//! AArch64 VMSAv8-64 translation table format descriptors.

use aarch64_cpu::registers::MAIR_EL1;
use core::fmt;
use memory_addr::PhysAddr;

use crate::{GenericPTE, MappingFlags};

bitflags::bitflags! {
    /// Memory attribute fields in the VMSAv8-64 translation table format descriptors.
    #[derive(Debug)]
    pub struct DescriptorAttr: u64 {
        // Attribute fields in stage 1 VMSAv8-64 Block and Page descriptors:

        /// Whether the descriptor is valid.
        const VALID =       1 << 0;
        /// The descriptor gives the address of the next level of translation table or 4KB page.
        /// (not a 2M, 1G block)
        const NON_BLOCK =   1 << 1;
        /// Memory attributes index field.
        const ATTR_INDX =   0b111 << 2;
        /// Non-secure bit. For memory accesses from Secure state, specifies whether the output
        /// address is in Secure or Non-secure memory.
        const NS =          1 << 5;
        /// Access permission: accessable at EL0.
        const AP_EL0 =      1 << 6;
        /// Access permission: read-only.
        const AP_RO =       1 << 7;
        /// Shareability: Inner Shareable (otherwise Outer Shareable).
        const INNER =       1 << 8;
        /// Shareability: Inner or Outer Shareable (otherwise Non-shareable).
        const SHAREABLE =   1 << 9;
        /// The Access flag.
        const AF =          1 << 10;
        /// The not global bit.
        const NG =          1 << 11;
        /// Indicates that 16 adjacent translation table entries point to contiguous memory regions.
        const CONTIGUOUS =  1 <<  52;
        /// The Privileged execute-never field.
        const PXN =         1 <<  53;
        /// The Execute-never or Unprivileged execute-never field.
        const UXN =         1 <<  54;

        // Next-level attributes in stage 1 VMSAv8-64 Table descriptors:

        /// PXN limit for subsequent levels of lookup.
        const PXN_TABLE =           1 << 59;
        /// XN limit for subsequent levels of lookup.
        const XN_TABLE =            1 << 60;
        /// Access permissions limit for subsequent levels of lookup: access at EL0 not permitted.
        const AP_NO_EL0_TABLE =     1 << 61;
        /// Access permissions limit for subsequent levels of lookup: write access not permitted.
        const AP_NO_WRITE_TABLE =   1 << 62;
        /// For memory accesses from Secure state, specifies the Security state for subsequent
        /// levels of lookup.
        const NS_TABLE =            1 << 63;
    }
}

/// The memory attributes index field in the descriptor, which is used to index
/// into the MAIR (Memory Attribute Indirection Register).
#[repr(u64)]
#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub enum MemAttr {
    /// Device-nGnRE memory
    Device = 0,
    /// Normal memory
    Normal = 1,
    /// Normal non-cacheable memory
    NormalNonCacheable = 2,
}

impl DescriptorAttr {
    #[allow(clippy::unusual_byte_groupings)]
    const ATTR_INDEX_MASK: u64 = 0b111_00;

    /// Constructs a descriptor from the memory index, leaving the other fields
    /// empty.
    pub const fn from_mem_attr(idx: MemAttr) -> Self {
        let mut bits = (idx as u64) << 2;
        if matches!(idx, MemAttr::Normal | MemAttr::NormalNonCacheable) {
            bits |= Self::INNER.bits() | Self::SHAREABLE.bits();
        }
        Self::from_bits_retain(bits)
    }

    /// Returns the memory attribute index field.
    pub const fn mem_attr(&self) -> Option<MemAttr> {
        let idx = (self.bits() & Self::ATTR_INDEX_MASK) >> 2;
        Some(match idx {
            0 => MemAttr::Device,
            1 => MemAttr::Normal,
            2 => MemAttr::NormalNonCacheable,
            _ => return None,
        })
    }
}

impl MemAttr {
    /// The MAIR_ELx register should be set to this value to match the memory
    /// attributes in the descriptors.
    pub const MAIR_VALUE: u64 = {
        // Device-nGnRE memory
        let attr0 = MAIR_EL1::Attr0_Device::nonGathering_nonReordering_EarlyWriteAck.value;
        // Normal memory
        let attr1 = MAIR_EL1::Attr1_Normal_Inner::WriteBack_NonTransient_ReadWriteAlloc.value
            | MAIR_EL1::Attr1_Normal_Outer::WriteBack_NonTransient_ReadWriteAlloc.value;
        let attr2 = MAIR_EL1::Attr2_Normal_Inner::NonCacheable.value
            + MAIR_EL1::Attr2_Normal_Outer::NonCacheable.value;
        attr0 | attr1 | attr2 // 0x44_ff_04
    };
}

impl From<DescriptorAttr> for MappingFlags {
    fn from(attr: DescriptorAttr) -> Self {
        let mut flags = Self::empty();
        if attr.contains(DescriptorAttr::VALID) {
            flags |= Self::READ;

