"""Standalone AI assistant chat endpoints.

  POST   /assistant/chats              — Create new chat
  GET    /assistant/chats              — List chats (paginated, newest first)
  GET    /assistant/chats/{id}         — Get chat with messages
  POST   /assistant/chats/{id}/messages — Send message
  PATCH  /assistant/chats/{id}         — Update title, pin/unpin
  DELETE /assistant/chats/{id}         — Delete single chat
  DELETE /assistant/chats              — Bulk delete (older_than_days query param)
  GET    /assistant/retention          — Get account retention settings
  PATCH  /assistant/retention          — Update retention settings (owner only)
"""
import logging
from datetime import datetime, timezone, timedelta
from typing import Annotated, Optional
from uuid import UUID

from fastapi import APIRouter, Depends, HTTPException, Query, Request, status
from sqlalchemy import select, delete, func
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.rate_limit import limiter
from app.api.deps import get_current_active_user, get_db, require_engineer_or_admin
from app.core.config import settings
from app.core.ai_quota_service import check_ai_quota, record_ai_usage, get_user_plan
from app.models.user import User
from app.models.account import Account
from app.models.assistant_chat import AssistantChat
from app.schemas.assistant_chat import (
    ChatCreateRequest,
    ChatMessageRequest,
    ChatMessageResponse,
    ChatListResponse,
    ChatDetailResponse,
    ChatUpdateRequest,
    RetentionSettingsResponse,
    RetentionSettingsUpdate,
)
from app.schemas.copilot import SuggestedFlow
from app.services import assistant_chat_service

logger = logging.getLogger(__name__)

router = APIRouter(prefix="/assistant", tags=["assistant-chat"])


def _require_ai_enabled() -> None:
    if not settings.ai_enabled:
        raise HTTPException(
            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
            detail="AI is not configured. Set GOOGLE_AI_API_KEY or ANTHROPIC_API_KEY.",
        )


@router.post("/chats", response_model=ChatDetailResponse, status_code=201)
@limiter.limit("10/minute")
async def create_chat(
    request: Request,
    data: ChatCreateRequest,
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
    _: None = Depends(require_engineer_or_admin),
):
    """Create a new empty chat conversation."""
    chat = await assistant_chat_service.create_chat(
        user_id=current_user.id,
        account_id=current_user.account_id,
        db=db,
    )
    await db.commit()
    return ChatDetailResponse.model_validate(chat)


@router.get("/chats", response_model=list[ChatListResponse])
async def list_chats(
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
    page: int = Query(1, ge=1),
    size: int = Query(20, ge=1, le=100),
):
    """List user's chat conversations (newest first, pinned on top)."""
    offset = (page - 1) * size
    result = await db.execute(
        select(AssistantChat)
        .where(AssistantChat.user_id == current_user.id)
        .order_by(AssistantChat.pinned.desc(), AssistantChat.updated_at.desc())
        .offset(offset)
        .limit(size)
    )
    chats = result.scalars().all()
    return [ChatListResponse.model_validate(c) for c in chats]


@router.get("/chats/{chat_id}", response_model=ChatDetailResponse)
async def get_chat(
    chat_id: UUID,
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
):
    """Get a chat with full message history."""
    result = await db.execute(
        select(AssistantChat).where(
            AssistantChat.id == chat_id,
            AssistantChat.user_id == current_user.id,
        )
    )
    chat = result.scalar_one_or_none()
    if not chat:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Chat not found")
    return ChatDetailResponse.model_validate(chat)


@router.post("/chats/{chat_id}/messages", response_model=ChatMessageResponse)
@limiter.limit("10/minute")
async def post_message(
    request: Request,
    chat_id: UUID,
    data: ChatMessageRequest,
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
    _: None = Depends(require_engineer_or_admin),
):
    """Send a message and get AI response."""
    _require_ai_enabled()

    allowed, quota_status = await check_ai_quota(
        user_id=current_user.id,
        account_id=current_user.account_id,
        db=db,
        billing_anchor=current_user.ai_billing_cycle_anchor_at,
        is_super_admin=current_user.is_super_admin,
    )
    if not allowed:
        reset_key = "daily_reset_at" if quota_status.get("deny_reason") == "daily" else "monthly_reset_at"
        raise HTTPException(
            status_code=status.HTTP_429_TOO_MANY_REQUESTS,
            detail={
                "message": f"AI limit exceeded ({quota_status['deny_reason']})",
                "reset_at": quota_status.get(reset_key),
                "quota": quota_status,
            },
        )

    plan = await get_user_plan(current_user.account_id, db)

