#!/bin/sh

# TODO:

# support setting flag when no upstream default

set -e +x

function fail {

    echo "$0: $1" >&2

    exit 1

}

USAGE="Usage: $0 FLAG [True|False]"

if [ $# -ne 2 ]; then

    fail "$USAGE"

fi

FLAG=$1

NEW=$2

case $NEW in

    True) OLD=False ;;

    False) OLD=True ;;

    *) echo "Flag value can only be set to True or False" ; exit 1 ;;

esac

CABALFILE=$(ls *.cabal)

if [ $(echo $CABALFILE | wc -w) -ne 1 ]; then

   fail "There needs to be one .cabal file in the current dir!"

fi

if ! grep -q -i "^flag *$FLAG" $CABALFILE; then

   fail "$CABALFILE does not have flag $FLAG"

fi

if ! grep -A3 -i "^flag *$FLAG" $CABALFILE | grep -q -i "default:"; then

   fail "$CABALFILE: $FLAG flag might not have a default"

fi

if ! grep -A3 -i "^flag *$FLAG" $CABALFILE | grep -q -i "default: *$OLD"; then

   fail "$CABALFILE: $FLAG flag already defaults to $NEW"

fi

if [ ! -f $CABALFILE.orig ]; then

    BACKUP=.orig

fi

sed -i$BACKUP -e "/[Ff]lag *$FLAG/,/[Dd]efault: *$OLD/ s/\( \+\)\([Dd]efault:[ \t]*\)$OLD/\1\2$NEW\n\1manual: True/" $CABALFILE