"""
Admin API endpoints for DocuVault.

All handlers require get_current_admin (SEC-07, D-08) — no handler uses
get_current_user alone.

Implements:
  GET    /api/admin/users                    — list all users (ADMIN-01)
  POST   /api/admin/users                    — create user (ADMIN-01)
  PATCH  /api/admin/users/{id}/status        — deactivate/reactivate (ADMIN-02)
  POST   /api/admin/users/{id}/password-reset — initiate reset email (ADMIN-03)
  GET    /api/admin/users/{id}/quota          — view quota (ADMIN-04)
  PATCH  /api/admin/users/{id}/quota          — adjust quota (ADMIN-04)
  PATCH  /api/admin/users/{id}/ai-config      — assign AI provider/model (ADMIN-05)

Security invariants:
  - Every handler injects Depends(get_current_admin) — verified by grep count
  - _user_to_dict() whitelist helper prevents accidental field leakage (T-02-27)
  - No impersonation endpoint — ADMIN-07 enforced by omission (T-02-28)
  - Admin-created users: password_must_change=True (ADMIN-01, T-02-32)
  - Deactivation of sole admin prevented (T-02-29)
  - Password reset sends email via Celery; does not return token (T-02-30)
"""
from __future__ import annotations

import re
import uuid
from datetime import datetime
from typing import Optional

from fastapi import APIRouter, Depends, HTTPException, Request, status
from pydantic import BaseModel, EmailStr, field_validator
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession

from db.models import CloudConnection, Document, Quota, RefreshToken, Topic, User
from deps.auth import get_current_admin
from deps.db import get_db
from services.audit import write_audit_log
from services.auth import hash_password, revoke_all_refresh_tokens, verify_password
from storage import get_storage_backend, get_storage_backend_for_document

router = APIRouter(prefix="/api/admin", tags=["admin"])

# ── Constants ─────────────────────────────────────────────────────────────────

_DEFAULT_QUOTA_BYTES = 104857600  # 100 MB free-tier default (D-06)

_PASSWORD_DETAIL = (
    "Password must be at least 12 characters and include uppercase, "
    "lowercase, a number, and a special character."
)


# ── Safe response helper ──────────────────────────────────────────────────────

def _user_to_dict(user: User) -> dict:
    """Return a safe subset of User fields — never includes password_hash,
    credentials_enc, totp_secret, or any document content (T-02-27, SEC-07).
    """
    return {
        "id": str(user.id),
        "handle": user.handle,
        "email": user.email,
        "role": user.role,
        "is_active": user.is_active,
        "totp_enabled": user.totp_enabled,
        "ai_provider": user.ai_provider,
        "ai_model": user.ai_model,
        "password_must_change": user.password_must_change,
        "created_at": user.created_at.isoformat() if user.created_at else None,
    }


# ── Password strength helper ──────────────────────────────────────────────────

def _validate_password_strength(password: str) -> None:
    """Raise ValueError with the spec message if password fails any strength rule.

    Rules (AUTH-01): min 12 chars, has uppercase, has lowercase, has digit,
    has special char (non-alphanumeric).
    """
    if len(password) < 12:
        raise ValueError(_PASSWORD_DETAIL)
    if not re.search(r"[A-Z]", password):
        raise ValueError(_PASSWORD_DETAIL)
    if not re.search(r"[a-z]", password):
        raise ValueError(_PASSWORD_DETAIL)
    if not re.search(r"[0-9]", password):
        raise ValueError(_PASSWORD_DETAIL)
    if not re.search(r"[^A-Za-z0-9]", password):
        raise ValueError(_PASSWORD_DETAIL)


# ── Request models ────────────────────────────────────────────────────────────

class UserCreate(BaseModel):
    handle: str
    email: EmailStr
    password: str
    role: str = "user"

    @field_validator("password")
    @classmethod
    def password_strength(cls, v: str) -> str:
        try:
            _validate_password_strength(v)
        except ValueError as exc:
            raise ValueError(str(exc)) from exc
        return v


class UserStatusUpdate(BaseModel):
    is_active: bool


class QuotaUpdate(BaseModel):
    limit_bytes: int

    @field_validator("limit_bytes")
    @classmethod
    def must_be_positive(cls, v: int) -> int:
        if v <= 0:
            raise ValueError("limit_bytes must be greater than 0")
        return v


class AiConfigUpdate(BaseModel):
    ai_provider: Optional[str] = None
    ai_model: Optional[str] = None


class SystemTopicCreate(BaseModel):
    """Request model for admin system topic creation (D-09)."""

    name: str
    description: str = ""
    color: str = "#6366f1"


class UserDeleteConfirm(BaseModel):
    """Admin password confirmation required before hard-deleting a user (ADMIN-02, T-05-11-01)."""

    admin_password: str


# ── SEC-08: Safe CloudConnection response model ───────────────────────────────

class CloudConnectionOut(BaseModel):
    """SEC-08: credentials_enc deliberately excluded from this response model.

