from sqlalchemy import select, insert
from sqlalchemy.exc import IntegrityError

from app.utils import encoder
from app.models import Url
from app.exceptions import ShortcodeConflict, ShortcodeNotFound

class UrlService:
    def __init__(self, db):
        self.db = db

    async def get_url_by_shortcode(self, shortcode: str) -> str:
        query = select(Url.url).where(Url.shortcode == shortcode)
        result = await self.db.fetch_val(query)

        if result is None:
            raise ShortcodeNotFound(f"Shortcode '{shortcode}' not found")

        return result

    async def generate_shortcode_and_save(self, url: str):
        try:
            # Get the next ID from the sequence
            next_id = await self.db.fetch_val("SELECT nextval('urls_id_seq')")
            shortcode = encoder.encode(next_id)

            # Insert the new URL entry
            insert_stmt = insert(Url).values(id=next_id, url=url, shortcode=shortcode)
            await self.db.execute(insert_stmt)

            return {"shortcode": shortcode, "url": url}

        except IntegrityError as e:
            if 'shortcode' in str(e):
                raise ShortcodeConflict(f"Shortcode '{shortcode}' already in use") from None
            raise