"""Entity history service — record, query, restore, and undo entity snapshots."""

from __future__ import annotations

import uuid
from datetime import UTC, datetime
from typing import Any

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.visibility import apply_visibility_filter, check_single_entity_access
from app.models.entity_history import EntityHistory


async def record_history(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    user_id: uuid.UUID | None,
    entity_type: str,
    entity_id: uuid.UUID,
    action: str,
    snapshot_before: dict[str, Any] | None = None,
    snapshot_after: dict[str, Any] | None = None,
    changes: dict[str, Any] | None = None,
) -> EntityHistory:
    """Create a history entry for a CRUD action."""
    entry = EntityHistory(
        tenant_id=tenant_id,
        user_id=user_id,
        entity_type=entity_type,
        entity_id=entity_id,
        action=action,
        snapshot_before=snapshot_before,
        snapshot_after=snapshot_after,
        changes=changes,
        owner_id=user_id,
    )
    db.add(entry)
    await db.flush()
    return entry


async def get_entity_history(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    entity_type: str,
    entity_id: uuid.UUID,
    limit: int = 50,
    user_id: uuid.UUID | None = None,
    is_system_admin: bool = False,
) -> list[EntityHistory]:
    """Get all history entries for an entity, newest first."""
    q = (
        select(EntityHistory)
        .where(
            EntityHistory.tenant_id == tenant_id,
            EntityHistory.entity_type == entity_type,
            EntityHistory.entity_id == entity_id,
        )
        .order_by(EntityHistory.created_at.desc())
        .limit(limit)
    )
    if user_id and not is_system_admin:
        q = await apply_visibility_filter(
            db, q, "entity_history", EntityHistory, user_id, tenant_id, is_system_admin
        )
    result = await db.execute(q)
    return list(result.scalars().all())


async def get_history_entry(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    history_id: uuid.UUID,
    user_id: uuid.UUID | None = None,
    is_system_admin: bool = False,
) -> EntityHistory | None:
    """Get a specific history entry by ID."""
    q = select(EntityHistory).where(
        EntityHistory.id == history_id,
        EntityHistory.tenant_id == tenant_id,
    )
    result = await db.execute(q)
    entry = result.scalar_one_or_none()
    if entry is None:
        return None
    if user_id and not is_system_admin:
        has_access = await check_single_entity_access(
            db, "entity_history", entry.id, user_id, tenant_id, "read", is_system_admin
        )
        if not has_access:
            raise PermissionError("No access")
    return entry


async def restore_from_history(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    history_id: uuid.UUID,
    user_id: uuid.UUID,
    is_system_admin: bool = False,
) -> dict[str, Any]:
    """Restore an entity to a previous snapshot state.

    For 'delete' actions: un-delete the entity (clear deleted_at).
    For 'update' actions: revert entity fields to snapshot_before.
    For 'create' actions: soft-delete the entity (undo creation).

    Uses the RestoreRegistry to find the entity configuration.
    Only explicitly registered entity types can be restored.

    Returns the restored data dict.
    """
    from app.core.restore_registry import get_restore_registry

    entry = await get_history_entry(db, tenant_id, history_id, user_id, is_system_admin)
    if entry is None:
        raise ValueError("History entry not found")

    entity_type = entry.entity_type
    entity_id = entry.entity_id
    action = entry.action

    # Look up restore configuration from registry
    config = get_restore_registry().get(entity_type)
    if config is None:
        raise ValueError(f"Unsupported entity type for restore: {entity_type}")

    # Load entity from database
    model_class = config.model_class
    q = select(model_class).where(
        model_class.id == entity_id,
        model_class.tenant_id == tenant_id,
    )
    result = await db.execute(q)
    entity = result.scalar_one_or_none()

    # Use special handler if registered (e.g. Mail with IMAP semantics)
    if config.special_handler is not None:
        context = {
            "user_id": user_id,
            "tenant_id": tenant_id,
            "is_system_admin": is_system_admin,
            "history_entry": entry,
        }
        snapshot = entry.snapshot_before if entry.snapshot_before else {}
        return await config.special_handler(db, entity, action, snapshot, context)

    # Generic restore logic

    if action == "delete":
        if entity is None:
            raise ValueError("Entity not found for restore")
        entity.deleted_at = None
        if hasattr(entity, "updated_by"):
            entity.updated_by = user_id
        await db.flush()
        return _serialize_entity(entity, entity_type)

    elif action == "update":
        if entity is None:
            raise ValueError("Entity not found for restore")
        if entry.snapshot_before is None:
            raise ValueError("No snapshot_before available for restore")
        excluded = config.all_excluded_fields
        for key, value in entry.snapshot_before.items():
            if hasattr(entity, key) and key not in excluded:
                setattr(entity, key, value)
        if hasattr(entity, "updated_by"):
            entity.updated_by = user_id
        await db.flush()
        return _serialize_entity(entity, entity_type)

    elif action == "create":
        if entity is None:
            raise ValueError("Entity not found for restore")
        entity.deleted_at = datetime.now(UTC)
        if hasattr(entity, "updated_by"):
            entity.updated_by = user_id
        await db.flush()
        return _serialize_entity(entity, entity_type)

    raise ValueError(f"Unsupported action for restore: {action}")


def _serialize_entity(entity: Any, entity_type: str) -> dict[str, Any]:
    """Serialize an entity to a dict for restore response.

