#![allow(missing_docs)]

use alloc::{string::ToString, vec, vec::Vec};
use core::{fmt::Display, mem, ptr};

use object::Endianness;

use crate::btf::{Btf, BtfError, MAX_RESOLVE_DEPTH};

#[derive(Clone, Debug)]
pub enum BtfType {
    Unknown,
    Fwd(Fwd),
    Const(Const),
    Volatile(Volatile),
    Restrict(Restrict),
    Ptr(Ptr),
    Typedef(Typedef),
    Func(Func),
    Int(Int),
    Float(Float),
    Enum(Enum),
    Array(Array),
    Struct(Struct),
    Union(Union),
    FuncProto(FuncProto),
    Var(Var),
    DataSec(DataSec),
    DeclTag(DeclTag),
    TypeTag(TypeTag),
    Enum64(Enum64),
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Fwd {
    pub(crate) name_offset: u32,
    info: u32,
    _unused: u32,
}

impl Fwd {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Fwd>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Fwd
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Const {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
}

impl Const {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Const>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Const
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub(crate) fn new(btf_type: u32) -> Self {
        let info = (BtfKind::Const as u32) << 24;
        Self {
            name_offset: 0,
            info,
            btf_type,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Volatile {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
}

impl Volatile {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Volatile>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Volatile
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }
}

#[derive(Clone, Debug)]
pub struct Restrict {
    pub(crate) name_offset: u32,
    _info: u32,
    pub(crate) btf_type: u32,
}

impl Restrict {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Restrict>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Restrict
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Ptr {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
}

impl Ptr {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Self>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Ptr
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub fn new(name_offset: u32, btf_type: u32) -> Self {
        let info = (BtfKind::Ptr as u32) << 24;
        Self {
            name_offset,
            info,
            btf_type,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Typedef {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
}

impl Typedef {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Self>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Typedef
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub(crate) fn new(name_offset: u32, btf_type: u32) -> Self {
        let info = (BtfKind::Typedef as u32) << 24;
        Self {
            name_offset,
            info,
            btf_type,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Float {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) size: u32,
}

impl Float {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Self>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Float
    }
    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub fn new(name_offset: u32, size: u32) -> Self {
        let info = (BtfKind::Float as u32) << 24;
        Self {
            name_offset,
            info,
            size,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Func {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
}

#[repr(u32)]
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum FuncLinkage {
    Static = 0,
    Global = 1,
    Extern = 2,
    Unknown,
}

impl From<u32> for FuncLinkage {
    fn from(v: u32) -> Self {
        match v {
            0 => FuncLinkage::Static,
            1 => FuncLinkage::Global,
            2 => FuncLinkage::Extern,
            _ => FuncLinkage::Unknown,
        }
    }
}

impl Func {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Self>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Func
    }
    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub fn new(name_offset: u32, proto: u32, linkage: FuncLinkage) -> Self {
        let mut info = (BtfKind::Func as u32) << 24;
        info |= (linkage as u32) & 0xFFFF;
        Self {
            name_offset,
            info,
            btf_type: proto,
        }
    }

    pub(crate) fn linkage(&self) -> FuncLinkage {
        (self.info & 0xFFF).into()
    }

    pub(crate) fn set_linkage(&mut self, linkage: FuncLinkage) {
        self.info = (self.info & 0xFFFF0000) | (linkage as u32) & 0xFFFF;
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct TypeTag {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
}

impl TypeTag {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        bytes_of::<Self>(self).to_vec()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::TypeTag
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub fn new(name_offset: u32, btf_type: u32) -> Self {
        let info = (BtfKind::TypeTag as u32) << 24;
        Self {
            name_offset,
            info,
            btf_type,
        }
    }
}

#[repr(u32)]
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum IntEncoding {
    None,
    Signed = 1,
    Char = 2,
    Bool = 4,
    Unknown,
}

impl From<u32> for IntEncoding {
    fn from(v: u32) -> Self {
        match v {
            0 => IntEncoding::None,
            1 => IntEncoding::Signed,
            2 => IntEncoding::Char,
            4 => IntEncoding::Bool,
            _ => IntEncoding::Unknown,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Int {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) size: u32,
    pub(crate) data: u32,
}

impl Int {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            size,
            data,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(size),
            bytes_of::<u32>(data),
        ]
        .concat()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Int
    }
    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub fn new(name_offset: u32, size: u32, encoding: IntEncoding, offset: u32) -> Self {
        let info = (BtfKind::Int as u32) << 24;
        let mut data = 0u32;
        data |= (encoding as u32 & 0x0f) << 24;
        data |= (offset & 0xff) << 16;
        data |= (size * 8) & 0xff;
        Self {
            name_offset,
            info,
            size,
            data,
        }
    }

    pub(crate) fn encoding(&self) -> IntEncoding {
        ((self.data & 0x0f000000) >> 24).into()
    }

    pub(crate) fn offset(&self) -> u32 {
        (self.data & 0x00ff0000) >> 16
    }

    // TODO: Remove directive this when this crate is pub
    #[cfg(test)]
    pub(crate) fn bits(&self) -> u32 {
        self.data & 0x000000ff
    }
}

