import logging
from contextlib import asynccontextmanager

from core.embeddings import get_embeddings
from langchain_postgres import PGVector
from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver
from langgraph.store.postgres import AsyncPostgresStore
from psycopg.rows import dict_row
from psycopg_pool import AsyncConnectionPool

from core.settings import settings

logger = logging.getLogger(__name__)


def validate_postgres_config() -> None:
    """
    Validate that all required PostgreSQL configuration is present.
    Raises ValueError if any required configuration is missing.
    """

    required_vars = [
        "POSTGRES_USER",
        "POSTGRES_PASSWORD",
        "POSTGRES_HOST",
        "POSTGRES_PORT",
        "POSTGRES_DB",
    ]

    missing = [var for var in required_vars if not getattr(settings, var, None)]
    if missing:
        raise ValueError(
            f"Missing required PostgreSQL configuration: {', '.join(missing)}. "
            "All individual POSTGRES_* environment variables must be set to use PostgreSQL persistence."
        )

    if settings.POSTGRES_MIN_CONNECTIONS_PER_POOL > settings.POSTGRES_MAX_CONNECTIONS_PER_POOL:
        raise ValueError(
            f"POSTGRES_MIN_CONNECTIONS_PER_POOL ({settings.POSTGRES_MIN_CONNECTIONS_PER_POOL}) must be less than or equal to POSTGRES_MAX_CONNECTIONS_PER_POOL ({settings.POSTGRES_MAX_CONNECTIONS_PER_POOL})"
        )


def get_postgres_connection_string() -> str:
    """Build and return the PostgreSQL connection string from settings."""
    if settings.POSTGRES_PASSWORD is None:
        raise ValueError("POSTGRES_PASSWORD is not set")
    return (
        f"postgresql://{settings.POSTGRES_USER}:"
        f"{settings.POSTGRES_PASSWORD.get_secret_value()}@"
        f"{settings.POSTGRES_HOST}:{settings.POSTGRES_PORT}/"
        f"{settings.POSTGRES_DB}?sslmode=require"
    )


@asynccontextmanager
async def get_postgres_saver():
    """Initialize and return a PostgreSQL saver instance based on a connection pool for more resilient connections."""
    validate_postgres_config()
    application_name = settings.POSTGRES_APPLICATION_NAME + "-" + "saver"

    async with AsyncConnectionPool(
        get_postgres_connection_string(),
        min_size=settings.POSTGRES_MIN_CONNECTIONS_PER_POOL,
        max_size=settings.POSTGRES_MAX_CONNECTIONS_PER_POOL,
        # Langgraph requires autocommmit=true and row_factory to be set to dict_row.
        # Application_name is passed so you can identify the connection in your Postgres database connection manager.
        kwargs={"autocommit": True, "row_factory": dict_row, "application_name": application_name},
        # makes sure that the connection is still valid before using it
        check=AsyncConnectionPool.check_connection,
    ) as pool:
        try:
            checkpointer = AsyncPostgresSaver(pool)
            await checkpointer.setup()
            yield checkpointer
        finally:
            await pool.close()


@asynccontextmanager
async def get_postgres_store():
    """
    Get a PostgreSQL store instance based on a connection pool for more resilient connections.

    Returns an AsyncPostgresStore instance that can be used with async context manager pattern.

    """
    validate_postgres_config()
    application_name = settings.POSTGRES_APPLICATION_NAME + "-" + "store"

    async with AsyncConnectionPool(
        get_postgres_connection_string(),
        min_size=settings.POSTGRES_MIN_CONNECTIONS_PER_POOL,
        max_size=settings.POSTGRES_MAX_CONNECTIONS_PER_POOL,
        # Langgraph requires autocommmit=true and row_factory to be set to dict_row
        # Application_name is passed so you can identify the connection in your Postgres database connection manager.
        kwargs={"autocommit": True, "row_factory": dict_row, "application_name": application_name},
        # makes sure that the connection is still valid before using it
        check=AsyncConnectionPool.check_connection,
    ) as pool:
        try:
            store = AsyncPostgresStore(pool)
            await store.setup()
            yield store
        finally:
            await pool.close()

def get_pgvector_connection_string() -> str:
    """Build and return the PostgreSQL connection string for vectors from settings."""
    return (
        f"postgresql+psycopg://{settings.POSTGRES_USER}:"
        f"{settings.POSTGRES_PASSWORD.get_secret_value()}@"
        f"{settings.POSTGRES_HOST}:{settings.POSTGRES_PORT}/"
        f"{settings.POSTGRES_DB}?sslmode=require"
    )

def load_pgvector_store():
    """Get a PostgreSQL vectors store instance."""
    validate_postgres_config()

    return PGVector(
        connection=get_pgvector_connection_string(),
        collection_name=settings.VECTOR_STORE_COLLECTION_NAME,
        embeddings=get_embeddings(settings.DEFAULT_EMBEDDING_MODEL),
    )

def load_pgvector_retriever(k: int = 6):
    store = load_pgvector_store()
    return store.as_retriever(
        search_type="mmr",
        search_kwargs={
            "k": k,
            "fetch_k": 20,                # candidates
            "lambda_mult": 0.6,           # relevance vs diversity
        },
    )