    For contacts, uses the detailed serializer with contact_persons.
    For other entities, uses a generic column-based serializer.
    """
    if entity_type == "contact":
        from app.services.contact_service import _serialize_contact_detail

        # This is called after flush, entity is still in session
        # but we need to reload with the relationship
        return _serialize_contact_detail(entity)

    # Generic serialization: extract column values
    result: dict[str, Any] = {}
    for column in entity.__table__.columns:
        val = getattr(entity, column.name, None)
        if val is not None:
            if hasattr(val, "isoformat"):
                result[column.name] = val.isoformat()
            elif hasattr(val, "hex"):
                result[column.name] = str(val)
            else:
                result[column.name] = val
    result["_entity_type"] = entity_type
    result["_restored"] = True
    return result


async def undo_last_action(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    user_id: uuid.UUID,
    entity_type: str,
    entity_id: uuid.UUID,
    is_system_admin: bool = False,
) -> dict[str, Any]:
    """Undo the most recent action for an entity.

    Returns the restored entity data.
    Raises ValueError if no history exists.
    """
    q = (
        select(EntityHistory)
        .where(
            EntityHistory.tenant_id == tenant_id,
            EntityHistory.entity_type == entity_type,
            EntityHistory.entity_id == entity_id,
        )
        .order_by(EntityHistory.created_at.desc())
        .limit(1)
    )
    if not is_system_admin:
        q = await apply_visibility_filter(
            db, q, "entity_history", EntityHistory, user_id, tenant_id, is_system_admin
        )
    result = await db.execute(q)
    entry = result.scalar_one_or_none()
    if entry is None:
        raise ValueError("No history found for this entity")

    return await restore_from_history(db, tenant_id, entry.id, user_id, is_system_admin)


async def list_trash(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    entity_type: str | None = None,
    limit: int = 50,
    offset: int = 0,
    user_id: uuid.UUID | None = None,
    is_system_admin: bool = False,
) -> dict[str, Any]:
    """List deleted entities from history (delete actions only).

    Returns paginated trash items with entity_type filter.
    """
    q = (
        select(EntityHistory)
        .where(
            EntityHistory.tenant_id == tenant_id,
            EntityHistory.action == "delete",
        )
        .order_by(EntityHistory.created_at.desc())
    )
    if entity_type:
        q = q.where(EntityHistory.entity_type == entity_type)
    if user_id and not is_system_admin:
        q = await apply_visibility_filter(
            db, q, "entity_history", EntityHistory, user_id, tenant_id, is_system_admin
        )

    # Count total
    from sqlalchemy import func as sa_func
    count_q = select(sa_func.count()).select_from(q.subquery())
    total = (await db.execute(count_q)).scalar() or 0

    # Paginate
    q = q.offset(offset).limit(limit)
    result = await db.execute(q)
    entries = result.scalars().all()

    items = []
    for e in entries:
        items.append({
            "history_id": str(e.id),
            "entity_type": e.entity_type,
            "entity_id": str(e.entity_id),
            "snapshot_before": e.snapshot_before,
            "deleted_at": e.created_at.isoformat() if e.created_at else None,
            "user_id": str(e.user_id) if e.user_id else None,
        })

    return {"items": items, "total": total, "limit": limit, "offset": offset}


async def bulk_restore(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    history_ids: list[uuid.UUID],
    user_id: uuid.UUID,
    is_system_admin: bool = False,
) -> dict[str, Any]:
    """Restore multiple entities from history entries.

    Returns partial_success semantics: if some fail, others still succeed.
    """
    results = []
    succeeded = 0
    failed = 0

    for hid in history_ids:
        try:
            restored = await restore_from_history(db, tenant_id, hid, user_id, is_system_admin)
            succeeded += 1
            results.append({
                "history_id": str(hid),
                "success": True,
                "entity_type": restored.get("_entity_type") or restored.get("entity_type"),
                "entity_id": restored.get("id"),
                "error": None,
            })
        except Exception as exc:
            failed += 1
            results.append({
                "history_id": str(hid),
                "success": False,
                "entity_type": None,
                "entity_id": None,
                "error": str(exc),
            })

    return {
        "total": len(history_ids),
        "succeeded": succeeded,
        "failed": failed,
        "results": results,
        "partial_success": failed > 0 and succeeded > 0,
    }


async def archive_old_history(
    db: AsyncSession,
    tenant_id: uuid.UUID,
    days: int = 90,
) -> int:
    """Archive (hard-delete) EntityHistory entries older than *days* days.

    GDPR compliance: after retention period, history snapshots are purged.
    Returns the number of archived entries.
    """
    from datetime import timedelta

    from sqlalchemy import delete as sa_delete

    cutoff = datetime.now(UTC) - timedelta(days=days)
    stmt = sa_delete(EntityHistory).where(
        EntityHistory.tenant_id == tenant_id,
        EntityHistory.created_at < cutoff,
    )
    result = await db.execute(stmt)
    await db.flush()
    return result.rowcount or 0