#[repr(C)]
#[derive(Debug, Clone)]
pub struct BtfEnum {
    pub name_offset: u32,
    pub value: u32,
}

impl BtfEnum {
    pub fn new(name_offset: u32, value: u32) -> Self {
        Self { name_offset, value }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Enum {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) size: u32,
    pub(crate) variants: Vec<BtfEnum>,
}

impl Enum {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            size,
            variants,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(size),
        ]
        .into_iter()
        .chain(variants.iter().flat_map(|BtfEnum { name_offset, value }| {
            [bytes_of::<u32>(name_offset), bytes_of::<u32>(value)]
        }))
        .flatten()
        .copied()
        .collect()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Enum
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Fwd>() + mem::size_of::<BtfEnum>() * self.variants.len()
    }

    pub fn new(name_offset: u32, signed: bool, variants: Vec<BtfEnum>) -> Self {
        let mut info = (BtfKind::Enum as u32) << 24;
        info |= (variants.len() as u32) & 0xFFFF;
        if signed {
            info |= 1 << 31;
        }
        Self {
            name_offset,
            info,
            size: 4,
            variants,
        }
    }

    pub(crate) fn is_signed(&self) -> bool {
        self.info >> 31 == 1
    }

    pub(crate) fn set_signed(&mut self, signed: bool) {
        if signed {
            self.info |= 1 << 31;
        } else {
            self.info &= !(1 << 31);
        }
    }
}

#[repr(C)]
#[derive(Debug, Clone)]
pub struct BtfEnum64 {
    pub(crate) name_offset: u32,
    pub(crate) value_low: u32,
    pub(crate) value_high: u32,
}

impl BtfEnum64 {
    pub fn new(name_offset: u32, value: u64) -> Self {
        Self {
            name_offset,
            value_low: value as u32,
            value_high: (value >> 32) as u32,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Enum64 {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) size: u32,
    pub(crate) variants: Vec<BtfEnum64>,
}

impl Enum64 {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            size,
            variants,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(size),
        ]
        .into_iter()
        .chain(variants.iter().flat_map(
            |BtfEnum64 {
                 name_offset,
                 value_low,
                 value_high,
             }| {
                [
                    bytes_of::<u32>(name_offset),
                    bytes_of::<u32>(value_low),
                    bytes_of::<u32>(value_high),
                ]
            },
        ))
        .flatten()
        .copied()
        .collect()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Enum64
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Fwd>() + mem::size_of::<BtfEnum64>() * self.variants.len()
    }

    pub(crate) fn is_signed(&self) -> bool {
        self.info >> 31 == 1
    }

    pub fn new(name_offset: u32, signed: bool, variants: Vec<BtfEnum64>) -> Self {
        let mut info = (BtfKind::Enum64 as u32) << 24;
        if signed {
            info |= 1 << 31
        };
        info |= (variants.len() as u32) & 0xFFFF;
        Enum64 {
            name_offset,
            info,
            // According to the documentation:
            //
            // https://www.kernel.org/doc/html/next/bpf/btf.html
            //
            // The size may be 1/2/4/8. Since BtfEnum64::new() takes a u64, we
            // can assume that the size is 8.
            size: 8,
            variants,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub(crate) struct BtfMember {
    pub(crate) name_offset: u32,
    pub(crate) btf_type: u32,
    pub(crate) offset: u32,
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Struct {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) size: u32,
    pub(crate) members: Vec<BtfMember>,
}

impl Struct {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            size,
            members,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(size),
        ]
        .into_iter()
        .chain(members.iter().flat_map(
            |BtfMember {
                 name_offset,
                 btf_type,
                 offset,
             }| {
                [
                    bytes_of::<u32>(name_offset),
                    bytes_of::<u32>(btf_type),
                    bytes_of::<u32>(offset),
                ]
            },
        ))
        .flatten()
        .copied()
        .collect()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Struct
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Fwd>() + mem::size_of::<BtfMember>() * self.members.len()
    }

    pub(crate) fn new(name_offset: u32, members: Vec<BtfMember>, size: u32) -> Self {
        let mut info = (BtfKind::Struct as u32) << 24;
        info |= (members.len() as u32) & 0xFFFF;
        Self {
            name_offset,
            info,
            size,
            members,
        }
    }

    pub(crate) fn member_bit_offset(&self, member: &BtfMember) -> usize {
        let k_flag = self.info >> 31 == 1;
        let bit_offset = if k_flag {
            member.offset & 0xFFFFFF
        } else {
            member.offset
        };

        bit_offset as usize
    }

    pub(crate) fn member_bit_field_size(&self, member: &BtfMember) -> usize {
        let k_flag = (self.info >> 31) == 1;
        let size = if k_flag { member.offset >> 24 } else { 0 };

        size as usize
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Union {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) size: u32,
    pub(crate) members: Vec<BtfMember>,
}

impl Union {
    pub(crate) fn new(name_offset: u32, size: u32, members: Vec<BtfMember>) -> Self {
        let mut info = (BtfKind::Union as u32) << 24;
        info |= (members.len() as u32) & 0xFFFF;
        Self {
            name_offset,
            info,
            size,
            members,
        }
    }

