"""
backlog_generator.py — Auto-generation of Engineering Backlog items
from Platform Priority / Risk digests.
DAARION.city | deterministic, no LLM.

Public API:
  load_backlog_policy() -> Dict
  generate_from_pressure_digest(digest_data, env, ...) -> GenerateResult
  generate_from_risk_digest(digest_data, env, ...) -> GenerateResult
  _build_item_from_rule(service, rule, context, policy, week_str, env) -> BacklogItem | None
  _make_dedupe_key(prefix, week_str, env, service, category) -> str
"""
from __future__ import annotations

import datetime
import json
import logging
import yaml
from pathlib import Path
from typing import Any, Dict, List, Optional

from backlog_store import (
    BacklogItem, BacklogEvent, BacklogStore,
    _new_id, _now_iso,
)

logger = logging.getLogger(__name__)

# ─── Policy ───────────────────────────────────────────────────────────────────

_BACKLOG_POLICY_CACHE: Optional[Dict] = None
_BACKLOG_POLICY_PATHS = [
    Path("config/backlog_policy.yml"),
    Path(__file__).resolve().parent.parent.parent / "config" / "backlog_policy.yml",
]


def load_backlog_policy() -> Dict:
    global _BACKLOG_POLICY_CACHE
    if _BACKLOG_POLICY_CACHE is not None:
        return _BACKLOG_POLICY_CACHE
    for p in _BACKLOG_POLICY_PATHS:
        if p.exists():
            try:
                with open(p) as f:
                    data = yaml.safe_load(f) or {}
                _BACKLOG_POLICY_CACHE = data
                return data
            except Exception as e:
                logger.warning("Failed to load backlog_policy from %s: %s", p, e)
    _BACKLOG_POLICY_CACHE = _builtin_backlog_defaults()
    return _BACKLOG_POLICY_CACHE


def _reload_backlog_policy() -> None:
    global _BACKLOG_POLICY_CACHE
    _BACKLOG_POLICY_CACHE = None


def _builtin_backlog_defaults() -> Dict:
    return {
        "defaults": {"env": "prod", "retention_days": 180, "max_items_per_run": 50},
        "dedupe": {
            "scheme": "YYYY-WW",
            "key_fields": ["service", "category", "env"],
            "key_prefix": "platform_backlog",
        },
        "categories": {
            "arch_review":      {"priority": "P1", "due_days": 14},
            "refactor":         {"priority": "P1", "due_days": 21},
            "slo_hardening":    {"priority": "P2", "due_days": 30},
            "cleanup_followups": {"priority": "P2", "due_days": 14},
            "security":         {"priority": "P0", "due_days": 7},
        },
        "generation": {
            "weekly_from_pressure_digest": True,
            "daily_from_risk_digest": False,
            "rules": [
                {
                    "name": "arch_review_required",
                    "when": {"pressure_requires_arch_review": True},
                    "create": {
                        "category": "arch_review",
                        "title_template": "[ARCH] Review required: {service}",
                    },
                },
                {
                    "name": "high_pressure_refactor",
                    "when": {
                        "pressure_band_in": ["high", "critical"],
                        "risk_band_in": ["high", "critical"],
                    },
                    "create": {
                        "category": "refactor",
                        "title_template": "[REF] Reduce pressure & risk: {service}",
                    },
                },
                {
                    "name": "slo_violations",
                    "when": {"risk_has_slo_violations": True},
                    "create": {
                        "category": "slo_hardening",
                        "title_template": "[SLO] Fix violations: {service}",
                    },
                },
                {
                    "name": "followup_backlog",
                    "when": {"followups_overdue_gt": 0},
                    "create": {
                        "category": "cleanup_followups",
                        "title_template": "[OPS] Close overdue followups: {service}",
                    },
                },
            ],
        },
        "ownership": {
            "default_owner": "oncall",
            "overrides": {"gateway": "cto"},
        },
        "workflow": {
            "statuses": ["open", "in_progress", "blocked", "done", "canceled"],
            "allowed_transitions": {
                "open":        ["in_progress", "blocked", "canceled"],
                "in_progress": ["blocked", "done", "canceled"],
                "blocked":     ["open", "in_progress", "canceled"],
                "done":        [],
                "canceled":    [],
            },
        },
    }