    Any admin or user endpoint returning CloudConnection ORM objects MUST use
    this model to prevent accidental exposure of encrypted credentials.
    Safe-by-default: whitelist of allowed fields (not blacklist).

    Note: id is declared as str and coerced via validator so UUID ORM values
    serialize correctly without json_encoders (Rule 1 fix — T-05-06 test suite).
    """

    id: str
    provider: str
    display_name: str
    status: str
    connected_at: datetime
    model_config = {"from_attributes": True}

    @field_validator("id", mode="before")
    @classmethod
    def coerce_id_to_str(cls, v) -> str:
        """Coerce UUID objects to str so the model validates from ORM instances."""
        return str(v)


# ── Endpoints ─────────────────────────────────────────────────────────────────


@router.get("/users")
async def list_users(
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """List all users, ordered by created_at DESC.

    Response shape: { items: [...safe user fields...] }
    Never includes password_hash, credentials_enc, or document content (T-02-27).
    """
    result = await session.execute(
        select(User).order_by(User.created_at.desc())
    )
    users = result.scalars().all()
    return {"items": [_user_to_dict(u) for u in users]}


@router.post("/users", status_code=status.HTTP_201_CREATED)
async def create_user(
    request: Request,
    body: UserCreate,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """Admin creates a new user account (ADMIN-01).

    - password_must_change=True forces the user to change their password on
      first login (T-02-32, D-06).
    - Quota row initialized at 100 MB (D-06).
    - Returns 409 if email or handle is already taken.
    """
    # Check uniqueness
    existing_email = await session.execute(
        select(User).where(User.email == str(body.email))
    )
    if existing_email.scalar_one_or_none() is not None:
        raise HTTPException(
            status_code=status.HTTP_409_CONFLICT,
            detail="Email already registered",
        )

    existing_handle = await session.execute(
        select(User).where(User.handle == body.handle)
    )
    if existing_handle.scalar_one_or_none() is not None:
        raise HTTPException(
            status_code=status.HTTP_409_CONFLICT,
            detail="Handle already taken",
        )

    new_user = User(
        id=uuid.uuid4(),
        handle=body.handle,
        email=str(body.email),
        password_hash=hash_password(body.password),
        role=body.role,
        is_active=True,
        totp_enabled=False,
        password_must_change=True,  # ADMIN-01: force password change on first login
    )
    session.add(new_user)

    quota = Quota(
        user_id=new_user.id,
        limit_bytes=_DEFAULT_QUOTA_BYTES,
        used_bytes=0,
    )
    session.add(quota)
    # D-13: admin user created event
    _ip = request.headers.get("X-Forwarded-For") or (request.client.host if request.client else None)
    await write_audit_log(
        session,
        event_type="admin.user_created",
        user_id=new_user.id,
        actor_id=_admin.id,
        resource_id=new_user.id,
        ip_address=_ip,
    )
    await session.commit()

    return {
        "id": str(new_user.id),
        "handle": new_user.handle,
        "email": new_user.email,
        "role": new_user.role,
        "created_at": new_user.created_at.isoformat() if new_user.created_at else None,
    }


@router.patch("/users/{user_id}/status")
async def update_user_status(
    user_id: uuid.UUID,
    body: UserStatusUpdate,
    request: Request,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """Deactivate or reactivate a user account (ADMIN-02).

