"""
backlog_store.py — Engineering Backlog Storage Layer.
DAARION.city | deterministic, no LLM.

Backends:
  MemoryBacklogStore   — in-process (tests + fallback)
  JsonlBacklogStore    — filesystem append-only JSONL (MVP)
  PostgresBacklogStore — Postgres primary (psycopg2 sync)
  AutoBacklogStore     — Postgres → JSONL → Memory cascade

Factory: get_backlog_store() → respects BACKLOG_BACKEND env var.

BACKLOG_BACKEND: auto | postgres | jsonl | memory | null
"""
from __future__ import annotations

import datetime
import json
import logging
import os
import threading
import uuid
from abc import ABC, abstractmethod
from dataclasses import dataclass, field, asdict
from pathlib import Path
from typing import Any, Dict, List, Optional

logger = logging.getLogger(__name__)

# ─── Data model ───────────────────────────────────────────────────────────────

_VALID_STATUSES = {"open", "in_progress", "blocked", "done", "canceled"}
_VALID_PRIORITIES = {"P0", "P1", "P2", "P3"}


def _now_iso() -> str:
    return datetime.datetime.utcnow().isoformat()


def _new_id(prefix: str = "bl") -> str:
    return f"{prefix}_{uuid.uuid4().hex[:12]}"


@dataclass
class BacklogItem:
    id: str
    created_at: str
    updated_at: str
    env: str
    service: str
    category: str              # arch_review / refactor / slo_hardening / cleanup_followups / security
    title: str
    description: str
    priority: str              # P0..P3
    status: str                # open / in_progress / blocked / done / canceled
    owner: str
    due_date: str              # YYYY-MM-DD
    source: str                # risk | pressure | digest | manual
    dedupe_key: str
    evidence_refs: Dict = field(default_factory=dict)   # alerts, incidents, release_checks, ...
    tags: List[str] = field(default_factory=list)
    meta: Dict = field(default_factory=dict)

    def to_dict(self) -> Dict:
        return asdict(self)

    @classmethod
    def from_dict(cls, d: Dict) -> "BacklogItem":
        return cls(
            id=d.get("id", _new_id()),
            created_at=d.get("created_at", _now_iso()),
            updated_at=d.get("updated_at", _now_iso()),
            env=d.get("env", "prod"),
            service=d.get("service", ""),
            category=d.get("category", ""),
            title=d.get("title", ""),
            description=d.get("description", ""),
            priority=d.get("priority", "P2"),
            status=d.get("status", "open"),
            owner=d.get("owner", "oncall"),
            due_date=d.get("due_date", ""),
            source=d.get("source", "manual"),
            dedupe_key=d.get("dedupe_key", ""),
            evidence_refs=d.get("evidence_refs") or {},
            tags=d.get("tags") or [],
            meta=d.get("meta") or {},
        )


@dataclass
class BacklogEvent:
    id: str
    item_id: str
    ts: str
    type: str       # created | status_change | comment | auto_update
    message: str
    actor: str
    meta: Dict = field(default_factory=dict)

    def to_dict(self) -> Dict:
        return asdict(self)

    @classmethod
    def from_dict(cls, d: Dict) -> "BacklogEvent":
        return cls(
            id=d.get("id", _new_id("ev")),
            item_id=d.get("item_id", ""),
            ts=d.get("ts", _now_iso()),
            type=d.get("type", "comment"),
            message=d.get("message", ""),
            actor=d.get("actor", "system"),
            meta=d.get("meta") or {},
        )


# ─── Abstract base ────────────────────────────────────────────────────────────

class BacklogStore(ABC):
    @abstractmethod
    def create(self, item: BacklogItem) -> BacklogItem: ...

    @abstractmethod
    def get(self, item_id: str) -> Optional[BacklogItem]: ...

    @abstractmethod
    def get_by_dedupe_key(self, key: str) -> Optional[BacklogItem]: ...

    @abstractmethod
    def update(self, item: BacklogItem) -> BacklogItem: ...

