"""Postgres-backed persistence for production deployments.

Uses psycopg2 (or asyncpg when available) for connection pooling.
Falls back gracefully to in-memory if Postgres is unavailable.
"""

from __future__ import annotations

import json
import threading
from typing import Any

from fusionagi._logger import logger
from fusionagi.core.persistence import StateBackend
from fusionagi.schemas.task import Task, TaskState

_CREATE_SCHEMA = """
CREATE TABLE IF NOT EXISTS tasks (
    task_id TEXT PRIMARY KEY,
    data JSONB NOT NULL,
    state TEXT NOT NULL DEFAULT 'pending',
    created_at TIMESTAMPTZ DEFAULT NOW(),
    updated_at TIMESTAMPTZ DEFAULT NOW()
);
CREATE TABLE IF NOT EXISTS traces (
    id SERIAL PRIMARY KEY,
    task_id TEXT NOT NULL REFERENCES tasks(task_id) ON DELETE CASCADE,
    entry JSONB NOT NULL,
    created_at TIMESTAMPTZ DEFAULT NOW()
);
CREATE INDEX IF NOT EXISTS idx_traces_task_id ON traces(task_id);
CREATE INDEX IF NOT EXISTS idx_tasks_state ON tasks(state);
"""


class PostgresStateBackend(StateBackend):
    """Postgres-backed implementation of StateBackend.

    Args:
        dsn: PostgreSQL connection string (e.g., "postgresql://user:pass@host/db").
        pool_size: Connection pool size (min connections kept open).
        max_overflow: Maximum extra connections beyond pool_size.
    """

    def __init__(
        self,
        dsn: str = "postgresql://localhost/fusionagi",
        pool_size: int = 5,
        max_overflow: int = 10,
    ) -> None:
        self._dsn = dsn
        self._pool_size = pool_size
        self._max_overflow = max_overflow
        self._lock = threading.Lock()
        self._pool: Any = None
        self._available = False
        self._init_pool()

    def _init_pool(self) -> None:
        """Initialize connection pool and create schema."""
        try:
            from psycopg2 import pool as pg_pool

            self._pool = pg_pool.ThreadedConnectionPool(
                minconn=1,
                maxconn=self._pool_size + self._max_overflow,
                dsn=self._dsn,
            )
            conn = self._pool.getconn()
            try:
                with conn.cursor() as cur:
                    cur.execute(_CREATE_SCHEMA)
                conn.commit()
            finally:
                self._pool.putconn(conn)
            self._available = True
            logger.info("PostgresStateBackend: connected", extra={"dsn": self._dsn.split("@")[-1]})
        except ImportError:
            logger.warning("PostgresStateBackend: psycopg2 not installed, operating as no-op")
        except Exception as e:
            logger.warning("PostgresStateBackend: connection failed, operating as no-op", extra={"error": str(e)})

    def _get_conn(self) -> Any:
        if not self._available or self._pool is None:
            return None
        return self._pool.getconn()

    def _put_conn(self, conn: Any) -> None:
        if self._pool is not None and conn is not None:
            self._pool.putconn(conn)

    def get_task(self, task_id: str) -> Task | None:
        """Load task by id from Postgres."""
        conn = self._get_conn()
        if conn is None:
            return None
        try:
            with conn.cursor() as cur:
                cur.execute("SELECT data FROM tasks WHERE task_id = %s", (task_id,))
                row = cur.fetchone()
                if row is None:
                    return None
                return Task.model_validate(row[0] if isinstance(row[0], dict) else json.loads(row[0]))
        finally:
            self._put_conn(conn)

    def set_task(self, task: Task) -> None:
        """Upsert task into Postgres."""
        if not self._available:
            return
        conn = self._get_conn()
        if conn is None:
            return
        try:
            with self._lock:
                with conn.cursor() as cur:
                    cur.execute(
                        """INSERT INTO tasks (task_id, data, state) VALUES (%s, %s, %s)
                           ON CONFLICT (task_id) DO UPDATE SET data = EXCLUDED.data, state = EXCLUDED.state, updated_at = NOW()""",
                        (task.task_id, task.model_dump_json(), task.state.value),
                    )
                conn.commit()
        finally:
            self._put_conn(conn)

