use core::fmt::Debug;
use core::{iter, mem, slice, str};

use crate::elf;
use crate::endian::{self, Endianness, U32Bytes};
use crate::pod::{Bytes, Pod};
use crate::read::{
    self, CompressedData, CompressionFormat, Error, ObjectSection, ReadError, SectionFlags,
    SectionIndex, SectionKind, StringTable,
};

use super::{
    CompressionHeader, ElfFile, ElfNoteIterator, ElfRelocationIterator, FileHeader,
    RelocationSections, SymbolTable,
};

/// The table of section headers in an ELF file.
///
/// Also includes the string table used for the section names.
#[derive(Debug, Default, Clone, Copy)]
pub struct SectionTable<'data, Elf: FileHeader> {
    sections: &'data [Elf::SectionHeader],
    strings: StringTable<'data>,
}

impl<'data, Elf: FileHeader> SectionTable<'data, Elf> {
    /// Create a new section table.
    #[inline]
    pub fn new(sections: &'data [Elf::SectionHeader], strings: StringTable<'data>) -> Self {
        SectionTable { sections, strings }
    }

    /// Iterate over the section headers.
    #[inline]
    pub fn iter(&self) -> slice::Iter<'data, Elf::SectionHeader> {
        self.sections.iter()
    }

    /// Return true if the section table is empty.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.sections.is_empty()
    }

    /// The number of section headers.
    #[inline]
    pub fn len(&self) -> usize {
        self.sections.len()
    }

    /// Return the section header at the given index.
    pub fn section(&self, index: usize) -> read::Result<&'data Elf::SectionHeader> {
        self.sections
            .get(index)
            .read_error("Invalid ELF section index")
    }

    /// Return the section header with the given name.
    ///
    /// Ignores sections with invalid names.
    pub fn section_by_name(
        &self,
        endian: Elf::Endian,
        name: &[u8],
    ) -> Option<(usize, &'data Elf::SectionHeader)> {
        self.sections
            .iter()
            .enumerate()
            .find(|(_, section)| self.section_name(endian, section) == Ok(name))
    }

    /// Return the section name for the given section header.
    pub fn section_name(
        &self,
        endian: Elf::Endian,
        section: &'data Elf::SectionHeader,
    ) -> read::Result<&'data [u8]> {
        self.strings
            .get(section.sh_name(endian))
            .read_error("Invalid ELF section name offset")
    }

    /// Return the symbol table of the given section type.
    ///
    /// Returns an empty symbol table if the symbol table does not exist.
    #[inline]
    pub fn symbols(
        &self,
        endian: Elf::Endian,
        data: Bytes<'data>,
        sh_type: u32,
    ) -> read::Result<SymbolTable<'data, Elf>> {
        SymbolTable::parse(endian, data, self, sh_type)
    }

    /// Create a mapping from section index to associated relocation sections.
    #[inline]
    pub fn relocation_sections(
        &self,
        endian: Elf::Endian,
        symbol_section: usize,
    ) -> read::Result<RelocationSections> {
        RelocationSections::parse(endian, self, symbol_section)
    }
}

/// An iterator over the sections of an `ElfFile32`.
pub type ElfSectionIterator32<'data, 'file, Endian = Endianness> =
    ElfSectionIterator<'data, 'file, elf::FileHeader32<Endian>>;
/// An iterator over the sections of an `ElfFile64`.
pub type ElfSectionIterator64<'data, 'file, Endian = Endianness> =
    ElfSectionIterator<'data, 'file, elf::FileHeader64<Endian>>;

/// An iterator over the sections of an `ElfFile`.
#[derive(Debug)]
pub struct ElfSectionIterator<'data, 'file, Elf>
where
    'data: 'file,
    Elf: FileHeader,
{
    pub(super) file: &'file ElfFile<'data, Elf>,
    pub(super) iter: iter::Enumerate<slice::Iter<'data, Elf::SectionHeader>>,
}

impl<'data, 'file, Elf: FileHeader> Iterator for ElfSectionIterator<'data, 'file, Elf> {
    type Item = ElfSection<'data, 'file, Elf>;

    fn next(&mut self) -> Option<Self::Item> {
        self.iter.next().map(|(index, section)| ElfSection {
            index: SectionIndex(index),
            file: self.file,
            section,
        })
    }
}