    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            size,
            members,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(size),
        ]
        .into_iter()
        .chain(members.iter().flat_map(
            |BtfMember {
                 name_offset,
                 btf_type,
                 offset,
             }| {
                [
                    bytes_of::<u32>(name_offset),
                    bytes_of::<u32>(btf_type),
                    bytes_of::<u32>(offset),
                ]
            },
        ))
        .flatten()
        .copied()
        .collect()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Union
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Fwd>() + mem::size_of::<BtfMember>() * self.members.len()
    }

    pub(crate) fn member_bit_offset(&self, member: &BtfMember) -> usize {
        let k_flag = self.info >> 31 == 1;
        let bit_offset = if k_flag {
            member.offset & 0xFFFFFF
        } else {
            member.offset
        };

        bit_offset as usize
    }

    pub(crate) fn member_bit_field_size(&self, member: &BtfMember) -> usize {
        let k_flag = (self.info >> 31) == 1;
        let size = if k_flag { member.offset >> 24 } else { 0 };

        size as usize
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub(crate) struct BtfArray {
    pub(crate) element_type: u32,
    pub(crate) index_type: u32,
    pub(crate) len: u32,
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Array {
    pub(crate) name_offset: u32,
    info: u32,
    _unused: u32,
    pub(crate) array: BtfArray,
}

impl Array {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            _unused,
            array,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(_unused),
            bytes_of::<BtfArray>(array),
        ]
        .concat()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Array
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    #[cfg(test)]
    pub(crate) fn new(name_offset: u32, element_type: u32, index_type: u32, len: u32) -> Self {
        let info = (BtfKind::Array as u32) << 24;
        Self {
            name_offset,
            info,
            _unused: 0,
            array: BtfArray {
                element_type,
                index_type,
                len,
            },
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct BtfParam {
    pub name_offset: u32,
    pub btf_type: u32,
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct FuncProto {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) return_type: u32,
    pub(crate) params: Vec<BtfParam>,
}

impl FuncProto {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            return_type,
            params,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(return_type),
        ]
        .into_iter()
        .chain(params.iter().flat_map(
            |BtfParam {
                 name_offset,
                 btf_type,
             }| { [bytes_of::<u32>(name_offset), bytes_of::<u32>(btf_type)] },
        ))
        .flatten()
        .copied()
        .collect()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::FuncProto
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Fwd>() + mem::size_of::<BtfParam>() * self.params.len()
    }

    pub fn new(params: Vec<BtfParam>, return_type: u32) -> Self {
        let mut info = (BtfKind::FuncProto as u32) << 24;
        info |= (params.len() as u32) & 0xFFFF;
        Self {
            name_offset: 0,
            info,
            return_type,
            params,
        }
    }
}

#[repr(u32)]
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum VarLinkage {
    Static,
    Global,
    Extern,
    Unknown,
}

impl From<u32> for VarLinkage {
    fn from(v: u32) -> Self {
        match v {
            0 => VarLinkage::Static,
            1 => VarLinkage::Global,
            2 => VarLinkage::Extern,
            _ => VarLinkage::Unknown,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct Var {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
    pub(crate) linkage: VarLinkage,
}

impl Var {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            btf_type,
            linkage,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(btf_type),
            bytes_of::<VarLinkage>(linkage),
        ]
        .concat()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::Var
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub fn new(name_offset: u32, btf_type: u32, linkage: VarLinkage) -> Self {
        let info = (BtfKind::Var as u32) << 24;
        Self {
            name_offset,
            info,
            btf_type,
            linkage,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct DataSecEntry {
    pub btf_type: u32,
    pub offset: u32,
    pub size: u32,
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct DataSec {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) size: u32,
    pub(crate) entries: Vec<DataSecEntry>,
}

impl DataSec {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            size,
            entries,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(size),
        ]
        .into_iter()
        .chain(entries.iter().flat_map(
            |DataSecEntry {
                 btf_type,
                 offset,
                 size,
             }| {
                [
                    bytes_of::<u32>(btf_type),
                    bytes_of::<u32>(offset),
                    bytes_of::<u32>(size),
                ]
            },
        ))
        .flatten()
        .copied()
        .collect()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::DataSec
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Fwd>() + mem::size_of::<DataSecEntry>() * self.entries.len()
    }

    pub fn new(name_offset: u32, entries: Vec<DataSecEntry>, size: u32) -> Self {
        let mut info = (BtfKind::DataSec as u32) << 24;
        info |= (entries.len() as u32) & 0xFFFF;
        Self {
            name_offset,
            info,
            size,
            entries,
        }
    }
}

#[repr(C)]
#[derive(Clone, Debug)]
pub struct DeclTag {
    pub(crate) name_offset: u32,
    info: u32,
    pub(crate) btf_type: u32,
    pub(crate) component_index: i32,
}

impl DeclTag {
    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        let Self {
            name_offset,
            info,
            btf_type,
            component_index,
        } = self;
        [
            bytes_of::<u32>(name_offset),
            bytes_of::<u32>(info),
            bytes_of::<u32>(btf_type),
            bytes_of::<i32>(component_index),
        ]
        .concat()
    }

    pub(crate) fn kind(&self) -> BtfKind {
        BtfKind::DeclTag
    }

    pub(crate) fn type_info_size(&self) -> usize {
        mem::size_of::<Self>()
    }

    pub fn new(name_offset: u32, btf_type: u32, component_index: i32) -> Self {
        let info = (BtfKind::DeclTag as u32) << 24;
        Self {
            name_offset,
            info,
            btf_type,
            component_index,
        }
    }
}