# ─── Helpers ──────────────────────────────────────────────────────────────────

def _now_week() -> str:
    return datetime.datetime.utcnow().strftime("%Y-W%V")


def _make_dedupe_key(prefix: str, week_str: str, env: str,
                     service: str, category: str) -> str:
    return f"{prefix}:{week_str}:{env}:{service}:{category}"


def _due_date(due_days: int) -> str:
    return (
        datetime.datetime.utcnow() + datetime.timedelta(days=due_days)
    ).strftime("%Y-%m-%d")


def _owner_for(service: str, policy: Dict) -> str:
    overrides = policy.get("ownership", {}).get("overrides", {})
    return overrides.get(service, policy.get("ownership", {}).get("default_owner", "oncall"))


def _match_rule(rule: Dict, ctx: Dict) -> bool:
    """
    Evaluate a rule's `when` conditions against the service context dict.
    All conditions must hold (AND logic).
    """
    when = rule.get("when", {})
    for key, expected in when.items():
        if key == "pressure_requires_arch_review":
            if bool(ctx.get("pressure_requires_arch_review")) is not bool(expected):
                return False

        elif key == "pressure_band_in":
            if ctx.get("pressure_band") not in expected:
                return False

        elif key == "risk_band_in":
            if ctx.get("risk_band") not in expected:
                return False

        elif key == "risk_has_slo_violations":
            slo_v = int(ctx.get("slo_violations", 0))
            if (slo_v > 0) is not bool(expected):
                return False

        elif key == "followups_overdue_gt":
            overdue = int(ctx.get("followups_overdue", 0))
            if not (overdue > int(expected)):
                return False

    return True


def _build_description(service: str, ctx: Dict, rule: Dict) -> str:
    """Generate deterministic bullet-list description from context."""
    lines = [f"Auto-generated by Engineering Backlog Bridge — rule: {rule.get('name', '?')}.", ""]
    p_score = ctx.get("pressure_score")
    p_band = ctx.get("pressure_band")
    r_score = ctx.get("risk_score")
    r_band = ctx.get("risk_band")
    r_delta = ctx.get("risk_delta_24h")

    if p_score is not None:
        lines.append(f"- Architecture Pressure: {p_score} ({p_band})")
    if r_score is not None:
        lines.append(f"- Risk Score: {r_score} ({r_band})"
                     + (f"  Δ24h: +{r_delta}" if r_delta else ""))
    slo_v = int(ctx.get("slo_violations", 0))
    if slo_v:
        lines.append(f"- Active SLO violations: {slo_v}")
    overdue = int(ctx.get("followups_overdue", 0))
    if overdue:
        lines.append(f"- Overdue follow-ups: {overdue}")
    if ctx.get("signals_summary"):
        lines.append(f"- Pressure signals: {'; '.join(ctx['signals_summary'][:3])}")
    if ctx.get("risk_reasons"):
        lines.append(f"- Risk signals: {'; '.join(ctx['risk_reasons'][:3])}")
    return "\n".join(lines)


def _build_item_from_rule(
    service: str,
    rule: Dict,
    ctx: Dict,
    policy: Dict,
    week_str: str,
    env: str,
) -> Optional[BacklogItem]:
    """Build a BacklogItem from a matched rule and service context."""
    create_cfg = rule.get("create", {})
    category = create_cfg.get("category", "arch_review")
    title_template = create_cfg.get("title_template", "[BACKLOG] {service}")
    title = title_template.format(service=service)

    cat_cfg = policy.get("categories", {}).get(category, {})
    priority = cat_cfg.get("priority", "P2")
    due_days = int(cat_cfg.get("due_days", 14))
    owner = _owner_for(service, policy)
    prefix = policy.get("dedupe", {}).get("key_prefix", "platform_backlog")
    dedupe_key = _make_dedupe_key(prefix, week_str, env, service, category)
    description = _build_description(service, ctx, rule)

    # Gather evidence_refs from context
    evidence_refs = dict(ctx.get("evidence_refs") or {})

    return BacklogItem(
        id=_new_id("bl"),
        created_at=_now_iso(),
        updated_at=_now_iso(),
        env=env,
        service=service,
        category=category,
        title=title,
        description=description,
        priority=priority,
        status="open",
        owner=owner,
        due_date=_due_date(due_days),
        source="digest",
        dedupe_key=dedupe_key,
        evidence_refs=evidence_refs,
        tags=["auto", f"week:{week_str}", f"rule:{rule.get('name', '?')}"],
        meta={
            "rule_name": rule.get("name", ""),
            "pressure_score": ctx.get("pressure_score"),
            "risk_score": ctx.get("risk_score"),
            "week": week_str,
        },
    )