    - Prevents deactivating the last active admin (T-02-29).
    - On deactivation: all refresh tokens are revoked (family revocation).
    """
    user = await session.get(User, user_id)
    if user is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")

    # Guard: cannot deactivate the only remaining active admin (T-02-29)
    if not body.is_active and user.role == "admin":
        count_result = await session.execute(
            select(func.count(User.id)).where(
                User.role == "admin",
                User.is_active.is_(True),
            )
        )
        active_admin_count = count_result.scalar_one()
        if active_admin_count <= 1:
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail="Cannot deactivate the only admin",
            )

    _ip = request.headers.get("X-Forwarded-For") or (request.client.host if request.client else None)
    user.is_active = body.is_active

    if not body.is_active:
        # Revoke all refresh tokens on deactivation
        await revoke_all_refresh_tokens(session, user.id)

    session.add(user)

    # D-13: user deactivated/activated event
    _event = "admin.user_deactivated" if not body.is_active else "admin.user_activated"
    await write_audit_log(
        session,
        event_type=_event,
        user_id=user.id,
        actor_id=_admin.id,
        resource_id=user.id,
        ip_address=_ip,
    )
    await session.commit()

    return {
        "id": str(user.id),
        "handle": user.handle,
        "email": user.email,
        "is_active": user.is_active,
    }


@router.post("/users/{user_id}/password-reset", status_code=status.HTTP_202_ACCEPTED)
async def initiate_password_reset(
    user_id: uuid.UUID,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """Admin initiates a password reset for a user (ADMIN-03).

    Sends the reset email via Celery. Does NOT:
      - return a reset token (T-02-30)
      - grant admin access to the account
      - log in as the target user (ADMIN-07 — no impersonation)

    Returns 202 immediately regardless of email delivery status.
    """
    user = await session.get(User, user_id)
    if user is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")

    from services.auth import create_password_reset_token  # noqa: PLC0415
    from config import settings as _settings  # noqa: PLC0415

    reset_token = create_password_reset_token(str(user.id))
    reset_link = f"{_settings.frontend_url}/password-reset/confirm?token={reset_token}"

    # Deferred import to avoid circular imports (same pattern as document_tasks)
    from tasks.email_tasks import send_reset_email  # noqa: PLC0415
    send_reset_email.delay(user.email, reset_link)

    return {"message": "Password reset email sent"}


@router.get("/users/{user_id}/quota")
async def get_user_quota(
    user_id: uuid.UUID,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """Return quota details for a user (ADMIN-04).

    Quota info is admin-visible operational data — no PII, no document content
    (T-02-31 disposition: accept).
    """
    quota = await session.get(Quota, user_id)
    if quota is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Quota not found")

    return {
        "user_id": str(quota.user_id),
        "limit_bytes": quota.limit_bytes,
        "used_bytes": quota.used_bytes,
        "limit_mb": quota.limit_bytes // 1048576,
        "used_mb": quota.used_bytes // 1048576,
    }


@router.patch("/users/{user_id}/quota")
async def update_user_quota(
    user_id: uuid.UUID,
    body: QuotaUpdate,
    request: Request,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """Adjust a user's storage quota (ADMIN-04).

    If the new limit is below current usage, still applies the change but
    returns warning=True with an explanatory message. Uploads will be blocked
    but existing documents are preserved.
    """
    quota = await session.get(Quota, user_id)
    if quota is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Quota not found")

    warning = body.limit_bytes < quota.used_bytes
    warning_message = (
        "New limit is below current usage. Uploads will be blocked but existing documents are preserved."
        if warning
        else None
    )

    _ip = request.headers.get("X-Forwarded-For") or (request.client.host if request.client else None)
    old_limit = quota.limit_bytes
    quota.limit_bytes = body.limit_bytes
    session.add(quota)

    # D-13: quota changed event
    await write_audit_log(
        session,
        event_type="admin.quota_changed",
        user_id=user_id,
        actor_id=_admin.id,
        resource_id=None,
        ip_address=_ip,
        metadata_={"old_bytes": old_limit, "new_bytes": body.limit_bytes},
    )
    await session.commit()

    response: dict = {
        "user_id": str(quota.user_id),
        "limit_bytes": quota.limit_bytes,
        "used_bytes": quota.used_bytes,
        "warning": warning,
    }
    if warning_message:
        response["message"] = warning_message
    return response


@router.patch("/users/{user_id}/ai-config")
async def update_ai_config(
    user_id: uuid.UUID,
    body: AiConfigUpdate,
    request: Request,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """Assign AI provider and model for a user (ADMIN-05).

