#!/usr/bin/env python3

"""Assemble Mbed TLS change log entries into the change log file.

Add changelog entries to the first level-2 section.
Create a new level-2 section for unreleased changes if needed.
Remove the input files unless --keep-entries is specified.

In each level-3 section, entries are sorted in chronological order
(oldest first). From oldest to newest:
* Merged entry files are sorted according to their merge date (date of
  the merge commit that brought the commit that created the file into
  the target branch).
* Committed but unmerged entry files are sorted according to the date
  of the commit that adds them.
* Uncommitted entry files are sorted according to their modification time.

You must run this program from within a git working directory.
"""

# Copyright (C) 2019, Arm Limited, All Rights Reserved
# SPDX-License-Identifier: Apache-2.0
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# This file is part of Mbed TLS (https://tls.mbed.org)

import argparse
from collections import OrderedDict, namedtuple
import datetime
import functools
import glob
import os
import re
import subprocess
import sys

class InputFormatError(Exception):
    def __init__(self, filename, line_number, message, *args, **kwargs):
        message = '{}:{}: {}'.format(filename, line_number,
                                     message.format(*args, **kwargs))
        super().__init__(message)

class LostContent(Exception):
    def __init__(self, filename, line):
        message = ('Lost content from {}: "{}"'.format(filename, line))
        super().__init__(message)

STANDARD_CATEGORIES = (
    b'API changes',
    b'Default behavior changes',
    b'Requirement changes',
    b'New deprecations',
    b'Removals',
    b'Features',
    b'Security',
    b'Bugfix',
    b'Changes',
)

CategoryContent = namedtuple('CategoryContent', [
    'name', 'title_line', # Title text and line number of the title
    'body', 'body_line', # Body text and starting line number of the body
])

class ChangelogFormat:
    """Virtual class documenting how to write a changelog format class."""

    @classmethod
    def extract_top_version(cls, changelog_file_content):
        """Split out the top version section.

        Return ``(header, top_version_title, top_version_body, trailer)``
        where ``changelog_file_content == header + top_version_title +
                                          top_version_body + trailer``.
        """
        raise NotImplementedError

    @classmethod
    def version_title_text(cls, version_title):
        """Return the text of a formatted version section title."""
        raise NotImplementedError

    @classmethod
    def split_categories(cls, version_body):
        """Split a changelog version section body into categories.

        Return a list of `CategoryContent` the name is category title
        without any formatting.
        """
        raise NotImplementedError

    @classmethod
    def format_category(cls, title, body):
        """Construct the text of a category section from its title and body."""
        raise NotImplementedError

class TextChangelogFormat(ChangelogFormat):
    """The traditional Mbed TLS changelog format."""

    _top_version_re = re.compile(br'(?:\A|\n)(=[^\n]*\n+)(.*?\n)(?:=|$)',
                                 re.DOTALL)
    @classmethod
    def extract_top_version(cls, changelog_file_content):
        """A version section starts with a line starting with '='."""
        m = re.search(cls._top_version_re, changelog_file_content)
        top_version_start = m.start(1)
        top_version_end = m.end(2)
        return (changelog_file_content[:top_version_start],
                m.group(1), m.group(2),
                changelog_file_content[top_version_end:])

    @classmethod
    def version_title_text(cls, version_title):
        return re.sub(br'\n.*', version_title, re.DOTALL)

    _category_title_re = re.compile(br'(^\w.*)\n+', re.MULTILINE)
    @classmethod
    def split_categories(cls, version_body):
        """A category title is a line with the title in column 0."""
        title_matches = list(re.finditer(cls._category_title_re, version_body))
        if not title_matches:
            return []
        title_starts = [m.start(1) for m in title_matches]
        body_starts = [m.end(0) for m in title_matches]
        body_ends = title_starts[1:] + [len(version_body)]
        bodies = [version_body[body_start:body_end].rstrip(b'\n') + b'\n'
                  for (body_start, body_end) in zip(body_starts, body_ends)]
        title_lines = [version_body[:pos].count(b'\n') for pos in title_starts]
        body_lines = [version_body[:pos].count(b'\n') for pos in body_starts]
        return [CategoryContent(title_match.group(1), title_line,
                                body, body_line)
                for title_match, title_line, body, body_line
                in zip(title_matches, title_lines, bodies, body_lines)]