/// A section of an `ElfFile32`.
pub type ElfSection32<'data, 'file, Endian = Endianness> =
    ElfSection<'data, 'file, elf::FileHeader32<Endian>>;
/// A section of an `ElfFile64`.
pub type ElfSection64<'data, 'file, Endian = Endianness> =
    ElfSection<'data, 'file, elf::FileHeader64<Endian>>;

/// A section of an `ElfFile`.
#[derive(Debug)]
pub struct ElfSection<'data, 'file, Elf>
where
    'data: 'file,
    Elf: FileHeader,
{
    pub(super) file: &'file ElfFile<'data, Elf>,
    pub(super) index: SectionIndex,
    pub(super) section: &'data Elf::SectionHeader,
}

impl<'data, 'file, Elf: FileHeader> ElfSection<'data, 'file, Elf> {
    fn bytes(&self) -> read::Result<Bytes<'data>> {
        self.section
            .data(self.file.endian, self.file.data)
            .read_error("Invalid ELF section size or offset")
    }

    fn maybe_compressed_data(&self) -> read::Result<Option<CompressedData<'data>>> {
        let endian = self.file.endian;
        if (self.section.sh_flags(endian).into() & u64::from(elf::SHF_COMPRESSED)) == 0 {
            return Ok(None);
        }

        let mut data = self
            .section
            .data(endian, self.file.data)
            .read_error("Invalid ELF compressed section offset or size")?;
        let header = data
            .read::<Elf::CompressionHeader>()
            .read_error("Invalid ELF compression header size or alignment")?;
        if header.ch_type(endian) != elf::ELFCOMPRESS_ZLIB {
            return Err(Error("Unsupported ELF compression type"));
        }
        let uncompressed_size: u64 = header.ch_size(endian).into();
        Ok(Some(CompressedData {
            format: CompressionFormat::Zlib,
            data: data.0,
            uncompressed_size: uncompressed_size as usize,
        }))
    }

    /// Try GNU-style "ZLIB" header decompression.
    fn maybe_compressed_data_gnu(&self) -> read::Result<Option<CompressedData<'data>>> {
        let name = match self.name() {
            Ok(name) => name,
            // I think it's ok to ignore this error?
            Err(_) => return Ok(None),
        };
        if !name.starts_with(".zdebug_") {
            return Ok(None);
        }
        let mut data = self.bytes()?;
        // Assume ZLIB-style uncompressed data is no more than 4GB to avoid accidentally
        // huge allocations. This also reduces the chance of accidentally matching on a
        // .debug_str that happens to start with "ZLIB".
        if data
            .read_bytes(8)
            .read_error("ELF GNU compressed section is too short")?
            .0
            != b"ZLIB\0\0\0\0"
        {
            return Err(Error("Invalid ELF GNU compressed section header"));
        }
        let uncompressed_size = data
            .read::<U32Bytes<_>>()
            .read_error("ELF GNU compressed section is too short")?
            .get(endian::BigEndian);
        Ok(Some(CompressedData {
            format: CompressionFormat::Zlib,
            data: data.0,
            uncompressed_size: uncompressed_size as usize,
        }))
    }
}

impl<'data, 'file, Elf: FileHeader> read::private::Sealed for ElfSection<'data, 'file, Elf> {}

impl<'data, 'file, Elf: FileHeader> ObjectSection<'data> for ElfSection<'data, 'file, Elf> {
    type RelocationIterator = ElfRelocationIterator<'data, 'file, Elf>;

    #[inline]
    fn index(&self) -> SectionIndex {
        self.index
    }

    #[inline]
    fn address(&self) -> u64 {
        self.section.sh_addr(self.file.endian).into()
    }

    #[inline]
    fn size(&self) -> u64 {
        self.section.sh_size(self.file.endian).into()
    }

    #[inline]
    fn align(&self) -> u64 {
        self.section.sh_addralign(self.file.endian).into()
    }

    #[inline]
    fn file_range(&self) -> Option<(u64, u64)> {
        self.section.file_range(self.file.endian)
    }

    #[inline]
    fn data(&self) -> read::Result<&'data [u8]> {
        Ok(self.bytes()?.0)
    }

    fn data_range(&self, address: u64, size: u64) -> read::Result<Option<&'data [u8]>> {
        Ok(read::data_range(
            self.bytes()?,
            self.address(),
            address,
            size,
        ))
    }

    fn compressed_data(&self) -> read::Result<CompressedData<'data>> {
        Ok(if let Some(data) = self.maybe_compressed_data()? {
            data
        } else if let Some(data) = self.maybe_compressed_data_gnu()? {
            data
        } else {
            CompressedData::none(self.data()?)
        })
    }

    fn name(&self) -> read::Result<&str> {
        let name = self
            .file
            .sections
            .section_name(self.file.endian, self.section)?;
        str::from_utf8(name)
            .ok()
            .read_error("Non UTF-8 ELF section name")
    }

