from __future__ import annotations

import os
import re
from contextlib import contextmanager
from datetime import datetime, timezone
from typing import List, Optional, Sequence

from sqlalchemy import (
    Column,
    DateTime,
    Float,
    ForeignKey,
    Index,
    Integer,
    String,
    Text,
    create_engine,
    func,
    select,
)
from sqlalchemy.engine import Engine
from sqlalchemy.orm import Session, declarative_base, relationship, sessionmaker

Base = declarative_base()


USERNAME_REGEX = re.compile(r"^[A-Za-z0-9_.-]{3,20}$")

_engine: Optional[Engine] = None
_SessionLocal: Optional[sessionmaker] = None


class User(Base):
    __tablename__ = "users"

    id = Column(Integer, primary_key=True)
    username = Column(String(20), unique=True, nullable=False, index=True)  # kanonisch (lowercase)
    display_name = Column(String(20), nullable=False)
    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)

    scores = relationship("Score", back_populates="user", cascade="all, delete-orphan")


class Score(Base):
    __tablename__ = "scores"

    id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True)
    username = Column(String(20), nullable=False)  # Originalschreibweise
    canonical_username = Column(String(20), nullable=False, index=True)
    image_id = Column(String(100), nullable=False, index=True)
    score = Column(Integer, nullable=False)
    similarity = Column(Float, nullable=False)
    text = Column(Text, nullable=False)
    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False, index=True)

    user = relationship("User", back_populates="scores")

    __table_args__ = (
        Index("ix_scores_global", score.desc(), created_at.asc(), id.asc()),
        Index("ix_scores_image", "image_id", score.desc(), created_at.asc()),
        Index("ix_scores_user", "canonical_username", created_at.desc(), id.desc()),
    )


def configure_database(database_url: Optional[str] = None) -> Engine:
    """Initialisiert Engine und SessionFactory."""

    global _engine, _SessionLocal

    if database_url is None:
        database_url = os.getenv("DATABASE_URL")
    if not database_url:
        raise RuntimeError("DATABASE_URL ist nicht gesetzt.")

    _engine = create_engine(database_url, future=True, pool_pre_ping=True)
    _SessionLocal = sessionmaker(bind=_engine, autoflush=False, expire_on_commit=False, future=True)
    return _engine


def get_engine() -> Engine:
    if _engine is None:
        raise RuntimeError("Datenbank wurde noch nicht konfiguriert. Rufen Sie configure_database() auf.")
    return _engine


def init_db() -> None:
    engine = get_engine()
    Base.metadata.create_all(engine)


@contextmanager
def session_scope() -> Session:
    if _SessionLocal is None:
        raise RuntimeError("SessionFactory nicht initialisiert. configure_database() zuerst aufrufen.")
    session: Session = _SessionLocal()
    try:
        yield session
        session.commit()
    except Exception:
        session.rollback()
        raise
    finally:
        session.close()


def normalize_username(username: str) -> str:
    return username.strip().lower()


def validate_username(username: str) -> bool:
    return bool(USERNAME_REGEX.match(username))


def ensure_user(session: Session, username_input: str) -> User:
    """Sucht oder erstellt einen Nutzer."""

    normalized = normalize_username(username_input)
    stmt = select(User).where(User.username == normalized)
    user = session.execute(stmt).scalar_one_or_none()
    if user:
        return user

    user = User(username=normalized, display_name=username_input.strip())
    session.add(user)
    session.flush()
    return user


def create_score(
    session: Session,
    *,
    user: User,
    image_id: str,
    score_value: int,
    similarity: float,
    text: str,
) -> Score:
    entry = Score(
        user_id=user.id,
        username=user.display_name,
        canonical_username=user.username,
        image_id=image_id,
        score=score_value,
        similarity=similarity,
        text=text,
    )
    session.add(entry)
    session.flush()
    return entry


def _format_timestamp(value: datetime | str | None) -> str:
    if value is None:
        return ""
    if isinstance(value, str):
        return value
    if value.tzinfo is None:
        value = value.replace(tzinfo=timezone.utc)
    return value.astimezone(timezone.utc).strftime("%Y-%m-%d %H:%M:%SZ")


def scores_to_rows(scores: Sequence[Score], include_rank: bool = True) -> List[List[object]]:
    rows: List[List[object]] = []
    for index, score in enumerate(scores, start=1):
        base_row = [
            score.username,
            score.image_id,
            score.score,
            round(score.similarity, 4),
            score.text,
            _format_timestamp(score.created_at),
        ]
        if include_rank:
            rows.append([index, *base_row])
        else:
            rows.append(base_row)
    return rows


def get_global_top(session: Session, limit: int = 50) -> List[Score]:
    stmt = (
        select(Score)
        .order_by(Score.score.desc(), Score.created_at.asc(), Score.id.asc())
        .limit(limit)
    )
    return list(session.scalars(stmt))


def get_image_top(session: Session, image_id: str, limit: int = 50) -> List[Score]:
    stmt = (
        select(Score)
        .where(Score.image_id == image_id)
        .order_by(Score.score.desc(), Score.created_at.asc(), Score.id.asc())
        .limit(limit)
    )
    return list(session.scalars(stmt))


def get_user_recent(session: Session, canonical_username: str, limit: int = 50) -> List[Score]:
    stmt = (
        select(Score)
        .where(Score.canonical_username == canonical_username)
        .order_by(Score.created_at.desc(), Score.id.desc())
        .limit(limit)
    )
    return list(session.scalars(stmt))


__all__ = [
    "Base",
    "Score",
    "User",
    "configure_database",
    "create_score",
    "ensure_user",
    "get_engine",
    "get_global_top",
    "get_image_top",
    "get_user_recent",
    "init_db",
    "normalize_username",
    "scores_to_rows",
    "session_scope",
    "validate_username",
]