#!/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