# ─── Context builder from digest ──────────────────────────────────────────────

def _build_service_context(
    service_entry: Dict,
    risk_entry: Optional[Dict] = None,
) -> Dict:
    """
    Build a unified service context dict from a platform_priority_digest
    top_pressure_services entry plus an optional risk_digest service entry.
    """
    p_score = service_entry.get("score")
    p_band = service_entry.get("band", "low")
    requires_review = bool(service_entry.get("requires_arch_review", False))
    signals_summary = service_entry.get("signals_summary", [])
    comp = service_entry.get("components", {})
    followups_overdue = int(comp.get("followups_overdue", 0))
    evidence_refs = service_entry.get("evidence_refs") or {}

    ctx: Dict[str, Any] = {
        "pressure_score": p_score,
        "pressure_band": p_band,
        "pressure_requires_arch_review": requires_review,
        "signals_summary": signals_summary,
        "followups_overdue": followups_overdue,
        "evidence_refs": dict(evidence_refs),
    }

    # Merge risk data
    if risk_entry:
        ctx["risk_score"] = risk_entry.get("score")
        ctx["risk_band"] = risk_entry.get("band", "low")
        ctx["risk_delta_24h"] = (risk_entry.get("trend") or {}).get("delta_24h")
        slo_comp = (risk_entry.get("components") or {}).get("slo") or {}
        ctx["slo_violations"] = int(slo_comp.get("violations", 0))
        ctx["risk_reasons"] = risk_entry.get("reasons", [])
        # Merge evidence_refs from risk
        risk_attrs = risk_entry.get("attribution") or {}
        risk_erefs = risk_attrs.get("evidence_refs") or {}
        for k, v in risk_erefs.items():
            if k not in ctx["evidence_refs"]:
                ctx["evidence_refs"][k] = v
    else:
        ctx.setdefault("risk_band", service_entry.get("risk_band", "low"))
        ctx.setdefault("risk_score", service_entry.get("risk_score"))
        ctx.setdefault("risk_delta_24h", service_entry.get("risk_delta_24h"))
        ctx.setdefault("slo_violations", 0)

    return ctx


# ─── Main generation function ─────────────────────────────────────────────────

def generate_from_pressure_digest(
    digest_data: Dict,
    env: str = "prod",
    *,
    store: Optional[BacklogStore] = None,
    policy: Optional[Dict] = None,
    week_str: Optional[str] = None,
    risk_digest_data: Optional[Dict] = None,
) -> Dict:
    """
    Generate backlog items from a weekly_platform_priority_digest JSON output.

    Args:
      digest_data: JSON dict from platform_priority_digest (top_pressure_services list)
      env: deployment environment
      store: backlog store (loaded from factory if None)
      policy: backlog_policy (loaded if None)
      week_str: override ISO week (defaults to digest's "week" field or current)
      risk_digest_data: optional daily risk digest JSON to enrich context

    Returns GenerateResult dict: created, updated, skipped, items
    """
    if policy is None:
        policy = load_backlog_policy()
    if store is None:
        from backlog_store import get_backlog_store
        store = get_backlog_store()

    gen_cfg = policy.get("generation", {})
    if not gen_cfg.get("weekly_from_pressure_digest", True):
        return {"created": 0, "updated": 0, "skipped": 0, "items": [],
                "skipped_reason": "weekly_from_pressure_digest disabled in policy"}

    effective_week = week_str or digest_data.get("week") or _now_week()
    max_items = int(policy.get("defaults", {}).get("max_items_per_run", 50))
    rules = gen_cfg.get("rules", [])

    # Build risk_by_service lookup
    risk_by_service: Dict[str, Dict] = {}
    if risk_digest_data:
        for rs in (risk_digest_data.get("top_services") or []):
            svc = rs.get("service", "")
            if svc:
                risk_by_service[svc] = rs

    created = updated = skipped = 0
    items_out: List[Dict] = []
    total_written = 0

    for svc_entry in (digest_data.get("top_pressure_services") or []):
        service = svc_entry.get("service", "")
        if not service:
            continue
        if total_written >= max_items:
            skipped += 1
            continue

        ctx = _build_service_context(svc_entry, risk_by_service.get(service))

        # Evaluate rules — one item per matched rule
        matched_categories: set = set()
        for rule in rules:
            try:
                if not _match_rule(rule, ctx):
                    continue
                category = rule.get("create", {}).get("category", "")
                if category in matched_categories:
                    continue   # dedupe same category within a service
                matched_categories.add(category)

                item = _build_item_from_rule(service, rule, ctx, policy,
                                             effective_week, env)
                if item is None:
                    continue

                result = store.upsert(item)
                action = result["action"]
                upserted = result["item"]

