use std::{
    any::TypeId,
    convert::TryFrom,
    fmt::{Debug, DebugStruct},
    mem::{size_of, transmute},
    string::FromUtf8Error,
};

use thiserror::Error;

use crate::{
    //expr::ExpressionHolder,
    nlmsg::{
        AttributeDecoder, NetlinkType, NfNetlinkAttribute, NfNetlinkDeserializable, NfNetlinkWriter,
    },
    sys::{
        nfgenmsg, nlattr, nlmsgerr, nlmsghdr, NFNETLINK_V0, NFNL_MSG_BATCH_BEGIN,
        NFNL_MSG_BATCH_END, NFNL_SUBSYS_NFTABLES, NLA_F_NESTED, NLA_TYPE_MASK, NLMSG_ALIGNTO,
        NLMSG_DONE, NLMSG_ERROR, NLMSG_MIN_TYPE, NLMSG_NOOP, NLM_F_DUMP_INTR,
    },
    ProtocolFamily,
};

#[derive(Error, Debug)]
pub enum DecodeError {
    #[error("The buffer is too small to hold a valid message")]
    BufTooSmall,

    #[error("The message is too small")]
    NlMsgTooSmall,

    #[error("The message holds unexpected data")]
    InvalidDataSize,

    #[error("Missing information in the chain to create a rule")]
    MissingChainInformationError,

    #[error("The length of the arguments are not compatible with each other")]
    IncompatibleLength,

    #[error("Invalid subsystem, expected NFTABLES")]
    InvalidSubsystem(u8),

    #[error("Invalid version, expected NFNETLINK_V0")]
    InvalidVersion(u8),

    #[error("Invalid port ID")]
    InvalidPortId(u32),

    #[error("Invalid sequence number")]
    InvalidSeq(u32),

    #[error("The generation number was bumped in the kernel while the operation was running, interrupting it")]
    ConcurrentGenerationUpdate,

    #[error("Unsupported message type")]
    UnsupportedType(u16),

    #[error("Invalid attribute type")]
    InvalidAttributeType,

    #[error("Invalid type for a chain")]
    UnknownChainType,

    #[error("Invalid policy for a chain")]
    UnknownChainPolicy,

    #[error("Unknown type for a Meta expression")]
    UnknownMetaType(u32),

    #[error("Unsupported value for an icmp reject type")]
    UnknownRejectType(u32),

    #[error("Unsupported value for an icmp code in a reject expression")]
    UnknownIcmpCode(u8),

    #[error("Invalid value for a register")]
    UnknownRegisterValue,

    #[error("Invalid type for a verdict expression")]
    UnknownExpressionVerdictType,

    #[error("The object does not contain a name for the expression being parsed")]
    MissingExpressionName,

    #[error("Unsupported attribute type")]
    UnsupportedAttributeType(u16),

    #[error("Unexpected message type")]
    UnexpectedType(u16),

    #[error("The decoded String is not UTF8 compliant")]
    StringDecodeFailure(#[from] FromUtf8Error),

    #[error("Invalid value for a protocol family")]
    InvalidProtocolFamily(i32),

    #[error("A custom error occured")]
    Custom(Box<dyn std::error::Error + 'static>),
}

/// The largest nf_tables netlink message is the set element message, which contains the
/// NFTA_SET_ELEM_LIST_ELEMENTS attribute. This attribute is a nest that describes the set
/// elements. Given that the netlink attribute length (nla_len) is 16 bits, the largest message is
/// a bit larger than 64 KBytes.
pub fn nft_nlmsg_maxsize() -> u32 {
    u32::from(::std::u16::MAX) + unsafe { libc::sysconf(libc::_SC_PAGESIZE) } as u32
}

#[inline]
pub const fn pad_netlink_object_with_variable_size(size: usize) -> usize {
    // align on a 4 bytes boundary
    (size + (NLMSG_ALIGNTO as usize - 1)) & !(NLMSG_ALIGNTO as usize - 1)
}

