#!/bin/sh
#
# Copyright (c) 2007 Andy Parkins
#
# An example hook script to mail out commit update information.  This hook
# sends emails listing new revisions to the repository introduced by the
# change being reported.  The rule is that (for branch updates) each commit
# will appear on one email and one email only.
#
# This hook is stored in the contrib/hooks directory.  Your distribution
# will have put this somewhere standard.  You should make this script
# executable then link to it in the repository you would like to use it in.
# For example, on debian the hook is stored in
# /usr/share/doc/git-core/contrib/hooks/post-receive-email:
#
#  chmod a+x post-receive-email
#  cd /path/to/your/repository.git
#  ln -sf /usr/share/doc/git-core/contrib/hooks/post-receive-email hooks/post-receive
#
# This hook script assumes it is enabled on the central repository of a
# project, with all users pushing only to it and not between each other.  It
# will still work if you don't operate in that style, but it would become
# possible for the email to be from someone other than the person doing the
# push.
#
# To help with debugging and use on pre-v1.5.1 git servers, this script will
# also obey the interface of hooks/update, taking its arguments on the
# command line.  Unfortunately, hooks/update is called once for each ref.
# To avoid firing one email per ref, this script just prints its output to
# the screen when used in this mode.  The output can then be redirected if
# wanted.
#
# Config
# ------
# hooks.mailinglist
#   This is the list that all pushes will go to; leave it blank to not send
#   emails for every ref update.
# hooks.announcelist
#   This is the list that all pushes of annotated tags will go to.  Leave it
#   blank to default to the mailinglist field.  The announce emails lists
#   the short log summary of the changes since the last annotated tag.
# hooks.envelopesender
#   If set then the -f option is passed to sendmail to allow the envelope
#   sender address to be set
# hooks.emailprefix
#   All emails have their subjects prefixed with this prefix, or "[SCM]"
#   if emailprefix is unset, to aid filtering
# hooks.showrev
#   The shell command used to format each revision in the email, with
#   "%s" replaced with the commit id.  Defaults to "git rev-list -1
#   --pretty %s", displaying the commit id, author, date and log
#   message.  To list full patches separated by a blank line, you
#   could set this to "git show -C %s; echo".
#   To list a gitweb/cgit URL *and* a full patch for each change set, use this:
#     "t=%s; printf 'http://.../?id=%%s' \$t; echo;echo; git show -C \$t; echo"
#   Be careful if "..." contains things that will be expanded by shell "eval"
#   or printf.
# hooks.emailmaxlines
#   The maximum number of lines that should be included in the generated
#   email body. If not specified, there is no limit.
#   Lines beyond the limit are suppressed and counted, and a final
#   line is added indicating the number of suppressed lines.
#
# Notes
# -----
# All emails include the headers "X-Git-Refname", "X-Git-Oldrev",
# "X-Git-Newrev", and "X-Git-Reftype" to enable fine tuned filtering and
# give information for debugging.
#

# ---------------------------- Functions

#
# Function to prepare for email generation. This decides what type
# of update this is and whether an email should even be generated.
#
prep_for_email()
{
  # --- Arguments
  oldrev=$(git rev-parse $1)
  newrev=$(git rev-parse $2)
  refname="$3"
  maxlines=$4

  # --- Interpret
  # 0000->1234 (create)
  # 1234->2345 (update)
  # 2345->0000 (delete)
  if expr "$oldrev" : '0*$' >/dev/null
  then
    change_type="create"
  else
    if expr "$newrev" : '0*$' >/dev/null
    then
      change_type="delete"
    else
      change_type="update"
    fi
  fi

  # --- Get the revision types
  newrev_type=$(git cat-file -t $newrev 2> /dev/null)
  oldrev_type=$(git cat-file -t "$oldrev" 2> /dev/null)
  case "$change_type" in
  create|update)
    rev="$newrev"
    rev_type="$newrev_type"
    ;;
  delete)
    rev="$oldrev"
    rev_type="$oldrev_type"
    ;;
  esac

