# Unlinks a directory (given as the first argument), and re-creates that
# directory as an actual directory. Then descends into the directory of
# the same name in the origin (arg_2/arg_3) and symlinks the contents of
# that directory into the passed end-location.
unlinkDirReSymlinkContents() {
    local dirToUnlink="$1"
    local origin="$2"
    local contentsLocation="$3"

    unlink $dirToUnlink/$contentsLocation
    mkdir -p $dirToUnlink/$contentsLocation
    for f in $origin/$contentsLocation/*; do
        ln -s -t "$dirToUnlink/$contentsLocation" "$f"
    done
}

# Using unlinkDirReSymlinkContents, un-symlinks directories down to
# $out/share/octave, and then creates the octave_packages directory.
createOctavePackagesPath() {
    local desiredOut=$1
    local origin=$2

    if [ -L "$out/share" ]; then
        unlinkDirReSymlinkContents "$desiredOut" "$origin" "share"
    fi

    if [ -L "$out/share/octave" ]; then
        unlinkDirReSymlinkContents "$desiredOut" "$origin" "share/octave"
    fi

    # Now that octave_packages has a path rather than symlinks, create the
    # octave_packages directory for installed packages.
    mkdir -p "$desiredOut/share/octave/octave_packages"
}

# First, descends down to $out/share/octave/site/m/startup/octaverc, and
# copies that start-up file. Once done, it performs a `chmod` to allow
# writing. Lastly, it `echo`s the location of the locally installed packages
# to the startup file, allowing octave to discover installed packages.
addPkgLocalList() {
    local desiredOut=$1
    local origin=$2
    local octaveSite="share/octave/site"
    local octaveSiteM="$octaveSite/m"
    local octaveSiteStartup="$octaveSiteM/startup"
    local siteOctavercStartup="$octaveSiteStartup/octaverc"

    unlinkDirReSymlinkContents "$desiredOut" "$origin" "$octaveSite"
    unlinkDirReSymlinkContents "$desiredOut" "$origin" "$octaveSiteM"
    unlinkDirReSymlinkContents "$desiredOut" "$origin" "$octaveSiteStartup"

    unlink "$out/$siteOctavercStartup"
    cp "$origin/$siteOctavercStartup" "$desiredOut/$siteOctavercStartup"
    chmod u+w "$desiredOut/$siteOctavercStartup"
    echo "pkg local_list $out/.octave_packages" >> "$desiredOut/$siteOctavercStartup"
}

# Wrapper function for wrapOctaveProgramsIn. Takes one argument, a
# space-delimited string of packages' paths that will be installed.
wrapOctavePrograms() {
    wrapOctaveProgramsIn "$out/bin" "$out" "$@"
}

# Wraps all octave programs in $out/bin with all the propagated inputs that
# a particular package requires. $1 is the directory to look for binaries in
# to wrap. $2 is the path to the octave ENVIRONMENT. $3 is the space-delimited
# string of packages.
wrapOctaveProgramsIn() {
    local dir="$1"
    local octavePath="$2"
    local pkgs="$3"
    local f

    buildOctavePath "$octavePath" "$pkgs"

    # Find all regular files in the output directory that are executable.
    if [ -d "$dir" ]; then
        find "$dir" -type f -perm -0100 -print0 | while read -d "" f; do
            echo "wrapping \`$f'..."
            local -a wrap_args=("$f"
                --prefix PATH ':' "$program_PATH"
                   )
            local -a wrapProgramArgs=("${wrap_args[@]}")
            wrapProgram "${wrapProgramArgs[@]}"
    done
    fi
}

# Build the PATH environment variable by walking through the closure of
# dependencies. Starts by constructing the `program_PATH` variable with the
# environment's path, then adding the original octave's location, and marking
# them in `octavePathsSeen`.
buildOctavePath() {
    local octavePath="$1"
    local packages="$2"

    local pathsToSearch="$octavePath $packages"

    # Create an empty table of Octave paths.
    declare -A octavePathsSeen=()
    program_PATH=
    octavePathsSeen["$out"]=1
    octavePathsSeen["@octave@"]=1
    addToSearchPath program_PATH "$out/bin"
    addToSearchPath program_PATH "@octave@/bin"
    echo "program_PATH to change to is: $program_PATH"
    for path in $pathsToSearch; do
    echo "Recurse to propagated-build-input: $path"
    _addToOctavePath $path
    done
}

# Adds the bin directories to the program_PATH variable.
# Recurses on any paths declared in `propagated-build-inputs`, while avoiding
# duplicating paths by flagging the directires it has seen in `octavePathsSeen`.
_addToOctavePath() {
    local dir="$1"
    # Stop if we've already visited this path.
    if [ -n "${octavePathsSeen[$dir]}" ]; then return; fi
    octavePathsSeen[$dir]=1
    # addToSearchPath is defined in stdenv/generic/setup.sh. It has the effect
    # of calling `export X=$dir/...:$X`.
    addToSearchPath program_PATH $dir/bin

    # Inspect the propagated inputs (if they exist) and recur on them.
    local prop="$dir/nix-support/propagated-build-inputs"
    if [ -e $prop ]; then
    for new_path in $(cat $prop); do
        _addToOctavePath $new_path
    done
    fi
}