#[derive(Copy, Clone, Debug, Eq, PartialEq, Default)]
#[repr(u32)]
pub enum BtfKind {
    #[default]
    Unknown = 0,
    Int = 1,
    Ptr = 2,
    Array = 3,
    Struct = 4,
    Union = 5,
    Enum = 6,
    Fwd = 7,
    Typedef = 8,
    Volatile = 9,
    Const = 10,
    Restrict = 11,
    Func = 12,
    FuncProto = 13,
    Var = 14,
    DataSec = 15,
    Float = 16,
    DeclTag = 17,
    TypeTag = 18,
    Enum64 = 19,
}

impl TryFrom<u32> for BtfKind {
    type Error = BtfError;

    fn try_from(v: u32) -> Result<Self, Self::Error> {
        use BtfKind::*;
        Ok(match v {
            0 => Unknown,
            1 => Int,
            2 => Ptr,
            3 => Array,
            4 => Struct,
            5 => Union,
            6 => Enum,
            7 => Fwd,
            8 => Typedef,
            9 => Volatile,
            10 => Const,
            11 => Restrict,
            12 => Func,
            13 => FuncProto,
            14 => Var,
            15 => DataSec,
            16 => Float,
            17 => DeclTag,
            18 => TypeTag,
            19 => Enum64,
            kind => return Err(BtfError::InvalidTypeKind { kind }),
        })
    }
}

impl Display for BtfKind {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        match self {
            BtfKind::Unknown => write!(f, "[UNKNOWN]"),
            BtfKind::Int => write!(f, "[INT]"),
            BtfKind::Float => write!(f, "[FLOAT]"),
            BtfKind::Ptr => write!(f, "[PTR]"),
            BtfKind::Array => write!(f, "[ARRAY]"),
            BtfKind::Struct => write!(f, "[STRUCT]"),
            BtfKind::Union => write!(f, "[UNION]"),
            BtfKind::Enum => write!(f, "[ENUM]"),
            BtfKind::Fwd => write!(f, "[FWD]"),
            BtfKind::Typedef => write!(f, "[TYPEDEF]"),
            BtfKind::Volatile => write!(f, "[VOLATILE]"),
            BtfKind::Const => write!(f, "[CONST]"),
            BtfKind::Restrict => write!(f, "[RESTRICT]"),
            BtfKind::Func => write!(f, "[FUNC]"),
            BtfKind::FuncProto => write!(f, "[FUNC_PROTO]"),
            BtfKind::Var => write!(f, "[VAR]"),
            BtfKind::DataSec => write!(f, "[DATASEC]"),
            BtfKind::DeclTag => write!(f, "[DECL_TAG]"),
            BtfKind::TypeTag => write!(f, "[TYPE_TAG]"),
            BtfKind::Enum64 => write!(f, "[ENUM64]"),
        }
    }
}

unsafe fn read<T>(data: &[u8]) -> Result<T, BtfError> {
    if mem::size_of::<T>() > data.len() {
        return Err(BtfError::InvalidTypeInfo);
    }

    Ok(ptr::read_unaligned::<T>(data.as_ptr() as *const T))
}

unsafe fn read_array<T>(data: &[u8], len: usize) -> Result<Vec<T>, BtfError> {
    if mem::size_of::<T>() * len > data.len() {
        return Err(BtfError::InvalidTypeInfo);
    }
    let data = &data[0..mem::size_of::<T>() * len];
    let r = data
        .chunks(mem::size_of::<T>())
        .map(|chunk| ptr::read_unaligned(chunk.as_ptr() as *const T))
        .collect();
    Ok(r)
}

