Add overwrite protection and --force flag

Also switch to argparse for correct parsing of arguments and help

journal_entry.py

@@ -5,10 +5,13 @@ Usage: The script can be used with or without arguments.
     ./journal_entry.py                  New entry for today
     ./journal_entry.py "YYYY-MM-DD"     New entry for specified date
 
+If the supplied date already has an entry, the program will be aborted,except if supplied with the "--force" flag.
+
 Note that a new entry always points to the newest previously created
-entry.
+entry. Inserting an entry anywhere but at the end is not supported.
 """
 
+import argparse
 import glob
 import os
 import re
@@ -21,24 +24,46 @@ def main():
     reponame = os.path.basename(os.getcwd())
     wikifolder = "../" + reponame + ".wiki"
 
-    if sys.argv[1:]:
-        new_date = datetime.strptime(sys.argv[1], "%Y-%m-%d").date()
-    else:
-        new_date = date.today()
+    parser = argparse.ArgumentParser(
+        description="Add a new journal entry to the wiki.\n\nNote that a new entry always points to the newest previously created entry. Inserting an entry anywhere but at the end is not supported."
+    )
+    parser.add_argument(
+        "date",
+        help='create entry for specified date, in "YYYY-MM-DD" format, default being the current date',
+        nargs="?",
+        default=f"{date.today()}",
+    )
+    parser.add_argument(
+        "-f",
+        "--force",
+        help="force overwrite if entry already exists",
+        action="store_true",
+    )
+    args = parser.parse_args()
+
+    # Parse the date argument
+    new_date = datetime.strptime(args.date, "%Y-%m-%d").date()
 
     os.chdir(wikifolder)
     os.system("git pull")
-    update(new_date)
+    update(new_date, args.force)
     os.system("git add .")
     os.system(f"git commit -m 'Create journal entry for {new_date}'")
     os.system("git push")
 
 
-def update(new_date):
+def update(new_date, forced):
     """Update previous entry, MoC, and _sidebar, and create new entry."""
 
     # Read previous entry
     previous = glob.glob("./journal/2*")[-1]
+
+    # Check if the file for `new_date` already exists
+    if previous == f"./journal/{new_date}.md" and not forced:
+        sys.exit(
+            f"Error: file journal/{new_date}.md already exists. Use `--force` to overwrite"
+        )
+
     with open(previous, "r") as file:
         lines = file.readlines()
     lines[2] = re.sub(r"next", r"[next](" + f"journal/{new_date}" + ")", lines[2])