backend/youtube.py

"""
YouTube transcript extraction.
"""

import re

from fastapi import HTTPException
from youtube_transcript_api import YouTubeTranscriptApi
from youtube_transcript_api._errors import (
    TranscriptsDisabled,
    NoTranscriptFound,
    VideoUnavailable,
)

YT_ID_RE = re.compile(r"(?:v=|youtu\.be/|embed/|shorts/)([A-Za-z0-9_-]{11})")


def extract_video_id(url: str) -> str:
    match = YT_ID_RE.search(url)
    if not match:
        raise HTTPException(status_code=400, detail="Could not extract a video ID from that URL.")
    return match.group(1)


def fetch_transcript(video_id: str) -> str:
    """Synchronous transcript fetch — call via asyncio.to_thread."""
    ytt = YouTubeTranscriptApi()
    try:
        transcript = ytt.fetch(video_id, languages=["en", "en-US", "en-GB"])
    except TranscriptsDisabled:
        raise HTTPException(status_code=422, detail="This video has transcripts disabled.")
    except NoTranscriptFound:
        raise HTTPException(status_code=422, detail="No transcript found for this video.")
    except VideoUnavailable:
        raise HTTPException(status_code=404, detail="Video is unavailable or does not exist.")
    except Exception as exc:
        raise HTTPException(status_code=502, detail=f"Transcript fetch failed: {exc}")

    return " ".join(snippet.text for snippet in transcript)