  # The revision type tells us what type the commit is, combined with
  # the location of the ref we can decide between
  #  - working branch
  #  - tracking branch
  #  - unannoted tag
  #  - annotated tag
  case "$refname","$rev_type" in
    refs/tags/*,commit)
      # un-annotated tag
      refname_type="tag"
      short_refname=${refname##refs/tags/}
      ;;
    refs/tags/*,tag)
      # annotated tag
      refname_type="annotated tag"
      short_refname=${refname##refs/tags/}
      # change recipients
      if [ -n "$announcerecipients" ]; then
        recipients="$announcerecipients"
      fi
      ;;
    refs/heads/*,commit)
      # branch
      refname_type="branch"
      short_refname=${refname##refs/heads/}
      ;;
    refs/remotes/*,commit)
      # tracking branch
      refname_type="tracking branch"
      short_refname=${refname##refs/remotes/}
      echo >&2 "*** Push-update of tracking branch, $refname"
      echo >&2 "***  - no email generated."
      return 1
      ;;
    *)
      # Anything else (is there anything else?)
      echo >&2 "*** Unknown type of update to $refname ($rev_type)"
      echo >&2 "***  - no email generated"
      return 1
      ;;
  esac

  # Check if we've got anyone to send to
  if [ -z "$recipients" ]; then
    case "$refname_type" in
      "annotated tag")
        config_name="hooks.announcelist"
        ;;
      *)
        config_name="hooks.mailinglist"
        ;;
    esac
    echo >&2 "*** $config_name is not set so no email will be sent"
    echo >&2 "*** for $refname update $oldrev->$newrev"
    return 1
  fi

  return 0
}

#
# Top level email generation function.  This calls the appropriate
# body-generation routine after outputting the common header.
#
# Note this function doesn't actually generate any email output, that is
# taken care of by the functions it calls:
#  - generate_email_header
#  - generate_create_XXXX_email
#  - generate_update_XXXX_email
#  - generate_delete_XXXX_email
#  - generate_email_footer
#
# Note also that this function cannot 'exit' from the script; when this
# function is running (in hook script mode), the send_mail() function
# is already executing in another process, connected via a pipe, and
# if this function exits without, whatever has been generated to that
# point will be sent as an email... even if nothing has been generated.
#
generate_email()
{
  # Email parameters
  # The email subject will contain the best description of the ref
  # that we can build from the parameters
  describe=$(git describe $rev 2>/dev/null)
  if [ -z "$describe" ]; then
    describe=$rev
  fi

  generate_email_header

  # Call the correct body generation function
  fn_name=general
  case "$refname_type" in
  "tracking branch"|branch)
    fn_name=branch
    ;;
  "annotated tag")
    fn_name=atag
    ;;
  esac

  if [ -z "$maxlines" ]; then
    generate_${change_type}_${fn_name}_email
  else
    generate_${change_type}_${fn_name}_email | limit_lines $maxlines
  fi

  generate_email_footer
}

generate_email_header()
{
  # --- Email (all stdout will be the email)
  # Generate header
  cat <<-EOF
  To: $recipients
  Subject: ${emailprefix}$projectdesc $refname_type $short_refname ${change_type}d. $describe
  X-Git-Refname: $refname
  X-Git-Reftype: $refname_type
  X-Git-Oldrev: $oldrev
  X-Git-Newrev: $newrev

  This is an automated email from the git hooks/post-receive script. It was
  generated because a ref change was pushed to the repository containing
  the project "$projectdesc".

  The $refname_type, $short_refname has been ${change_type}d
  EOF
}

generate_email_footer()
{
  SPACE=" "
  cat <<-EOF


  hooks/post-receive
  --${SPACE}
  $projectdesc
  EOF
}

# --------------- Branches

#
# Called for the creation of a branch
#
generate_create_branch_email()
{
  # This is a new branch and so oldrev is not valid
  echo "        at  $newrev ($newrev_type)"
  echo ""