impl BtfType {
    #[allow(unused_unsafe)]
    pub(crate) unsafe fn read(data: &[u8], endianness: Endianness) -> Result<BtfType, BtfError> {
        let ty = unsafe { read_array::<u32>(data, 3)? };
        let data = &data[mem::size_of::<u32>() * 3..];
        let vlen = type_vlen(ty[1]);
        Ok(match type_kind(ty[1])? {
            BtfKind::Unknown => BtfType::Unknown,
            BtfKind::Fwd => BtfType::Fwd(Fwd {
                name_offset: ty[0],
                info: ty[1],
                _unused: 0,
            }),
            BtfKind::Const => BtfType::Const(Const {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
            }),
            BtfKind::Volatile => BtfType::Volatile(Volatile {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
            }),
            BtfKind::Restrict => BtfType::Restrict(Restrict {
                name_offset: ty[0],
                _info: ty[1],
                btf_type: ty[2],
            }),
            BtfKind::Ptr => BtfType::Ptr(Ptr {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
            }),
            BtfKind::Typedef => BtfType::Typedef(Typedef {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
            }),
            BtfKind::Func => BtfType::Func(Func {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
            }),
            BtfKind::Int => {
                if mem::size_of::<u32>() > data.len() {
                    return Err(BtfError::InvalidTypeInfo);
                }
                let read_u32 = if endianness == Endianness::Little {
                    u32::from_le_bytes
                } else {
                    u32::from_be_bytes
                };
                BtfType::Int(Int {
                    name_offset: ty[0],
                    info: ty[1],
                    size: ty[2],
                    data: read_u32(data[..mem::size_of::<u32>()].try_into().unwrap()),
                })
            }
            BtfKind::Float => BtfType::Float(Float {
                name_offset: ty[0],
                info: ty[1],
                size: ty[2],
            }),
            BtfKind::Enum => BtfType::Enum(Enum {
                name_offset: ty[0],
                info: ty[1],
                size: ty[2],
                variants: unsafe { read_array::<BtfEnum>(data, vlen)? },
            }),
            BtfKind::Enum64 => BtfType::Enum64(Enum64 {
                name_offset: ty[0],
                info: ty[1],
                size: ty[2],
                variants: unsafe { read_array::<BtfEnum64>(data, vlen)? },
            }),
            BtfKind::Array => BtfType::Array(Array {
                name_offset: ty[0],
                info: ty[1],
                _unused: 0,
                array: unsafe { read(data)? },
            }),
            BtfKind::Struct => BtfType::Struct(Struct {
                name_offset: ty[0],
                info: ty[1],
                size: ty[2],
                members: unsafe { read_array::<BtfMember>(data, vlen)? },
            }),
            BtfKind::Union => BtfType::Union(Union {
                name_offset: ty[0],
                info: ty[1],
                size: ty[2],
                members: unsafe { read_array::<BtfMember>(data, vlen)? },
            }),
            BtfKind::FuncProto => BtfType::FuncProto(FuncProto {
                name_offset: ty[0],
                info: ty[1],
                return_type: ty[2],
                params: unsafe { read_array::<BtfParam>(data, vlen)? },
            }),
            BtfKind::Var => BtfType::Var(Var {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
                linkage: unsafe { read(data)? },
            }),
            BtfKind::DataSec => BtfType::DataSec(DataSec {
                name_offset: ty[0],
                info: ty[1],
                size: ty[2],
                entries: unsafe { read_array::<DataSecEntry>(data, vlen)? },
            }),
            BtfKind::DeclTag => BtfType::DeclTag(DeclTag {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
                component_index: unsafe { read(data)? },
            }),
            BtfKind::TypeTag => BtfType::TypeTag(TypeTag {
                name_offset: ty[0],
                info: ty[1],
                btf_type: ty[2],
            }),
        })
    }

    pub(crate) fn to_bytes(&self) -> Vec<u8> {
        match self {
            BtfType::Unknown => vec![],
            BtfType::Fwd(t) => t.to_bytes(),
            BtfType::Const(t) => t.to_bytes(),
            BtfType::Volatile(t) => t.to_bytes(),
            BtfType::Restrict(t) => t.to_bytes(),
            BtfType::Ptr(t) => t.to_bytes(),
            BtfType::Typedef(t) => t.to_bytes(),
            BtfType::Func(t) => t.to_bytes(),
            BtfType::Int(t) => t.to_bytes(),
            BtfType::Float(t) => t.to_bytes(),
            BtfType::Enum(t) => t.to_bytes(),
            BtfType::Enum64(t) => t.to_bytes(),
            BtfType::Array(t) => t.to_bytes(),
            BtfType::Struct(t) => t.to_bytes(),
            BtfType::Union(t) => t.to_bytes(),
            BtfType::FuncProto(t) => t.to_bytes(),
            BtfType::Var(t) => t.to_bytes(),
            BtfType::DataSec(t) => t.to_bytes(),
            BtfType::DeclTag(t) => t.to_bytes(),
            BtfType::TypeTag(t) => t.to_bytes(),
        }
    }

    pub(crate) fn size(&self) -> Option<u32> {
        match self {
            BtfType::Int(t) => Some(t.size),
            BtfType::Float(t) => Some(t.size),
            BtfType::Enum(t) => Some(t.size),
            BtfType::Enum64(t) => Some(t.size),
            BtfType::Struct(t) => Some(t.size),
            BtfType::Union(t) => Some(t.size),
            BtfType::DataSec(t) => Some(t.size),
            BtfType::Ptr(_) => Some(mem::size_of::<&()>() as u32),
            _ => None,
        }
    }

    pub(crate) fn btf_type(&self) -> Option<u32> {
        match self {
            BtfType::Const(t) => Some(t.btf_type),
            BtfType::Volatile(t) => Some(t.btf_type),
            BtfType::Restrict(t) => Some(t.btf_type),
            BtfType::Ptr(t) => Some(t.btf_type),
            BtfType::Typedef(t) => Some(t.btf_type),
            // FuncProto contains the return type here, and doesn't directly reference another type
            BtfType::FuncProto(t) => Some(t.return_type),
            BtfType::Var(t) => Some(t.btf_type),
            BtfType::DeclTag(t) => Some(t.btf_type),
            BtfType::TypeTag(t) => Some(t.btf_type),
            _ => None,
        }
    }