#[inline]
pub const fn pad_netlink_object<T>() -> usize {
    let size = size_of::<T>();
    pad_netlink_object_with_variable_size(size)
}

pub fn get_subsystem_from_nlmsghdr_type(x: u16) -> u8 {
    ((x & 0xff00) >> 8) as u8
}

pub fn get_operation_from_nlmsghdr_type(x: u16) -> u8 {
    (x & 0x00ff) as u8
}

pub fn get_nlmsghdr(buf: &[u8]) -> Result<nlmsghdr, DecodeError> {
    let size_of_hdr = size_of::<nlmsghdr>();

    if buf.len() < size_of_hdr {
        return Err(DecodeError::BufTooSmall);
    }

    let nlmsghdr_ptr = buf[0..size_of_hdr].as_ptr() as *const nlmsghdr;
    let nlmsghdr = unsafe { *nlmsghdr_ptr };

    if nlmsghdr.nlmsg_len as usize > buf.len() || (nlmsghdr.nlmsg_len as usize) < size_of_hdr {
        return Err(DecodeError::NlMsgTooSmall);
    }

    if nlmsghdr.nlmsg_flags & NLM_F_DUMP_INTR as u16 != 0 {
        return Err(DecodeError::ConcurrentGenerationUpdate);
    }

    Ok(nlmsghdr)
}

#[derive(Debug, Clone, PartialEq)]
pub enum NlMsg<'a> {
    Done,
    Noop,
    Error(nlmsgerr),
    NfGenMsg(nfgenmsg, &'a [u8]),
}

pub fn parse_nlmsg<'a>(buf: &'a [u8]) -> Result<(nlmsghdr, NlMsg<'a>), DecodeError> {
    // in theory the message is composed of the following parts:
    // - nlmsghdr (contains the message size and type)
    // - struct nlmsgerr OR nfgenmsg (nftables header that describes the message family)
    // - the raw value that we want to validate (if the previous part is nfgenmsg)
    let hdr = get_nlmsghdr(buf)?;

    let size_of_hdr = pad_netlink_object::<nlmsghdr>();

    if hdr.nlmsg_type < NLMSG_MIN_TYPE as u16 {
        match hdr.nlmsg_type as u32 {
            x if x == NLMSG_NOOP => return Ok((hdr, NlMsg::Noop)),
            x if x == NLMSG_ERROR => {
                if (hdr.nlmsg_len as usize) < size_of_hdr + size_of::<nlmsgerr>() {
                    return Err(DecodeError::NlMsgTooSmall);
                }
                let mut err = unsafe {
                    *(buf[size_of_hdr..size_of_hdr + size_of::<nlmsgerr>()].as_ptr()
                        as *const nlmsgerr)
                };
                // some APIs return negative values, while other return positive values
                err.error = err.error.abs();
                return Ok((hdr, NlMsg::Error(err)));
            }
            x if x == NLMSG_DONE => return Ok((hdr, NlMsg::Done)),
            x => return Err(DecodeError::UnsupportedType(x as u16)),
        }
    }

    // batch messages are not specific to the nftables subsystem
    if hdr.nlmsg_type != NFNL_MSG_BATCH_BEGIN as u16 && hdr.nlmsg_type != NFNL_MSG_BATCH_END as u16
    {
        // verify that we are decoding nftables messages
        let subsys = get_subsystem_from_nlmsghdr_type(hdr.nlmsg_type);
        if subsys != NFNL_SUBSYS_NFTABLES as u8 {
            return Err(DecodeError::InvalidSubsystem(subsys));
        }
    }

    let size_of_nfgenmsg = pad_netlink_object::<nfgenmsg>();
    if hdr.nlmsg_len as usize > buf.len()
        || (hdr.nlmsg_len as usize) < size_of_hdr + size_of_nfgenmsg
    {
        return Err(DecodeError::NlMsgTooSmall);
    }

    let nfgenmsg_ptr = buf[size_of_hdr..size_of_hdr + size_of_nfgenmsg].as_ptr() as *const nfgenmsg;
    let nfgenmsg = unsafe { *nfgenmsg_ptr };

    if nfgenmsg.version != NFNETLINK_V0 as u8 {
        return Err(DecodeError::InvalidVersion(nfgenmsg.version));
    }

    let raw_value = &buf[size_of_hdr + size_of_nfgenmsg..hdr.nlmsg_len as usize];