  echo $LOGBEGIN
  show_new_revisions
  echo $LOGEND
}

#
# Called for the change of a pre-existing branch
#
generate_update_branch_email()
{
  # Consider this:
  #   1 --- 2 --- O --- X --- 3 --- 4 --- N
  #
  # O is $oldrev for $refname
  # N is $newrev for $refname
  # X is a revision pointed to by some other ref, for which we may
  #   assume that an email has already been generated.
  # In this case we want to issue an email containing only revisions
  # 3, 4, and N.  Given (almost) by
  #
  #  git rev-list N ^O --not --all
  #
  # The reason for the "almost", is that the "--not --all" will take
  # precedence over the "N", and effectively will translate to
  #
  #  git rev-list N ^O ^X ^N
  #
  # So, we need to build up the list more carefully.  git rev-parse
  # will generate a list of revs that may be fed into git rev-list.
  # We can get it to make the "--not --all" part and then filter out
  # the "^N" with:
  #
  #  git rev-parse --not --all | grep -v N
  #
  # Then, using the --stdin switch to git rev-list we have effectively
  # manufactured
  #
  #  git rev-list N ^O ^X
  #
  # This leaves a problem when someone else updates the repository
  # while this script is running.  Their new value of the ref we're
  # working on would be included in the "--not --all" output; and as
  # our $newrev would be an ancestor of that commit, it would exclude
  # all of our commits.  What we really want is to exclude the current
  # value of $refname from the --not list, rather than N itself.  So:
  #
  #  git rev-parse --not --all | grep -v $(git rev-parse $refname)
  #
  # Get's us to something pretty safe (apart from the small time
  # between refname being read, and git rev-parse running - for that,
  # I give up)
  #
  #
  # Next problem, consider this:
  #   * --- B --- * --- O ($oldrev)
  #          \
  #           * --- X --- * --- N ($newrev)
  #
  # That is to say, there is no guarantee that oldrev is a strict
  # subset of newrev (it would have required a --force, but that's
  # allowed).  So, we can't simply say rev-list $oldrev..$newrev.
  # Instead we find the common base of the two revs and list from
  # there.
  #
  # As above, we need to take into account the presence of X; if
  # another branch is already in the repository and points at some of
  # the revisions that we are about to output - we don't want them.
  # The solution is as before: git rev-parse output filtered.
  #
  # Finally, tags: 1 --- 2 --- O --- T --- 3 --- 4 --- N
  #
  # Tags pushed into the repository generate nice shortlog emails that
  # summarise the commits between them and the previous tag.  However,
  # those emails don't include the full commit messages that we output
  # for a branch update.  Therefore we still want to output revisions
  # that have been output on a tag email.
  #
  # Luckily, git rev-parse includes just the tool.  Instead of using
  # "--all" we use "--branches"; this has the added benefit that
  # "remotes/" will be ignored as well.

  # List all of the revisions that were removed by this update, in a
  # fast-forward update, this list will be empty, because rev-list O
  # ^N is empty.  For a non-fast-forward, O ^N is the list of removed
  # revisions
  fast_forward=""
  rev=""
  for rev in $(git rev-list $newrev..$oldrev)
  do
    revtype=$(git cat-file -t "$rev")
    echo "  discards  $rev ($revtype)"
  done
  if [ -z "$rev" ]; then
    fast_forward=1
  fi

  # List all the revisions from baserev to newrev in a kind of
  # "table-of-contents"; note this list can include revisions that
  # have already had notification emails and is present to show the
  # full detail of the change from rolling back the old revision to
  # the base revision and then forward to the new revision
  for rev in $(git rev-list $oldrev..$newrev)
  do
    revtype=$(git cat-file -t "$rev")
    echo "       via  $rev ($revtype)"
  done

  if [ "$fast_forward" ]; then
    echo "      from  $oldrev ($oldrev_type)"
  else
    #  1. Existing revisions were removed.  In this case newrev
    #     is a subset of oldrev - this is the reverse of a
    #     fast-forward, a rewind
    #  2. New revisions were added on top of an old revision,
    #     this is a rewind and addition.

    # (1) certainly happened, (2) possibly.  When (2) hasn't
    # happened, we set a flag to indicate that no log printout
    # is required.

    echo ""

    # Find the common ancestor of the old and new revisions and
    # compare it with newrev
    baserev=$(git merge-base $oldrev $newrev)
    rewind_only=""
    if [ "$baserev" = "$newrev" ]; then
      echo "This update discarded existing revisions and left the branch pointing at"
      echo "a previous point in the repository history."
      echo ""
      echo " * -- * -- N ($newrev)"
      echo "            \\"
      echo "             O -- O -- O ($oldrev)"
      echo ""
      echo "The removed revisions are not necessarilly gone - if another reference"
      echo "still refers to them they will stay in the repository."
      rewind_only=1
    else
      echo "This update added new revisions after undoing existing revisions.  That is"
      echo "to say, the old revision is not a strict subset of the new revision.  This"
      echo "situation occurs when you --force push a change and generate a repository"
      echo "containing something like this:"
      echo ""
      echo " * -- * -- B -- O -- O -- O ($oldrev)"
      echo "            \\"
      echo "             N -- N -- N ($newrev)"
      echo ""
      echo "When this happens we assume that you've already had alert emails for all"
      echo "of the O revisions, and so we here report only the revisions in the N"
      echo "branch from the common base, B."
    fi
  fi

  echo ""
  if [ -z "$rewind_only" ]; then
    echo "Those revisions listed above that are new to this repository have"
    echo "not appeared on any other notification email; so we list those"
    echo "revisions in full, below."

