commit b926f604a9c412cb22f159523c02c03e4659fed5
Author: Legaeli <depperschmidtchristian@gmail.com>
Date:   Fri Jan 9 16:53:37 2026 +0100

    Backend v1 (Prototype)

diff --git a/api.py b/api.py
new file mode 100644
index 0000000..b1930a5
--- /dev/null
+++ b/api.py
@@ -0,0 +1,131 @@
+from fastapi import FastAPI, HTTPException
+from fastapi.middleware.cors import CORSMiddleware
+from pydantic import BaseModel, EmailStr
+from typing import List, Optional, Any
+
+from db import SecretSantaDB
+from generator import SecretSantaGenerator
+
+app = FastAPI()
+database = SecretSantaDB()
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=[
+        "http://localhost:5173",
+        "http://127.0.0.1:5173",
+        "http://localhost:5500",
+        "http://127.0.0.1:5500",
+        "http://localhost:3000",
+        "http://127.0.0.1:3000",
+    ],
+    allow_credentials=True,
+    allow_methods=["*"],
+)
+
+class Participant(BaseModel):
+    name: str
+    email: EmailStr
+    wish: str | None = None
+
+class CreateRoundRequest(BaseModel):
+    round_name: Optional[str]
+    participants: List[Participant]
+
+class CreateRoundResponse(BaseModel):
+    round_id: int
+    created_at: str
+
+class RevealRequest(BaseModel):
+    email: EmailStr
+    choice_index: Optional[int] = None
+
+class RoundChoice(BaseModel):
+    index: int
+    round_name: str
+    created_at: str
+    participants: list[str]
+
+class RevealResponse(BaseModel):
+    giver: Optional[str] = None
+    receiver: Optional[str] = None
+    wish: Optional[str] = None
+    choices: Optional[List[RoundChoice]] = None
+
+
+@app.post("/api/rounds", response_model=CreateRoundResponse)
+def create_round(req: CreateRoundRequest):
+    participants_list = req.participants
+    round_name = req.round_name
+    if len(participants_list) < 3:
+        raise HTTPException(status_code=400, detail="Mindestens 3 Teilnehmer nötig.")
+
+    participants = {
+        participant.name: {"email": str(participant.email), "wish": participant.wish}
+        for participant in participants_list
+    }
+
+    generator = SecretSantaGenerator(imp_size=len(participants_list), db=database)
+    round_id, created_at = generator.create_new_round(round_name, participants)
+
+    return {
+        "round_id": round_id,
+        "created_at": created_at
+    }
+
+
+
+@app.post("/api/reveal", response_model=RevealResponse)
+def reveal(req: RevealRequest):
+    email = str(req.email).strip().lower()
+
+    rows = database.get_rows_from_email(email)
+    appearances = len(rows)
+
+    if appearances > 1:
+        choices = get_choices(email)
+
+        response_choice = req.choice_index
+        if response_choice is None:
+            public_choices = [
+                RoundChoice(index=i, created_at=choice["date"], participants=choice.get("participants", []), round_name=choice["round_name"])
+                for i, choice in choices.items()
+            ]
+            return RevealResponse(choices=public_choices)
+
+        if response_choice not in choices:
+            raise HTTPException(status_code=400, detail="Ungültige Auswahl.")
+
+        round_id = choices[response_choice]["round_id"]
+
+
+        giver = database.get_name_from_email_and_round_id(email, round_id)
+        imp_pairs = database.get_pairs(round_id)
+
+    else:
+        giver = database.get_name_from_email(email)
+        try:
+            round_id = database.get_round_id_from_email(email)
+            imp_pairs = database.get_pairs(round_id)
+        except Exception:
+            raise RuntimeError("Bitte erst eine Runde erstellen...")
