"""Validate plain UTF-8 SRT cue timing; do not modify the source file."""
from pathlib import Path
import re
import sys

STAMP = r"(\d{2,}):(\d{2}):(\d{2}),(\d{3})"
TIMING = re.compile(rf"^{STAMP}\s*-->\s*{STAMP}$")

def milliseconds(parts):
    hours, minutes, seconds, fraction = map(int, parts)
    if minutes > 59 or seconds > 59:
        raise ValueError("minutes and seconds must be 00-59")
    return ((hours * 60 + minutes) * 60 + seconds) * 1000 + fraction

def check(path):
    text = path.read_text(encoding="utf-8-sig")
    blocks = re.split(r"\n\s*\n", text.replace("\r\n", "\n").strip())
    if not text.strip():
        raise ValueError("file is empty")
    errors = []
    warnings = []
    previous_end = None
    for number, block in enumerate(blocks, 1):
        lines = block.splitlines()
        if len(lines) < 3 or not lines[0].isdigit():
            errors.append(f"Cue {number}: expected numeric index, timing and text")
            continue
        match = TIMING.fullmatch(lines[1].strip())
        if not match:
            errors.append(f"Cue {number}: expected HH:MM:SS,mmm --> HH:MM:SS,mmm")
            continue
        try:
            start = milliseconds(match.groups()[:4])
            end = milliseconds(match.groups()[4:])
        except ValueError as exc:
            errors.append(f"Cue {number}: {exc}")
            continue
        if end <= start:
            errors.append(f"Cue {number}: end must be later than start")
        if previous_end is not None and start < previous_end:
            warnings.append(f"Cue {number}: overlaps or precedes the previous cue")
        previous_end = end
    for message in errors:
        print("ERROR " + message)
    for message in warnings:
        print("WARN " + message)
    if errors:
        return 1
    print(f"PASS {len(blocks)} cues; basic timing is valid")
    return 0

if __name__ == "__main__":
    if len(sys.argv) != 2:
        print("Usage: python3 check-srt-timing.py captions.srt", file=sys.stderr)
        sys.exit(2)
    try:
        sys.exit(check(Path(sys.argv[1])))
    except (OSError, UnicodeError, ValueError) as exc:
        print(f"ERROR {exc}", file=sys.stderr)
        sys.exit(2)