    echo ""
    echo $LOGBEGIN
    show_new_revisions

    # XXX: Need a way of detecting whether git rev-list actually
    # outputted anything, so that we can issue a "no new
    # revisions added by this update" message

    echo $LOGEND
  else
    echo "No new revisions were added by this update."
  fi

  # The diffstat is shown from the old revision to the new revision.
  # This is to show the truth of what happened in this change.
  # There's no point showing the stat from the base to the new
  # revision because the base is effectively a random revision at this
  # point - the user will be interested in what this revision changed
  # - including the undoing of previous revisions in the case of
  # non-fast-forward updates.
  echo ""
  echo "Summary of changes:"
  git diff-tree --stat --summary --find-copies-harder $oldrev..$newrev
}

#
# Called for the deletion of a branch
#
generate_delete_branch_email()
{
  echo "       was  $oldrev"
  echo ""
  echo $LOGEND
  git show -s --pretty=oneline $oldrev
  echo $LOGEND
}

# --------------- Annotated tags

#
# Called for the creation of an annotated tag
#
generate_create_atag_email()
{
  echo "        at  $newrev ($newrev_type)"

  generate_atag_email
}

#
# Called for the update of an annotated tag (this is probably a rare event
# and may not even be allowed)
#
generate_update_atag_email()
{
  echo "        to  $newrev ($newrev_type)"
  echo "      from  $oldrev (which is now obsolete)"

  generate_atag_email
}

#
# Called when an annotated tag is created or changed
#
generate_atag_email()
{
  # Use git for-each-ref to pull out the individual fields from the
  # tag
  eval $(git for-each-ref --shell --format='
  tagobject=%(*objectname)
  tagtype=%(*objecttype)
  tagger=%(taggername)
  tagged=%(taggerdate)' $refname
  )

  echo "   tagging  $tagobject ($tagtype)"
  case "$tagtype" in
  commit)

    # If the tagged object is a commit, then we assume this is a
    # release, and so we calculate which tag this tag is
    # replacing
    prevtag=$(git describe --abbrev=0 $newrev^ 2>/dev/null)

    if [ -n "$prevtag" ]; then
      echo "  replaces  $prevtag"
    fi
    ;;
  *)
    echo "    length  $(git cat-file -s $tagobject) bytes"
    ;;
  esac
  echo " tagged by  $tagger"
  echo "        on  $tagged"

  echo ""
  echo $LOGBEGIN

  # Show the content of the tag message; this might contain a change
  # log or release notes so is worth displaying.
  git cat-file tag $newrev | sed -e '1,/^$/d'

  echo ""
  case "$tagtype" in
  commit)
    # Only commit tags make sense to have rev-list operations
    # performed on them
    if [ -n "$prevtag" ]; then
      # Show changes since the previous release
      git rev-list --pretty=short "$prevtag..$newrev" | git shortlog
    else
      # No previous tag, show all the changes since time
      # began
      git rev-list --pretty=short $newrev | git shortlog
    fi
    ;;
  *)
    # XXX: Is there anything useful we can do for non-commit
    # objects?
    ;;
  esac

  echo $LOGEND
}

#
# Called for the deletion of an annotated tag
#
generate_delete_atag_email()
{
  echo "       was  $oldrev"
  echo ""
  echo $LOGEND
  git show -s --pretty=oneline $oldrev
  echo $LOGEND
}