    pub(crate) fn type_info_size(&self) -> usize {
        match self {
            BtfType::Unknown => mem::size_of::<Fwd>(),
            BtfType::Fwd(t) => t.type_info_size(),
            BtfType::Const(t) => t.type_info_size(),
            BtfType::Volatile(t) => t.type_info_size(),
            BtfType::Restrict(t) => t.type_info_size(),
            BtfType::Ptr(t) => t.type_info_size(),
            BtfType::Typedef(t) => t.type_info_size(),
            BtfType::Func(t) => t.type_info_size(),
            BtfType::Int(t) => t.type_info_size(),
            BtfType::Float(t) => t.type_info_size(),
            BtfType::Enum(t) => t.type_info_size(),
            BtfType::Enum64(t) => t.type_info_size(),
            BtfType::Array(t) => t.type_info_size(),
            BtfType::Struct(t) => t.type_info_size(),
            BtfType::Union(t) => t.type_info_size(),
            BtfType::FuncProto(t) => t.type_info_size(),
            BtfType::Var(t) => t.type_info_size(),
            BtfType::DataSec(t) => t.type_info_size(),
            BtfType::DeclTag(t) => t.type_info_size(),
            BtfType::TypeTag(t) => t.type_info_size(),
        }
    }

    pub(crate) fn name_offset(&self) -> u32 {
        match self {
            BtfType::Unknown => 0,
            BtfType::Fwd(t) => t.name_offset,
            BtfType::Const(t) => t.name_offset,
            BtfType::Volatile(t) => t.name_offset,
            BtfType::Restrict(t) => t.name_offset,
            BtfType::Ptr(t) => t.name_offset,
            BtfType::Typedef(t) => t.name_offset,
            BtfType::Func(t) => t.name_offset,
            BtfType::Int(t) => t.name_offset,
            BtfType::Float(t) => t.name_offset,
            BtfType::Enum(t) => t.name_offset,
            BtfType::Enum64(t) => t.name_offset,
            BtfType::Array(t) => t.name_offset,
            BtfType::Struct(t) => t.name_offset,
            BtfType::Union(t) => t.name_offset,
            BtfType::FuncProto(t) => t.name_offset,
            BtfType::Var(t) => t.name_offset,
            BtfType::DataSec(t) => t.name_offset,
            BtfType::DeclTag(t) => t.name_offset,
            BtfType::TypeTag(t) => t.name_offset,
        }
    }

    pub(crate) fn kind(&self) -> BtfKind {
        match self {
            BtfType::Unknown => BtfKind::Unknown,
            BtfType::Fwd(t) => t.kind(),
            BtfType::Const(t) => t.kind(),
            BtfType::Volatile(t) => t.kind(),
            BtfType::Restrict(t) => t.kind(),
            BtfType::Ptr(t) => t.kind(),
            BtfType::Typedef(t) => t.kind(),
            BtfType::Func(t) => t.kind(),
            BtfType::Int(t) => t.kind(),
            BtfType::Float(t) => t.kind(),
            BtfType::Enum(t) => t.kind(),
            BtfType::Enum64(t) => t.kind(),
            BtfType::Array(t) => t.kind(),
            BtfType::Struct(t) => t.kind(),
            BtfType::Union(t) => t.kind(),
            BtfType::FuncProto(t) => t.kind(),
            BtfType::Var(t) => t.kind(),
            BtfType::DataSec(t) => t.kind(),
            BtfType::DeclTag(t) => t.kind(),
            BtfType::TypeTag(t) => t.kind(),
        }
    }

    pub(crate) fn is_composite(&self) -> bool {
        matches!(self, BtfType::Struct(_) | BtfType::Union(_))
    }

    pub(crate) fn members(&self) -> Option<impl Iterator<Item = &BtfMember>> {
        match self {
            BtfType::Struct(t) => Some(t.members.iter()),
            BtfType::Union(t) => Some(t.members.iter()),
            _ => None,
        }
    }

    pub(crate) fn member_bit_field_size(&self, member: &BtfMember) -> Option<usize> {
        match self {
            BtfType::Struct(t) => Some(t.member_bit_field_size(member)),
            BtfType::Union(t) => Some(t.member_bit_field_size(member)),
            _ => None,
        }
    }

    pub(crate) fn member_bit_offset(&self, member: &BtfMember) -> Option<usize> {
        match self {
            BtfType::Struct(t) => Some(t.member_bit_offset(member)),
            BtfType::Union(t) => Some(t.member_bit_offset(member)),
            _ => None,
        }
    }

    pub(crate) fn is_compatible(&self, other: &BtfType) -> bool {
        if self.kind() == other.kind() {
            return true;
        }

        matches!(
            (self.kind(), other.kind()),
            (BtfKind::Enum, BtfKind::Enum64) | (BtfKind::Enum64, BtfKind::Enum)
        )
    }
}

fn type_kind(info: u32) -> Result<BtfKind, BtfError> {
    ((info >> 24) & 0x1F).try_into()
}

fn type_vlen(info: u32) -> usize {
    (info & 0xFFFF) as usize
}

pub(crate) fn types_are_compatible(
    local_btf: &Btf,
    root_local_id: u32,
    target_btf: &Btf,
    root_target_id: u32,
) -> Result<bool, BtfError> {
    let mut local_id = root_local_id;
    let mut target_id = root_target_id;
    let local_ty = local_btf.type_by_id(local_id)?;
    let target_ty = target_btf.type_by_id(target_id)?;

