Fix ICA ICS

fix_ics.py

#!/usr/bin/env python3
"""
fix_ics.py — Fix malformed ICS files for Outlook import.

Fixes applied:
  - Removes UTF-8 BOM
  - Adds UID and DTSTAMP to any VEVENT missing them
  - Adds CALSCALE:GREGORIAN and METHOD:PUBLISH if missing
  - Folds long lines to ≤75 bytes per RFC 5545
  - Normalizes all line endings to CRLF

Usage:
  python3 fix_ics.py input.ics
  python3 fix_ics.py input.ics output.ics   (optional custom output path)
"""

import re, sys, uuid, os
from datetime import datetime, timezone


VTIMEZONE_SAST = """\
BEGIN:VTIMEZONE
TZID:Africa/Johannesburg
BEGIN:STANDARD
TZNAME:SAST
DTSTART:19700101T000000
TZOFFSETFROM:+0200
TZOFFSETTO:+0200
END:STANDARD
END:VTIMEZONE"""


def fix_ics(src: str, dst: str, tzid: str = "Africa/Johannesburg") -> None:
    with open(src, encoding="utf-8-sig") as f:
        content = f.read()

    # Normalize line endings
    content = content.replace("\r\n", "\n").replace("\r", "\n")

    # Add CALSCALE and METHOD after VERSION:2.0 if missing
    if "CALSCALE:" not in content:
        content = content.replace("VERSION:2.0\n", "VERSION:2.0\nCALSCALE:GREGORIAN\n", 1)
    if "METHOD:" not in content:
        content = content.replace("CALSCALE:GREGORIAN\n", "CALSCALE:GREGORIAN\nMETHOD:PUBLISH\n", 1)

    # Inject VTIMEZONE block before first VEVENT if not already present
    if "BEGIN:VTIMEZONE" not in content:
        content = content.replace("BEGIN:VEVENT\n", VTIMEZONE_SAST + "\n" + "BEGIN:VEVENT\n", 1)

    # Tag bare DTSTART/DTEND inside VEVENTs only (not inside VTIMEZONE)
    def tag_vevent_times(match):
        block = match.group(0)
        block = re.sub(
            r"(DTSTART|DTEND):([\dT]+)(?!\d|Z)",
            lambda m: f"{m.group(1)};TZID={tzid}:{m.group(2)}",
            block,
        )
        return block

    content = re.sub(
        r"BEGIN:VEVENT.*?END:VEVENT",
        tag_vevent_times,
        content,
        flags=re.DOTALL,
    )

    # Add UID + DTSTAMP to each VEVENT that lacks them
    stamp = datetime.now(timezone.utc).strftime("%Y%m%dT%H%M%SZ")

    def add_required(match):
        block = match.group(0)
        uid = f"UID:{uuid.uuid4()}@fixed"
        dtstamp = f"DTSTAMP:{stamp}"
        return block.replace("BEGIN:VEVENT\n", f"BEGIN:VEVENT\n{uid}\n{dtstamp}\n", 1)

    content = re.sub(
        r"BEGIN:VEVENT\n(?!UID:).*?END:VEVENT",
        add_required,
        content,
        flags=re.DOTALL,
    )

    # Fold lines at 75 bytes per RFC 5545
    def fold_line(line: str) -> str:
        if len(line.encode("utf-8")) <= 75:
            return line
        chunks = []
        buf = b""
        for char in line:
            cb = char.encode("utf-8")
            limit = 75 if not chunks else 74
            if len(buf) + len(cb) > limit:
                chunks.append(buf.decode("utf-8"))
                buf = b" " + cb
            else:
                buf += cb
        if buf:
            chunks.append(buf.decode("utf-8"))
        return "\r\n".join(chunks)

    out_lines = [fold_line(line) for line in content.split("\n")]

    # Write with CRLF, no BOM
    with open(dst, "w", encoding="utf-8", newline="") as f:
        f.write("\r\n".join(out_lines))

    # Report
    with open(dst, "rb") as f:
        raw = f.read()
    events = raw.count(b"BEGIN:VEVENT")
    long_lines = len([l for l in raw.split(b"\r\n") if len(l) > 75])
    bare_lf = raw.count(b"\n") - raw.count(b"\r\n")
    print(f"Fixed: {dst}")
    print(f"  Events   : {events}")
    print(f"  Long lines: {long_lines}")
    print(f"  Bare LFs : {bare_lf}")


if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: python3 fix_ics.py input.ics [output.ics] [--tz TZID]")
        print("  Default TZID: Africa/Johannesburg (SAST, UTC+2)")
        sys.exit(1)

    args = sys.argv[1:]
    tzid = "Africa/Johannesburg"
    if "--tz" in args:
        idx = args.index("--tz")
        tzid = args[idx + 1]
        args = args[:idx] + args[idx + 2:]

    src = args[0]
    if len(args) >= 2:
        dst = args[1]
    else:
        base, ext = os.path.splitext(src)
        dst = f"{base}_fixed{ext}"

    fix_ics(src, dst, tzid=tzid)