                    MapPermission::R | MapPermission::W,
                ),
                None,
            );
            (
                memory_set,
                user_stack_top,
                elf.header.pt2.entry_point() as usize,
            )
        }
        pub fn from_existed_user(user_space: &MemorySet) -> MemorySet {
            let mut memory_set = Self::new_bare();
            // map trampoline
            memory_set.map_trampoline();
            // copy data sections/trap_context/user_stack
            for area in user_space.areas.iter() {
                let new_area = MapArea::from_another(area);
                memory_set.push(new_area, None);
                // copy data from another space
                for vpn in area.vpn_range {
                    let src_ppn = user_space.translate(vpn).unwrap().ppn();
                    let dst_ppn = memory_set.translate(vpn).unwrap().ppn();
                    dst_ppn
                        .get_bytes_array()
                        .copy_from_slice(src_ppn.get_bytes_array());
                }
            }
            memory_set
        }
        pub fn activate(&self) {
            let satp = self.page_table.token();
            unsafe {
                satp::write(satp);
                asm!("sfence.vma");
            }
        }
        pub fn translate(&self, vpn: VirtPageNum) -> Option<PageTableEntry> {
            self.page_table.translate(vpn)
        }
        pub fn recycle_data_pages(&mut self) {
            //*self = Self::new_bare();
            self.areas.clear();
        }
    }

    pub struct MapArea {
        vpn_range: VPNRange,
        data_frames: BTreeMap<VirtPageNum, FrameTracker>,
        map_type: MapType,
        map_perm: MapPermission,
    }

    impl MapArea {
        pub fn new(
            start_va: VirtAddr,
            end_va: VirtAddr,
            map_type: MapType,
            map_perm: MapPermission,
        ) -> Self {
            let start_vpn: VirtPageNum = start_va.floor();
            let end_vpn: VirtPageNum = end_va.ceil();
            Self {
                vpn_range: VPNRange::new(start_vpn, end_vpn),
                data_frames: BTreeMap::new(),
                map_type,
                map_perm,
            }
        }
        pub fn from_another(another: &MapArea) -> Self {
            Self {
                vpn_range: VPNRange::new(another.vpn_range.get_start(), another.vpn_range.get_end()),
                data_frames: BTreeMap::new(),
                map_type: another.map_type,
                map_perm: another.map_perm,
            }
        }
        pub fn map_one(&mut self, page_table: &mut PageTable, vpn: VirtPageNum) {
            let ppn: PhysPageNum;
            match self.map_type {
                MapType::Identical => {
                    ppn = PhysPageNum(vpn.0);
                }
                MapType::Framed => {
                    let frame = frame_alloc().unwrap();
                    ppn = frame.ppn;
                    self.data_frames.insert(vpn, frame);
                }
            }
            let pte_flags = PTEFlags::from_bits(self.map_perm.bits).unwrap();
            page_table.map(vpn, ppn, pte_flags);
        }
        pub fn unmap_one(&mut self, page_table: &mut PageTable, vpn: VirtPageNum) {
            if self.map_type == MapType::Framed {
                self.data_frames.remove(&vpn);
            }
            page_table.unmap(vpn);
        }
        pub fn map(&mut self, page_table: &mut PageTable) {
            for vpn in self.vpn_range {
                self.map_one(page_table, vpn);
            }
        }
        pub fn unmap(&mut self, page_table: &mut PageTable) {
            for vpn in self.vpn_range {
                self.unmap_one(page_table, vpn);
            }
        }
        /// data: start-aligned but maybe with shorter length
        /// assume that all frames were cleared before
        pub fn copy_data(&mut self, page_table: &mut PageTable, data: &[u8]) {
            assert_eq!(self.map_type, MapType::Framed);
            let mut start: usize = 0;
            let mut current_vpn = self.vpn_range.get_start();
            let len = data.len();
            loop {
                let src = &data[start..len.min(start + PAGE_SIZE)];
                let dst = &mut page_table
                    .translate(current_vpn)
                    .unwrap()
                    .ppn()
                    .get_bytes_array()[..src.len()];
                dst.copy_from_slice(src);
                start += PAGE_SIZE;
                if start >= len {
                    break;
                }
                current_vpn.step();
            }
        }
    }

    #[derive(Copy, Clone, PartialEq, Debug)]
    pub enum MapType {
        Identical,
        Framed,
    }

    bitflags! {
        pub struct MapPermission: u8 {
            const R = 1 << 1;
            const W = 1 << 2;
            const X = 1 << 3;
            const U = 1 << 4;
        }
    }

    #[allow(unused)]
    pub fn remap_test() {
        let mut kernel_space = KERNEL_SPACE.exclusive_access();
        let mid_text: VirtAddr = ((stext as usize + etext as usize) / 2).into();
        let mid_rodata: VirtAddr = ((srodata as usize + erodata as usize) / 2).into();
        let mid_data: VirtAddr = ((sdata as usize + edata as usize) / 2).into();
        assert!(
            !kernel_space
                .page_table
                .translate(mid_text.floor())
                .unwrap()
                .writable(),
        );
        assert!(
            !kernel_space
                .page_table
                .translate(mid_rodata.floor())
                .unwrap()
                .writable(),
        );
        assert!(
            !kernel_space
                .page_table
                .translate(mid_data.floor())
                .unwrap()
                .executable(),
        );
        println!("remap_test passed!");
    }