# Copyright 2015 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2

from portage.util.elf.constants import (
    E_ENTRY,
    E_MACHINE,
    E_TYPE,
    EI_CLASS,
    ELFCLASS32,
    ELFCLASS64,
    ELFDATA2LSB,
    ELFDATA2MSB,
)
from portage.util.endian.decode import (
    decode_uint16_be,
    decode_uint16_le,
    decode_uint32_be,
    decode_uint32_le,
)


class ELFHeader:
    __slots__ = ("e_flags", "e_machine", "e_type", "ei_class", "ei_data")

    @classmethod
    def read(cls, f):
        """
        @param f: an open ELF file
        @type f: file
        @rtype: ELFHeader
        @return: A new ELFHeader instance containing data from f
        """
        f.seek(EI_CLASS)
        ei_class = ord(f.read(1))
        ei_data = ord(f.read(1))

        if ei_class == ELFCLASS32:
            width = 32
        elif ei_class == ELFCLASS64:
            width = 64
        else:
            width = None

        if ei_data == ELFDATA2LSB:
            uint16 = decode_uint16_le
            uint32 = decode_uint32_le
        elif ei_data == ELFDATA2MSB:
            uint16 = decode_uint16_be
            uint32 = decode_uint32_be
        else:
            uint16 = None
            uint32 = None

        if width is None or uint16 is None:
            e_flags = None
            e_machine = None
            e_type = None
        else:
            f.seek(E_TYPE)
            e_type = uint16(f.read(2))
            f.seek(E_MACHINE)
            e_machine = uint16(f.read(2))

            # E_ENTRY + 3 * sizeof(uintN)
            e_flags_offset = E_ENTRY + 3 * width // 8
            f.seek(e_flags_offset)
            e_flags = uint32(f.read(4))

        obj = cls()
        obj.e_flags = e_flags
        obj.e_machine = e_machine
        obj.e_type = e_type
        obj.ei_class = ei_class
        obj.ei_data = ei_data

        return obj
