#!/usr/bin/env python3
# (c) 2015 Taeyeon Mori
# A simple script to make ln -s less painful
#
# Because of how symbolic links work (they're just a pathname that the OS reads and follows),
# the link target path must always be relative to the symlink's containing directory, OR
# an absolute path altogether. Unfortunately, ln -s does not automatically solve this issue
# which makes it painful to create a relative symlink somewhere outside the current working
# directory (It screws up shell completion for instance)
# This script performs the path transformation before creating the link and can therefore be
# used without worries of creating broken symlinks because one forgot to apply the correct
# relative adjustment to the target path
#
# ex:
# $ lns -v some-file dir/some-link
# ln -s '../some-file' 'dir/some-link'
# $ lns -v file ../derp/link # inside a directory called 'herp'
# ln -s '../herp/file' '../derp/link'


import os
import argparse


def transport_relpath(path, old_anchor, new_anchor):
    """
    :brief: Transport a relative path from one anchor to another
    Anchors must both be absolute paths, path must be relative (to old_anchor)
    """
    return os.path.relpath(os.path.normpath(os.path.join(old_anchor, path)), new_anchor)


def verbose_symlink(target, dest):
    print("ln -s '%s' '%s'" % (target, dest))
    return os.symlink(target, dest)


def main(argv):
    # Command line interface to make_symlink()
    parser = argparse.ArgumentParser(prog=argv[0],
                                     description="A 'ln -s' command that automatically translates relative target paths to be relative to the resulting symlink's containing directory when necessary.")
    parser.add_argument("target", help="The file(s) to create symlink(s) to", nargs="+")
    parser.add_argument("destination", help="The path of the symbolic link(s) to create")
    parser.add_argument("-v", "--verbose", help="Print every operation",
                        dest="symlink", const=verbose_symlink, action="store_const", default=os.symlink)

    args = parser.parse_args(argv[1:])

    # Multiple
    if len(args.target) > 1:
        if not os.path.isdir(args.destination):
            print("Destination must be an existing directory when multiple targets are passed!")
        for target in args.target:
            dest = os.path.join(args.destination, os.path.basename(target))
            args.symlink(target if os.path.isabs(target) else transport_relpath(target, os.curdir, args.destination), dest)

    # One
    else:
        target = args.target[0]

        dest = ldir = args.destination
        if os.path.isdir(dest):
            dest = os.path.join(dest, os.path.basename(target))
        else:
            ldir = os.path.dirname(dest)

        args.symlink(target if os.path.isabs(target) else transport_relpath(target, os.curdir, ldir), dest)

    return 0


if __name__ == "__main__":
    import sys
    sys.exit(main(sys.argv))