+
+    if giver and imp_pairs:
+        try:
+            receiver = imp_pairs[giver]
+            receiver_id = database.get_imp_id_from_name(round_id, receiver)
+            wish = database.get_wish_from_id_and_round_id(receiver_id, round_id)
+            return {"giver": giver, "receiver": receiver, "wish": wish}
+
+        except Exception as e:
+            raise HTTPException(status_code=500, detail=f"Etwas ist schiefgelaufen: {e}")
+
+
+def get_choices(email) -> dict[int, dict[str, list[str] | Any]]:
+    choices = {}
+    rows = database.get_dates_with_round_ids_and_round_names_from_email(email)
+    for i, row in enumerate(rows, start=1):
+        round_id = row[0]
+        participants = database.get_participants_from_round_id(round_id)
+        choices[i] = {"round_id": row[0], "round_name": row[1], "date": row[2], "participants": participants}
+    return choices
\ No newline at end of file
diff --git a/db.py b/db.py
new file mode 100644
index 0000000..5079b56
--- /dev/null
+++ b/db.py
@@ -0,0 +1,354 @@
+import datetime
+import sqlite3
+from datetime import datetime
+
+class SecretSantaDB:
+
+    def __init__(self):
+        self.connection = sqlite3.connect("secret_santa_db.db", check_same_thread=False)
+        self.connection.execute("PRAGMA foreign_keys = ON;")
+        self.cursor = self.connection.cursor()
+        self.create_tables()
+
+
+    def create_tables(self):
+        self.cursor.executescript(
+            """
+            CREATE TABLE IF NOT EXISTS CYCLES
+            (
+              CYCLE_ID INTEGER PRIMARY KEY,
+              CONSTELLATION_KEY TEXT NOT NULL,
+              START_DATE TEXT NOT NULL
+            );
+            
+            CREATE TABLE IF NOT EXISTS ROUNDS 
+            (
+              ROUND_ID INTEGER PRIMARY KEY,
+              CYCLE_ID INTEGER NOT NULL,
+              ROUND_NAME TEXT,
+              CONSTELLATION_KEY TEXT NOT NULL,
+              CREATION_DATE TEXT NOT NULL,
+              FOREIGN KEY (CYCLE_ID) REFERENCES CYCLES (CYCLE_ID)
+            );
+            
+            CREATE TABLE IF NOT EXISTS PARTICIPANTS 
+            (
+              IMP_ID INTEGER PRIMARY KEY,
+              ROUND_ID INTEGER NOT NULL,
+              NAME TEXT NOT NULL,
+              WISH TEXT,
+              EMAIL TEXT,
+              FOREIGN KEY (ROUND_ID) REFERENCES ROUNDS (ROUND_ID),
+              UNIQUE (ROUND_ID, EMAIL)
+            );
+            
+            CREATE TABLE IF NOT EXISTS PAIRS 
+            (
+              ROUND_ID INTEGER NOT NULL,
+              GIVER_IMP_ID INTEGER NOT NULL,
+              RECEIVER_IMP_ID INTEGER NOT NULL,
+              FOREIGN KEY (ROUND_ID) REFERENCES ROUNDS (ROUND_ID),
+              FOREIGN KEY (GIVER_IMP_ID) REFERENCES PARTICIPANTS (IMP_ID),
+              FOREIGN KEY (RECEIVER_IMP_ID) REFERENCES PARTICIPANTS (IMP_ID),
+              UNIQUE (ROUND_ID, GIVER_IMP_ID),
+              UNIQUE (ROUND_ID, RECEIVER_IMP_ID),
+              CHECK (GIVER_IMP_ID != RECEIVER_IMP_ID)
+            );
+            
+            """
+        )
+        self.commit_to_db()
+
+    def flush_tables(self):
+        self.connection.execute("PRAGMA foreign_keys = OFF;")
+        self.cursor.executescript(
+            """
+            DROP TABLE ROUNDS;
+            DROP TABLE PARTICIPANTS;
+            DROP TABLE PAIRS;
+            DROP TABLE CYCLES;
+            """
+        )
+        self.commit_to_db()
+        self.connection.execute("PRAGMA foreign_keys = ON;")
+
+    def add_new_cycle(self, constellation_key: str) -> int:
+        now = datetime.now().isoformat(timespec="seconds")
+        self.cursor.execute(
+            """
+            INSERT INTO CYCLES (CONSTELLATION_KEY, START_DATE)
+            VALUES (?, ?)
+            """,
+            (constellation_key, now,)
+        )
+        return self.cursor.lastrowid
+
+    def get_latest_cycle_id(self, constellation_key: str) -> int | None:
+        self.cursor.execute(
+            """
+            SELECT CYCLE_ID
+            FROM CYCLES
+            WHERE CONSTELLATION_KEY = ?
+            ORDER BY CYCLE_ID DESC
+            LIMIT 1
+            """,
+            (constellation_key,)
+        )
+        row = self.cursor.fetchone()
+        return row[0] if row else None
+
+    def count_rounds_in_cycle(self, cycle_id: int) -> int:
+        self.cursor.execute(
+            """
+            SELECT COUNT(*)
+            FROM ROUNDS
+            WHERE CYCLE_ID = ?