    if !local_ty.is_compatible(target_ty) {
        return Ok(false);
    }

    for () in core::iter::repeat_n((), MAX_RESOLVE_DEPTH) {
        local_id = local_btf.resolve_type(local_id)?;
        target_id = target_btf.resolve_type(target_id)?;
        let local_ty = local_btf.type_by_id(local_id)?;
        let target_ty = target_btf.type_by_id(target_id)?;

        if !local_ty.is_compatible(target_ty) {
            return Ok(false);
        }

        match local_ty {
            BtfType::Unknown
            | BtfType::Struct(_)
            | BtfType::Union(_)
            | BtfType::Enum(_)
            | BtfType::Enum64(_)
            | BtfType::Fwd(_)
            | BtfType::Float(_) => return Ok(true),
            BtfType::Int(local) => {
                if let BtfType::Int(target) = target_ty {
                    return Ok(local.offset() == 0 && target.offset() == 0);
                }
            }
            BtfType::Ptr(local) => {
                if let BtfType::Ptr(target) = target_ty {
                    local_id = local.btf_type;
                    target_id = target.btf_type;
                    continue;
                }
            }
            BtfType::Array(Array { array: local, .. }) => {
                if let BtfType::Array(Array { array: target, .. }) = target_ty {
                    local_id = local.element_type;
                    target_id = target.element_type;
                    continue;
                }
            }
            BtfType::FuncProto(local) => {
                if let BtfType::FuncProto(target) = target_ty {
                    if local.params.len() != target.params.len() {
                        return Ok(false);
                    }

                    for (l_param, t_param) in local.params.iter().zip(target.params.iter()) {
                        let local_id = local_btf.resolve_type(l_param.btf_type)?;
                        let target_id = target_btf.resolve_type(t_param.btf_type)?;
                        if !types_are_compatible(local_btf, local_id, target_btf, target_id)? {
                            return Ok(false);
                        }
                    }

                    local_id = local.return_type;
                    target_id = target.return_type;
                    continue;
                }
            }
            local_ty => panic!("unexpected type {:?}", local_ty),
        }
    }

    Err(BtfError::MaximumTypeDepthReached { type_id: local_id })
}

pub(crate) fn fields_are_compatible(
    local_btf: &Btf,
    mut local_id: u32,
    target_btf: &Btf,
    mut target_id: u32,
) -> Result<bool, BtfError> {
    for () in core::iter::repeat_n((), MAX_RESOLVE_DEPTH) {
        local_id = local_btf.resolve_type(local_id)?;
        target_id = target_btf.resolve_type(target_id)?;
        let local_ty = local_btf.type_by_id(local_id)?;
        let target_ty = target_btf.type_by_id(target_id)?;

        if local_ty.is_composite() && target_ty.is_composite() {
            return Ok(true);
        }

        if !local_ty.is_compatible(target_ty) {
            return Ok(false);
        }

        match local_ty {
            BtfType::Fwd(_) | BtfType::Enum(_) | BtfType::Enum64(_) => {
                let flavorless_name =
                    |name: &str| name.split_once("___").map_or(name, |x| x.0).to_string();

                let local_name = flavorless_name(&local_btf.type_name(local_ty)?);
                let target_name = flavorless_name(&target_btf.type_name(target_ty)?);

                return Ok(local_name == target_name);
            }
            BtfType::Int(local) => {
                if let BtfType::Int(target) = target_ty {
                    return Ok(local.offset() == 0 && target.offset() == 0);
                }
            }
            BtfType::Float(_) => return Ok(true),
            BtfType::Ptr(_) => return Ok(true),
            BtfType::Array(Array { array: local, .. }) => {
                if let BtfType::Array(Array { array: target, .. }) = target_ty {
                    local_id = local.element_type;
                    target_id = target.element_type;
                    continue;
                }
            }
            local_ty => panic!("unexpected type {:?}", local_ty),
        }
    }

    Err(BtfError::MaximumTypeDepthReached { type_id: local_id })
}

fn bytes_of<T>(val: &T) -> &[u8] {
    // Safety: all btf types are POD
    unsafe { crate::util::bytes_of(val) }
}
#[cfg(test)]
mod tests {
    use assert_matches::assert_matches;

    use super::*;