    @abstractmethod
    def list_items(self, filters: Optional[Dict] = None, limit: int = 50,
                   offset: int = 0) -> List[BacklogItem]: ...

    @abstractmethod
    def add_event(self, event: BacklogEvent) -> BacklogEvent: ...

    @abstractmethod
    def get_events(self, item_id: str, limit: int = 50) -> List[BacklogEvent]: ...

    @abstractmethod
    def cleanup(self, retention_days: int = 180) -> int: ...

    def upsert(self, item: BacklogItem) -> Dict:
        """Create or update by dedupe_key. Returns {"action": created|updated, "item": ...}"""
        existing = self.get_by_dedupe_key(item.dedupe_key)
        if existing is None:
            created = self.create(item)
            return {"action": "created", "item": created}
        # Update title/description/evidence_refs/tags/meta; preserve status/owner
        existing.title = item.title
        existing.description = item.description
        existing.evidence_refs = item.evidence_refs
        existing.tags = list(set(existing.tags + item.tags))
        existing.meta.update(item.meta or {})
        existing.updated_at = _now_iso()
        updated = self.update(existing)
        return {"action": "updated", "item": updated}

    def dashboard(self, env: str = "prod") -> Dict:
        """Return aggregated backlog counts."""
        items = self.list_items({"env": env}, limit=1000)
        today = datetime.datetime.utcnow().strftime("%Y-%m-%d")
        status_counts: Dict[str, int] = {}
        priority_counts: Dict[str, int] = {}
        category_counts: Dict[str, int] = {}
        overdue: List[Dict] = []
        service_counts: Dict[str, int] = {}

        for it in items:
            status_counts[it.status] = status_counts.get(it.status, 0) + 1
            priority_counts[it.priority] = priority_counts.get(it.priority, 0) + 1
            category_counts[it.category] = category_counts.get(it.category, 0) + 1
            service_counts[it.service] = service_counts.get(it.service, 0) + 1
            if (it.status not in ("done", "canceled")
                    and it.due_date and it.due_date < today):
                overdue.append({
                    "id": it.id, "service": it.service,
                    "title": it.title, "priority": it.priority,
                    "due_date": it.due_date, "owner": it.owner,
                })

        overdue.sort(key=lambda x: (x["priority"], x["due_date"]))
        top_services = sorted(service_counts.items(), key=lambda x: -x[1])[:10]

        return {
            "env": env,
            "total": len(items),
            "status_counts": status_counts,
            "priority_counts": priority_counts,
            "category_counts": category_counts,
            "overdue": overdue[:20],
            "overdue_count": len(overdue),
            "top_services": [{"service": s, "count": c} for s, c in top_services],
        }


# ─── Workflow helper ──────────────────────────────────────────────────────────

def validate_transition(current_status: str, new_status: str,
                        policy: Optional[Dict] = None) -> bool:
    """Return True if transition is allowed, False otherwise."""
    defaults = _builtin_workflow()
    if policy is None:
        allowed = defaults
    else:
        allowed = policy.get("workflow", {}).get("allowed_transitions", defaults)
    return new_status in allowed.get(current_status, [])


def _builtin_workflow() -> Dict:
    return {
        "open":        ["in_progress", "blocked", "canceled"],
        "in_progress": ["blocked", "done", "canceled"],
        "blocked":     ["open", "in_progress", "canceled"],
        "done":        [],
        "canceled":    [],
    }


# ─── Memory backend ───────────────────────────────────────────────────────────

class MemoryBacklogStore(BacklogStore):
    def __init__(self) -> None:
        self._items: Dict[str, BacklogItem] = {}
        self._events: List[BacklogEvent] = []
        self._lock = threading.Lock()

    def create(self, item: BacklogItem) -> BacklogItem:
        with self._lock:
            self._items[item.id] = item
        return item

    def get(self, item_id: str) -> Optional[BacklogItem]:
        with self._lock:
            return self._items.get(item_id)

    def get_by_dedupe_key(self, key: str) -> Optional[BacklogItem]:
        with self._lock:
            for it in self._items.values():
                if it.dedupe_key == key:
                    return it
        return None