    #[inline]
    fn segment_name(&self) -> read::Result<Option<&str>> {
        Ok(None)
    }

    fn kind(&self) -> SectionKind {
        let flags = self.section.sh_flags(self.file.endian).into();
        match self.section.sh_type(self.file.endian) {
            elf::SHT_PROGBITS => {
                if flags & u64::from(elf::SHF_ALLOC) != 0 {
                    if flags & u64::from(elf::SHF_EXECINSTR) != 0 {
                        SectionKind::Text
                    } else if flags & u64::from(elf::SHF_TLS) != 0 {
                        SectionKind::Tls
                    } else if flags & u64::from(elf::SHF_WRITE) != 0 {
                        SectionKind::Data
                    } else if flags & u64::from(elf::SHF_STRINGS) != 0 {
                        SectionKind::ReadOnlyString
                    } else {
                        SectionKind::ReadOnlyData
                    }
                } else if flags & u64::from(elf::SHF_STRINGS) != 0 {
                    SectionKind::OtherString
                } else {
                    SectionKind::Other
                }
            }
            elf::SHT_NOBITS => {
                if flags & u64::from(elf::SHF_TLS) != 0 {
                    SectionKind::UninitializedTls
                } else {
                    SectionKind::UninitializedData
                }
            }
            elf::SHT_NULL
            | elf::SHT_SYMTAB
            | elf::SHT_STRTAB
            | elf::SHT_RELA
            | elf::SHT_HASH
            | elf::SHT_DYNAMIC
            | elf::SHT_REL
            | elf::SHT_DYNSYM => SectionKind::Metadata,
            _ => {
                // TODO: maybe add more specialised kinds based on sh_type (e.g. Unwind)
                SectionKind::Unknown
            }
        }
    }

    fn relocations(&self) -> ElfRelocationIterator<'data, 'file, Elf> {
        ElfRelocationIterator {
            section_index: self.index.0,
            file: self.file,
            relocations: None,
        }
    }

    fn flags(&self) -> SectionFlags {
        SectionFlags::Elf {
            sh_flags: self.section.sh_flags(self.file.endian).into(),
        }
    }
}

/// A trait for generic access to `SectionHeader32` and `SectionHeader64`.
#[allow(missing_docs)]
pub trait SectionHeader: Debug + Pod {
    type Word: Into<u64>;
    type Endian: endian::Endian;
    type Elf: FileHeader<Word = Self::Word, Endian = Self::Endian>;

    fn sh_name(&self, endian: Self::Endian) -> u32;
    fn sh_type(&self, endian: Self::Endian) -> u32;
    fn sh_flags(&self, endian: Self::Endian) -> Self::Word;
    fn sh_addr(&self, endian: Self::Endian) -> Self::Word;
    fn sh_offset(&self, endian: Self::Endian) -> Self::Word;
    fn sh_size(&self, endian: Self::Endian) -> Self::Word;
    fn sh_link(&self, endian: Self::Endian) -> u32;
    fn sh_info(&self, endian: Self::Endian) -> u32;
    fn sh_addralign(&self, endian: Self::Endian) -> Self::Word;
    fn sh_entsize(&self, endian: Self::Endian) -> Self::Word;

    /// Return the offset and size of the section in the file.
    ///
    /// Returns `None` for sections that have no data in the file.
    fn file_range(&self, endian: Self::Endian) -> Option<(u64, u64)> {
        if self.sh_type(endian) == elf::SHT_NOBITS {
            None
        } else {
            Some((self.sh_offset(endian).into(), self.sh_size(endian).into()))
        }
    }

    /// Return the section data.
    ///
    /// Returns `Ok(&[])` if the section has no data.
    /// Returns `Err` for invalid values.
    fn data<'data>(&self, endian: Self::Endian, data: Bytes<'data>) -> Result<Bytes<'data>, ()> {
        if let Some((offset, size)) = self.file_range(endian) {
            data.read_bytes_at(offset as usize, size as usize)
        } else {
            Ok(Bytes(&[]))
        }
    }

