"""Governance audit normalization and tamper-evident evidence sealing."""

from __future__ import annotations

import hashlib
import hmac
import json
from datetime import UTC, datetime
from typing import Any

from app.core.common.identifiers import new_governance_uid
from app.core.data_source.redaction import redact_mapping

AUDIT_CATEGORIES = (
    "authentication",
    "ingestion",
    "entity_resolution",
    "publication",
    "remediation",
    "knowledge_query",
)
MAX_SEAL_EVENTS = 50_000


class GovernanceAuditInvalid(ValueError):
    """Raised when an audit query or seal request is invalid."""


class GovernanceAuditNotFound(LookupError):
    """Raised when a requested evidence seal does not exist."""


def _utc(value: datetime, label: str) -> datetime:
    if not isinstance(value, datetime):
        raise GovernanceAuditInvalid(f"{label} must be a datetime")
    if value.tzinfo is None:
        raise GovernanceAuditInvalid(f"{label} must include a timezone")
    return value.astimezone(UTC)


def _iso(value: datetime, label: str) -> str:
    return _utc(value, label).isoformat().replace("+00:00", "Z")


def _canonical(value: Any) -> bytes:
    return json.dumps(
        value,
        ensure_ascii=False,
        sort_keys=True,
        separators=(",", ":"),
    ).encode("utf-8")


def _digest(value: Any) -> str:
    return hashlib.sha256(_canonical(value)).hexdigest()


def _required_text(value: Any, label: str, maximum: int) -> str:
    normalized = str(value or "").strip()
    if not normalized:
        raise GovernanceAuditInvalid(f"{label} is required")
    if len(normalized) > maximum:
        raise GovernanceAuditInvalid(f"{label} exceeds {maximum} characters")
    return normalized


def _normalize_categories(categories=None) -> tuple[str, ...]:
    if categories is None:
        return AUDIT_CATEGORIES
    if isinstance(categories, str):
        categories = [categories]
    normalized = tuple(
        dict.fromkeys(str(item).strip() for item in categories if str(item).strip())
    )
    if not normalized:
        raise GovernanceAuditInvalid("at least one category is required")
    unsupported = sorted(set(normalized) - set(AUDIT_CATEGORIES))
    if unsupported:
        raise GovernanceAuditInvalid(
            f"unsupported category: {', '.join(unsupported)}"
        )
    return tuple(item for item in AUDIT_CATEGORIES if item in normalized)


def _normalize_window(period_start, period_end) -> tuple[datetime, datetime]:
    start = _utc(period_start, "period_start")
    end = _utc(period_end, "period_end")
    if end <= start:
        raise GovernanceAuditInvalid("period_end must be after period_start")
    return start, end


def _normalize_event(event: dict[str, Any]) -> dict[str, Any]:
    category = _required_text(event.get("category"), "category", 40)
    if category not in AUDIT_CATEGORIES:
        raise GovernanceAuditInvalid(f"unsupported category: {category}")
    occurred_at = event.get("occurred_at")
    return {
        "event_uid": _required_text(event.get("event_uid"), "event_uid", 160),
        "category": category,
        "action": _required_text(event.get("action"), "action", 80),
        "status": _required_text(event.get("status"), "status", 40),
        "actor_uid": str(event.get("actor_uid") or "")[:160] or None,
        "resource_type": _required_text(
            event.get("resource_type"), "resource_type", 80
        ),
        "resource_uid": str(event.get("resource_uid") or "")[:200] or None,
        "occurred_at": _iso(occurred_at, "occurred_at"),
        "safe_detail": redact_mapping(dict(event.get("safe_detail") or {})),
    }


def _event_sort_key(event: dict[str, Any]) -> tuple[str, str]:
    return event["occurred_at"], event["event_uid"]


def _root(events: list[dict[str, Any]]) -> str:
    ordered = sorted(events, key=_event_sort_key)
    return _digest([_digest(event) for event in ordered])


def _signature_payload(seal: dict[str, Any]) -> dict[str, Any]:
    return {
        "uid": seal["uid"],
        "period_start": seal["period_start"],
        "period_end": seal["period_end"],
        "categories": list(seal["categories"]),
        "event_count": int(seal["event_count"]),
        "root_hash": seal["root_hash"],
        "key_version": seal["key_version"],
        "sealed_by": seal["sealed_by"],
    }


class GovernanceAuditService:
    """Normalize distributed audit evidence and create signed evidence seals."""

