#!/usr/bin/env bash

shopt -s extglob

export LC_ALL="C.UTF-8"
export TZ=:/etc/localtime

Help()
{
  echo "Generate an OPML 2.0 file to follow releases of starred repositories on Github"
  echo "Default to all starred repos of the user, or a specific list with [-l list]."
  echo "Uses the Github API to check lists and if the starred repos contain Release (preferred) or Tag entries."
  echo
  echo "Syntax: ./gh-starred-to-opml.sh [-h] -u user [-l listname] [-d date] [-o filename] [-n filename] -t token"
  echo "options:"
  echo "-h              Print this Help"
  echo "-u string       required: Github username"
  echo "-l string       optional: Github Stars List (url shortname)"
  echo "-d string       optional: ISO8601 date to filter out starred before (YYYY-mm-ddTHH:MM:SSZ)"
  echo "-o string.opml  optional: destination opml filename"
  echo "-n string.opml  Use a previous file to generate updates,"
  echo "                it does not require any other option,"
  echo "                but it uses starred_at dates, not starred in a list."
  echo "-t string       required: Github API token to avoid rate limits."
  echo
}

unset -v _USERNAME _LISTNAME _DATEFILTER _FILENAME _OLDFILENAME _DATA

while getopts "hu:l:d:o:n:t:" option; do
  case $option in
     h) Help; exit;;
     u) _USERNAME="$OPTARG";;
     l) _LISTNAME="$OPTARG";;
     d) _DATEFILTER="$OPTARG";;
     o) _FILENAME="$OPTARG";;
     n) _OLDFILENAME="$OPTARG"
        unset -v _USERNAME _LISTNAME _DATEFILTER _FILENAME _DATA;;
     t) _GITHUBTOKEN="$OPTARG";;
    \?) echo -e "Unknown option: -$OPTARG \n" >&2; Help; exit 1;;
    : ) echo -e "Missing argument for -$OPTARG \n" >&2; Help; exit 1;;
    * ) echo -e "Unimplemented option: -$option \n" >&2; Help; exit 1;;
  esac
done

if [[ -n $_OLDFILENAME ]]; then
  # parsing the source OPML file to generate values for the update
  if [[ ! -f "${_OLDFILENAME}" ]]; then
    echo "Missing source file ${_OLDFILENAME}" >&2
    echo
    Help
    exit 1
  fi
  _FILENAME=${_OLDFILENAME/%*(_+([0-9]).opml)*(.opml)/_$(date '+%y%m%d%H%M').opml}
  _USERNAME=$(grep "ownerName" "${_OLDFILENAME}" | sed -nr 's,.+Name>(.+)<\/ownerName.+,\1,p')
  _LISTNAME=$(grep "outline" "${_OLDFILENAME}" | sed -nr 's,.+Github - (.+) - .+,\1,p')
  _DATEFILTER=$(LC_ALL="C.UTF-8"  date -u -d "$(grep "dateModified" "${_OLDFILENAME}" | sed -nr 's,.+dateModified>(.+)<\/dateModified.+,\1,p')" '+%Y-%m-%dT%H:%M:%S%Z')
fi

if [[ -z $_USERNAME ]]; then
  echo 'Missing Github username' >&2
  echo
  Help
  exit 1
fi

if [[ -z $_GITHUBTOKEN ]]; then
  echo 'Missing Github API token' >&2
  echo
  Help
  exit 1
fi

if [[ -z $_FILENAME ]]; then
  if [[ -z $_LISTNAME ]]; then
    _FILENAME="gh_starred_${_USERNAME}.opml"
  else
    _FILENAME="gh_starred_${_USERNAME}_${_LISTNAME}.opml"
  fi
fi


_CMD_ARRAY=( curl jq pup )
for cmd in "${_CMD_ARRAY[@]}"; do
  if [[ -z $(command -v "$cmd") ]]; then
    echo "Requirements: $cmd could not be found" >&2
    echo '  - sudo apt install curl jq' >&2
    echo '  - go install github.com/ericchiang/pup@latest' >&2
    exit 1
  fi
done

trap "echo '⯅ Github API rate limit exceeded or Token issue.'; exit 1" TERM
export MAIN_PID=$$

# request to Github API with rate limit trap
ghapirequest() {
  local _GITHUB
  _GITHUB=$(curl \
    --max-time 120 \
    -H "Authorization: token ${_GITHUBTOKEN}" \
    -H "Accept: application/vnd.github.v3.star+json" \
    -sSL "https://api.github.com/$1")
  if (echo "${_GITHUB}" | grep -q 'API rate limit exceeded'); then
    kill -s TERM $MAIN_PID
  else
    echo "${_GITHUB}"
  fi
}

# request to Github lists
ghrequest() {
  curl --max-time 120 -sSL "https://github.com/$1"
}

# parsing Github API for all user's starred repositories
_PAGE=1

echo "- Parsing Github API for ${_USERNAME}: page $_PAGE"
_DATA=$(ghapirequest "users/${_USERNAME}/starred?page=${_PAGE}&per_page=100" | jq '.[] | {id: .repo.id, name: .repo.full_name, desc: .repo.description, date: .starred_at}')
_PAGE=$((_PAGE+1))

while [ $_PAGE -ge 2 ]; do
  unset _NEW_DATA
  echo "- Parsing Github API for ${_USERNAME}: page $_PAGE"
  _NEW_DATA=$(ghapirequest "users/${_USERNAME}/starred?page=${_PAGE}&per_page=100" | jq '.[] | {id: .repo.id, name: .repo.full_name, desc: .repo.description, date: .starred_at}')
  if [ "$_NEW_DATA" ]; then
    _DATA=$(echo -e "${_DATA}\n${_NEW_DATA}")
    _PAGE=$((_PAGE+1))
  else
    echo "- Page ${_PAGE} was the last one"
    _PAGE=1
  fi
done

echo "- Sorting results by name"
_DATA=$(echo "${_DATA}" | jq -s -c 'sort_by(.name) | .[]')

if [[ -n $_DATEFILTER ]]; then
  echo "- Filtering out repositories starred before ${_DATEFILTER}"
  _DATA=$(echo "${_DATA}" | jq -c --arg date "${_DATEFILTER}" 'select( .date > $date )')
fi

