#!/bin/sh
#
# Note: Letters A-Z are branch names, not revs.
#
# Old tree:
#                        *--F
#                       /
#     origin=master--A--B--G
#                    \
#                     *--D--H
#                         \
#                          *--*--K
#
# Set "git config follow.tree" to:
#   master A
#   A B
#   B F
#   B G
#   A D
#   D H
#   D K
#
# After "git-fetch -v":
#                        *--F
#                       /
#           master---A--B--G
#            \        \
#             *        *--D--H
#              \           \
#               *--origin'  *--*--K
#
# After "git-rebase-subtree origin master":
#
#                          *'--F'
#                         /
#   origin'=master'--A'--B'--G'
#                     \
#                      *'--D'--H'
#                          \
#                           *'--*'--K'

unset CDPATH
SED="${SED-sed}"

self=`basename "$0"`
selfdir=`dirname "$0"`
selfdir=`cd "$selfdir" && pwd`
. "$selfdir/git-ndim-sh"

SUBDIRECTORY_OK="yes"
USAGE="<command> [params...]"

LONG_USAGE="\
Let a local subtree of branches follow a remote origin without too much merging.
For more details, see the ${self}(1) man page."
. git-sh-setup

require_work_tree

# Abort on error
set -e


cmd() {
    echo "CMD>" "$@"
    gitk --all
    "$@"
}


gf_init() {
    echo "$self: Examining configuration"
    git config follow.tree | while read from to restofline; do
	if test "x#" = "x$(echo "$from" | sed -n '1s/^\(.\).*/\1/p')"; then continue; fi
	echo ""
	echo "  From: $from"
	echo "    To: $to"
    done
}

gf_branch() {
    branch="$1"
    newbranch="follow-old/$branch"
    if git-rev-parse --verify "$branch" > /dev/null 2>&1; then
	# valid branch
	if git-rev-parse --verify "$newbranch" > /dev/null 2>&1; then
	    : # branch already exists, do nothing
	else
	    cmd git-branch "${newbranch}" "${branch}"
	fi
    else
	echo "$self: gf_branch called with invalid branch \"$branch\"" >&2
	exit 1
    fi
}


gf_rmbranch() {
    branch="$1"
    newbranch="follow-old/$branch"
    if git-rev-parse --verify "$branch" > /dev/null 2>&1; then
	if git-rev-parse --verify "$newbranch" > /dev/null 2>&1; then
	    cmd git-branch -D "${newbranch}"
	fi
    fi
}


gf_rebase_tree() {
    newroot="$1"
    test "x$newroot" = "x" && die "Need <newroot> parameter"
    oldroot="$2"
    test "x$oldroot" = "x" && die "Need <oldroot> parameter"
    echo
    echo "$self: Preparing subtree rebase"
    git config follow.tree | while read from to restofline; do
	if test "x#" = "x$(echo "$from" | sed -n '1s/^\(.\).*/\1/p')"; then continue; fi
	gf_branch "$from"
	gf_branch "$to"
    done
    gitk --all
    echo
    echo "$self: Executing subtree rebase"
    git config follow.tree | while read from to restofline; do
	if test "x#" = "x$(echo "$from" | sed -n '1s/^\(.\).*/\1/p')"; then continue; fi
	cmd git-rebase --onto "$from" "follow-old/$from" "$to"
    done
    gitk --all
    echo
    echo "$self: Cleaning up after subtree rebase"
    git config follow.tree | while read from to restofline; do
	if test "x#" = "x$(echo "$from" | sed -n '1s/^\(.\).*/\1/p')"; then continue; fi
	gf_rmbranch "$from"
	gf_rmbranch "$to"
    done
    gitk --all
}


# The great command case
command="$1"
if shift; then
    case "$command" in
	rebase-subtree)
	    gf_init
	    gf_rebase_tree "$@"
	    ;;
	*)
	    die "Invalid command line parameter: \"$command\""
	    ;;
    esac
else
    gf_init
fi

# End of file.