    @classmethod
    def format_category(cls, title, body):
        # `split_categories` ensures that each body ends with a newline.
        # Make sure that there is additionally a blank line between categories.
        if not body.endswith(b'\n\n'):
            body += b'\n'
        return title + b'\n' + body

class ChangeLog:
    """An Mbed TLS changelog.

    A changelog file consists of some header text followed by one or
    more version sections. The version sections are in reverse
    chronological order. Each version section consists of a title and a body.

    The body of a version section consists of zero or more category
    subsections. Each category subsection consists of a title and a body.

    A changelog entry file has the same format as the body of a version section.

    A `ChangelogFormat` object defines the concrete syntax of the changelog.
    Entry files must have the same format as the changelog file.
    """

    # Only accept dotted version numbers (e.g. "3.1", not "3").
    # Refuse ".x" in a version number where x is a letter: this indicates
    # a version that is not yet released. Something like "3.1a" is accepted.
    _version_number_re = re.compile(br'[0-9]+\.[0-9A-Za-z.]+')
    _incomplete_version_number_re = re.compile(br'.*\.[A-Za-z]')

    def section_is_released_version(self, title):
        """Whether this section is for a released version.

        True if the given level-2 section title indicates that this section
        contains released changes, otherwise False.
        """
        # Assume that a released version has a numerical version number
        # that follows a particular pattern. These criteria may be revised
        # as needed in future versions of this script.
        version_number = re.search(self._version_number_re, title)
        if version_number:
            return not re.search(self._incomplete_version_number_re,
                                 version_number.group(0))
        else:
            return False

    def unreleased_version_title(self):
        """The title to use if creating a new section for an unreleased version."""
        # pylint: disable=no-self-use; this method may be overridden
        return b'Unreleased changes'

    def add_categories_from_text(self, filename, line_offset,
                                 text, allow_unknown_category):
        """Parse a version section or entry file."""
        categories = self.format.split_categories(text)
        for category in categories:
            if not allow_unknown_category and \
               category.name not in self.categories:
                raise InputFormatError(filename,
                                       line_offset + category.title_line,
                                       'Unknown category: "{}"',
                                       category.name.decode('utf8'))
            self.categories[category.name] += category.body

    def __init__(self, input_stream, changelog_format):
        """Create a changelog object.

        Populate the changelog object from the content of the file
        input_stream.
        """
        self.format = changelog_format
        whole_file = input_stream.read()
        (self.header,
         self.top_version_title, top_version_body,
         self.trailer) = self.format.extract_top_version(whole_file)
        # Split the top version section into categories.
        self.categories = OrderedDict()
        for category in STANDARD_CATEGORIES:
            self.categories[category] = b''
        offset = (self.header + self.top_version_title).count(b'\n')
        self.add_categories_from_text(input_stream.name, offset,
                                      top_version_body, True)

    def add_file(self, input_stream):
        """Add changelog entries from a file.
        """
        self.add_categories_from_text(input_stream.name, 0,
                                      input_stream.read(), False)

    def write(self, filename):
        """Write the changelog to the specified file.
        """
        with open(filename, 'wb') as out:
            out.write(self.header)
            out.write(self.top_version_title)
            for title, body in self.categories.items():
                if not body:
                    continue
                out.write(self.format.format_category(title, body))
            out.write(self.trailer)


@functools.total_ordering
class EntryFileSortKey:
    """This classes defines an ordering on changelog entry files: older < newer.

