#!/usr/bin/python3
# Copyright (C) 2018 Jelmer Vernooij
# This file is a part of debmutate.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

"""Utility functions for dealing with deb822 files."""

__all__ = [
    'dump_paragraphs',
    'reformat_deb822',
    'ChangeConflict',
    'Deb822Editor',
    'new_deb822_paragraph',
    'parse_deb822_file',
    'parse_deb822_paragraph',
    'Deb822Paragraph',
    ]

from io import BytesIO
from typing import List, Optional

from debian.changelog import Version

from debian import __version__ as python_debian_version
try:
    from debian._deb822_repro.parsing import (
        parse_deb822_file,
        Deb822ParagraphElement as Deb822Paragraph,
        Deb822FileElement as Deb822File,
        )
except TypeError:
    # This happens on python 3.7 with older versions of python3-debian
    raise ModuleNotFoundError('python too old; need >= 3.9')

from .reformatting import (
    Editor,
    )

parsed_python_debian_version = Version(python_debian_version)
if parsed_python_debian_version < Version('0.1.44'):
    raise ModuleNotFoundError('need python-debian >= 0.1.44')


if parse_deb822_file is None:
    # On python < 3.9, this is the case
    raise ModuleNotFoundError('python too old; need >= 3.9')


def parse_deb822_paragraph(p):
    f = parse_deb822_file(p)
    [p] = f.iter_parts_of_type(Deb822Paragraph)
    return p


def new_deb822_paragraph():
    return Deb822Paragraph.new_empty_paragraph()


def dump_paragraphs(paragraphs: Deb822File) -> bytes:
    """Dump a set of deb822 paragraphs to a file.

    Args:
      paragraphs: iterable over paragraphs
    Returns:
      formatted text (as bytes)
    """
    outf = BytesIO()
    if hasattr(paragraphs, 'dump'):
        # deb822_repro
        paragraphs.dump(outf)
    else:
        first = True
        for paragraph in paragraphs:
            if paragraph:
                if not first:
                    outf.write(b'\n')
                paragraph.dump(fd=outf)
                first = False
    return outf.getvalue()


def reformat_deb822(contents: bytes) -> bytes:
    """Check whether it's possible to preserve a control file.

    Args:
      contents: Original contents
    Returns:
      New contents
    """
    return dump_paragraphs(parse_deb822_file(BytesIO(contents)))


class ChangeConflict(Exception):
    """Indicates that a proposed change didn't match what was found.
    """

    def __init__(self, para_key, field, expected_old_value, actual_old_value,
                 new_value):
        self.paragraph_key = para_key
        self.field = field
        self.expected_old_value = expected_old_value
        self.actual_old_value = actual_old_value
        self.new_value = new_value

    def __repr__(self):
        return ("%s(para_key=%r, field=%r, expected_old_value=%r, "
                "actual_old_value=%r, new_value=%r)" % (
                    type(self).__name__,
                    self.paragraph_key, self.field, self.expected_old_value,
                    self.actual_old_value, self.new_value))


class Deb822Editor(Editor):
    """Update the contents of a Deb822-style file.

    """

    def __init__(self, path: str, allow_generated: bool = False,
                 allow_reformatting: Optional[bool] = None,
                 allow_missing: bool = False) -> None:
        super(Deb822Editor, self).__init__(
            path, allow_generated=allow_generated,
            allow_reformatting=allow_reformatting,
            mode='b')
        self.allow_missing = allow_missing

    def apply_changes(self, changes, resolve_conflict=None):
        """Apply a set of changes to this deb822 instance.

        Args:
          changes: dict mapping paragraph types to
              list of (field_name, old_value, new_value)
            resolve_conflict: callback that receives
                (para_key, field, actual_old_value, template_old_value,
                 actual_new_value) and returns a new template value
        """
        def _default_resolve_conflict(
                para_key, field, actual_old_value,
                template_old_value, actual_new_value):
            raise ChangeConflict(
                para_key, field, actual_old_value, template_old_value,
                actual_new_value)

        if resolve_conflict is None:
            resolve_conflict = _default_resolve_conflict

        changes = dict(changes.items())
        for paragraph in self.paragraphs:
            for item_ in list(paragraph.items()):
                item = (str(item_[0]), str(item_[1]))
                for key, old_value, new_value in changes.pop(item, []):
                    if paragraph.get(key) != old_value:
                        new_value = resolve_conflict(
                            item, key, old_value, paragraph.get(key),
                            new_value)
                    if new_value is None:
                        del paragraph[key]
                    else:
                        paragraph[key] = new_value
        # Add any new paragraphs that weren't processed earlier
        for key, p in changes.items():
            paragraph = new_deb822_paragraph()
            for (field, old_value, new_value) in p:
                if old_value is not None:
                    new_value = resolve_conflict(
                        key, field, old_value, None, new_value)
                if new_value is None:
                    continue
                paragraph[field] = new_value
            self.paragraphs.append(paragraph)

    def _parse(self, content):
        return parse_deb822_file(content.splitlines(True))

    @property
    def paragraphs(self) -> List[Deb822Paragraph]:
        return self._parsed

    def _format(self, paragraphs):
        return dump_paragraphs(paragraphs)

    def _nonexistant(self):
        if self.allow_missing:
            return parse_deb822_file([])
        raise

    def sort_paragraphs(self, sort_key, skip=0):
        sortable = list(self.paragraphs)[skip:]
        for i, p in reversed(list(enumerate(self.paragraphs))):
            if i < skip:
                continue
            try:
                self.paragraphs.remove(p)
            except AttributeError:
                raise NotImplementedError(
                    'version of python-debian does not have '
                    'Deb822FileElement.remove')
        for p in sorted(sortable, key=sort_key):
            self.paragraphs.append(p)