            if !attr.contains(DescriptorAttr::AP_RO) {
                flags |= Self::WRITE;
            }
        }

        if attr.contains(DescriptorAttr::AP_EL0) {
            flags |= Self::USER;
            if !attr.contains(DescriptorAttr::UXN) {
                flags |= Self::EXECUTE;
            }
        } else {
            if !attr.intersects(DescriptorAttr::PXN) {
                flags |= Self::EXECUTE;
            }

            match attr.mem_attr() {
                Some(MemAttr::Device) => flags |= Self::DEVICE,
                Some(MemAttr::NormalNonCacheable) => flags |= Self::UNCACHED,
                _ => {}
            }
        }
        flags
    }
}

impl From<MappingFlags> for DescriptorAttr {
    fn from(flags: MappingFlags) -> Self {
        let mut attr = if flags.contains(MappingFlags::DEVICE) {
            Self::from_mem_attr(MemAttr::Device)
        } else if flags.contains(MappingFlags::UNCACHED) {
            Self::from_mem_attr(MemAttr::NormalNonCacheable)
        } else {
            Self::from_mem_attr(MemAttr::Normal)
        };

        if flags.contains(MappingFlags::READ) {
            attr |= Self::VALID;
        }

        if !flags.contains(MappingFlags::WRITE) {
            attr |= Self::AP_RO;
        }

        if flags.contains(MappingFlags::USER) {
            attr |= Self::AP_EL0 | Self::PXN;
            if !flags.contains(MappingFlags::EXECUTE) {
                attr |= Self::UXN;
            }
        } else {
            attr |= Self::UXN;
            if !flags.contains(MappingFlags::EXECUTE) {
                attr |= Self::PXN;
            }
        }
        attr
    }
}

/// A VMSAv8-64 translation table descriptor.
///
/// Note that the **AttrIndx\[2:0\]** (bit\[4:2\]) field is set to `0` for device
/// memory, and `1` for normal memory. The system must configure the MAIR_ELx
/// system register accordingly.
#[derive(Clone, Copy)]
#[repr(transparent)]
pub struct A64PTE(u64);

impl A64PTE {
    const PHYS_ADDR_MASK: u64 = 0x0000_ffff_ffff_f000; // bits 12..48

    /// Creates an empty descriptor with all bits set to zero.
    pub const fn empty() -> Self {
        Self(0)
    }
}

impl GenericPTE for A64PTE {
    fn new_page(paddr: PhysAddr, flags: MappingFlags, is_huge: bool) -> Self {
        let mut attr = DescriptorAttr::from(flags) | DescriptorAttr::AF;
        if !is_huge {
            attr |= DescriptorAttr::NON_BLOCK;
        }
        Self(attr.bits() | (paddr.as_usize() as u64 & Self::PHYS_ADDR_MASK))
    }

    fn new_fault_page(flags: MappingFlags, _is_huge: bool) -> Self {
        let mut attr = DescriptorAttr::from(flags) | DescriptorAttr::AF;
        attr &= !DescriptorAttr::VALID;
        Self(attr.bits())
    }

    fn new_table(paddr: PhysAddr) -> Self {
        let attr = DescriptorAttr::NON_BLOCK | DescriptorAttr::VALID;
        Self(attr.bits() | (paddr.as_usize() as u64 & Self::PHYS_ADDR_MASK))
    }
    fn paddr(&self) -> PhysAddr {
        PhysAddr::from((self.0 & Self::PHYS_ADDR_MASK) as usize)
    }
    fn flags(&self) -> MappingFlags {
        DescriptorAttr::from_bits_truncate(self.0).into()
    }
    fn set_paddr(&mut self, paddr: PhysAddr) {
        self.0 = (self.0 & !Self::PHYS_ADDR_MASK) | (paddr.as_usize() as u64 & Self::PHYS_ADDR_MASK)
    }
    fn set_flags(&mut self, flags: MappingFlags, is_huge: bool) {
        let mut attr = DescriptorAttr::from(flags) | DescriptorAttr::AF;
        if !is_huge {
            attr |= DescriptorAttr::NON_BLOCK;
        }
        self.0 = (self.0 & Self::PHYS_ADDR_MASK) | attr.bits();
    }

    fn is_unused(&self) -> bool {
        self.0 == 0
    }
    fn is_present(&self) -> bool {
        DescriptorAttr::from_bits_truncate(self.0).contains(DescriptorAttr::VALID)
    }
    fn is_huge(&self) -> bool {
        !DescriptorAttr::from_bits_truncate(self.0).contains(DescriptorAttr::NON_BLOCK)
    }
    fn clear(&mut self) {
        self.0 = 0
    }
}

impl fmt::Debug for A64PTE {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut f = f.debug_struct("A64PTE");
        f.field("raw", &self.0)
            .field("paddr", &self.paddr())
            .field("attr", &DescriptorAttr::from_bits_truncate(self.0))
            .field("flags", &self.flags())
            .finish()
    }
}