import asyncio
import logging
from datetime import datetime, timezone
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.exc import SQLAlchemyError
from app.core.config import get_settings
from app.core.db import SessionLocal
from app.models.models import Metric, QueryStat, Target
from app.services.crypto import decrypt_secret

import asyncpg

logger = logging.getLogger(__name__)
settings = get_settings()


def build_target_dsn(target: Target) -> str:
    password = decrypt_secret(target.encrypted_password)
    return (
        f"postgresql://{target.username}:{password}"
        f"@{target.host}:{target.port}/{target.dbname}?sslmode={target.sslmode}"
    )


async def _store_metric(db: AsyncSession, target_id: int, name: str, value: float, labels: dict | None = None) -> None:
    db.add(
        Metric(
            target_id=target_id,
            ts=datetime.now(timezone.utc),
            metric_name=name,
            value=float(value),
            labels=labels or {},
        )
    )


async def collect_target(target: Target) -> None:
    dsn = build_target_dsn(target)
    conn = await asyncpg.connect(dsn=dsn)
    try:
        stat_db = await conn.fetchrow(
            """
            SELECT numbackends, xact_commit, xact_rollback, blks_hit, blks_read, tup_returned, tup_fetched
            FROM pg_stat_database
            WHERE datname = current_database()
            """
        )
        activity = await conn.fetchrow(
            """
            SELECT
              count(*) FILTER (WHERE state = 'active') AS active_connections,
              count(*) AS total_connections
            FROM pg_stat_activity
            WHERE datname = current_database()
            """
        )
        bgwriter = await conn.fetchrow(
            """
            SELECT checkpoints_timed, checkpoints_req, buffers_checkpoint, buffers_clean, maxwritten_clean
            FROM pg_stat_bgwriter
            """
        )

        if stat_db is None:
            stat_db = {
                "numbackends": 0,
                "xact_commit": 0,
                "xact_rollback": 0,
                "blks_hit": 0,
                "blks_read": 0,
                "tup_returned": 0,
                "tup_fetched": 0,
            }
        if activity is None:
            activity = {"active_connections": 0, "total_connections": 0}
        if bgwriter is None:
            bgwriter = {
                "checkpoints_timed": 0,
                "checkpoints_req": 0,
                "buffers_checkpoint": 0,
                "buffers_clean": 0,
                "maxwritten_clean": 0,
            }

        lock_count = await conn.fetchval("SELECT count(*) FROM pg_locks")
        cache_hit_ratio = 0.0
        if stat_db and (stat_db["blks_hit"] + stat_db["blks_read"]) > 0:
            cache_hit_ratio = stat_db["blks_hit"] / (stat_db["blks_hit"] + stat_db["blks_read"])

        query_rows = []
        try:
            query_rows = await conn.fetch(
                """
                SELECT queryid::text, calls, total_exec_time, mean_exec_time, rows, left(query, 2000) AS query_text
                FROM pg_stat_statements
                ORDER BY total_exec_time DESC
                LIMIT 20
                """
            )
        except Exception:
            # Extension may be disabled on monitored instance.
            query_rows = []

        async with SessionLocal() as db:
            await _store_metric(db, target.id, "connections_total", activity["total_connections"], {})
            await _store_metric(db, target.id, "connections_active", activity["active_connections"], {})
            await _store_metric(db, target.id, "xacts_total", stat_db["xact_commit"] + stat_db["xact_rollback"], {})
            await _store_metric(db, target.id, "cache_hit_ratio", cache_hit_ratio, {})
            await _store_metric(db, target.id, "locks_total", lock_count, {})
            await _store_metric(db, target.id, "checkpoints_timed", bgwriter["checkpoints_timed"], {})
            await _store_metric(db, target.id, "checkpoints_req", bgwriter["checkpoints_req"], {})

            for row in query_rows:
                db.add(
                    QueryStat(
                        target_id=target.id,
                        ts=datetime.now(timezone.utc),
                        queryid=row["queryid"] or "0",
                        calls=row["calls"] or 0,
                        total_time=row["total_exec_time"] or 0.0,
                        mean_time=row["mean_exec_time"] or 0.0,
                        rows=row["rows"] or 0,
                        query_text=row["query_text"],
                    )
                )
            await db.commit()
    finally:
        await conn.close()


async def collect_once() -> None:
    async with SessionLocal() as db:
        targets = (await db.scalars(select(Target))).all()

    for target in targets:
        try:
            await collect_target(target)
        except (OSError, SQLAlchemyError, asyncpg.PostgresError, Exception) as exc:
            logger.exception("collector_error target=%s err=%s", target.id, exc)


async def collector_loop(stop_event: asyncio.Event) -> None:
    while not stop_event.is_set():
        await collect_once()
        try:
            await asyncio.wait_for(stop_event.wait(), timeout=settings.poll_interval_seconds)
        except asyncio.TimeoutError:
            pass