#!/bin/bash -e

fail () {
    echo "$1" 2>&1
    exit 1
}

help () {
    fail "Usage:
$0 --merge --dst location [--verbose] base-src diff-src1 diff-src2 ..."
}

filter_suffix () {
    sed -e 's/.patch$//' -e 's/.delete$//'
}

# exists as file or symbolic link
exfl () {
    [ -f "$1" -o -L "$1" ]
}

merge_file () {
    c="$(ls $2{,.patch,.delete} 2>/dev/null | wc -l)"
    [ $c -le 1 ] || fail "more than one operation available for $2"
    if [ $c -eq 0 ]; then
	$quiet || echo "  ignoring $2"
	return 0
    else
	$quiet || echo "  using $2"
    fi
    if exfl "$2"; then
	cp --no-dereference "$2" "$1"
    else
	exfl "$1" || fail "$1 requested but does not exist"
	if [ -f "$2.patch" ]; then
	    [ -f "$1" ] || fail "$1 is no regular file, not patching"
	    patch $(! $quiet || echo --silent) -B .trash/ "$1" <"$2.patch" 
	elif [ -f "$2.delete" ]; then
	    rm "$1"
	fi
    fi
}

merge_dir () {
    if [ -d $2 ]; then
	$quiet || echo "from directory $2"
	find -H $2 -printf "%P\n" | grep -v '^$' | filter_suffix | sort -u | (
	    while read f; do
		if [ -d "$2/$f" ]; then
		    mkdir -p "$1/$f"
		else
		    merge_file "$1/$f" "$2/$f"
		fi		
	    done)
    else
	$quiet || echo "ignoring $2"
    fi
}

# parse cmd line options (except merge srcs)
[ $# -gt 0 ] || help
quiet=true
while [ $# -gt 0 ]; do
    case "$1" in
	--merge)
	    op=merge
	    ;;
	--verbose)
	    quiet=false
	    ;;
	--dst)
	    [ $# -gt 1 ] || help
	    dst="$2"
	    shift
	    ;;
	*)
	    break
	    ;;
    esac
    shift
done
[ -n "$op" -a -n "$dst" ] || help

# determine wether merging dirs or files
[ $# -gt 0 ] || help
if [ -f "$1" ]; then
    mode=file
elif [ -d "$1" ]; then
    mode=dir
    [ -d "$dst~" ] && rm -r "$dst~"
    mkdir "$dst~"
else
    fail "$1 is neiter file nor directory"
fi

# iterate over all dirs
mkdir -p .trash
while [ $# -gt 0 ]; do
    ${op}_${mode} "$dst~" "$1"
    shift
done

[ -d "$dst" ] && rm -r "$dst"
mv "$dst~" "$dst"
rm -r .trash/* 2>/dev/null || true