    * Merged entry files are sorted according to their merge date (date of
      the merge commit that brought the commit that created the file into
      the target branch).
    * Committed but unmerged entry files are sorted according to the date
      of the commit that adds them.
    * Uncommitted entry files are sorted according to their modification time.

    This class assumes that the file is in a git working directory with
    the target branch checked out.
    """

    # Categories of files. A lower number is considered older.
    MERGED = 0
    COMMITTED = 1
    LOCAL = 2

    @staticmethod
    def creation_hash(filename):
        """Return the git commit id at which the given file was created.

        Return None if the file was never checked into git.
        """
        hashes = subprocess.check_output(['git', 'log', '--format=%H',
                                          '--follow',
                                          '--', filename])
        m = re.search(b'(.+)$', hashes)
        if not m:
            # The git output is empty. This means that the file was
            # never checked in.
            return None
        # The last commit in the log is the oldest one, which is when the
        # file was created.
        return m.group(0)

    @staticmethod
    def list_merges(some_hash, target, *options):
        """List merge commits from some_hash to target.

        Pass options to git to select which commits are included.
        """
        text = subprocess.check_output(['git', 'rev-list',
                                        '--merges', *options,
                                        b'..'.join([some_hash, target])])
        return text.rstrip(b'\n').split(b'\n')

    @classmethod
    def merge_hash(cls, some_hash):
        """Return the git commit id at which the given commit was merged.

        Return None if the given commit was never merged.
        """
        target = b'HEAD'
        # List the merges from some_hash to the target in two ways.
        # The ancestry list is the ones that are both descendants of
        # some_hash and ancestors of the target.
        ancestry = frozenset(cls.list_merges(some_hash, target,
                                             '--ancestry-path'))
        # The first_parents list only contains merges that are directly
        # on the target branch. We want it in reverse order (oldest first).
        first_parents = cls.list_merges(some_hash, target,
                                        '--first-parent', '--reverse')
        # Look for the oldest merge commit that's both on the direct path
        # and directly on the target branch. That's the place where some_hash
        # was merged on the target branch. See
        # https://stackoverflow.com/questions/8475448/find-merge-commit-which-include-a-specific-commit
        for commit in first_parents:
            if commit in ancestry:
                return commit
        return None

    @staticmethod
    def commit_timestamp(commit_id):
        """Return the timestamp of the given commit."""
        text = subprocess.check_output(['git', 'show', '-s',
                                        '--format=%ct',
                                        commit_id])
        return datetime.datetime.utcfromtimestamp(int(text))

    @staticmethod
    def file_timestamp(filename):
        """Return the modification timestamp of the given file."""
        mtime = os.stat(filename).st_mtime
        return datetime.datetime.fromtimestamp(mtime)

    def __init__(self, filename):
        """Determine position of the file in the changelog entry order.

        This constructor returns an object that can be used with comparison
        operators, with `sort` and `sorted`, etc. Older entries are sorted
        before newer entries.
        """
        self.filename = filename
        creation_hash = self.creation_hash(filename)
        if not creation_hash:
            self.category = self.LOCAL
            self.datetime = self.file_timestamp(filename)
            return
        merge_hash = self.merge_hash(creation_hash)
        if not merge_hash:
            self.category = self.COMMITTED
            self.datetime = self.commit_timestamp(creation_hash)
            return
        self.category = self.MERGED
        self.datetime = self.commit_timestamp(merge_hash)

    def sort_key(self):
        """"Return a concrete sort key for this entry file sort key object.

        ``ts1 < ts2`` is implemented as ``ts1.sort_key() < ts2.sort_key()``.
        """
        return (self.category, self.datetime, self.filename)

    def __eq__(self, other):
        return self.sort_key() == other.sort_key()

    def __lt__(self, other):
        return self.sort_key() < other.sort_key()


def check_output(generated_output_file, main_input_file, merged_files):
    """Make sanity checks on the generated output.

    The intent of these sanity checks is to have reasonable confidence
    that no content has been lost.