    def update(self, item: BacklogItem) -> BacklogItem:
        with self._lock:
            self._items[item.id] = item
        return item

    def list_items(self, filters: Optional[Dict] = None,
                   limit: int = 50, offset: int = 0) -> List[BacklogItem]:
        filters = filters or {}
        with self._lock:
            items = list(self._items.values())
        items = _apply_filters(items, filters)
        items.sort(key=lambda x: (x.priority, x.due_date or "9999"))
        return items[offset: offset + limit]

    def add_event(self, event: BacklogEvent) -> BacklogEvent:
        with self._lock:
            self._events.append(event)
        return event

    def get_events(self, item_id: str, limit: int = 50) -> List[BacklogEvent]:
        with self._lock:
            evs = [e for e in self._events if e.item_id == item_id]
        return evs[-limit:]

    def cleanup(self, retention_days: int = 180) -> int:
        cutoff = (
            datetime.datetime.utcnow() - datetime.timedelta(days=retention_days)
        ).isoformat()
        with self._lock:
            to_delete = [
                iid for iid, it in self._items.items()
                if it.status in ("done", "canceled") and it.updated_at < cutoff
            ]
            for iid in to_delete:
                del self._items[iid]
        return len(to_delete)


# ─── JSONL backend ────────────────────────────────────────────────────────────

_JSONL_ITEMS = "ops/backlog/items.jsonl"
_JSONL_EVENTS = "ops/backlog/events.jsonl"
_JSONL_CACHE_MAX = 50_000   # lines to scan


class JsonlBacklogStore(BacklogStore):
    """
    Append-only JSONL filesystem store.
    Last-write-wins: items keyed by id, updates appended (read returns latest).
    """
    def __init__(
        self,
        items_path: str = _JSONL_ITEMS,
        events_path: str = _JSONL_EVENTS,
    ) -> None:
        self._items_path = Path(items_path)
        self._events_path = Path(events_path)
        self._lock = threading.Lock()
        self._items_path.parent.mkdir(parents=True, exist_ok=True)
        self._events_path.parent.mkdir(parents=True, exist_ok=True)

    def _load_items(self) -> Dict[str, BacklogItem]:
        """Scan file, last-write-wins per id."""
        items: Dict[str, BacklogItem] = {}
        if not self._items_path.exists():
            return items
        try:
            with open(self._items_path, "r", encoding="utf-8") as f:
                for line in f:
                    line = line.strip()
                    if not line:
                        continue
                    try:
                        d = json.loads(line)
                        items[d["id"]] = BacklogItem.from_dict(d)
                    except Exception:
                        pass
        except Exception as e:
            logger.warning("JsonlBacklogStore: load_items error: %s", e)
        return items

    def _append_item(self, item: BacklogItem) -> None:
        with open(self._items_path, "a", encoding="utf-8") as f:
            f.write(json.dumps(item.to_dict(), default=str) + "\n")

    def create(self, item: BacklogItem) -> BacklogItem:
        with self._lock:
            self._append_item(item)
        return item

    def get(self, item_id: str) -> Optional[BacklogItem]:
        with self._lock:
            items = self._load_items()
        return items.get(item_id)

    def get_by_dedupe_key(self, key: str) -> Optional[BacklogItem]:
        with self._lock:
            items = self._load_items()
        for it in items.values():
            if it.dedupe_key == key:
                return it
        return None

    def update(self, item: BacklogItem) -> BacklogItem:
        item.updated_at = _now_iso()
        with self._lock:
            self._append_item(item)
        return item

    def list_items(self, filters: Optional[Dict] = None,
                   limit: int = 50, offset: int = 0) -> List[BacklogItem]:
        with self._lock:
            items = list(self._load_items().values())
        items = _apply_filters(items, filters or {})
        items.sort(key=lambda x: (x.priority, x.due_date or "9999"))
        return items[offset: offset + limit]

