#!/usr/bin/env python3

# usage: python3 pep2rss.py .

import datetime
import glob
import os
import re
import sys
import time
import PyRSS2Gen as rssgen
import docutils.frontend
import docutils.nodes
import docutils.parsers.rst
import docutils.utils

RSS_PATH = os.path.join(sys.argv[1], 'peps.rss')


def remove_prefix(text: str, prefix: str) -> str:
    try:
        # Python 3.9+
        return text.removeprefix(prefix)
    except AttributeError:
        if text.startswith(prefix):
            return text[len(prefix):]
        return text


def parse_rst(text: str) -> docutils.nodes.document:
    parser = docutils.parsers.rst.Parser()
    components = (docutils.parsers.rst.Parser,)
    settings = docutils.frontend.OptionParser(components=components).get_default_values()
    document = docutils.utils.new_document('<rst-doc>', settings=settings)
    parser.parse(text, document)
    return document


def pep_abstract(full_path: str) -> str:
    """Return the first paragraph of the PEP abstract"""
    abstract = None
    with open(full_path, encoding="utf-8") as f:
        text = f.read()
        document = parse_rst(text)
        nodes = list(document)
        for node in nodes:
            if "<title>Abstract</title>" in str(node):
                for child in node:
                    if child.tagname == "paragraph":
                        abstract = child.astext()
                        # Just fetch the first paragraph
                        break
    return abstract


def firstline_startingwith(full_path, text):
    for line in open(full_path, encoding="utf-8"):
        if line.startswith(text):
            return line[len(text):].strip()
    return None


# get list of peps with creation time
# (from "Created:" string in pep .rst or .txt)
peps = glob.glob('pep-*.txt')
peps.extend(glob.glob('pep-*.rst'))


def pep_creation_dt(full_path):
    created_str = firstline_startingwith(full_path, 'Created:')
    # bleh, I was hoping to avoid re but some PEPs editorialize
    # on the Created line
    m = re.search(r'''(\d+-\w+-\d{4})''', created_str)
    if not m:
        # some older ones have an empty line, that's okay, if it's old
        # we ipso facto don't care about it.
        # "return None" would make the most sense but datetime objects
        # refuse to compare with that. :-|
        return datetime.datetime(*time.localtime(0)[:6])
    created_str = m.group(1)
    try:
        t = time.strptime(created_str, '%d-%b-%Y')
    except ValueError:
        t = time.strptime(created_str, '%d-%B-%Y')
    return datetime.datetime(*t[:6])


peps_with_dt = [(pep_creation_dt(full_path), full_path) for full_path in peps]
# sort peps by date, newest first
peps_with_dt.sort(reverse=True)

# generate rss items for 10 most recent peps
items = []
for dt, full_path in peps_with_dt[:10]:
    try:
        n = int(full_path.split('-')[-1].split('.')[0])
    except ValueError:
        pass
    title = firstline_startingwith(full_path, 'Title:')
    author = firstline_startingwith(full_path, 'Author:')
    abstract = pep_abstract(full_path)
    url = 'https://www.python.org/dev/peps/pep-%0.4d/' % n
    item = rssgen.RSSItem(
        title='PEP %d: %s' % (n, title),
        link=url,
        description=abstract,
        author=author,
        guid=rssgen.Guid(url),
        pubDate=dt)
    items.append(item)

# the rss envelope
desc = """
Newest Python Enhancement Proposals (PEPs) - Information on new
language features, and some meta-information like release
procedure and schedules
""".strip()
rss = rssgen.RSS2(
    title='Newest Python PEPs',
    link = 'https://www.python.org/dev/peps/',
    description=desc,
    lastBuildDate=datetime.datetime.now(),
    items=items)

with open(RSS_PATH, 'w', encoding="utf-8") as fp:
    fp.write(rss.to_xml(encoding="utf-8"))