# --------------- General references

#
# Called when any other type of reference is created (most likely a
# non-annotated tag)
#
generate_create_general_email()
{
  echo "        at  $newrev ($newrev_type)"

  generate_general_email
}

#
# Called when any other type of reference is updated (most likely a
# non-annotated tag)
#
generate_update_general_email()
{
  echo "        to  $newrev ($newrev_type)"
  echo "      from  $oldrev"

  generate_general_email
}

#
# Called for creation or update of any other type of reference
#
generate_general_email()
{
  # Unannotated tags are more about marking a point than releasing a
  # version; therefore we don't do the shortlog summary that we do for
  # annotated tags above - we simply show that the point has been
  # marked, and print the log message for the marked point for
  # reference purposes
  #
  # Note this section also catches any other reference type (although
  # there aren't any) and deals with them in the same way.

  echo ""
  if [ "$newrev_type" = "commit" ]; then
    echo $LOGBEGIN
    git show --no-color --root -s --pretty=medium $newrev
    echo $LOGEND
  else
    # What can we do here?  The tag marks an object that is not
    # a commit, so there is no log for us to display.  It's
    # probably not wise to output git cat-file as it could be a
    # binary blob.  We'll just say how big it is
    echo "$newrev is a $newrev_type, and is $(git cat-file -s $newrev) bytes long."
  fi
}

#
# Called for the deletion of any other type of reference
#
generate_delete_general_email()
{
  echo "       was  $oldrev"
  echo ""
  echo $LOGEND
  git show -s --pretty=oneline $oldrev
  echo $LOGEND
}


# --------------- Miscellaneous utilities

#
# Show new revisions as the user would like to see them in the email.
#
show_new_revisions()
{
  # This shows all log entries that are not already covered by
  # another ref - i.e. commits that are now accessible from this
  # ref that were previously not accessible
  # (see generate_update_branch_email for the explanation of this
  # command)

  # Revision range passed to rev-list differs for new vs. updated
  # branches.
  if [ "$change_type" = create ]
  then
    # Show all revisions exclusive to this (new) branch.
    revspec=$newrev
  else
    # Branch update; show revisions not part of $oldrev.
    revspec=$oldrev..$newrev
  fi

  other_branches=$(git for-each-ref --format='%(refname)' refs/heads/ |
      grep -F -v $refname)
  git rev-parse --not $other_branches |
  if [ -z "$custom_showrev" ]
  then
    git rev-list --pretty --stdin $revspec
  else
    git rev-list --stdin $revspec |
    while read onerev
    do
      eval $(printf "$custom_showrev" $onerev)
    done
  fi
}


limit_lines()
{
  lines=0
  skipped=0
  while IFS="" read -r line; do
    lines=$((lines + 1))
    if [ $lines -gt $1 ]; then
      skipped=$((skipped + 1))
    else
      printf "%s\n" "$line"
    fi
  done
  if [ $skipped -ne 0 ]; then
    echo "... $skipped lines suppressed ..."
  fi
}


send_mail()
{
  if [ -n "$envelopesender" ]; then
    /usr/sbin/sendmail -t -f "$envelopesender"
  else
    /usr/sbin/sendmail -t
  fi
}

# ---------------------------- main()

# --- Constants
LOGBEGIN="- Log -----------------------------------------------------------------"
LOGEND="-----------------------------------------------------------------------"

# --- Config
# Set GIT_DIR either from the working directory, or from the environment
# variable.
GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
if [ -z "$GIT_DIR" ]; then
  echo >&2 "fatal: post-receive: GIT_DIR not set"
  exit 1
fi

projectdesc=$(sed -ne '1p' "$GIT_DIR/description" 2>/dev/null)
# Check if the description is unchanged from it's default, and shorten it to
# a more manageable length if it is
if expr "$projectdesc" : "Unnamed repository.*$" >/dev/null
then
  projectdesc="UNNAMED PROJECT"
fi

recipients=$(git config hooks.mailinglist)
announcerecipients=$(git config hooks.announcelist)
envelopesender=$(git config hooks.envelopesender)
emailprefix=$(git config hooks.emailprefix || echo '[SCM] ')
custom_showrev=$(git config hooks.showrev)
maxlines=$(git config hooks.emailmaxlines)

# --- Main loop
# Allow dual mode: run from the command line just like the update hook, or
# if no arguments are given then run as a hook script
if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
  # Output to the terminal in command line mode - if someone wanted to
  # resend an email; they could redirect the output to sendmail
  # themselves
  prep_for_email $2 $3 $1 && PAGER= generate_email
else
  while read oldrev newrev refname
  do
    prep_for_email $oldrev $newrev $refname || continue
    generate_email $maxlines | send_mail
  done
fi
