#!/usr/bin/python3
"""Upload a gist containing packages installed on the system.

Dependencies
============
* pacman
* gist
"""

import configparser
import re
import subprocess
import sys

# ========== Constants ==========
# Paths
CONFIG_FILE = "/etc/packaging-scripts.conf"
DEFAULT_FILENAME = "pacman-packages.txt"

# Config file options
CONFIG_SECTION = "pug2"
CONFIG_OPTION_DESCRIPTION = "GIST_DESCRIPTION"
CONFIG_OPTION_ENABLE = "GIST_PUG_ENABLE"
CONFIG_OPTION_FILENAME = "GIST_FILENAME"
CONFIG_OPTION_ID = "GIST_ID"


# ========== Functions ==========
def extract_gist_id(url):
    """Extract the gist id from a gist URL.

    Normalizes URLs from
    * http(s)?://<subdomain>.<second level domain>.<top level domain>/<username>/<gist ID>
    * <username>/<gist ID>
    * <gist ID>

    to one of

    * <username>/<gist ID>
    * <gist ID>

    both of which are valid for use with gist

    :param url: a valid URL containing the gist id
    :type url: str
    :returns: the valid gist ID
    :rtype: str
    """
    return re.sub("^http(s)?://[\\w]*.[\\w]*.[\\w]/", "", url)


def retrieve_gist_info(gist_id):
    """Retrieve info from gist ID that is specified in the config file.

    :param gist_id: string id to read gist info
    :returns: data read from gist
    :rtype: bytes
    """
    return subprocess.run(f"gist --read {gist_id}", capture_output=True).stdout


def package_lists_match(gist_id):
    """Compare local package list to that of pacman and gist, return if they match."""
    local_packages = subprocess.run(["pacman", "-Qqen"], capture_output=True).stdout
    gist_packages = subprocess.run(
        ["gist", "--read", gist_id], capture_output=True
    ).stdout
    return local_packages == gist_packages


# ========== Main Script ==========
if __name__ == "__main__":
    config = configparser.ConfigParser()
    config.read(CONFIG_FILE)

    # Check if script is enabled to run; if not, exit silently
    if not config.getboolean(CONFIG_SECTION, CONFIG_OPTION_ENABLE):
        sys.exit(0)

    gist_description = config.get(CONFIG_SECTION, CONFIG_OPTION_DESCRIPTION)
    gist_filename = config.get(CONFIG_SECTION, CONFIG_OPTION_FILENAME)
    gist_id = config.get(CONFIG_SECTION, CONFIG_OPTION_ID)

    if gist_id == "":
        print("No gist ID detected, creating new.")
        gist_process = subprocess.run(
            f"pacman -Qqen | gist --filename {gist_filename} --description {gist_description}",
            capture_output=True,
            shell=True,
        )
        config[CONFIG_SECTION][CONFIG_OPTION_ID] = extract_gist_id(gist_process.stdout)
    elif package_lists_match(gist_id):
        print("Package lists match, no update necessary.")
        sys.exit(0)
    else:
        print("Package lists differ, updating.")
        subprocess.run(
            f"pacman -Qqen | gist --update {gist_id} --filename {gist_filename} --description {gist_description}",
            capture_output=True,
            shell=True,
        )