[PATCH 1/2] git-am foreign patch support: format autodetection

[Giuseppe Bilotta <giuseppe.bilotta@gmail.com>]

This patch is the first step towards the introduction of a framework to
allow git-am to import patches not in mailbox format.

Currently detected formats are
  * the mailbox format itself, which is assumed by default if input is
    form stdin
  * Mercurial's output from 'hg export'
  * Stacked Git's output from 'stg export' with the default export
    template; StGIT patch series are also detected and expanded.

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
---
 git-am.sh |  108 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 files changed, 105 insertions(+), 3 deletions(-)

diff --git a/git-am.sh b/git-am.sh
index 578780b..3508b7e 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -274,10 +274,112 @@ else
 		done
 		shift
 	fi
-	git mailsplit -d"$prec" -o"$dotest" -b -- "$@" > "$dotest/last" ||  {
-		rm -fr "$dotest"
+
+	# format of the patch(es) to be processed. we assume they are all
+	# of the same kind
+	patch_format=none
+
+	# from stdin we only accept mboxes, because peeking at stdin
+	# to detect the format is destructive
+	case $# in
+	0)
+		patch_format=mbox
+		;;
+	1)
+		if test x"$1" = x"-"
+		then
+			# stdin, so assume mbox
+			patch_format=mbox
+		else
+# a single non-stdin argument was passed, check if it's a StGit patch series
+# index by checking if the first line begins with '# This series'
+			{
+				read l1
+				case "$l1" in
+				'# This series '*)
+# replace the argument list with the files listed in the series index,
+# prefixing them with the series index dirname, skipping comment lines
+					series_dir=`dirname "$1"`
+					while read filename
+					do
+						set "$@" "$series_dir/$filename"
+					done
+					# remove the series index name
+					shift
+					# set the patch format appropriately
+					patch_format=stgit
+					;;
+				*)
+					;;
+				esac
+			} < "$1"
+		fi
+		;;
+	*)
+		;;
+	esac
+
+	# if the format is not defined yet, we can look at the first patch
+	# (which is not stdin) to try to understand the format.
+	if test $patch_format = none
+	then
+		echo "$patch_format"
+		# if it's a directory, assume mbox format
+		# TODO we could suppot StGIT patch series here too
+		if test -d "$1"
+		then
+			patch_format=mbox
+		else
+			# read the first four lines
+			{
+				read l1
+				read l2
+				read l3
+				read l4
+			} < "$1"
+			case "$l1" in
+			"# HG changeset patch")
+				patch_format=hg
+				;;
+			From\ *)
+				patch_format=mbox
+				;;
+			From:\ *)
+				patch_format=mbox
+				;;
+			*)
+				# if the second and fourth lines are empty,
+				# this might be an StGIT patch
+				if test x"$l2$l4" = x
+				then
+					case "$l3" in
+						From:\ *)
+							patch_format=stgit
+							;;
+						Author:\ *)
+							patch_format=stgit
+							;;
+						*)
+							;;
+					esac
+				fi
+				;;
+			esac
+		fi
+	fi
+
+	case "$patch_format" in
+	mbox)
+		git mailsplit -d"$prec" -o"$dotest" -b -- "$@" > "$dotest/last" ||  {
+			rm -fr "$dotest"
+			exit 1
+		}
+		;;
+	*)
+		echo "Patch format $patch_format is not currently handled, sorry"
 		exit 1
-	}
+		;;
+	esac
 
 	# -s, -u, -k, --whitespace, -3, -C and -p flags are kept
 	# for the resuming session after a patch failure.
-- 
1.6.3.1.245.g4529.dirty