// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
//
// Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE-BSD-3-Clause file.
//
// Copyright © 2019 Intel Corporation
//
// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause

pub mod testing {
    use std::marker::PhantomData;
    use std::mem;

    use virtio_queue::desc::split::VirtqUsedElem;
    use virtio_queue::{Queue, QueueT};
    use vm_memory::bitmap::AtomicBitmap;
    use vm_memory::{Address, Bytes, GuestAddress, GuestUsize};

    type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;

    // Represents a location in GuestMemoryMmap which holds a given type.
    pub struct SomeplaceInMemory<'a, T> {
        pub location: GuestAddress,
        mem: &'a GuestMemoryMmap,
        phantom: PhantomData<*const T>,
    }

    // The ByteValued trait is required to use mem.read_obj and write_obj.
    impl<'a, T> SomeplaceInMemory<'a, T>
    where
        T: vm_memory::ByteValued,
    {
        fn new(location: GuestAddress, mem: &'a GuestMemoryMmap) -> Self {
            SomeplaceInMemory {
                location,
                mem,
                phantom: PhantomData,
            }
        }

        // Reads from the actual memory location.
        pub fn get(&self) -> T {
            self.mem.read_obj(self.location).unwrap()
        }

        // Writes to the actual memory location.
        pub fn set(&self, val: T) {
            self.mem.write_obj(val, self.location).unwrap();
        }

        // This function returns a place in memory which holds a value of type U, and starts
        // offset bytes after the current location.
        fn map_offset<U>(&self, offset: GuestUsize) -> SomeplaceInMemory<'a, U> {
            SomeplaceInMemory {
                location: self.location.checked_add(offset).unwrap(),
                mem: self.mem,
                phantom: PhantomData,
            }
        }

        // This function returns a place in memory which holds a value of type U, and starts
        // immediately after the end of self (which is location + sizeof(T)).
        fn next_place<U>(&self) -> SomeplaceInMemory<'a, U> {
            self.map_offset::<U>(mem::size_of::<T>() as u64)
        }

        fn end(&self) -> GuestAddress {
            self.location
                .checked_add(mem::size_of::<T>() as u64)
                .unwrap()
        }
    }

    // Represents a virtio descriptor in guest memory.
    pub struct VirtqDesc<'a> {
        pub addr: SomeplaceInMemory<'a, u64>,
        pub len: SomeplaceInMemory<'a, u32>,
        pub flags: SomeplaceInMemory<'a, u16>,
        pub next: SomeplaceInMemory<'a, u16>,
    }

    impl<'a> VirtqDesc<'a> {
        pub fn new(start: GuestAddress, mem: &'a GuestMemoryMmap) -> Self {
            assert_eq!(start.0 & 0xf, 0);

            let addr = SomeplaceInMemory::new(start, mem);
            let len = addr.next_place();
            let flags = len.next_place();
            let next = flags.next_place();

            VirtqDesc {
                addr,
                len,
                flags,
                next,
            }
        }

        fn start(&self) -> GuestAddress {
            self.addr.location
        }

        fn end(&self) -> GuestAddress {
            self.next.end()
        }

        pub fn set(&self, addr: u64, len: u32, flags: u16, next: u16) {
            self.addr.set(addr);
            self.len.set(len);
            self.flags.set(flags);
            self.next.set(next);
        }
    }

    // Represents a virtio queue ring. The only difference between the used and available rings,
    // is the ring element type.
    pub struct VirtqRing<'a, T> {
        pub flags: SomeplaceInMemory<'a, u16>,
        pub idx: SomeplaceInMemory<'a, u16>,
        pub ring: Vec<SomeplaceInMemory<'a, T>>,
        pub event: SomeplaceInMemory<'a, u16>,
    }

    impl<'a, T> VirtqRing<'a, T>
    where
        T: vm_memory::ByteValued,
    {
        fn new(
            start: GuestAddress,
            mem: &'a GuestMemoryMmap,
            qsize: u16,
            alignment: GuestUsize,
        ) -> Self {
            assert_eq!(start.0 & (alignment - 1), 0);

            let flags = SomeplaceInMemory::new(start, mem);
            let idx = flags.next_place();

            let mut ring = Vec::with_capacity(qsize as usize);

            ring.push(idx.next_place());

            for _ in 1..qsize as usize {
                let x = ring.last().unwrap().next_place();
                ring.push(x);
            }

            let event = ring.last().unwrap().next_place();

            flags.set(0);
            idx.set(0);
            event.set(0);

            VirtqRing {
                flags,
                idx,
                ring,
                event,
            }
        }

        pub fn end(&self) -> GuestAddress {
            self.event.end()
        }
    }

    pub type VirtqAvail<'a> = VirtqRing<'a, u16>;
    pub type VirtqUsed<'a> = VirtqRing<'a, VirtqUsedElem>;

    pub struct VirtQueue<'a> {
        pub dtable: Vec<VirtqDesc<'a>>,
        pub avail: VirtqAvail<'a>,
        pub used: VirtqUsed<'a>,
        pub mem: &'a GuestMemoryMmap,
    }

    impl<'a> VirtQueue<'a> {
        // We try to make sure things are aligned properly :-s
        pub fn new(start: GuestAddress, mem: &'a GuestMemoryMmap, qsize: u16) -> Self {
            // power of 2?
            assert!(qsize.is_power_of_two());

            let mut dtable = Vec::with_capacity(qsize as usize);

            let mut end = start;

            for _ in 0..qsize {
                let d = VirtqDesc::new(end, mem);
                end = d.end();
                dtable.push(d);
            }

            const AVAIL_ALIGN: u64 = 2;

            let avail = VirtqAvail::new(end, mem, qsize, AVAIL_ALIGN);

            const USED_ALIGN: u64 = 4;

            let mut x = avail.end().0;
            x = (x + USED_ALIGN - 1) & !(USED_ALIGN - 1);

            let used = VirtqUsed::new(GuestAddress(x), mem, qsize, USED_ALIGN);

            VirtQueue {
                dtable,
                avail,
                used,
                mem,
            }
        }

        fn size(&self) -> u16 {
            self.dtable.len() as u16
        }

        pub fn dtable_start(&self) -> GuestAddress {
            self.dtable.first().unwrap().start()
        }

        pub fn avail_start(&self) -> GuestAddress {
            self.avail.flags.location
        }

        pub fn used_start(&self) -> GuestAddress {
            self.used.flags.location
        }

        // Creates a new Queue, using the underlying memory regions represented by the VirtQueue.
        pub fn create_queue(&self) -> Queue {
            let mut q = Queue::new(self.size()).unwrap();

            q.set_size(self.size());
            q.set_ready(true);
            q.try_set_desc_table_address(self.dtable_start()).unwrap();
            q.try_set_avail_ring_address(self.avail_start()).unwrap();
            q.try_set_used_ring_address(self.used_start()).unwrap();

            q
        }

        pub fn start(&self) -> GuestAddress {
            self.dtable_start()
        }

        pub fn end(&self) -> GuestAddress {
            self.used.end()
        }
    }
}
