use super::{frame_alloc, PhysPageNum, FrameTracker, VirtPageNum};
use alloc::vec::Vec;
use alloc::vec;
use bitflags::*;

bitflags! {
    pub struct PTEFlags: u8 {
        const V = 1 << 0;
        const R = 1 << 1;
        const W = 1 << 2;
        const X = 1 << 3;
        const U = 1 << 4;
        const G = 1 << 5;
        const A = 1 << 6;
        const D = 1 << 7;
    }
}

#[derive(Copy, Clone)]
#[repr(C)]
pub struct PageTableEntry {
    pub bits: usize,
}

impl PageTableEntry {
    pub fn new(ppn: PhysPageNum, flags: PTEFlags) -> Self {
        PageTableEntry {
            bits: ppn.0 << 10 | flags.bits as usize,
        }
    }
    pub fn empty() -> Self {
        PageTableEntry {
            bits: 0,
        }
    }
    pub fn ppn(&self) -> PhysPageNum {
        (self.bits >> 10 & ((1usize << 44) - 1)).into()
    }
    pub fn flags(&self) -> PTEFlags {
        PTEFlags::from_bits(self.bits as u8).unwrap()
    }
    pub fn is_valid(&self) -> bool {
        (self.flags() & PTEFlags::V) != PTEFlags::empty()
    }
    pub fn readable(&self) -> bool {
        (self.flags() & PTEFlags::R) != PTEFlags::empty()
    }
    pub fn writable(&self) -> bool {
        (self.flags() & PTEFlags::W) != PTEFlags::empty()
    }
    pub fn executable(&self) -> bool {
        (self.flags() & PTEFlags::X) != PTEFlags::empty()
    }
}

pub struct PageTable {
    root_ppn: PhysPageNum,
    frames: Vec<FrameTracker>,
}

/// Assume that it won't oom when creating/mapping.
impl PageTable {
    pub fn new() -> Self {
        //println!("into PageTable::new()");
        let frame = frame_alloc().unwrap();
        PageTable {
            root_ppn: frame.ppn,
            frames: vec![frame],
        }
    }
    fn find_pte(&mut self, vpn: VirtPageNum, create: bool) -> Option<&mut PageTableEntry> {
        let idxs = vpn.indexes();
        let mut ppn = self.root_ppn;
        let mut result: Option<&mut PageTableEntry> = None;
        for i in 0..3 {
            let pte = &mut ppn.get_pte_array()[idxs[i]];
            if i == 2 {
                result = Some(pte);
                break;
            }
            if !pte.is_valid() {
                if !create {
                    return None;
                }
                let frame = frame_alloc().unwrap();
                *pte = PageTableEntry::new(frame.ppn, PTEFlags::V);
                self.frames.push(frame);
            }
            ppn = pte.ppn();
        }
        result
    }
    pub fn map(&mut self, vpn: VirtPageNum, ppn: PhysPageNum, flags: PTEFlags) {
        //println!("mapping {:?} {:?}", vpn, ppn);
        let pte = self.find_pte(vpn, true).unwrap();
        assert!(!pte.is_valid(), "vpn {:?} is mapped before mapping", vpn);
        *pte = PageTableEntry::new(ppn, flags | PTEFlags::V);
    }
    pub fn unmap(&mut self, vpn: VirtPageNum) {
        let pte = self.find_pte(vpn, false).unwrap();
        assert!(pte.is_valid(), "vpn {:?} is invalid before unmapping", vpn);
        *pte = PageTableEntry::empty();
    }
    pub fn translate(&mut self, vpn: VirtPageNum) -> Option<PageTableEntry> {
        self.find_pte(vpn, false)
            .map(|pte| {pte.clone()})
    }
    pub fn token(&self) -> usize {
        8usize << 60 | self.root_ppn.0
    }
}