    The sanity check is that every line that is present in an input file
    is also present in an output file. This is not perfect but good enough
    for now.
    """
    generated_output = set(open(generated_output_file, 'rb'))
    for line in open(main_input_file, 'rb'):
        if line not in generated_output:
            raise LostContent('original file', line)
    for merged_file in merged_files:
        for line in open(merged_file, 'rb'):
            if line not in generated_output:
                raise LostContent(merged_file, line)

def finish_output(changelog, output_file, input_file, merged_files):
    """Write the changelog to the output file.

    The input file and the list of merged files are used only for sanity
    checks on the output.
    """
    if os.path.exists(output_file) and not os.path.isfile(output_file):
        # The output is a non-regular file (e.g. pipe). Write to it directly.
        output_temp = output_file
    else:
        # The output is a regular file. Write to a temporary file,
        # then move it into place atomically.
        output_temp = output_file + '.tmp'
    changelog.write(output_temp)
    check_output(output_temp, input_file, merged_files)
    if output_temp != output_file:
        os.rename(output_temp, output_file)

def remove_merged_entries(files_to_remove):
    for filename in files_to_remove:
        os.remove(filename)

def list_files_to_merge(options):
    """List the entry files to merge, oldest first.

    "Oldest" is defined by `EntryFileSortKey`.
    """
    files_to_merge = glob.glob(os.path.join(options.dir, '*.txt'))
    files_to_merge.sort(key=EntryFileSortKey)
    return files_to_merge

def merge_entries(options):
    """Merge changelog entries into the changelog file.

    Read the changelog file from options.input.
    Read entries to merge from the directory options.dir.
    Write the new changelog to options.output.
    Remove the merged entries if options.keep_entries is false.
    """
    with open(options.input, 'rb') as input_file:
        changelog = ChangeLog(input_file, TextChangelogFormat)
    files_to_merge = list_files_to_merge(options)
    if not files_to_merge:
        sys.stderr.write('There are no pending changelog entries.\n')
        return
    for filename in files_to_merge:
        with open(filename, 'rb') as input_file:
            changelog.add_file(input_file)
    finish_output(changelog, options.output, options.input, files_to_merge)
    if not options.keep_entries:
        remove_merged_entries(files_to_merge)

def show_file_timestamps(options):
    """List the files to merge and their timestamp.

    This is only intended for debugging purposes.
    """
    files = list_files_to_merge(options)
    for filename in files:
        ts = EntryFileSortKey(filename)
        print(ts.category, ts.datetime, filename)

def set_defaults(options):
    """Add default values for missing options."""
    output_file = getattr(options, 'output', None)
    if output_file is None:
        options.output = options.input
    if getattr(options, 'keep_entries', None) is None:
        options.keep_entries = (output_file is not None)

def main():
    """Command line entry point."""
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--dir', '-d', metavar='DIR',
                        default='ChangeLog.d',
                        help='Directory to read entries from'
                             ' (default: ChangeLog.d)')
    parser.add_argument('--input', '-i', metavar='FILE',
                        default='ChangeLog',
                        help='Existing changelog file to read from and augment'
                             ' (default: ChangeLog)')
    parser.add_argument('--keep-entries',
                        action='store_true', dest='keep_entries', default=None,
                        help='Keep the files containing entries'
                             ' (default: remove them if --output/-o is not specified)')
    parser.add_argument('--no-keep-entries',
                        action='store_false', dest='keep_entries',
                        help='Remove the files containing entries after they are merged'
                             ' (default: remove them if --output/-o is not specified)')
    parser.add_argument('--output', '-o', metavar='FILE',
                        help='Output changelog file'
                             ' (default: overwrite the input)')
    parser.add_argument('--list-files-only',
                        action='store_true',
                        help=('Only list the files that would be processed '
                              '(with some debugging information)'))
    options = parser.parse_args()
    set_defaults(options)
    if options.list_files_only:
        show_file_timestamps(options)
        return
    merge_entries(options)

if __name__ == '__main__':
    main()