    #[test]
    fn test_read_btf_type_int() {
        let endianness = Endianness::default();
        let bpf_type = BtfType::Int(Int::new(1, 8, IntEncoding::None, 0));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Int(new @ Int {
            name_offset,
            info: _,
            size,
            data: _,
        }) => {
                assert_eq!(name_offset, 1);
                assert_eq!(size, 8);
                assert_eq!(new.bits(), 64);
                assert_eq!(new.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_ptr() {
        let endianness = Endianness::default();
        let bpf_type = BtfType::Ptr(Ptr::new(0, 0x06));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Ptr(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_array() {
        let endianness = Endianness::default();
        let bpf_type = BtfType::Array(Array::new(0, 1, 0x12, 2));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Array(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_struct() {
        let endianness = Endianness::default();
        let members = vec![BtfMember {
            name_offset: 0x0247,
            btf_type: 0x12,
            offset: 0,
        }];
        let bpf_type = BtfType::Struct(Struct::new(0, members, 4));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Struct(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_union() {
        let endianness = Endianness::default();
        let members = vec![BtfMember {
            name_offset: 0x040d,
            btf_type: 0x68,
            offset: 0,
        }];
        let bpf_type = BtfType::Union(Union::new(0, 4, members));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Union(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_enum() {
        let endianness = Endianness::default();
        let enum1 = BtfEnum::new(0xc9, 0);
        let enum2 = BtfEnum::new(0xcf, 1);
        let variants = vec![enum1, enum2];
        let bpf_type = BtfType::Enum(Enum::new(0, false, variants));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Enum(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_fwd() {
        let endianness = Endianness::default();
        let info = (BtfKind::Fwd as u32) << 24;
        let bpf_type = BtfType::Fwd(Fwd {
            name_offset: 0x550b,
            info,
            _unused: 0,
        });
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Fwd(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_typedef() {
        let endianness = Endianness::default();
        let bpf_type = BtfType::Typedef(Typedef::new(0x31, 0x0b));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Typedef(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_volatile() {
        let endianness = Endianness::default();
        let info = (BtfKind::Volatile as u32) << 24;
        let bpf_type = BtfType::Volatile(Volatile {
            name_offset: 0,
            info,
            btf_type: 0x24,
        });
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Volatile(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_const() {
        let endianness = Endianness::default();
        let bpf_type = BtfType::Const(Const::new(1));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Const(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_restrict() {
        let endianness = Endianness::default();
        let info = (BtfKind::Restrict as u32) << 24;
        let bpf_type = BtfType::Restrict(Restrict {
            name_offset: 0,
            _info: info,
            btf_type: 4,
        });
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Restrict(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_func() {
        let endianness = Endianness::default();
        let bpf_type = BtfType::Func(Func::new(0x000f8b17, 0xe4f0, FuncLinkage::Global));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Func(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_func_proto() {
        let endianness = Endianness::default();
        let params = vec![BtfParam {
            name_offset: 0,
            btf_type: 0x12,
        }];
        let bpf_type = BtfType::FuncProto(FuncProto::new(params, 0));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::FuncProto(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_func_var() {
        let endianness = Endianness::default();
        // NOTE: There was no data in /sys/kernell/btf/vmlinux for this type
        let bpf_type = BtfType::Var(Var::new(0, 0xf0, VarLinkage::Static));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Var(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_read_btf_type_func_datasec() {
        let endianness = Endianness::default();
        let entries = vec![DataSecEntry {
            btf_type: 11,
            offset: 0,
            size: 4,
        }];
        let bpf_type = BtfType::DataSec(DataSec::new(0xd9, entries, 0));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::DataSec(DataSec {
            name_offset: _,
            info: _,
            size,
            entries,
         }) => {
                assert_eq!(size, 0);
                assert_matches!(*entries, [
                    DataSecEntry {
                        btf_type: 11,
                        offset: 0,
                        size: 4,
                    }
                ]);
            }
        );
    }

    #[test]
    fn test_read_btf_type_float() {
        let endianness = Endianness::default();
        let bpf_type = BtfType::Float(Float::new(0x02fd, 8));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Float(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }

    #[test]
    fn test_write_btf_func_proto() {
        let params = vec![
            BtfParam {
                name_offset: 1,
                btf_type: 1,
            },
            BtfParam {
                name_offset: 3,
                btf_type: 1,
            },
        ];
        let func_proto = FuncProto::new(params, 2);
        let data = func_proto.to_bytes();
        assert_matches!(unsafe { BtfType::read(&data, Endianness::default()) }.unwrap(), BtfType::FuncProto(FuncProto {
            name_offset: _,
            info: _,
            return_type: _,
            params,
        }) => {
            assert_matches!(*params, [
                _,
                _,
            ])
        });
    }

    #[test]
    fn test_types_are_compatible() {
        let mut btf = Btf::new();
        let name_offset = btf.add_string("u32");
        let u32t = btf.add_type(BtfType::Int(Int::new(name_offset, 4, IntEncoding::None, 0)));
        let name_offset = btf.add_string("u64");
        let u64t = btf.add_type(BtfType::Int(Int::new(name_offset, 8, IntEncoding::None, 0)));
        let name_offset = btf.add_string("widgets");
        let array_type = btf.add_type(BtfType::Array(Array::new(name_offset, u64t, u32t, 16)));

        assert!(types_are_compatible(&btf, u32t, &btf, u32t).unwrap());
        // int types are compatible if offsets match. size and encoding aren't compared
        assert!(types_are_compatible(&btf, u32t, &btf, u64t).unwrap());
        assert!(types_are_compatible(&btf, array_type, &btf, array_type).unwrap());
    }

    #[test]
    pub fn test_read_btf_type_enum64() {
        let endianness = Endianness::default();
        let variants = vec![BtfEnum64::new(0, 0xbbbbbbbbaaaaaaaau64)];
        let bpf_type = BtfType::Enum64(Enum64::new(0, false, variants));
        let data: &[u8] = &bpf_type.to_bytes();
        assert_matches!(unsafe { BtfType::read(data, endianness) }.unwrap(), BtfType::Enum64(got) => {
            assert_eq!(got.to_bytes(), data);
        });
    }
}