prefs: support --lib flag

bsc/prefs.py

@@ -9,18 +9,23 @@
 class Prefs:
     def __init__(self):
         self.input = ""
+        self.is_library = False
 
     def parse_args(self):
         parser = argparse.ArgumentParser(
             prog = 'bsc', description = 'The BlueScript compiler'
         )
         parser.add_argument('input', help = "the input file")
+        parser.add_argument('--lib', action='store_true', help='specifies whether the entry is a library or not')
         args = parser.parse_args()
 
+        self.is_library = args.lib
+
         # check input file
         self.input = args.input
-        if os.path.exists(self.input):
-            if not os.path.isfile(self.input):
-                utils.error(f"`{self.input}` is a directory, expected a file")
-        else:
+        if os.path.isdir(self.input):
+            input_file = "lib.bs" if self.is_library else "main.bs"
+            self.input = os.path.join(self.input, input_file)
+
+        if not os.path.exists(self.input):
             utils.error(f"file `{self.input}` does not exist")