    def get_task_state(self, task_id: str) -> TaskState | None:
        """Return current task state."""
        conn = self._get_conn()
        if conn is None:
            return None
        try:
            with conn.cursor() as cur:
                cur.execute("SELECT state FROM tasks WHERE task_id = %s", (task_id,))
                row = cur.fetchone()
                return TaskState(row[0]) if row else None
        finally:
            self._put_conn(conn)

    def set_task_state(self, task_id: str, state: TaskState) -> None:
        """Update task state in Postgres."""
        if not self._available:
            return
        conn = self._get_conn()
        if conn is None:
            return
        try:
            with self._lock:
                with conn.cursor() as cur:
                    cur.execute(
                        "UPDATE tasks SET state = %s, updated_at = NOW() WHERE task_id = %s",
                        (state.value, task_id),
                    )
                conn.commit()
        finally:
            self._put_conn(conn)

    def append_trace(self, task_id: str, entry: dict[str, Any]) -> None:
        """Append trace entry to Postgres."""
        if not self._available:
            return
        conn = self._get_conn()
        if conn is None:
            return
        try:
            with self._lock:
                with conn.cursor() as cur:
                    cur.execute(
                        "INSERT INTO traces (task_id, entry) VALUES (%s, %s)",
                        (task_id, json.dumps(entry)),
                    )
                conn.commit()
        finally:
            self._put_conn(conn)

    def get_trace(self, task_id: str) -> list[dict[str, Any]]:
        """Load trace entries from Postgres."""
        conn = self._get_conn()
        if conn is None:
            return []
        try:
            with conn.cursor() as cur:
                cur.execute(
                    "SELECT entry FROM traces WHERE task_id = %s ORDER BY id",
                    (task_id,),
                )
                return [
                    row[0] if isinstance(row[0], dict) else json.loads(row[0])
                    for row in cur.fetchall()
                ]
        finally:
            self._put_conn(conn)

    def list_tasks(self, state: TaskState | None = None, limit: int = 100) -> list[Task]:
        """List tasks from Postgres."""
        conn = self._get_conn()
        if conn is None:
            return []
        try:
            with conn.cursor() as cur:
                if state is not None:
                    cur.execute("SELECT data FROM tasks WHERE state = %s ORDER BY updated_at DESC LIMIT %s", (state.value, limit))
                else:
                    cur.execute("SELECT data FROM tasks ORDER BY updated_at DESC LIMIT %s", (limit,))
                return [
                    Task.model_validate(row[0] if isinstance(row[0], dict) else json.loads(row[0]))
                    for row in cur.fetchall()
                ]
        finally:
            self._put_conn(conn)

    def delete_task(self, task_id: str) -> bool:
        """Delete task and its traces from Postgres."""
        if not self._available:
            return False
        conn = self._get_conn()
        if conn is None:
            return False
        try:
            with self._lock:
                with conn.cursor() as cur:
                    cur.execute("DELETE FROM tasks WHERE task_id = %s", (task_id,))
                    deleted = cur.rowcount > 0
                conn.commit()
            return deleted
        finally:
            self._put_conn(conn)

    def count_tasks(self) -> int:
        """Count tasks in Postgres."""
        conn = self._get_conn()
        if conn is None:
            return 0
        try:
            with conn.cursor() as cur:
                cur.execute("SELECT COUNT(*) FROM tasks")
                row = cur.fetchone()
                return row[0] if row else 0
        finally:
            self._put_conn(conn)

    def close(self) -> None:
        """Close the connection pool."""
        if self._pool is not None:
            self._pool.closeall()
            self._available = False