+            """,
+            (cycle_id,)
+        )
+        return self.cursor.fetchone()[0]
+
+    def pair_used_in_cycle(self, cycle_id: int, giver_email: str, receiver_email: str) -> bool:
+        self.cursor.execute(
+            """
+            SELECT 1
+            FROM PAIRS p
+            JOIN ROUNDS r ON r.ROUND_ID = p.ROUND_ID
+            JOIN PARTICIPANTS g ON g.IMP_ID = p.GIVER_IMP_ID
+            JOIN PARTICIPANTS rec ON rec.IMP_ID = p.RECEIVER_IMP_ID
+            WHERE r.CYCLE_ID = ?
+              AND lower(g.EMAIL) = lower(?)
+              AND lower(rec.EMAIL) = lower(?)
+            LIMIT 1
+            """,
+            (cycle_id, giver_email, receiver_email)
+        )
+        return self.cursor.fetchone() is not None
+
+    def add_participants(self, round_id:int, imps: dict):
+        for name, data in imps.items():
+            wish = data["wish"]
+            email = data["email"]
+            self.add_new_participant(round_id, name, wish, email)
+
+    def add_new_round(self,round_name:str, constellation_key: str, cycle_id: int) -> tuple[int, str]:
+        created_at = datetime.now().isoformat(timespec="seconds")
+        self.cursor.execute(
+            """
+            INSERT INTO ROUNDS (CREATION_DATE, CONSTELLATION_KEY, CYCLE_ID, ROUND_NAME)
+            VALUES (?, ?, ?, ?)
+            """,
+            (created_at, constellation_key, cycle_id, round_name,)
+        )
+        return self.cursor.lastrowid, created_at
+
+    def add_new_participant(self, round_id:int, name:str, wish: str | None, email: str) -> int:
+        self.cursor.execute(
+            """
+            INSERT INTO PARTICIPANTS (ROUND_ID, NAME, WISH, EMAIL)
+            VALUES (?, ?, ?, ?)
+            """,
+            (round_id, name, wish, email,)
+        )
+        return self.cursor.lastrowid
+
+
+    def add_new_pair(self, round_id:int, giver_id:int, receiver_id:int):
+        self.cursor.execute(
+            """
+            INSERT INTO PAIRS (ROUND_ID, GIVER_IMP_ID, RECEIVER_IMP_ID)
+            VALUES (?, ?, ?)
+            """,
+            (round_id, giver_id, receiver_id,)
+        )
+
+    def check_constellation(self, imps: dict) -> bool:
+        prev_id = None
+        for name, email, wish in imps.items():
+            self.cursor.execute(
+                """
+                SELECT ROUND_ID
+                FROM PARTICIPANTS
+                WHERE EMAIL = ?
+                """,
+                (imps[email])
+            )
+            row = self.cursor.fetchone()
+            current_id = row[0]
+            if prev_id is None:
+                prev_id = current_id
+            if current_id != prev_id:
+                return False
+            else:
+                prev_id = current_id
+        return True
+
+
+    def get_imp_id_from_name(self, round_id, name:str) -> int | None:
+        self.cursor.execute(
+            """
+            SELECT IMP_ID
+            FROM PARTICIPANTS
+            WHERE ROUND_ID = ? AND NAME = ?
+            """,
+            (round_id, name,)
+        )
+
+        row = self.cursor.fetchone()
+        return row[0] if row else None
+
+    def get_rows_from_email(self, email:str) -> list[tuple]:
+        self.cursor.execute(
+            """
+            SELECT *
+            FROM PARTICIPANTS
+            WHERE EMAIL = ?
+            """,
+            (email,)
+        )
+        return self.cursor.fetchall()
+
+    def get_dates_with_round_ids_and_round_names_from_email(self, email:str) -> list[list]:
+        self.cursor.execute(
+            """
+            SELECT rounds.ROUND_ID, rounds.ROUND_NAME, rounds.CREATION_DATE
+            FROM ROUNDS rounds
+            JOIN PARTICIPANTS participants ON participants.ROUND_ID = rounds.ROUND_ID AND participants.email = ?
+            ORDER BY rounds.CREATION_DATE ASC
+            """,
+            (email,)
+        )
+
+        return [[row[0], row[1], row[2]] for row in self.cursor.fetchall()]
+
+    def get_round_id_from_date(self, date:str) -> int:
+        self.cursor.execute(
+            """
+            SELECT ROUND_ID
+            FROM ROUNDS
+            WHERE CREATION_DATE = ?