    def add_event(self, event: BacklogEvent) -> BacklogEvent:
        with self._lock:
            if not self._events_path.parent.exists():
                self._events_path.parent.mkdir(parents=True, exist_ok=True)
            with open(self._events_path, "a", encoding="utf-8") as f:
                f.write(json.dumps(event.to_dict(), default=str) + "\n")
        return event

    def get_events(self, item_id: str, limit: int = 50) -> List[BacklogEvent]:
        events: List[BacklogEvent] = []
        if not self._events_path.exists():
            return events
        try:
            with open(self._events_path, "r", encoding="utf-8") as f:
                for line in f:
                    line = line.strip()
                    if not line:
                        continue
                    try:
                        d = json.loads(line)
                        if d.get("item_id") == item_id:
                            events.append(BacklogEvent.from_dict(d))
                    except Exception:
                        pass
        except Exception as e:
            logger.warning("JsonlBacklogStore: get_events error: %s", e)
        return events[-limit:]

    def cleanup(self, retention_days: int = 180) -> int:
        cutoff = (
            datetime.datetime.utcnow() - datetime.timedelta(days=retention_days)
        ).isoformat()
        with self._lock:
            items = self._load_items()
            to_keep = {
                iid: it for iid, it in items.items()
                if not (it.status in ("done", "canceled") and it.updated_at < cutoff)
            }
            deleted = len(items) - len(to_keep)
            if deleted:
                # Rewrite the file
                with open(self._items_path, "w", encoding="utf-8") as f:
                    for it in to_keep.values():
                        f.write(json.dumps(it.to_dict(), default=str) + "\n")
        return deleted


# ─── Postgres backend ─────────────────────────────────────────────────────────

class PostgresBacklogStore(BacklogStore):
    """
    Postgres-backed store using psycopg2 (sync).
    Tables: backlog_items, backlog_events  (created by migration script).
    """
    def __init__(self, dsn: Optional[str] = None) -> None:
        self._dsn = dsn or os.environ.get(
            "BACKLOG_POSTGRES_DSN",
            os.environ.get("POSTGRES_DSN", "postgresql://localhost/daarion")
        )
        self._lock = threading.Lock()

    def _conn(self):
        import psycopg2
        import psycopg2.extras
        return psycopg2.connect(self._dsn)

    def create(self, item: BacklogItem) -> BacklogItem:
        sql = """
            INSERT INTO backlog_items
              (id, created_at, updated_at, env, service, category, title, description,
               priority, status, owner, due_date, source, dedupe_key,
               evidence_refs, tags, meta)
            VALUES
              (%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s)
            ON CONFLICT (dedupe_key) DO NOTHING
        """
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute(sql, (
                    item.id, item.created_at, item.updated_at,
                    item.env, item.service, item.category,
                    item.title, item.description, item.priority,
                    item.status, item.owner, item.due_date or None,
                    item.source, item.dedupe_key,
                    json.dumps(item.evidence_refs),
                    json.dumps(item.tags),
                    json.dumps(item.meta),
                ))
        return item

    def get(self, item_id: str) -> Optional[BacklogItem]:
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute("SELECT * FROM backlog_items WHERE id=%s", (item_id,))
                row = cur.fetchone()
                if row:
                    return self._row_to_item(row, cur.description)
        return None

    def get_by_dedupe_key(self, key: str) -> Optional[BacklogItem]:
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute("SELECT * FROM backlog_items WHERE dedupe_key=%s", (key,))
                row = cur.fetchone()
                if row:
                    return self._row_to_item(row, cur.description)
        return None

    def update(self, item: BacklogItem) -> BacklogItem:
        item.updated_at = _now_iso()
        sql = """
            UPDATE backlog_items SET
              updated_at=%s, title=%s, description=%s, priority=%s,
              status=%s, owner=%s, due_date=%s, evidence_refs=%s, tags=%s, meta=%s
            WHERE id=%s
        """
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute(sql, (
                    item.updated_at, item.title, item.description,
                    item.priority, item.status, item.owner,
                    item.due_date or None,
                    json.dumps(item.evidence_refs),
                    json.dumps(item.tags),
                    json.dumps(item.meta),
                    item.id,
                ))
        return item