    Ok((hdr, NlMsg::NfGenMsg(nfgenmsg, raw_value)))
}

/// Write the attribute, preceded by a `libc::nlattr`
// rewrite of `mnl_attr_put`
pub unsafe fn write_attribute<'a>(
    ty: NetlinkType,
    obj: &impl NfNetlinkAttribute,
    mut buf: *mut u8,
) {
    let header_len = pad_netlink_object::<libc::nlattr>();
    // copy the header
    *(buf as *mut nlattr) = nlattr {
        // nla_len contains the header size + the unpadded attribute length
        nla_len: (header_len + obj.get_size() as usize) as u16,
        nla_type: if obj.is_nested() {
            ty | NLA_F_NESTED as u16
        } else {
            ty
        },
    };
    buf = buf.offset(pad_netlink_object::<nlattr>() as isize);
    // copy the attribute data itself
    obj.write_payload(buf);
}

impl NfNetlinkAttribute for u8 {
    unsafe fn write_payload(&self, addr: *mut u8) {
        *addr = *self;
    }
}

impl NfNetlinkDeserializable for u8 {
    fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        Ok((buf[0], &buf[1..]))
    }
}

impl NfNetlinkAttribute for u16 {
    unsafe fn write_payload(&self, addr: *mut u8) {
        *(addr as *mut Self) = self.to_be();
    }
}

impl NfNetlinkDeserializable for u16 {
    fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        Ok((u16::from_be_bytes([buf[0], buf[1]]), &buf[2..]))
    }
}

impl NfNetlinkAttribute for i32 {
    unsafe fn write_payload(&self, addr: *mut u8) {
        *(addr as *mut Self) = self.to_be();
    }
}

impl NfNetlinkDeserializable for i32 {
    fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        Ok((
            i32::from_be_bytes([buf[0], buf[1], buf[2], buf[3]]),
            &buf[4..],
        ))
    }
}

impl NfNetlinkAttribute for u32 {
    unsafe fn write_payload(&self, addr: *mut u8) {
        *(addr as *mut Self) = self.to_be();
    }
}

impl NfNetlinkDeserializable for u32 {
    fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        Ok((
            u32::from_be_bytes([buf[0], buf[1], buf[2], buf[3]]),
            &buf[4..],
        ))
    }
}

impl NfNetlinkAttribute for u64 {
    unsafe fn write_payload(&self, addr: *mut u8) {
        *(addr as *mut Self) = self.to_be();
    }
}

impl NfNetlinkDeserializable for u64 {
    fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        Ok((
            u64::from_be_bytes([
                buf[0], buf[1], buf[2], buf[3], buf[4], buf[5], buf[6], buf[7],
            ]),
            &buf[8..],
        ))
    }
}

impl NfNetlinkAttribute for String {
    fn get_size(&self) -> usize {
        self.len()
    }

    unsafe fn write_payload(&self, addr: *mut u8) {
        std::ptr::copy_nonoverlapping(self.as_bytes().as_ptr(), addr, self.len());
    }
}

impl NfNetlinkDeserializable for String {
    fn deserialize(mut buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        // ignore the NULL byte terminator, if any
        if buf.len() > 0 && buf[buf.len() - 1] == 0 {
            buf = &buf[..buf.len() - 1];
        }
        Ok((String::from_utf8(buf.to_vec())?, &[]))
    }
}

impl NfNetlinkAttribute for Vec<u8> {
    fn get_size(&self) -> usize {
        self.len()
    }

    unsafe fn write_payload(&self, addr: *mut u8) {
        std::ptr::copy_nonoverlapping(self.as_ptr(), addr, self.len());
    }
}

impl NfNetlinkDeserializable for Vec<u8> {
    fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        Ok((buf.to_vec(), &[]))
    }
}

impl NfNetlinkAttribute for ProtocolFamily {
    unsafe fn write_payload(&self, addr: *mut u8) {
        (*self as i32).write_payload(addr);
    }
}