    Users cannot change their own AI provider or model (PROJECT.md Key Decision).
    Only admins have this capability.
    """
    user = await session.get(User, user_id)
    if user is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")

    _ip = request.headers.get("X-Forwarded-For") or (request.client.host if request.client else None)
    user.ai_provider = body.ai_provider
    user.ai_model = body.ai_model
    session.add(user)

    # D-13: AI provider assigned event
    await write_audit_log(
        session,
        event_type="admin.ai_provider_assigned",
        user_id=user_id,
        actor_id=_admin.id,
        resource_id=None,
        ip_address=_ip,
        metadata_={"provider": body.ai_provider, "model": body.ai_model},
    )
    await session.commit()

    return {
        "id": str(user.id),
        "email": user.email,
        "ai_provider": user.ai_provider,
        "ai_model": user.ai_model,
    }


@router.delete("/users/{user_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_user(
    user_id: uuid.UUID,
    body: UserDeleteConfirm,
    request: Request,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> None:
    """Delete a user account and clean up all their MinIO objects (SEC-09, D-19).

    Security invariants:
      - Admin password verified via Argon2 before any deletion (T-05-11-01)
      - Cannot delete admin accounts (T-04-07-04)
      - MinIO objects are deleted BEFORE DB records are removed (SEC-09)
      - MinIO deletion is best-effort (try/except) — DB row is deleted regardless
      - Audit log written with event_type="admin.user_deleted"
    """
    # T-05-11-01: Verify admin password before performing any destructive action.
    # Fail fast — no DB reads for the target user until the admin is confirmed.
    if not verify_password(body.admin_password, _admin.password_hash):
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Invalid admin password",
        )

    user = await session.get(User, user_id)
    if user is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")

    # T-04-07-04: Cannot delete admin accounts
    if user.role == "admin":
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Cannot delete admin accounts",
        )

    _ip = request.headers.get("X-Forwarded-For") or (request.client.host if request.client else None)

    # SEC-09 (cloud): purge cloud-stored documents and credentials BEFORE DB delete.
    # Must run before MinIO cleanup so that credentials are still available to build
    # the cloud backend instances for delete_object calls.
    cloud_conns_result = await session.execute(
        select(CloudConnection).where(CloudConnection.user_id == user_id)
    )
    cloud_conns = cloud_conns_result.scalars().all()
    for conn in cloud_conns:
        # Delete cloud objects stored in this provider for this user
        cloud_docs_result = await session.execute(
            select(Document).where(
                Document.user_id == user_id,
                Document.storage_backend == conn.provider,
            )
        )
        for doc in cloud_docs_result.scalars().all():
            try:
                backend = await get_storage_backend_for_document(doc, user, session)
                await backend.delete_object(doc.object_key)
            except Exception:
                pass  # Best-effort cloud object cleanup; deletion proceeds regardless
        # Purge the credentials row (FK cascade would also remove it, but explicit
        # deletion here guarantees credentials_enc is gone before commit — SEC-09)
        await session.delete(conn)
    if cloud_conns:
        await session.flush()  # Flush connection deletes before user delete
        await write_audit_log(
            session,
            event_type="cloud.credentials_purged",
            user_id=user_id,
            actor_id=_admin.id,
            resource_id=user_id,
            ip_address=_ip,
            metadata_={"providers": [c.provider for c in cloud_conns]},
        )

    # SEC-09 (minio): collect all user documents and delete MinIO objects BEFORE DB delete
    docs_result = await session.execute(
        select(Document).where(Document.user_id == user_id)
    )
    user_docs = docs_result.scalars().all()

    storage = get_storage_backend()
    for doc in user_docs:
        try:
            await storage.delete_object(doc.object_key)
        except Exception:
            pass  # Best-effort MinIO cleanup; DB deletion proceeds regardless

    # D-13: audit log BEFORE deleting the user row (user FK still valid at flush time)
    await write_audit_log(
        session,
        event_type="admin.user_deleted",
        user_id=user_id,
        actor_id=_admin.id,
        resource_id=user_id,
        ip_address=_ip,
    )
    await session.flush()

    # Delete user record (CASCADE removes quota, documents, refresh_tokens, etc.)
    await session.delete(user)
    await session.commit()


@router.post("/topics", status_code=status.HTTP_201_CREATED)
async def create_system_topic(
    body: SystemTopicCreate,
    session: AsyncSession = Depends(get_db),
    _admin: User = Depends(get_current_admin),
) -> dict:
    """Create a system topic visible to all users (D-09, DOC-04).

    System topics have user_id = NULL, making them visible to every user as
    defaults in their topic namespace. Only admins can create system topics.
    Regular users create per-user topics via POST /api/topics.

    Deduplication: case-insensitive match within the system namespace (user_id IS NULL).
    Returns the existing system topic if one with the same name already exists.
    """
    from services import storage  # noqa: PLC0415

    topic = await storage.create_topic(
        session, body.name, body.description, body.color, user_id=None
    )
    return topic