    def list_items(self, filters: Optional[Dict] = None,
                   limit: int = 50, offset: int = 0) -> List[BacklogItem]:
        filters = filters or {}
        where, params = _pg_where_clause(filters)
        sql = f"""
            SELECT * FROM backlog_items {where}
            ORDER BY priority ASC, due_date ASC NULLS LAST
            LIMIT %s OFFSET %s
        """
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute(sql, params + [limit, offset])
                rows = cur.fetchall()
                desc = cur.description
                return [self._row_to_item(r, desc) for r in rows]

    def add_event(self, event: BacklogEvent) -> BacklogEvent:
        sql = """
            INSERT INTO backlog_events (id, item_id, ts, type, message, actor, meta)
            VALUES (%s,%s,%s,%s,%s,%s,%s)
        """
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute(sql, (
                    event.id, event.item_id, event.ts,
                    event.type, event.message, event.actor,
                    json.dumps(event.meta),
                ))
        return event

    def get_events(self, item_id: str, limit: int = 50) -> List[BacklogEvent]:
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute(
                    "SELECT * FROM backlog_events WHERE item_id=%s ORDER BY ts DESC LIMIT %s",
                    (item_id, limit)
                )
                rows = cur.fetchall()
                desc = cur.description
                return [self._row_to_event(r, desc) for r in rows]

    def cleanup(self, retention_days: int = 180) -> int:
        cutoff = (
            datetime.datetime.utcnow() - datetime.timedelta(days=retention_days)
        ).isoformat()
        with self._conn() as conn:
            with conn.cursor() as cur:
                cur.execute(
                    """DELETE FROM backlog_items
                       WHERE status IN ('done','canceled') AND updated_at < %s""",
                    (cutoff,)
                )
                return cur.rowcount

    @staticmethod
    def _row_to_item(row, description) -> BacklogItem:
        d = {col.name: val for col, val in zip(description, row)}
        for json_key in ("evidence_refs", "tags", "meta"):
            v = d.get(json_key)
            if isinstance(v, str):
                try:
                    d[json_key] = json.loads(v)
                except Exception:
                    d[json_key] = {} if json_key != "tags" else []
        return BacklogItem.from_dict(d)

    @staticmethod
    def _row_to_event(row, description) -> BacklogEvent:
        d = {col.name: val for col, val in zip(description, row)}
        if isinstance(d.get("meta"), str):
            try:
                d["meta"] = json.loads(d["meta"])
            except Exception:
                d["meta"] = {}
        return BacklogEvent.from_dict(d)


def _pg_where_clause(filters: Dict):
    clauses, params = [], []
    if filters.get("env"):
        clauses.append("env=%s"); params.append(filters["env"])
    if filters.get("service"):
        clauses.append("service=%s"); params.append(filters["service"])
    if filters.get("status"):
        if isinstance(filters["status"], list):
            ph = ",".join(["%s"] * len(filters["status"]))
            clauses.append(f"status IN ({ph})"); params.extend(filters["status"])
        else:
            clauses.append("status=%s"); params.append(filters["status"])
    if filters.get("owner"):
        clauses.append("owner=%s"); params.append(filters["owner"])
    if filters.get("category"):
        clauses.append("category=%s"); params.append(filters["category"])
    if filters.get("due_before"):
        clauses.append("due_date < %s"); params.append(filters["due_before"])
    return ("WHERE " + " AND ".join(clauses)) if clauses else "", params


# ─── Null backend ─────────────────────────────────────────────────────────────

class NullBacklogStore(BacklogStore):
    def create(self, item): return item
    def get(self, item_id): return None
    def get_by_dedupe_key(self, key): return None
    def update(self, item): return item
    def list_items(self, filters=None, limit=50, offset=0): return []
    def add_event(self, event): return event
    def get_events(self, item_id, limit=50): return []
    def cleanup(self, retention_days=180): return 0


