Adds get_paths_to_sync and organise it in a class

This refactors the paths functions in a class called PathsManager
allowing to share some data like the Paths to the various directories
unisync works with.
This commit also creates the get_paths_to_sync method which simply reads
the paths file and returns its content as a list

src/unisync/paths.py

@@ -3,13 +3,36 @@
 
 import subprocess
 
-def user_select_files(local_dir:str, choice_timeout:int=120) -> list[str]:
+from pathlib import Path, PosixPath
+
+class PathsManager:
+
+    def __init__(self, local_dir:PosixPath, cache_dir:PosixPath):
+        """
+        Creates a PathsManager with the necessary data
+        Args:
+            local_dir: Path to the top directory of the synchronisation
+            cache_dir: Path to the cache directory that contains the paths file
+        """
+        if not local_dir.is_dir():
+            raise ValueError("Invalid local directory")
+        self.local_dir = local_dir
+
+        if not cache_dir.is_dir():
+            raise ValueError("Invalid cache directory")
+        self.cache_dir = cache_dir
+
+        self.paths_file:PosixPath = self.cache_dir / "paths"
+        if not self.paths_file.is_file():
+            raise ValueError("The paths file does not exist")
+
+
+    def user_select_files(self, choice_timeout:int=120) -> list[str]:
         """
         Make the user select files in the top directory.
         Currently uses nnn for the selection.
         The goal is to replace it in order to avoid using external programs.
         Args:
-        local_dir: The absolute path to the top synchronisation directory
             choice_timeout: Time given to make choices in nnn
         Returns:
             list[str]: The list of paths that was selected
@@ -18,7 +41,7 @@ def user_select_files(local_dir:str, choice_timeout:int=120) -> list[str]:
                 "/usr/bin/nnn",
                 "-H",
                 "-p", "-",
-            local_dir
+                self.local_dir
                 ]
         nnn_process = subprocess.Popen(command, stdout=subprocess.PIPE)
         try:
@@ -35,10 +58,17 @@ def user_select_files(local_dir:str, choice_timeout:int=120) -> list[str]:
         while (next_path := nnn_process.stdout.readline()) != b'':
             next_path = next_path.decode().strip()
             # Make the path relative to the top directory
-        next_path = next_path[len(local_dir):].lstrip("/")
+            next_path = next_path[len(self.local_dir):].lstrip("/")
             paths_list.append(next_path)
-
         return paths_list
 
+    def get_paths_to_sync(self) -> list[str]:
+        """
+        Return the paths to synchronise as list.
+        """
+        paths:list[str] = self.paths_file.read_text().split("\n")
+        if paths[-1] == "":
+            paths.pop()
+        return paths