    try:
        ai_content, suggested_flows, chat = await assistant_chat_service.send_message(
            chat_id=chat_id,
            user_id=current_user.id,
            account_id=current_user.account_id,
            message=data.message,
            db=db,
        )
    except ValueError as e:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=str(e))
    except Exception as e:
        logger.exception("Assistant chat message failed: %s", e)
        await db.rollback()
        await record_ai_usage(
            user_id=current_user.id,
            account_id=current_user.account_id,
            conversation_id=None,
            generation_type="assistant_message",
            tier=plan,
            input_tokens=0,
            output_tokens=0,
            estimated_cost=0,
            succeeded=False,
            counts_toward_quota=False,
            error_code=type(e).__name__,
            extra_data={"assistant_chat_id": str(chat_id)},
            db=db,
        )
        await db.commit()
        raise HTTPException(
            status_code=status.HTTP_502_BAD_GATEWAY,
            detail=f"AI provider error ({type(e).__name__}). Please try again.",
        )

    await record_ai_usage(
        user_id=current_user.id,
        account_id=current_user.account_id,
        conversation_id=None,
        generation_type="assistant_message",
        tier=plan,
        input_tokens=chat.total_input_tokens,
        output_tokens=chat.total_output_tokens,
        estimated_cost=(
            chat.total_input_tokens * 1.0 / 1_000_000
            + chat.total_output_tokens * 5.0 / 1_000_000
        ),
        succeeded=True,
        counts_toward_quota=False,
        error_code=None,
        extra_data={"assistant_chat_id": str(chat_id)},
        db=db,
    )
    await db.commit()

    return ChatMessageResponse(
        content=ai_content,
        suggested_flows=[SuggestedFlow.model_validate(sf) for sf in suggested_flows],
    )


@router.patch("/chats/{chat_id}", response_model=ChatDetailResponse)
async def update_chat(
    chat_id: UUID,
    data: ChatUpdateRequest,
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
):
    """Update chat title or pin/unpin."""
    result = await db.execute(
        select(AssistantChat).where(
            AssistantChat.id == chat_id,
            AssistantChat.user_id == current_user.id,
        )
    )
    chat = result.scalar_one_or_none()
    if not chat:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Chat not found")

    if data.title is not None:
        chat.title = data.title
    if data.pinned is not None:
        chat.pinned = data.pinned

    await db.commit()
    return ChatDetailResponse.model_validate(chat)


@router.delete("/chats/{chat_id}", status_code=204)
async def delete_chat(
    chat_id: UUID,
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
):
    """Delete a single chat."""
    result = await db.execute(
        select(AssistantChat).where(
            AssistantChat.id == chat_id,
            AssistantChat.user_id == current_user.id,
        )
    )
    chat = result.scalar_one_or_none()
    if not chat:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Chat not found")

    await db.delete(chat)
    await db.commit()


@router.delete("/chats", status_code=204)
async def bulk_delete_chats(
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
    older_than_days: int = Query(..., ge=1),
):
    """Bulk delete chats older than N days (skips pinned)."""
    cutoff = datetime.now(timezone.utc) - timedelta(days=older_than_days)
    await db.execute(
        delete(AssistantChat).where(
            AssistantChat.user_id == current_user.id,
            AssistantChat.pinned == False,  # noqa: E712
            AssistantChat.updated_at < cutoff,
        )
    )
    await db.commit()


@router.get("/retention", response_model=RetentionSettingsResponse)
async def get_retention_settings(
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
):
    """Get account chat retention settings."""
    result = await db.execute(
        select(Account).where(Account.id == current_user.account_id)
    )
    account = result.scalar_one_or_none()
    if not account:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Account not found")

    return RetentionSettingsResponse(
        chat_retention_days=account.chat_retention_days,
        chat_retention_max_count=account.chat_retention_max_count,
    )


@router.patch("/retention", response_model=RetentionSettingsResponse)
async def update_retention_settings(
    data: RetentionSettingsUpdate,
    current_user: Annotated[User, Depends(get_current_active_user)],
    db: Annotated[AsyncSession, Depends(get_db)],
):
    """Update account chat retention settings (account owner only)."""
    result = await db.execute(
        select(Account).where(Account.id == current_user.account_id)
    )
    account = result.scalar_one_or_none()
    if not account:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Account not found")

    if account.owner_id != current_user.id and not current_user.is_super_admin:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Only the account owner can update retention settings",
        )

    if data.chat_retention_days is not None:
        account.chat_retention_days = data.chat_retention_days
    if data.chat_retention_max_count is not None:
        account.chat_retention_max_count = data.chat_retention_max_count

    await db.commit()

    return RetentionSettingsResponse(
        chat_retention_days=account.chat_retention_days,
        chat_retention_max_count=account.chat_retention_max_count,
    )