impl NfNetlinkDeserializable for ProtocolFamily {
    fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), DecodeError> {
        let (v, remaining_data) = i32::deserialize(buf)?;
        Ok((Self::try_from(v)?, remaining_data))
    }
}

pub(crate) fn read_attributes<T: AttributeDecoder + Default>(buf: &[u8]) -> Result<T, DecodeError> {
    debug!(
        "Calling <{} as NfNetlinkDeserialize>::deserialize()",
        std::any::type_name::<T>()
    );
    let mut remaining_size = buf.len();
    let mut pos = 0;
    let mut res = T::default();
    while remaining_size > pad_netlink_object::<nlattr>() {
        let nlattr = unsafe { *transmute::<*const u8, *const nlattr>(buf[pos..].as_ptr()) };
        // ignore the byteorder and nested attributes
        let nla_type = nlattr.nla_type & NLA_TYPE_MASK as u16;

        pos += pad_netlink_object::<nlattr>();
        let attr_remaining_size = nlattr.nla_len as usize - pad_netlink_object::<nlattr>();
        match T::decode_attribute(&mut res, nla_type, &buf[pos..pos + attr_remaining_size]) {
            Ok(()) => {}
            Err(DecodeError::UnsupportedAttributeType(t)) => info!(
                "Ignoring unsupported attribute type {} for type {}",
                t,
                std::any::type_name::<T>()
            ),
            Err(e) => return Err(e),
        }
        pos += pad_netlink_object_with_variable_size(attr_remaining_size);

        remaining_size -= pad_netlink_object_with_variable_size(nlattr.nla_len as usize);
    }

    if remaining_size != 0 {
        Err(DecodeError::InvalidDataSize)
    } else {
        Ok(res)
    }
}

pub trait InnerFormat {
    fn inner_format_struct<'a, 'b: 'a>(
        &'a self,
        s: DebugStruct<'a, 'b>,
    ) -> Result<DebugStruct<'a, 'b>, std::fmt::Error>;
}

#[macro_export]
macro_rules! impl_attr_getters_and_setters {
    (without_deser $struct:ident, [$(($getter_name:ident, $setter_name:ident, $in_place_edit_name:ident, $attr_name:expr, $internal_name:ident, $type:ty)),+]) => {
        impl $struct {
            $(
                #[allow(dead_code)]
                pub fn $getter_name(&self) -> Option<&$type> {
                    self.$internal_name.as_ref()
                }

                #[allow(dead_code)]
                pub fn $setter_name(&mut self, val: impl Into<$type>) {
                    self.$internal_name = Some(val.into());
                }

                #[allow(dead_code)]
                pub fn $in_place_edit_name(mut self, val: impl Into<$type>) -> Self {
                    self.$internal_name = Some(val.into());
                    self
                }

            )+
        }

        impl $crate::parser::InnerFormat for $struct {
            fn inner_format_struct<'a, 'b: 'a>(&'a self, mut s: std::fmt::DebugStruct<'a, 'b>) -> Result<std::fmt::DebugStruct<'a, 'b>, std::fmt::Error> {
                $(
                    // Rewrite attributes names to be readable: 'sys::NFTA_CHAIN_NAME' -> 'name'
                    // Performance must be terrible, but this is the Debug impl anyway, so that
                    // must mean we can afford to be slow, right? ;)
                    if let Some(val) = self.$getter_name() {
                        let mut attr = stringify!($attr_name);
                        if let Some((nfta_idx, _match )) = attr.rmatch_indices("NFTA_").next() {
                            if let Some(underscore_idx) = &attr[nfta_idx+5..].find('_') {
                                attr = &attr[nfta_idx+underscore_idx+6..];
                            }
                        }
                        let attr = attr.to_lowercase();
                        s.field(&attr, val);
                    }
                )+
                Ok(s)
            }
        }

