"""
infrastructure/database/connection.py
───────────────────────────────────────
SQLAlchemy async engine + session factory — Supabase / PostgreSQL ready.

Supports:
  • PostgreSQL via asyncpg   (Supabase direct    port 5432)
  • PostgreSQL via asyncpg   (Supabase pooler    port 6543 — Transaction mode)
  • SQLite    via aiosqlite  (local dev / tests)

Supabase-specific tuning:
  • pool_size / max_overflow read from Settings (default: 5 / 10)
  • pool_recycle set to 1800 s (30 min) — avoids idle connection drops
  • connect_args.server_settings identifies the app in pg_stat_activity
  • Pooler (port 6543) mode disables prepared_statement_cache_size because
    pgBouncer Transaction mode does not support server-side prepared stmts.
"""
from __future__ import annotations

from collections.abc import AsyncGenerator

from sqlalchemy.ext.asyncio import (
    AsyncEngine,
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)

from src.shared.config import get_settings
from src.shared.logger import get_logger
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.dialects.postgresql import JSONB
from sqlalchemy.sql.elements import TextClause

logger = get_logger(__name__)

# ── SQLite Compatibility Compilers ───────────────────────────────────────────
# Registers global overrides to compile PostgreSQL-specific DDL for SQLite fallback.

@compiles(JSONB, "sqlite")
def compile_jsonb_sqlite(type_, compiler, **kw):
    """Compile JSONB to standard JSON in SQLite."""
    return "JSON"

@compiles(TextClause, "sqlite")
def compile_text_sqlite(element, compiler, **kw):
    """Compile gen_random_uuid() to random hex blob in SQLite."""
    if element.text == "gen_random_uuid()":
        return (
            "(lower(hex(randomblob(4))) || '-' || "
            "lower(hex(randomblob(2))) || '-4' || "
            "substr(lower(hex(randomblob(2))),2) || '-' || "
            "substr('89ab',abs(random()) % 4 + 1, 1) || "
            "substr(lower(hex(randomblob(2))),2) || '-' || "
            "lower(hex(randomblob(6))))"
        )
    return element.text

# ── Module-level singletons (created once per process) ───────────────────────
_engine: AsyncEngine | None = None
_session_factory: async_sessionmaker[AsyncSession] | None = None


def get_engine() -> AsyncEngine:
    """Return (or create) the async SQLAlchemy engine singleton."""
    global _engine
    if _engine is None:
        settings = get_settings()
        db_url = settings.database_url

        connect_args: dict = {}

        if settings.is_sqlite:
            # SQLite does not support connection pools or server_settings.
            connect_args = {"check_same_thread": False}
            _engine = create_async_engine(
                db_url,
                echo=settings.debug,
                connect_args=connect_args,
            )
        else:
            # PostgreSQL / Supabase path ──────────────────────────────────────
            server_settings: dict[str, str] = {
                "application_name": "bp_monitoring_pipeline",
            }

            if settings.uses_pooler:
                # Supabase Transaction Pooler (pgBouncer, port 6543):
                # Prepared statements are not supported in transaction mode.
                server_settings["options"] = "-c statement_timeout=30000"
                connect_args = {
                    "server_settings": server_settings,
                    "prepared_statement_cache_size": 0,
                }
                logger.info(
                    "Supabase Connection Pooler (port 6543) detected — "
                    "prepared statement cache disabled."
                )
            else:
                # Supabase Direct Connection (port 5432):
                # Full asyncpg feature set available.
                connect_args = {"server_settings": server_settings}

            _engine = create_async_engine(
                db_url,
                echo=settings.debug,
                pool_pre_ping=True,             # Validate connections before use
                pool_size=settings.db_pool_size,
                max_overflow=settings.db_max_overflow,
                pool_recycle=settings.db_pool_recycle,
                connect_args=connect_args,
            )

        # Log host only (strip credentials)
        safe_url = db_url.split("@")[-1] if "@" in db_url else db_url
        logger.info("Database engine created → %s", safe_url)

    return _engine


def get_session_factory() -> async_sessionmaker[AsyncSession]:
    """Return (or create) the async session factory singleton."""
    global _session_factory
    if _session_factory is None:
        _session_factory = async_sessionmaker(
            bind=get_engine(),
            class_=AsyncSession,
            expire_on_commit=False,   # Avoid lazy-load issues after commit
            autoflush=False,
            autocommit=False,
        )
    return _session_factory


async def get_async_session() -> AsyncGenerator[AsyncSession, None]:
    """
    FastAPI dependency: yield a scoped AsyncSession per request.

    Usage::

        @router.post("/...")
        async def endpoint(session: AsyncSession = Depends(get_async_session)):
            ...
    """
    factory = get_session_factory()
    async with factory() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise


async def ping_database() -> bool:
    """
    Send a lightweight ``SELECT 1`` to verify the database connection.

    Returns:
        True  — connection is healthy.
        False — connection failed (logs the error).

    Used by the health-check endpoint and startup validation.
    """
    from sqlalchemy import text

    try:
        async with get_engine().connect() as conn:
            await conn.execute(text("SELECT 1"))
        return True
    except Exception as exc:
        logger.error("Database ping failed: %s", exc)
        return False


async def create_all_tables() -> None:
    """
    Create all ORM tables — **development and test environments only**.

    In production (Supabase), always use Alembic migrations::

        alembic upgrade head

    This function is intentionally guarded by a debug/SQLite check in app.py.
    """
    settings = get_settings()
    if settings.is_supabase and not settings.debug:
        logger.warning(
            "create_all_tables() skipped — Supabase production detected. "
            "Run 'alembic upgrade head' to apply migrations."
        )
        return

    from src.infrastructure.database.models.base import Base  # noqa: F401 – registers models
    import src.infrastructure.database.models.ppg_model  # noqa: F401
    import src.infrastructure.database.models.prediction_model  # noqa: F401

    engine = get_engine()
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    logger.info("All database tables created.")


async def dispose_engine() -> None:
    """Dispose the engine and all pooled connections (call on application shutdown)."""
    global _engine
    if _engine is not None:
        await _engine.dispose()
        _engine = None
        logger.info("Database engine disposed.")