#!/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.
#
# 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.
# hook.envelopesender
#   If set then the -f option is passed to sendmail to allow the envelope sender
#   address to be set
#
# Notes
# -----
# All emails have their subjects prefixed with "[SCM]" to aid filtering.
# 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

#
# Top level email generation function.  This decides what type of update
# this is and 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
#
generate_email()
{
        # --- Arguments
        oldrev=$(git rev-parse $1)
        newrev=$(git rev-parse $2)
        refname="$3"

        # --- 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."
                        exit 0
                        ;;
                *)
                        # Anything else (is there anything else?)
                        echo >&2 "*** Unknown type of update to $refname ($rev_type)"
                        echo >&2 "***  - no email generated"
                        exit 1
                        ;;
        esac

        # Check if we've got anyone to send to
        if [ -z "$recipients" ]; then
                echo >&2 "*** hooks.recipients is not set so no email will be sent"
                echo >&2 "*** for $refname update $oldrev->$newrev"
                exit 0
        fi

        # Email parameters
        # The committer will be obtained from the latest existing rev; so
        # for a deletion it will be the oldrev, for the others, then newrev
        committer=$(git show --pretty=full -s $rev | sed -ne "s/^Commit: //p" |
                sed -ne 's/\(.*\) </"\1" </p')
        # 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 "$refname_type" in
        "tracking branch"|branch)
                fn_name=branch
                ;;
        "annotated tag")
                fn_name=atag
                ;;
        esac
        generate_${change_type}_${fn_name}_email

        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()
{
        cat <<-EOF


        hooks/post-receive
        --
        $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
        # 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)
        git rev-parse --not --branches | grep -v $(git rev-parse $refname) |
        git rev-list --pretty --stdin $newrev
        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 [ -z "$fastforward" ]; 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
                git rev-parse --not --branches | grep -v $(git rev-parse $refname) |
                git rev-list --pretty --stdin $oldrev..$newrev

                # 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 $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
}

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

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

# --- Constants
EMAILPREFIX="[SCM] "
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")
# 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=$(git repo-config hooks.mailinglist)
announcerecipients=$(git repo-config hooks.announcelist)
envelopesender=$(git-repo-config hooks.envelopesender)

# --- 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
        PAGER= generate_email $2 $3 $1
else
        while read oldrev newrev refname
        do
                generate_email $oldrev $newrev $refname | send_mail
        done
fi