    };
    (deser $struct:ident, [$(($getter_name:ident, $setter_name:ident, $in_place_edit_name:ident, $attr_name:expr, $internal_name:ident, $type:ty)),+]) => {
        impl $crate::nlmsg::AttributeDecoder for $struct {
            #[allow(dead_code)]
            fn decode_attribute(&mut self, attr_type: u16, buf: &[u8]) -> Result<(), $crate::parser::DecodeError> {
                use $crate::nlmsg::NfNetlinkDeserializable;
                debug!("Decoding attribute {} in type {}", attr_type, std::any::type_name::<$struct>());
                match attr_type {
                    $(
                        x if x == $attr_name => {
                            debug!("Calling {}::deserialize()", std::any::type_name::<$type>());
                            let (val, remaining) = <$type>::deserialize(buf)?;
                            if remaining.len() != 0 {
                                return Err($crate::parser::DecodeError::InvalidDataSize);
                            }
                            self.$setter_name(val);
                            Ok(())
                        },
                    )+
                    _ => Err($crate::parser::DecodeError::UnsupportedAttributeType(attr_type)),
                }
            }
        }
    };
    ($struct:ident, [$(($getter_name:ident, $setter_name:ident, $in_place_edit_name:ident, $attr_name:expr, $internal_name:ident, $type:ty)),+]) => {
        $crate::impl_attr_getters_and_setters!(without_deser $struct, [$(($getter_name, $setter_name, $in_place_edit_name, $attr_name, $internal_name, $type)),+]);
        $crate::impl_attr_getters_and_setters!(deser $struct, [$(($getter_name, $setter_name, $in_place_edit_name, $attr_name, $internal_name, $type)),+]);
    };
}

pub trait Parsable
where
    Self: Sized,
{
    fn parse_object(
        buf: &[u8],
        add_obj: u32,
        del_obj: u32,
    ) -> Result<(Self, nfgenmsg, &[u8]), DecodeError>;
}

impl<T> Parsable for T
where
    T: AttributeDecoder + Default + Sized,
{
    fn parse_object(
        buf: &[u8],
        add_obj: u32,
        del_obj: u32,
    ) -> Result<(Self, nfgenmsg, &[u8]), DecodeError> {
        debug!("parse_object() started");
        let (hdr, msg) = parse_nlmsg(buf)?;

        let op = get_operation_from_nlmsghdr_type(hdr.nlmsg_type) as u32;

        if op != add_obj && op != del_obj {
            return Err(DecodeError::UnexpectedType(hdr.nlmsg_type));
        }

        let obj_size = hdr.nlmsg_len as usize
            - pad_netlink_object_with_variable_size(size_of::<nlmsghdr>() + size_of::<nfgenmsg>());

        let remaining_data_offset = pad_netlink_object_with_variable_size(hdr.nlmsg_len as usize);
        let remaining_data = &buf[remaining_data_offset..];

        let (nfgenmsg, res) = match msg {
            NlMsg::NfGenMsg(nfgenmsg, content) => {
                (nfgenmsg, read_attributes(&content[..obj_size])?)
            }
            _ => return Err(DecodeError::UnexpectedType(hdr.nlmsg_type)),
        };

        Ok((res, nfgenmsg, remaining_data))
    }
}

#[macro_export]
macro_rules! impl_nfnetlinkattribute {
    (__inner : $struct:ident, [$(($attr_name:expr, $internal_name:ident)),+]) => {
        impl $struct {
            fn inner_get_size(&self) -> usize {
                use $crate::nlmsg::NfNetlinkAttribute;
                use $crate::parser::{pad_netlink_object, pad_netlink_object_with_variable_size};
                use $crate::sys::nlattr;
                let mut size = 0;

                $(
                    if let Some(val) = &self.$internal_name {
                        // Attribute header + attribute value
                        size += pad_netlink_object::<nlattr>()
                            + pad_netlink_object_with_variable_size(val.get_size());
                    }
                )+

                size
            }

            unsafe fn inner_write_payload(&self, mut addr: *mut u8) {
                use $crate::nlmsg::NfNetlinkAttribute;
                use $crate::parser::{pad_netlink_object, pad_netlink_object_with_variable_size};
                use $crate::sys::nlattr;
                $(
                    if let Some(val) = &self.$internal_name {
                        debug!("writing attribute {} - {:?}", $attr_name, val);

