#!/bin/bash
#
# this patch can be found here:
#    http://www.jukie.net/~bart/scripts/tmp/vimdiff-over-unapplied-patch
#
# this script uses git-cat, inspired by cg-admin-cat, it can be found here:
#    http://www.jukie.net/~bart/scripts/tmp/git-cat
#
# use case: you have a patch that you only want to apply, but you don't want to 
#      apply all of it.  This script runs vimdiff over each of the files 
#      modified by the patch.  You select which deltas you want with 'do'
#      (see :help do in vim)
#
# example: you went too long without commiting and you don't want to commit 
#      everything...
#
#   git diff > /tmp/patch ; git clean ; vimdiff-over-unapplied-patch -p 1 /tmp/patch
#

set -u -e

prog=$(basename $0)
USAGE="$prog [-h] [-p <patch-level>] <patch-file>"

function bail {
        rc=$1 ; shift
        ((to=(rc?2:1)))
        echo $@ >&$to
        exit $rc
}

function warn {
        echo $@ >&2
}

function help {
        rc=$1 ; shift
        ((to=($rc?2:1)))
        cat >&$to <<END 
$USAGE
    -p <patch-level>    same as patch -p
    -f                  force; overwrite temporary files if they exist
    -h                  print this help
END
        exit $rc
}

# return true if repeat requested
function cleanup_repeat_prompt {
        tmp_file=$1
        res=xxx
        echo "Options:"
        echo " y - yes, cleanup and move to the next file"
        echo " n - no, don't cleanup but move to the next file"
        echo " r - reset and repeat same file"
        echo " q - stop everything"
        while true ; do
                read -n 1 -p "Cleanup? [y/n/r/q] " res
                echo
                case $res in 
                        q) exit 0                  ;; # bail
                        y) rm -f "$tmp" ; return 0 ;; # cleanup, next
                        n)                return 0 ;; # next
                        r) rm -f "$tmp" ; return 1 ;; # cleanup, repeat
                esac
        done
        exit 1
}

PLVL=1
FORCE=false
REV=HEAD
while [ "${1:0:1}" = '-' ] ; do
        cmd=$1 ; shift
        case "$cmd" in
        -p)
                PLVL=$1
                shift
                ;;
        -f)
                FORCE=true
                ;;
        -r)
                REV=$1
                shift
                ;;
        -h|--help)
                help 0
                ;;
        *)
                warn "invlid option $cmd"
                help 1
                ;;
        esac
done

PATCH=$1
if ! [ -f "$PATCH" ] ; then
        warn "need to specify patch file"
        help 1
fi

for need in diffstat patch filterdiff git-cat ; do 
        ( type $need >/dev/null 2>/dev/null ) || bail "$0 needs $need"
done

FILES=$(diffstat -l -p$PLVL "$PATCH")

for file in $FILES ; do

        echo "Working on: $file"

        finished=false
        until $finished ; do

                tmp=".tmp."$(echo -n "$file" | tr -c 'A-Za-z0-9_.-' '_')

                $FORCE && rm -f "$tmp"

                git-cat -r "$REV" "$file" > "$tmp"

                filterdiff -p$PLVL -i "$file" < "$PATCH" | patch -p$PLVL "$tmp"

                if ( diff "$file" "$tmp" >/dev/null ) ; then

                        echo "... identical, skipping."
                        echo

                        finished=true

                else

                        chmod -w "$tmp"

                        vimdiff "$file" "$tmp"

                        if cleanup_repeat_prompt "$file" ; then
                                finished=true
                        fi

                fi
        done
done