+            """,
+            (date,)
+        )
+        row = self.cursor.fetchone()
+        return row[0]
+
+    def get_name_from_email_and_round_id(self, email:str, round_id:int) -> str:
+        self.cursor.execute(
+            """
+            SELECT NAME
+            FROM PARTICIPANTS
+            WHERE EMAIL = ? AND ROUND_ID = ?
+            """,
+            (email, round_id,)
+        )
+        row = self.cursor.fetchone()
+        return row[0]
+
+    def get_name_from_email(self, email:str) -> str:
+        self.cursor.execute(
+            """
+            SELECT NAME
+            FROM PARTICIPANTS
+            WHERE EMAIL = ?
+            """,
+            (email,)
+        )
+        row = self.cursor.fetchone()
+        return row[0]
+
+    def get_wish_from_id_and_round_id(self, imp_id:int, round_id:int) -> str:
+        self.cursor.execute(
+            """
+            SELECT WISH
+            FROM PARTICIPANTS
+            WHERE IMP_ID = ? AND ROUND_ID = ?
+            """,
+            (imp_id, round_id,)
+        )
+        row = self.cursor.fetchone()
+        return row[0]
+
+
+    def get_participants_from_round_id(self, round_id:int) -> list[str]:
+        self.cursor.execute(
+            """
+            SELECT NAME
+            FROM PARTICIPANTS
+            WHERE ROUND_ID = ?
+            """,
+            (round_id,)
+        )
+        rows = self.cursor.fetchall()
+        return [row[0] for row in rows]
+
+    def get_round_id_from_email(self, email:str) -> int:
+        self.cursor.execute(
+            """
+            SELECT rounds.ROUND_ID
+            FROM ROUNDS rounds
+            JOIN PARTICIPANTS participants ON participants.ROUND_ID = rounds.ROUND_ID
+            WHERE lower(participants.EMAIL) = lower(?)
+            ORDER BY rounds.CREATION_DATE DESC
+            LIMIT 1
+            """,
+            (email,)
+        )
+        row = self.cursor.fetchone()
+        if not row:
+            raise ValueError("Keine Runde für diese Email gefunden.")
+        return row[0]
+
+    def get_pairs(self, round_id:int) -> dict:
+        pairs = {}
+        self.cursor.execute(
+            """
+                SELECT giver.NAME AS giver_name,
+                       receiver.NAME AS receiver_name
+                FROM PAIRS p
+                JOIN PARTICIPANTS giver
+                  ON giver.IMP_ID = p.GIVER_IMP_ID AND giver.ROUND_ID = p.ROUND_ID
+                JOIN PARTICIPANTS receiver
+                  ON receiver.IMP_ID = p.RECEIVER_IMP_ID AND receiver.ROUND_ID = p.ROUND_ID
+                WHERE p.ROUND_ID = ?
+                """,
+            (round_id,)
+        )
+        rows = self.cursor.fetchall()
+        for row in rows:
+            giver_name = row[0]
+            receiver_name = row[1]
+            pairs[giver_name] = receiver_name
+
+        return pairs
+
+    def delete_round(self, round_id: int):
+        self.cursor.execute("DELETE FROM PAIRS WHERE ROUND_ID = ?", (round_id,))
+        self.cursor.execute("DELETE FROM PARTICIPANTS WHERE ROUND_ID = ?", (round_id,))
+        self.cursor.execute("DELETE FROM ROUNDS WHERE ROUND_ID = ?", (round_id,))
+
+    def commit_to_db(self):
+        try:
+            self.connection.commit()
+        except Exception:
+            self.connection.rollback()
+            raise
+
+
+    def debug_print_table(self, table: str, limit: int = 50):
+        self.cursor.execute(f"SELECT * FROM {table} LIMIT ?", (limit,))
+        rows = self.cursor.fetchall()
+        print(f"--- {table} ({len(rows)} rows) ---")
+        for r in rows:
+            print(r)
+
+
+if __name__ == "__main__":
+    db_test = SecretSantaDB()
+    #db_test.flush_tables()
+    #db_test.create_tables()
+    #db_test.debug_print_table("CYCLES")
+    db_test.debug_print_table("ROUNDS")
+    db_test.debug_print_table("PARTICIPANTS")
+    db_test.debug_print_table("PAIRS")
+
diff --git a/generator.py b/generator.py
new file mode 100644
index 0000000..14b2b3d
--- /dev/null
+++ b/generator.py
@@ -0,0 +1,120 @@
+import random
+from db import SecretSantaDB
+import hashlib
+
+class SecretSantaGenerator:
+
+    def __init__(self, imp_size: int, db: SecretSantaDB):
+        self.imp_size = imp_size
+        self.db = db
