#!/bin/sh
#
# Copyright (c) 2007 Andy Parkins
# Copyright (c) 2008 Stephen Haberman
#
# 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 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.post-receive-email.mailinglist
#   This is the list that all pushes will go to; leave it blank to not send
#   emails for every ref update.
# hooks.post-receive-email.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.post-receive-email.envelopesender
#   If set then the -f option is passed to sendmail to allow the envelope
#   sender address to be set
# hooks.post-receive-email.sendmail
#   The path to sendmail, e.g. /usr/sbin/sendmail or /bin/msmtp
# USER_EMAIL
#   Environment variable that should be set by your repository-specific
#   post-receive hook. E.g. export USER_EMAIL=${USER}@example.com
#
# 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

. $(dirname $0)/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()
{
	# --- Arguments
	oldrev=$(git rev-parse $1)
	newrev=$(git rev-parse $2)
	refname="$3"

	set_change_type
	set_rev_types
	set_describe_tags

	# 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"
			function="ltag"
			short_refname=${refname##refs/tags/}
			;;
		refs/tags/*,tag)
			# annotated tag
			refname_type="annotated tag"
			function="atag"
			short_refname=${refname##refs/tags/}
			# change recipients
			if [ -n "$announcerecipients" ]; then
				recipients="$announcerecipients"
			fi
			;;
		refs/heads/*,commit)
			# branch
			refname_type="branch"
			function="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 "$recipients" ]; then
		case "$refname_type" in
			"annotated tag")
				config_name="hooks.post-receive-email.announcelist"
				;;
			*)
				config_name="hooks.post-receive-email.mailinglist"
				;;
		esac
		echo >&2 "*** $config_name is not set so no email will be sent"
		echo >&2 "*** for $refname update $oldrev->$newrev"
		exit 0
	fi

	generate_email_header
	generate_${change_type}_${function}_email
}

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

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


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

#
# Called for the creation of a branch
#
generate_create_branch_email()
{
	# This is a new branch and so oldrev is not valid
	git rev-list --pretty=format:"        at %h %s" --no-walk "$newrev" | grep -vP "^commit"

	set_new_commits

	echo ""
	echo $LOGBEGIN
	echo "$new_commits" | git rev-list --reverse --stdin | while read commit ; do
		echo ""
		git rev-list --no-walk --pretty "$commit"
		git diff-tree --cc "$commit"
		echo ""
		echo $LOGEND
	done

	oldest_new=$(echo "$new_commits" | git rev-list --stdin | tail -n 1)
	if [ "$oldest_new" != "" ] ; then
		echo ""
		echo "Summary of changes:"
		git diff-tree --stat $oldest_new^..$newrev
	fi
}

#
# Called for the change of a pre-existing branch
#
generate_update_branch_email()
{
	# List all of the revisions that were removed by this update (hopefully empty)
	git rev-list --first-parent --pretty=format:"  discards %h %s" $newrev..$oldrev | grep -vP "^commit"

	# List all of the revisions that were added by this update
	git rev-list --first-parent --pretty=format:"       via %h %s" $oldrev..$newrev | grep -vP "^commit"

	removed=$(git rev-list $newrev..$oldrev)
	if [ "$removed" == "" ] ; then
		git rev-list --no-walk --pretty=format:"      from %h %s" $oldrev | grep -vP "^commit"
	else
		# Must be rewind, could be rewind+addition
		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."

		set_new_commits

		echo ""
		echo $LOGBEGIN
		echo "$new_commits" | git rev-list --reverse --stdin | while read commit ; do
			echo ""
			git rev-list --no-walk --pretty "$commit"
			git diff-tree --cc "$commit"
			echo ""
			echo $LOGEND
		done

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

	# Show the diffstat which is what really happened (new commits/whatever aside)
	echo ""
	echo "Summary of changes:"
	git diff-tree --stat --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 $oldrev ($oldrev_type)"
	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_ltag_email()
{
	echo "        at $newrev ($newrev_type)"
	generate_ltag_email
}

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

#
# Called for creation or update of any other type of reference
#
generate_ltag_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_ltag_email()
{
	echo "       was $oldrev ($oldrev_type)"
	echo ""
	echo $LOGEND
	git show -s --pretty=oneline $oldrev
	echo $LOGEND
}

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

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

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

# --- Config
# Set GIT_DIR either from the working directory or 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")
# Shorten the description if it's the default
if expr "$projectdesc" : "Unnamed repository.*$" >/dev/null ; then
	projectdesc="UNNAMED"
fi

recipients=$(git config hooks.post-receive-email.mailinglist)
announcerecipients=$(git config hooks.post-receive-email.announcelist)
envelopesender=$(git config hooks.post-receive-email.envelopesender)
emailprefix="[$projectdesc]"
debug=$(git config hooks.post-receive-email.debug)
sendmail=$(git config hooks.post-receive-email.sendmail)

# --- 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 $1
else
	while read oldrev newrev refname
	do
		if [ "$debug" == "true" ] ; then
			generate_email $oldrev $newrev $refname > "${refname//\//.}.out"
		else
			generate_email $oldrev $newrev $refname | send_mail
		fi
	done
fi