# ─── Auto backend (Postgres → JSONL fallback) ─────────────────────────────────

class AutoBacklogStore(BacklogStore):
    """Postgres primary with JSONL fallback. Retries Postgres after 5 min."""
    _RETRY_SEC = 300

    def __init__(
        self,
        postgres_dsn: Optional[str] = None,
        jsonl_items: str = _JSONL_ITEMS,
        jsonl_events: str = _JSONL_EVENTS,
    ) -> None:
        self._pg: Optional[PostgresBacklogStore] = None
        self._jsonl = JsonlBacklogStore(jsonl_items, jsonl_events)
        self._dsn = postgres_dsn
        self._pg_failed_at: Optional[float] = None
        self._lock = threading.Lock()
        self._try_init_pg()

    def _try_init_pg(self) -> None:
        try:
            self._pg = PostgresBacklogStore(self._dsn)
            self._pg._conn().close()   # test connection
            self._pg_failed_at = None
            logger.info("AutoBacklogStore: Postgres backend active")
        except Exception as e:
            logger.warning("AutoBacklogStore: Postgres unavailable, using JSONL: %s", e)
            self._pg = None
            import time
            self._pg_failed_at = time.time()

    def _backend(self) -> BacklogStore:
        if self._pg is not None:
            return self._pg
        import time
        if (self._pg_failed_at is None
                or time.time() - self._pg_failed_at >= self._RETRY_SEC):
            self._try_init_pg()
        return self._pg if self._pg is not None else self._jsonl

    def create(self, item): return self._backend().create(item)
    def get(self, item_id): return self._backend().get(item_id)
    def get_by_dedupe_key(self, key): return self._backend().get_by_dedupe_key(key)
    def update(self, item): return self._backend().update(item)
    def list_items(self, filters=None, limit=50, offset=0):
        return self._backend().list_items(filters, limit, offset)
    def add_event(self, event): return self._backend().add_event(event)
    def get_events(self, item_id, limit=50): return self._backend().get_events(item_id, limit)
    def cleanup(self, retention_days=180): return self._backend().cleanup(retention_days)


# ─── Filters helper ───────────────────────────────────────────────────────────

def _apply_filters(items: List[BacklogItem], filters: Dict) -> List[BacklogItem]:
    result = []
    for it in items:
        if filters.get("env") and it.env != filters["env"]:
            continue
        if filters.get("service") and it.service != filters["service"]:
            continue
        if filters.get("status"):
            statuses = filters["status"] if isinstance(filters["status"], list) else [filters["status"]]
            if it.status not in statuses:
                continue
        if filters.get("owner") and it.owner != filters["owner"]:
            continue
        if filters.get("category") and it.category != filters["category"]:
            continue
        if filters.get("due_before") and it.due_date and it.due_date >= filters["due_before"]:
            continue
        result.append(it)
    return result


# ─── Factory ──────────────────────────────────────────────────────────────────

_STORE_INSTANCE: Optional[BacklogStore] = None
_STORE_LOCK = threading.Lock()


def get_backlog_store() -> BacklogStore:
    global _STORE_INSTANCE
    with _STORE_LOCK:
        if _STORE_INSTANCE is not None:
            return _STORE_INSTANCE
        backend = os.environ.get("BACKLOG_BACKEND", "auto").lower()
        if backend == "memory":
            _STORE_INSTANCE = MemoryBacklogStore()
        elif backend == "jsonl":
            _STORE_INSTANCE = JsonlBacklogStore()
        elif backend == "postgres":
            _STORE_INSTANCE = PostgresBacklogStore()
        elif backend == "null":
            _STORE_INSTANCE = NullBacklogStore()
        else:  # auto
            _STORE_INSTANCE = AutoBacklogStore()
        logger.info("backlog_store: using %s backend", type(_STORE_INSTANCE).__name__)
        return _STORE_INSTANCE


def _reset_store_for_tests() -> None:
    global _STORE_INSTANCE
    with _STORE_LOCK:
        _STORE_INSTANCE = None