    def __init__(
        self,
        repository,
        *,
        evidence_secret: str,
        key_version: str,
        uid_factory=new_governance_uid,
        now_factory=None,
    ):
        secret = str(evidence_secret or "").encode("utf-8")
        if len(secret) < 32:
            raise GovernanceAuditInvalid(
                "audit evidence secret must contain at least 32 bytes"
            )
        self.repository = repository
        self._secret = secret
        self.key_version = _required_text(key_version, "key_version", 80)
        self.uid_factory = uid_factory
        self.now_factory = now_factory or (lambda: datetime.now(UTC))

    def _events(self, *, categories, period_start, period_end):
        normalized_categories = _normalize_categories(categories)
        start, end = _normalize_window(period_start, period_end)
        events = [
            _normalize_event(event)
            for event in self.repository.fetch_events(
                categories=normalized_categories,
                period_start=start,
                period_end=end,
            )
        ]
        return normalized_categories, start, end, events

    def list_events(
        self,
        *,
        period_start,
        period_end,
        categories=None,
        action=None,
        status=None,
        page=1,
        page_size=20,
    ) -> dict[str, Any]:
        try:
            page = int(page)
            page_size = int(page_size)
        except (TypeError, ValueError) as exc:
            raise GovernanceAuditInvalid(
                "page and page_size must be integers"
            ) from exc
        if page < 1:
            raise GovernanceAuditInvalid("page must be at least 1")
        if page_size < 1 or page_size > 100:
            raise GovernanceAuditInvalid("page_size must be between 1 and 100")

        selected, start, end, events = self._events(
            categories=categories,
            period_start=period_start,
            period_end=period_end,
        )
        if action:
            events = [event for event in events if event["action"] == action]
        if status:
            events = [event for event in events if event["status"] == status]
        events.sort(key=_event_sort_key, reverse=True)
        offset = (page - 1) * page_size
        return {
            "period_start": _iso(start, "period_start"),
            "period_end": _iso(end, "period_end"),
            "categories": list(selected),
            "records": events[offset : offset + page_size],
            "page": page,
            "page_size": page_size,
            "total": len(events),
        }

    def coverage(self, *, period_start, period_end) -> dict[str, Any]:
        _, start, end, events = self._events(
            categories=AUDIT_CATEGORIES,
            period_start=period_start,
            period_end=period_end,
        )
        counts = dict.fromkeys(AUDIT_CATEGORIES, 0)
        latest = dict.fromkeys(AUDIT_CATEGORIES)
        for event in sorted(events, key=_event_sort_key):
            category = event["category"]
            counts[category] += 1
            latest[category] = event["occurred_at"]
        return {
            "period_start": _iso(start, "period_start"),
            "period_end": _iso(end, "period_end"),
            "categories": [
                {
                    "category": category,
                    "count": counts[category],
                    "latest_at": latest[category],
                    "available": counts[category] > 0,
                }
                for category in AUDIT_CATEGORIES
            ],
        }

    def _sign(self, seal: dict[str, Any]) -> str:
        return hmac.new(
            self._secret,
            _canonical(_signature_payload(seal)),
            hashlib.sha256,
        ).hexdigest()

    def create_seal(
        self,
        *,
        period_start,
        period_end,
        actor_uid,
        categories=None,
    ) -> dict[str, Any]:
        selected, start, end, events = self._events(
            categories=categories,
            period_start=period_start,
            period_end=period_end,
        )
        if end > _utc(self.now_factory(), "current_time"):
            raise GovernanceAuditInvalid(
                "evidence seal period_end cannot be in the future"
            )
        if len(events) > MAX_SEAL_EVENTS:
            raise GovernanceAuditInvalid(
                "evidence seal cannot contain more than 50,000 events"
            )
        seal = {
            "uid": self.uid_factory(),
            "period_start": _iso(start, "period_start"),
            "period_end": _iso(end, "period_end"),
            "categories": list(selected),
            "event_count": len(events),
            "root_hash": _root(events),
            "key_version": self.key_version,
            "sealed_by": _required_text(actor_uid, "actor_uid", 160),
        }
        seal["signature"] = self._sign(seal)
        return self.repository.save_seal(seal)

    def verify_seal(self, seal_uid) -> dict[str, Any]:
        seal = self.repository.get_seal(
            _required_text(seal_uid, "seal_uid", 160)
        )
        if seal is None:
            raise GovernanceAuditNotFound("evidence seal not found")
        expected_signature = self._sign(seal)
        if not hmac.compare_digest(
            expected_signature, str(seal.get("signature") or "")
        ):
            return {
                **seal,
                "integrity_status": "invalid_signature",
                "actual_event_count": None,
                "actual_root_hash": None,
            }

        categories, _, _, events = self._events(
            categories=seal["categories"],
            period_start=datetime.fromisoformat(
                seal["period_start"].replace("Z", "+00:00")
            ),
            period_end=datetime.fromisoformat(
                seal["period_end"].replace("Z", "+00:00")
            ),
        )
        actual_root = _root(events)
        intact = (
            list(categories) == list(seal["categories"])
            and len(events) == int(seal["event_count"])
            and hmac.compare_digest(actual_root, seal["root_hash"])
        )
        return {
            **seal,
            "integrity_status": "intact" if intact else "tampered",
            "actual_event_count": len(events),
            "actual_root_hash": actual_root,
        }

    def list_seals(self, *, limit=50):
        try:
            limit = int(limit)
        except (TypeError, ValueError) as exc:
            raise GovernanceAuditInvalid("limit must be an integer") from exc
        if limit < 1 or limit > 100:
            raise GovernanceAuditInvalid("limit must be between 1 and 100")
        return list(self.repository.list_seals(limit=limit))