#!/usr/bin/env python3
# File: s2slib.py
# Locations: 
#    /mnt/public/Support/Programs/shortcuts/
#    https://gitlab.com/bgstack15/s2s
# Author: bgstack15@gmail.com
# SPDX-License-Identifier: GPL-3.0
# Startdate: 2021-02-11 20:00
# Title: Shortcut To Symlink library
# Purpose: Convert .lnk files to POSIX symlinks within a single filesystem
# History:
# Usage:
#    see s2s.py
# Reference:
#    https://stackoverflow.com/questions/25146960/python-convert-back-slashes-to-forward-slashes/25147093#25147093
#    https://github.com/libyal/liblnk/blob/main/documentation/Windows%20Shortcut%20File%20(LNK)%20format.asciidoc#file_attribute_flags
# Improve:
#    Handle absolute paths when relative paths are absent?
#    Add a force=True option to overwrite existing symlink that points to something else
# Dependencies:
#    devuan-req: python3-liblnk
import pylnk # python3-liblnk
import os, re, posixpath
from sys import stderr

debuglevel = 8

# Functions
def eprint(*args, **kwargs):
   print(*args, file=stderr, **kwargs)

# to benefit from caching outside of the function, maybe
lnkregex = re.compile(".*\.lnk$")

def replace_one_symlink(
   lnkfile
   , delete = False
   , debuglevel = debuglevel
   , dryrun = False
   ):

   thislnk = pylnk.file()
   basename = os.path.basename(lnkfile)
   #workdir = os.path.dirname(lnkfile) # not used

   # Exit if this is not a .lnk file
   if not re.match(lnkregex,basename):
      eprint(f"Cannot operate on {lnkfile}")
      return -1

   thislnk.open(lnkfile)

   # Get relative path
   # we are really expecting a relative path for every single one, because we are dealing with Windows shortcuts to files all on the same network share.
   # Although I suppose a symlink could work if you could somehow map the expected SMB path to a POSIX filesystem
   try:
      relative_path = thislnk.relative_path
   except:
      eprint(f"No relative path for {lnkfile}, and abs path not yet implemented.")
      return -1
   # and make it a Unix-style path
   relative_path = posixpath.join(*thislnk.relative_path.split('\\'))

   # Not used for anything, but here if we want it.
   linktype = "file"
   if thislnk.file_attribute_flags & 0x10:
      linktype = "dir"

   # Get preferred name, and strip any " - Shortcut"
   pn = os.path.splitext(lnkfile)[:-1][0] # remove the .lnk part, but preserve any other dots
   symlink_path = re.sub(' - Shortcut$', "",pn)

   # take action
   if debuglevel >= 5:
      eprint(f"Want symlink \"{symlink_path}\" ({linktype})--> \"{relative_path}\"")

   ready_to_delete = False

   if os.path.exists(symlink_path):
      current_source = ""
      try:
         current_source = os.path.realpath(symlink_path)
      except:
         eprint(f"Unable to determine current_source for {symlink_path} which already exists.")
      normpath = os.path.normpath(os.path.join(os.path.dirname(symlink_path),relative_path))
      #eprint(f"Please ensure {current_source} matches {relative_path} which is {normpath}")
      if normpath != current_source:
         # The existing symlink points to something else. Not sure how to proceed.
         # probably need to add a --force option to overwrite
         eprint(f"Warning: Existing symlink {symlink_path} points to {current_source} and not {normpath} as requested")
      else:
         # it exists and already points to what we want it to point to.
         if debuglevel >= 3:
            eprint(f"symlink {symlink_path} already points to {current_source} which is {normpath}")
         ready_to_delete = True
   else:
      # symlink does not exist, so make it!
      if debuglevel >= 1:
         eprint(f"ln -s {relative_path} {symlink_path}")
      if not dryrun:
         try:
            os.symlink(relative_path,symlink_path)
            ready_to_delete = True
         except Exception as e:
            eprint(e)

   if delete:
      if ready_to_delete:
         if debuglevel >= 2:
            eprint(f"rm {lnkfile}")
         if not dryrun:
            os.remove(lnkfile)
   return 0

def list_all_child_lnk_files(indir):
   mylist = []
   for root, dirs, files in os.walk(indir):
      for name in files:
         if ".lnk" in name:
            mylist.append(os.path.join(root,name))
            #eprint(os.path.join(root,name))
   return mylist

def replace_all_symlinks(
   indir
   , delete = False
   , debuglevel = debuglevel
   , dryrun = False
   ):
   result = 0

   # get list of all lnk files
   mylist = list_all_child_lnk_files(indir)
   for lnkfile in mylist:
      replace_one_symlink(
         lnkfile
         , delete = delete
         , debuglevel = debuglevel
         , dryrun = dryrun
         )

   return result

if __name__ == "__main__":
   print("running the main loop")