                        unsafe {
                            $crate::parser::write_attribute($attr_name, val, addr);
                        }
                        let size = pad_netlink_object::<nlattr>()
                            + pad_netlink_object_with_variable_size(val.get_size());
                        #[allow(unused)]
                        {
                            addr = addr.offset(size as isize);
                        }
                    }
                )+
            }
        }
    };
    (inline : $struct:ident, [$(($attr_name:expr, $internal_name:ident)),+]) => {
        $crate::impl_nfnetlinkattribute!(__inner : $struct, [$(($attr_name, $internal_name)),+]);

        impl $crate::nlmsg::NfNetlinkAttribute for $struct {
            fn get_size(&self) -> usize {
                self.inner_get_size()
            }

            unsafe fn write_payload(&self, addr: *mut u8) {
                self.inner_write_payload(addr);
            }
        }
    };
    (nested : $struct:ident, [$(($attr_name:expr, $internal_name:ident)),+]) => {
        $crate::impl_nfnetlinkattribute!(__inner : $struct, [$(($attr_name, $internal_name)),+]);

        impl $crate::nlmsg::NfNetlinkAttribute for $struct {
            fn is_nested(&self) -> bool {
                true
            }

            fn get_size(&self) -> usize {
                self.inner_get_size()
            }

            unsafe fn write_payload(&self, addr: *mut u8) {
                self.inner_write_payload(addr);
            }
        }
    };
}

#[macro_export]
macro_rules! create_wrapper_type {
    (without_deser : $struct:ident, [$(($getter_name:ident, $setter_name:ident, $in_place_edit_name:ident, $attr_name:expr, $internal_name:ident, $type:ty)),+]) => {
        #[derive(Clone, PartialEq, Eq, Default)]
        pub struct $struct {
            $(
                $internal_name: Option<$type>
            ),+
        }

        $crate::impl_attr_getters_and_setters!(without_deser $struct, [$(($getter_name, $setter_name, $in_place_edit_name, $attr_name, $internal_name, $type)),+]);

        impl std::fmt::Debug for $struct {
            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
                use $crate::parser::InnerFormat;
                self.inner_format_struct(f.debug_struct(stringify!($struct)))?
                    .finish()
            }
        }

        impl $crate::nlmsg::NfNetlinkDeserializable for $struct {
            fn deserialize(buf: &[u8]) -> Result<(Self, &[u8]), $crate::parser::DecodeError> {
                Ok(($crate::parser::read_attributes(buf)?, &[]))
            }
        }
    };
    ($struct:ident, [$(($getter_name:ident, $setter_name:ident, $in_place_edit_name:ident, $attr_name:expr, $internal_name:ident, $type:ty)),+]) => {
        create_wrapper_type!(without_deser : $struct, [$(($getter_name, $setter_name, $in_place_edit_name, $attr_name, $internal_name, $type)),+]);
        $crate::impl_attr_getters_and_setters!(deser $struct, [$(($getter_name, $setter_name, $in_place_edit_name, $attr_name, $internal_name, $type)),+]);
    };
    (inline $($($attrs:ident) +)? :  $struct:ident, [$(($getter_name:ident, $setter_name:ident, $in_place_edit_name:ident, $attr_name:expr, $internal_name:ident, $type:ty)),+]) => {
        create_wrapper_type!($($($attrs) + :)? $struct, [$(($getter_name, $setter_name, $in_place_edit_name, $attr_name, $internal_name, $type)),+]);
        $crate::impl_nfnetlinkattribute!(inline : $struct, [$(($attr_name, $internal_name)),+]);
    };
    (nested $($($attrs:ident) +)? : $struct:ident, [$(($getter_name:ident, $setter_name:ident, $in_place_edit_name:ident, $attr_name:expr, $internal_name:ident, $type:ty)),+]) => {
        create_wrapper_type!($($($attrs) + :)? $struct, [$(($getter_name, $setter_name, $in_place_edit_name, $attr_name, $internal_name, $type)),+]);
        $crate::impl_nfnetlinkattribute!(nested : $struct, [$(($attr_name, $internal_name)),+]);
    };
}