                # Emit event
                ev_type = "created" if action == "created" else "auto_update"
                store.add_event(BacklogEvent(
                    id=_new_id("ev"),
                    item_id=upserted.id,
                    ts=_now_iso(),
                    type=ev_type,
                    message=f"Auto-generated by weekly digest — rule: {rule.get('name', '?')}",
                    actor="backlog_generator",
                    meta={"week": effective_week, "rule": rule.get("name", "")},
                ))

                if action == "created":
                    created += 1
                else:
                    updated += 1
                total_written += 1
                items_out.append({
                    "id": upserted.id,
                    "service": service,
                    "category": upserted.category,
                    "status": upserted.status,
                    "action": action,
                })
            except Exception as e:
                logger.warning("backlog_generator: skip rule %s for %s: %s",
                                rule.get("name"), service, e)
                skipped += 1

    return {
        "created": created,
        "updated": updated,
        "skipped": skipped,
        "items": items_out,
        "week": effective_week,
    }


def generate_from_risk_digest(
    risk_digest_data: Dict,
    env: str = "prod",
    *,
    store: Optional[BacklogStore] = None,
    policy: Optional[Dict] = None,
    week_str: Optional[str] = None,
) -> Dict:
    """
    Optional: generate items from a daily risk digest JSON.
    Only active when generation.daily_from_risk_digest=true.
    """
    if policy is None:
        policy = load_backlog_policy()

    gen_cfg = policy.get("generation", {})
    if not gen_cfg.get("daily_from_risk_digest", False):
        return {"created": 0, "updated": 0, "skipped": 0, "items": [],
                "skipped_reason": "daily_from_risk_digest disabled in policy"}

    if store is None:
        from backlog_store import get_backlog_store
        store = get_backlog_store()

    # Convert risk digest top_services into pressure-like entries
    effective_week = week_str or _now_week()
    max_items = int(policy.get("defaults", {}).get("max_items_per_run", 50))
    rules = gen_cfg.get("rules", [])

    created = updated = skipped = 0
    items_out: List[Dict] = []
    total_written = 0

    for svc_entry in (risk_digest_data.get("top_services") or []):
        service = svc_entry.get("service", "")
        if not service or total_written >= max_items:
            skipped += 1
            continue

        # Build a minimal pressure context from risk data
        ctx: Dict = {
            "pressure_score": None,
            "pressure_band": "low",
            "pressure_requires_arch_review": False,
            "signals_summary": [],
            "followups_overdue": 0,
            "risk_score": svc_entry.get("score"),
            "risk_band": svc_entry.get("band", "low"),
            "risk_delta_24h": (svc_entry.get("trend") or {}).get("delta_24h"),
            "slo_violations": (svc_entry.get("components") or {}).get("slo", {}).get("violations", 0) if svc_entry.get("components") else 0,
            "risk_reasons": svc_entry.get("reasons", []),
            "evidence_refs": (svc_entry.get("attribution") or {}).get("evidence_refs") or {},
        }

        matched_categories: set = set()
        for rule in rules:
            try:
                if not _match_rule(rule, ctx):
                    continue
                category = rule.get("create", {}).get("category", "")
                if category in matched_categories:
                    continue
                matched_categories.add(category)

                item = _build_item_from_rule(service, rule, ctx, policy,
                                             effective_week, env)
                if item is None:
                    continue
                result = store.upsert(item)
                action = result["action"]
                upserted = result["item"]
                store.add_event(BacklogEvent(
                    id=_new_id("ev"),
                    item_id=upserted.id,
                    ts=_now_iso(),
                    type="created" if action == "created" else "auto_update",
                    message="Auto-generated from daily risk digest",
                    actor="backlog_generator",
                    meta={"week": effective_week},
                ))
                if action == "created":
                    created += 1
                else:
                    updated += 1
                total_written += 1
                items_out.append({
                    "id": upserted.id, "service": service,
                    "category": upserted.category, "status": upserted.status,
                    "action": action,
                })
            except Exception as e:
                logger.warning("backlog_generator(risk): skip rule %s for %s: %s",
                                rule.get("name"), service, e)
                skipped += 1

    return {"created": created, "updated": updated, "skipped": skipped,
            "items": items_out, "week": effective_week}