    /// Return the section data as a slice of the given type.
    ///
    /// Allows padding at the end of the data.
    /// Returns `Ok(&[])` if the section has no data.
    /// Returns `Err` for invalid values, including bad alignment.
    fn data_as_array<'data, T: Pod>(
        &self,
        endian: Self::Endian,
        data: Bytes<'data>,
    ) -> Result<&'data [T], ()> {
        let mut data = self.data(endian, data)?;
        data.read_slice(data.len() / mem::size_of::<T>())
    }

    /// Return a note iterator for the section data.
    ///
    /// Returns `Ok(None)` if the section does not contain notes.
    /// Returns `Err` for invalid values.
    fn notes<'data>(
        &self,
        endian: Self::Endian,
        data: Bytes<'data>,
    ) -> read::Result<Option<ElfNoteIterator<'data, Self::Elf>>> {
        if self.sh_type(endian) != elf::SHT_NOTE {
            return Ok(None);
        }
        let data = self
            .data(endian, data)
            .read_error("Invalid ELF note section offset or size")?;
        let notes = ElfNoteIterator::new(endian, self.sh_addralign(endian), data)?;
        Ok(Some(notes))
    }
}

impl<Endian: endian::Endian> SectionHeader for elf::SectionHeader32<Endian> {
    type Word = u32;
    type Endian = Endian;
    type Elf = elf::FileHeader32<Endian>;

    #[inline]
    fn sh_name(&self, endian: Self::Endian) -> u32 {
        self.sh_name.get(endian)
    }

    #[inline]
    fn sh_type(&self, endian: Self::Endian) -> u32 {
        self.sh_type.get(endian)
    }

    #[inline]
    fn sh_flags(&self, endian: Self::Endian) -> Self::Word {
        self.sh_flags.get(endian)
    }

    #[inline]
    fn sh_addr(&self, endian: Self::Endian) -> Self::Word {
        self.sh_addr.get(endian)
    }

    #[inline]
    fn sh_offset(&self, endian: Self::Endian) -> Self::Word {
        self.sh_offset.get(endian)
    }

    #[inline]
    fn sh_size(&self, endian: Self::Endian) -> Self::Word {
        self.sh_size.get(endian)
    }

    #[inline]
    fn sh_link(&self, endian: Self::Endian) -> u32 {
        self.sh_link.get(endian)
    }

    #[inline]
    fn sh_info(&self, endian: Self::Endian) -> u32 {
        self.sh_info.get(endian)
    }

    #[inline]
    fn sh_addralign(&self, endian: Self::Endian) -> Self::Word {
        self.sh_addralign.get(endian)
    }

    #[inline]
    fn sh_entsize(&self, endian: Self::Endian) -> Self::Word {
        self.sh_entsize.get(endian)
    }
}

impl<Endian: endian::Endian> SectionHeader for elf::SectionHeader64<Endian> {
    type Word = u64;
    type Endian = Endian;
    type Elf = elf::FileHeader64<Endian>;

    #[inline]
    fn sh_name(&self, endian: Self::Endian) -> u32 {
        self.sh_name.get(endian)
    }

    #[inline]
    fn sh_type(&self, endian: Self::Endian) -> u32 {
        self.sh_type.get(endian)
    }

    #[inline]
    fn sh_flags(&self, endian: Self::Endian) -> Self::Word {
        self.sh_flags.get(endian)
    }

    #[inline]
    fn sh_addr(&self, endian: Self::Endian) -> Self::Word {
        self.sh_addr.get(endian)
    }

    #[inline]
    fn sh_offset(&self, endian: Self::Endian) -> Self::Word {
        self.sh_offset.get(endian)
    }

    #[inline]
    fn sh_size(&self, endian: Self::Endian) -> Self::Word {
        self.sh_size.get(endian)
    }

    #[inline]
    fn sh_link(&self, endian: Self::Endian) -> u32 {
        self.sh_link.get(endian)
    }

    #[inline]
    fn sh_info(&self, endian: Self::Endian) -> u32 {
        self.sh_info.get(endian)
    }

    #[inline]
    fn sh_addralign(&self, endian: Self::Endian) -> Self::Word {
        self.sh_addralign.get(endian)
    }

    #[inline]
    fn sh_entsize(&self, endian: Self::Endian) -> Self::Word {
        self.sh_entsize.get(endian)
    }
}