# -*- coding: utf-8 -*-
#
# Copyright (c) 2019, Felix Fontein <felix@fontein.de>
# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
# SPDX-License-Identifier: GPL-3.0-or-later

from __future__ import absolute_import, division, print_function
__metaclass__ = type


PEM_START = '-----BEGIN '
PEM_END_START = '-----END '
PEM_END = '-----'
PKCS8_PRIVATEKEY_NAMES = ('PRIVATE KEY', 'ENCRYPTED PRIVATE KEY')
PKCS1_PRIVATEKEY_SUFFIX = ' PRIVATE KEY'


def identify_pem_format(content, encoding='utf-8'):
    '''Given the contents of a binary file, tests whether this could be a PEM file.'''
    try:
        first_pem = extract_first_pem(content.decode(encoding))
        if first_pem is None:
            return False
        lines = first_pem.splitlines(False)
        if lines[0].startswith(PEM_START) and lines[0].endswith(PEM_END) and len(lines[0]) > len(PEM_START) + len(PEM_END):
            return True
    except UnicodeDecodeError:
        pass
    return False


def identify_private_key_format(content, encoding='utf-8'):
    '''Given the contents of a private key file, identifies its format.'''
    # See https://github.com/openssl/openssl/blob/master/crypto/pem/pem_pkey.c#L40-L85
    # (PEM_read_bio_PrivateKey)
    # and https://github.com/openssl/openssl/blob/master/include/openssl/pem.h#L46-L47
    # (PEM_STRING_PKCS8, PEM_STRING_PKCS8INF)
    try:
        first_pem = extract_first_pem(content.decode(encoding))
        if first_pem is None:
            return 'raw'
        lines = first_pem.splitlines(False)
        if lines[0].startswith(PEM_START) and lines[0].endswith(PEM_END) and len(lines[0]) > len(PEM_START) + len(PEM_END):
            name = lines[0][len(PEM_START):-len(PEM_END)]
            if name in PKCS8_PRIVATEKEY_NAMES:
                return 'pkcs8'
            if len(name) > len(PKCS1_PRIVATEKEY_SUFFIX) and name.endswith(PKCS1_PRIVATEKEY_SUFFIX):
                return 'pkcs1'
            return 'unknown-pem'
    except UnicodeDecodeError:
        pass
    return 'raw'


def split_pem_list(text, keep_inbetween=False):
    '''
    Split concatenated PEM objects into a list of strings, where each is one PEM object.
    '''
    result = []
    current = [] if keep_inbetween else None
    for line in text.splitlines(True):
        if line.strip():
            if not keep_inbetween and line.startswith('-----BEGIN '):
                current = []
            if current is not None:
                current.append(line)
                if line.startswith('-----END '):
                    result.append(''.join(current))
                    current = [] if keep_inbetween else None
    return result


def extract_first_pem(text):
    '''
    Given one PEM or multiple concatenated PEM objects, return only the first one, or None if there is none.
    '''
    all_pems = split_pem_list(text)
    if not all_pems:
        return None
    return all_pems[0]


def _extract_type(line, start=PEM_START):
    if not line.startswith(start):
        return None
    if not line.endswith(PEM_END):
        return None
    return line[len(start):-len(PEM_END)]


def extract_pem(content, strict=False):
    lines = content.splitlines()
    if len(lines) < 3:
        raise ValueError('PEM must have at least 3 lines, have only {count}'.format(count=len(lines)))
    header_type = _extract_type(lines[0])
    if header_type is None:
        raise ValueError('First line is not of format {start}...{end}: {line!r}'.format(start=PEM_START, end=PEM_END, line=lines[0]))
    footer_type = _extract_type(lines[-1], start=PEM_END_START)
    if strict:
        if header_type != footer_type:
            raise ValueError('Header type ({header}) is different from footer type ({footer})'.format(header=header_type, footer=footer_type))
        for idx, line in enumerate(lines[1:-2]):
            if len(line) != 64:
                raise ValueError('Line {idx} has length {len} instead of 64'.format(idx=idx, len=len(line)))
        if not (0 < len(lines[-2]) <= 64):
            raise ValueError('Last line has length {len}, should be in (0, 64]'.format(len=len(lines[-2])))
    content = lines[1:-1]
    return header_type, ''.join(content)