#!/bin/sh
# Copyright (c) 2015 The Bitcoin Core developers
# Distributed under the MIT software license, see the accompanying
# file COPYING or http://www.opensource.org/licenses/mit-license.php.

DIR="$1"
COMMIT="$2"
if [ -z "$COMMIT" ]; then
    COMMIT=HEAD
fi

# Taken from git-subtree (Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>)
find_latest_squash()
{
	dir="$1"
	sq=
	main=
	sub=
	git log --grep="^git-subtree-dir: $dir/*\$" \
		--pretty=format:'START %H%n%s%n%n%b%nEND%n' "$COMMIT" |
	while read a b _; do
		case "$a" in
			START) sq="$b" ;;
			git-subtree-mainline:) main="$b" ;;
			git-subtree-split:) sub="$b" ;;
			END)
				if [ -n "$sub" ]; then
					if [ -n "$main" ]; then
						# a rejoin commit?
						# Pretend its sub was a squash.
						sq="$sub"
					fi
					echo "$sq" "$sub"
					break
				fi
				sq=
				main=
				sub=
				;;
		esac
	done
}

# find latest subtree update
latest_squash="$(find_latest_squash "$DIR")"
if [ -z "$latest_squash" ]; then
    echo "ERROR: $DIR is not a subtree" >&2
    exit 2
fi
set $latest_squash
old=$1
rev=$2

# get the tree in the current commit
tree_actual=$(git ls-tree -d "$COMMIT" "$DIR" | head -n 1)
if [ -z "$tree_actual" ]; then
    echo "FAIL: subtree directory $DIR not found in $COMMIT" >&2
    exit 1
fi
set $tree_actual
tree_actual_type=$2
tree_actual_tree=$3
echo "$DIR in $COMMIT currently refers to $tree_actual_type $tree_actual_tree"
if [ "d$tree_actual_type" != "dtree" ]; then
    echo "FAIL: subtree directory $DIR is not a tree in $COMMIT" >&2
    exit 1
fi

# get the tree at the time of the last subtree update
tree_commit=$(git show -s --format="%T" $old)
echo "$DIR in $COMMIT was last updated in commit $old (tree $tree_commit)"

# ... and compare the actual tree with it
if [ "$tree_actual_tree" != "$tree_commit" ]; then
    git diff $tree_commit $tree_actual_tree >&2
    echo "FAIL: subtree directory was touched without subtree merge" >&2
    exit 1
fi

# get the tree in the subtree commit referred to
if [ "d$(git cat-file -t $rev 2>/dev/null)" != dcommit ]; then
    echo "subtree commit $rev unavailable: cannot compare" >&2
    exit
fi
tree_subtree=$(git show -s --format="%T" $rev)
echo "$DIR in $COMMIT was last updated to upstream commit $rev (tree $tree_subtree)"

# ... and compare the actual tree with it
if [ "$tree_actual_tree" != "$tree_subtree" ]; then
    echo "FAIL: subtree update commit differs from upstream tree!" >&2
    exit 1
fi

echo "GOOD"
