feat: add frontend project to repo

backend/services/__init__.py

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+from .url_service import UrlService

backend/services/url_service.py

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+from sqlalchemy import select, insert
+from sqlalchemy.exc import IntegrityError
+
+from backend.utils import encoder
+from backend.models import Url
+from backend.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