#!/bin/bash
# Copyright (C) 2014-2016 Ian Kelling
# This program is under GPL v. 3 or later, see <http://www.gnu.org/licenses/>

lnf() {
    local help="Usage:
       lnf -T TARGET LINK_NAME     (1st form)
       lnf TARGET                  (2nd form)
       lnf TARGET... DIRECTORY     (3rd form)
Create symlinks forcefully

Removes existing files using trash-put or rm -rf if it is not available,
or trash-put fails due to a limitation such as a cross-filesystem link.
Create directory if needed. Slightly more restrictive arguments than ln.

In the 1st form, create a link to TARGET with the name LINK_NAME.  In the 2nd
form, create a link to TARGET in the current directory.  In the 3rd form, create
links to each TARGET in DIRECTORY."

    if [[ $1 == --help || $# -eq 0 ]]; then
        echo "$help"
        return 0
    fi

    local nodir
    if [[ $1 == -T ]]; then
        nodir=-T
        shift
        if (( $# != 2 )); then
            echo "lnf error: expected 2 arguments with -T flag. Got $#"
            return 1
        fi
    fi

    local reset_extglob=false
    ! shopt extglob >/dev/null && reset_extglob=true
    shopt -s extglob


    local x ret prefix dir to_remove
    local mkdir=false

    to_remove=()
    if [[ $nodir ]]; then
        dir="$(dirname "$2")"
        if [[ -e $2 || -L $2 ]]; then
            to_remove+=("$2")
        elif [[ ! -d $dir ]]; then
            mkdir=true
            if [[ -e $dir || -L $dir ]]; then
                to_remove+=("$dir")
            fi
        fi
    elif (( $# >= 2 )); then
        if [[ -d ${!#} ]]; then
            prefix="${!#}/" # last arg
            for x in "${@:1:$(( $# - 1 ))}"; do # all but last arg
                # Remove 1 or more trailing slashes, using.
                x="${x%%+(/)}"
                # remove any leading directory components, add prefix
                x="$prefix/${x##*/}"
                [[ -e "$x" || -L "$x" ]] && to_remove+=("$x")
            done
        else
            if ! mkdir -p "${!#}"; then
                echo "lnf error: failed to make directory ${!#}"
                return 1
            fi
        fi
    elif  [[ $# -eq 1 ]]; then
        [[ -e "${1##*/}" || -L "${1##*/}" ]] && to_remove+=("${1##*/}")
    fi
    if (( ${#to_remove[@]} >= 1 )); then
        if type -P trash-put >/dev/null; then
            trash-put -- "${to_remove[@]}" || ret=$?
            # trash-put will fail to trash a link that goes across filesystems (72),
            # and for empty files (74)
            # so revert to rm -rf in that case
            if [[ $ret == 72 ]]; then
                echo "$0: using rm -rf to overcome cross filesystem trash-put limitation"
                rm -rf -- "${to_remove[@]}"
            elif [[ $ret == 74 ]]; then
                echo "$0: using rm -rf to overcome empty file & hardlink trash-put limitation"
                rm -rf -- "${to_remove[@]}"
            elif [[ $ret && $ret != 0 ]]; then
                return $x
            fi
        else
            rm -rf -- "${to_remove[@]}"
        fi
    fi

    $reset_extglob && shopt -u extglob

    if $mkdir; then
        if ! mkdir -p "$(dirname "$2")"; then
            echo "lnf error: failed to make directory $(dirname "$2")"
            return 1
        fi
    fi

    ln -s $nodir -- "$@"
}
lnf "$@"