#!/usr/bin/env bash

# Land a pull request
# Creates a PR-### branch, pulls the commits, opens up an interactive rebase to
# squash, and then annotates the commit with the changelog goobers
#
# Usage:
#   pr <url|number> [<upstream remote>=origin]

main () {
  if [ "$1" = "finish" ]; then
    shift
    finish "$@"
    return $?
  fi

  local url="$(prurl "$@")"
  local num=$(basename $url)
  local prpath="${url#git@github.com:}"
  local repo=${prpath%/pull/$num}
  local prweb="https://github.com/$prpath"
  local root="$(prroot "$url")"
  local api="https://api.github.com/repos/${repo}/pulls/${num}"
  local user=$(curl -s $api | json user.login)
  local ref="$(prref "$url" "$root")"
  local curhead="$(git show --no-patch --pretty=%H HEAD)"
  local curbranch="$(git rev-parse --abbrev-ref HEAD)"
  local cleanlines
  IFS=$'\n' cleanlines=($(git status -s -uno))
  if [ ${#cleanlines[@]} -ne 0 ]; then
    echo "working dir not clean" >&2
    IFS=$'\n' echo "${cleanlines[@]}" >&2
    echo "aborting PR merge" >&2
  fi

  # ok, ready to rock
  branch=PR-$num
  if [ "$curbranch" == "$branch" ]; then
    echo "already on $branch, you're on your own" >&2
    return 1
  fi

  me=$(git config github.user || git config user.name)
  if [ "$me" == "" ]; then
    echo "run 'git config --add github.user <username>'" >&2
    return 1
  fi

  exists=$(git show --no-patch --pretty=%H $branch 2>/dev/null)
  if [ "$exists" == "" ]; then
    git fetch origin pull/$num/head:$branch
    git checkout $branch
  else
    git checkout $branch
    git pull --rebase origin pull/$num/head
  fi

  git rebase -i $curbranch # squash and test

  if [ $? -eq 0 ]; then
    finish "${curbranch}"
  else
    echo "resolve conflicts and run: $0 finish "'"'${curbranch}'"'
  fi
}

# add the PR-URL to the last commit, after squashing
finish () {
  if [ $# -eq 0 ]; then
    echo "Usage: $0 finish <branch> (while on a PR-### branch)" >&2
    return 1
  fi

  local curbranch="$1"
  local ref=$(cat .git/HEAD)
  local prnum
  case $ref in
    "ref: refs/heads/PR-"*)
      prnum=${ref#ref: refs/heads/PR-}
      ;;
    *)
      echo "not on the PR-## branch any more!" >&2
      return 1
      ;;
  esac

  local me=$(git config github.user || git config user.name)
  if [ "$me" == "" ]; then
    echo "run 'git config --add github.user <username>'" >&2
    return 1
  fi

  set -x

  local url="$(prurl "$prnum")"
  local num=$prnum
  local prpath="${url#git@github.com:}"
  local repo=${prpath%/pull/$num}
  local prweb="https://github.com/$prpath"
  local root="$(prroot "$url")"

  local api="https://api.github.com/repos/${repo}/pulls/${num}"
  local user=$(curl -s $api | json user.login)

  local lastmsg="$(git log -1 --pretty=%B)"
  local newmsg="${lastmsg}

PR-URL: ${prweb}
Credit: @${user}
Close: #${num}
Reviewed-by: @${me}
"
  git commit --amend -m "$newmsg"
  git checkout $curbranch
  git merge PR-${prnum} --ff-only
  set +x
}


prurl () {
  local url="$1"
  if [ "$url" == "" ] && type pbpaste &>/dev/null; then
    url="$(pbpaste)"
  fi
  if [[ "$url" =~ ^[0-9]+$ ]]; then
    local us="$2"
    if [ "$us" == "" ]; then
      us="origin"
    fi
    local num="$url"
    local o="$(git config --get remote.${us}.url)"
    url="${o}"
    url="${url#(git:\/\/|https:\/\/)}"
    url="${url#git@}"
    url="${url#github.com[:\/]}"
    url="${url%.git}"
    url="https://github.com/${url}/pull/$num"
  fi
  url=${url%/commits}
  url=${url%/files}
  url="$(echo $url | perl -p -e 's/#issuecomment-[0-9]+$//g')"

  local p='^https:\/\/github.com\/[^\/]+\/[^\/]+\/pull\/[0-9]+$'
  if ! [[ "$url" =~ $p ]]; then
    echo "Usage:"
    echo "  $0 <pull req url>"
    echo "  $0 <pull req number> [<remote name>=origin]"
    type pbpaste &>/dev/null &&
      echo "(will read url/id from clipboard if not specified)"
    exit 1
  fi
  url="${url/https:\/\/github\.com\//git@github.com:}"
  echo "$url"
}

prroot () {
  local url="$1"
  echo "${url/\/pull\/+([0-9])/}"
}

prref () {
  local url="$1"
  local root="$2"
  echo "refs${url:${#root}}/head"
}

main "$@"