#!/usr/bin/env nix-shell
#! nix-shell -i python3 -p python3

# It creates a jobs database suitable for this task from a given OPML file
# typically exported through Thunderbird and newsboat. This script considers
# the outline hierarchy as part of tag hierarchy similar to Newsboat import
# script. Additionally, `categories` attribute in the element are also
# considered.
#
# Anywho, the following document URL at <http://opml.org/spec2.opml> is used as
# the basis for how OPML subscription lists work.
#
# Additionally, this script just assumes a subscription list is just a flat
# list of 'rss' nodes and no assumption for arbitrary structure of
# ``<outline>`` elements is created. This means if you're using Thunderbird
# with a structured folder of subscriptions, it's only going to consider the
# 'rss' nodes and ignore the structure.
#
# Most applications I've used don't easily export categories into the
# 'category' attribute which is unfortunate. There seems to be little respect
# for the attribute. Not to mention, there could be many assumptions for the
# structure for these various applications so I'm taking the simplest way.
#
# Welp, the disadvantage of OPML being a very flexible format it seems. :(

import argparse
import json
import re
from xml.etree import ElementTree

FALLBACK_CATEGORY = "Uncategorized"


def kebab_case(string: str):
    s = re.sub("[^a-zA-Z0-9]+", "-", string)
    s = re.sub("-+", "-", s)
    s = re.sub("^-|-$", "", s)
    s = string.lower()
    return s


def list_categories_from_opml(tree: ElementTree.ElementTree):
    categories = [ outline.get("category", None) for outline in tree.findall("body//outline[@type='rss']") ]
    data = set()
    for category_string in categories:
        if category_string is None:
            continue

        categories_list = category_string.split(",")
        for category in categories_list:
            data.add(category.strip().lstrip("/"))

    return data


def create_db_from_opml(tree: ElementTree.ElementTree, categories):
    data = { kebab_case(category): {
        "extraArgs": [],
        "subscriptions": []
        } for category in categories }

    for outline in tree.findall("body//outline[@type='rss']"):
        outline_data = { "name": outline.get("title"),
                        "url": outline.get("xmlUrl") }

        description = outline.get("description", None)
        if description is not None:
            outline_data["description"] = description

        for outline_category in outline.get("category", FALLBACK_CATEGORY).split(","):
            outline_category = kebab_case(outline_category).strip().lstrip("/")
            if outline_category in data:
                data[outline_category]["subscriptions"].append(outline_data)

    return data


if __name__ == "__main__":
    # Accept a filename.
    # > $SCRIPT OPML_FILE [CATEGORIES...]
    # Print the output as JSON for the jobs database.
    #
    # * Make it accept categories from stdin.
    parser = argparse.ArgumentParser(description="Create a job database from an OPML file.")
    parser.add_argument("file", metavar="OPML_FILE", help="The OPML file.")
    parser.add_argument("categories", nargs="*", metavar="CATEGORY", help="A list of categories to be extracted. If no categories are given, assumes that all categories are to be extracted.")
    parser.add_argument("--list", "-l", action="store_true", help="List all categories from the given file.")
    parser.add_argument("--output", "-o", action="store", metavar="FILE", help="The file where the output will be written.")
    parser.add_argument("--with-others", action="store_true", help=f"List all uncategorized feeds into '{FALLBACK_CATEGORY}'.")

    args = parser.parse_args()

    with open(args.file, mode='r') as f:
        opml_xml = ElementTree.parse(f)
        if args.list:
            for category in list_categories_from_opml(opml_xml):
                print(category)
        else:
            categories = args.categories if args.categories else list_categories_from_opml(opml_xml)

            if args.with_others:
                categories.add(FALLBACK_CATEGORY)

            data = create_db_from_opml(opml_xml, categories)

            if "output_file" in args:
                with open(args.file, mode='r') as output_file:
                    json.dump(data, output_file)
            else:
                print(json.dumps(data, sort_keys=True, indent=2))
    pass

# vi:ft=python:ts=4