+
+    def constellation_key(self, imps: dict) -> str:
+        emails = sorted([data["email"].strip().lower() for data in imps.values()])
+        raw = "|".join(emails)
+        return hashlib.sha256(raw.encode("utf-8")).hexdigest()
+
+    def derangements(self, n: int) -> int:
+        if n == 0: return 1
+        if n == 1: return 0
+        a, b = 1, 0
+        for k in range(2, n + 1):
+            a, b = b, (k - 1) * (a + b)
+        return b
+
+    def pair_exists(self, cycle_id: int, imp_pairs: dict, giver: str, receiver: str, imps: dict) -> bool:
+        if giver == receiver:
+            return True
+        if giver in imp_pairs:
+            return True
+        if receiver in imp_pairs.values():
+            return True
+
+        giver_email = imps[giver]["email"]
+        receiver_email = imps[receiver]["email"]
+
+        if self.db.pair_used_in_cycle(cycle_id, giver_email, receiver_email):
+            return True
+
+        return False
+
+    def generate_imp_pairs(self, round_id: int, imps: dict, cycle_id: int):
+        names = list(imps.keys())
+        n = len(names)
+
+        emails = {name: imps[name]["email"] for name in names}
+
+        def is_allowed(giver: str, receiver: str, current: dict) -> bool:
+            if giver == receiver:
+                return False
+            if giver in current:
+                return False
+            if receiver in current.values():
+                return False
+            return not self.db.pair_used_in_cycle(cycle_id, emails[giver], emails[receiver])
+
+        givers = names[:]
+
+        def backtrack(i: int, current: dict) -> dict | None:
+            if i == n:
+                return current
+
+            giver = givers[i]
+
+            candidates = names[:]
+            random.shuffle(candidates)
+
+            for receiver in candidates:
+                if not is_allowed(giver, receiver, current):
+                    continue
+                current[giver] = receiver
+                result = backtrack(i + 1, current)
+                if result is not None:
+                    return result
+                del current[giver]
+
+            return None
+
+        pairs = backtrack(0, {})
+        if pairs is None:
+            raise RuntimeError("Keine gültige Zuordnung im aktuellen Cycle möglich. Neuer Cycle nötig.")
+
+        for giver, receiver in pairs.items():
+            giver_id = self.db.get_imp_id_from_name(round_id, giver)
+            receiver_id = self.db.get_imp_id_from_name(round_id, receiver)
+            self.db.add_new_pair(round_id, giver_id, receiver_id)
+
+    def create_new_round(self,round_name: str, participants: dict[str, dict]) -> tuple[int, str]:
+
+        try:
+            key = self.constellation_key(participants)
+
+            latest_cycle = self.db.get_latest_cycle_id(key)
+
+            max_permutations = self.derangements(len(participants))
+
+            if latest_cycle is None:
+                cycle_id = self.db.add_new_cycle(key)
+            else:
+                used_permutations = self.db.count_rounds_in_cycle(latest_cycle)
+                if used_permutations < max_permutations:
+                    cycle_id = latest_cycle
+                else:
+                    cycle_id = self.db.add_new_cycle(key)
+
+            round_id, created_at = self.db.add_new_round(round_name, key, cycle_id)
+
+            self.db.add_participants(round_id, participants)
+            try:
+                self.generate_imp_pairs(round_id, participants, cycle_id)
+            except RuntimeError:
+                cycle_id = self.db.add_new_cycle(key)
+                round_id, created_at = self.db.add_new_round(round_name, key, cycle_id)
+                self.db.add_participants(round_id, participants)
+                self.generate_imp_pairs(round_id, participants, cycle_id)
+
+            self.db.commit_to_db()
+            return round_id, created_at
+
+        except Exception as e:
+            self.db.connection.rollback()
+            raise RuntimeError(f"Fehler beim Erstellen der Runde: {e}")
diff --git a/secret_santa_db.db b/secret_santa_db.db
new file mode 100644
index 0000000..aad085a
Binary files /dev/null and b/secret_santa_db.db differ