# parsing Github list pages (not available in the API)
if [[ -n $_LISTNAME ]]; then
  _PAGE=1

  echo "- Parsing Github \"${_LISTNAME}\" List for ${_USERNAME}: page $_PAGE"
  _LIST=$(ghrequest "stars/${_USERNAME}/lists/${_LISTNAME}?page=1")
  _NEXT=$(echo "${_LIST}" | pup '#user-list-repositories div div a[class="next_page"] text{}')
  _LIST=$(echo "${_LIST}" | pup '#user-list-repositories div div h3 a attr{href}')
  if [[ -n $_NEXT ]]; then
    _PAGE=$((_PAGE+1))
  fi

  while [ $_PAGE -ge 2 ]; do
    unset _NEW_LIST _NEXT
    echo "- Parsing Github \"${_LISTNAME}\" List for ${_USERNAME}: page $_PAGE"
    _NEW_LIST=$(ghrequest "stars/${_USERNAME}/lists/${_LISTNAME}?page=${_PAGE}")
    _NEXT=$(echo "${_NEW_LIST}" | pup '#user-list-repositories div div a[class="next_page"] text{}')
    _NEW_LIST=$(echo "${_NEW_LIST}" | pup '#user-list-repositories div div h3 a attr{href}')
    _LIST=$(echo -e "${_LIST}\n${_NEW_LIST}")
    if [[ -n $_NEXT ]]; then
      _PAGE=$((_PAGE+1))
    else
      echo "- Page ${_PAGE} was the last one"
      _PAGE=1
    fi
  done

  _LIST=$(echo "${_LIST}" | sed -r 's,^\/,,g')
fi

# filtering down repositories by the List
if [[ -n $_LIST ]]; then
  echo "- Filtering all starred repositories by the ones in the list."
  _DATA=$(echo "${_DATA}" | jq --argjson names "$(echo "${_LIST}" | jq -R . | jq -s .)" 'select( .name as $name | $names | index($name) )')
fi

if [[ "$(echo "${_DATA}" | jq '.name' | wc -l)" == "0" ]]; then
  echo 'No entries found. Aborting.' >&2
  echo
  exit 1
fi

# opml file generation
echo "- Generating OPML file Header"
_FIRSTDATE=$(LC_ALL="C.UTF-8" TZ=GMT date -d "$(echo "${_DATA}" | jq -sr 'sort_by(.date) | reverse[-1].date')" '+%a, %d %b %Y %H:%M:%S %Z')
_LASTDATE=$(LC_ALL="C.UTF-8" TZ=GMT date -d "$(echo "${_DATA}" | jq -sr 'sort_by(.date)[-1].date')" '+%a, %d %b %Y %H:%M:%S %Z')
if [[ -z $_LISTNAME ]]; then
  _CATEGORY="Github - ${_USERNAME}"
else
  _CATEGORY="Github - ${_LISTNAME} - ${_USERNAME}"
fi
cat <<- EOF > "${_FILENAME}"
	<?xml version="1.0" encoding="UTF-8"?>
	    <opml version="2.0">
	        <head>
	            <title>${_FILENAME}</title>
	            <dateCreated>${_FIRSTDATE}</dateCreated>
	            <dateModified>${_LASTDATE}</dateModified>
	            <ownerName>${_USERNAME}</ownerName>
	        </head>
	        <body>
	            <outline text="${_CATEGORY}">
EOF

echo "- Generating OPML file Feeds"
for id in $(echo "$_DATA" | jq .id); do
  _REPO_NAME=$(echo "$_DATA" | jq -r --argjson v "$id" ' . | select(.id==$v).name')
  _REPO_DESC=$(echo "$_DATA" | jq -r --argjson v "$id" ' . | select(.id==$v).desc' | sed -e 's~\&~\&amp;~g' -e 's~<~\&lt;~g' -e 's~>~\&gt;~g' -e 's~\"~\&quot;~g' -e "s~'~\&apos;~g")
  _RELEASES=$(ghapirequest "repos/${_REPO_NAME}/releases" | jq '.[]')
  _TYPE="releases"
  if [[ -z "$_RELEASE" ]]; then
    _TAGS=$(ghapirequest "repos/${_REPO_NAME}/tags" | jq '.[]')
    if [[ -n "$_TAGS" ]]; then
      _TYPE="tags"
    fi
  fi
  cat <<- EOF >> "${_FILENAME}"
	                <outline title="${_REPO_NAME}" text="${_REPO_NAME}" type="rss" version="ATOM1" description="${_REPO_DESC}" xmlUrl="https://github.com/${_REPO_NAME}/${_TYPE}.atom" htmlUrl="https://github.com/${_REPO_NAME}"></outline>
EOF
done

echo "- Generating OPML file Footer"
cat <<- EOF >> "${_FILENAME}"
	            </outline>
	        </body>
	    </opml>
EOF

echo "- Done: Generated $(echo "${_DATA}" | jq '.name' | wc -l) entries for \"${_CATEGORY}\" in ${_FILENAME}"