import csv
from math import ceil

from django.contrib.auth import get_user_model
from django.db.models import Q
from django.http import HttpResponse
from django.utils import timezone
from ninja import Router
from ninja.errors import HttpError

from apps.accounts.api import require_permission
from apps.audit.models import OperationAuditLog
from apps.tickets.models import Ticket, TicketAttachment, TicketComment, TicketEvent
from apps.tickets.schemas import (
    TicketAttachmentIn,
    TicketAttachmentOut,
    TicketCommentIn,
    TicketCommentOut,
    TicketIn,
    TicketListOut,
    TicketOut,
    TicketStatusIn,
    TicketUpdateIn,
)
from apps.tickets.services import transition_ticket

router = Router(tags=["tickets"])


def next_ticket_no() -> str:
    prefix = timezone.localdate().strftime("TK%Y%m%d")
    count = Ticket.objects.filter(ticket_no__startswith=prefix).count() + 1
    return f"{prefix}{count:04d}"


def serialize_ticket_user(user):
    if user is None:
        return None
    return {
        "id": user.id,
        "username": user.username,
        "display_name": user.get_full_name() or user.username,
    }


def serialize_ticket(ticket: Ticket) -> dict:
    return {
        "id": ticket.id,
        "ticket_no": ticket.ticket_no,
        "title": ticket.title,
        "description": ticket.description,
        "status": ticket.status,
        "priority": ticket.priority,
        "impact_scope": ticket.impact_scope,
        "environment": ticket.environment,
        "related_system": ticket.related_system,
        "requester_id": ticket.requester_id,
        "assignee_id": ticket.assignee_id,
        "requester": serialize_ticket_user(ticket.requester),
        "assignee": serialize_ticket_user(ticket.assignee),
        "created_at": ticket.created_at,
        "updated_at": ticket.updated_at,
    }


@router.post("", response=TicketOut)
def create_ticket(request, payload: TicketIn):
    require_permission(request, "ticket.create")
    assignee = None
    if payload.assignee_id:
        assignee = get_user_model().objects.filter(id=payload.assignee_id).first()
    ticket = Ticket.objects.create(
        ticket_no=next_ticket_no(),
        title=payload.title,
        description=payload.description,
        priority=payload.priority,
        impact_scope=payload.impact_scope,
        environment=payload.environment,
        related_system=payload.related_system,
        assignee=assignee,
        requester=request.user if request.user.is_authenticated else None,
        created_by=request.user if request.user.is_authenticated else None,
    )
    TicketEvent.objects.create(
        ticket=ticket,
        event_type="created",
        to_value={"status": ticket.status},
    )
    return serialize_ticket(ticket)


@router.get("", response=TicketListOut)
def list_tickets(
    request,
    page: int = 1,
    page_size: int = 20,
    status: str | None = None,
    priority: str | None = None,
    q: str | None = None,
    related_system: str | None = None,
    assignee_id: int | None = None,
    view: str = "all",
):
    require_permission(request, "ticket.view")
    queryset = Ticket.objects.select_related("requester", "assignee").all()
    if status:
        queryset = queryset.filter(status=status)
    if priority:
        queryset = queryset.filter(priority=priority)
    if q:
        queryset = queryset.filter(
            Q(ticket_no__icontains=q)
            | Q(title__icontains=q)
            | Q(description__icontains=q)
        )
    if related_system:
        queryset = queryset.filter(related_system__icontains=related_system)
    if assignee_id:
        queryset = queryset.filter(assignee_id=assignee_id)
    if view == "assigned_to_me":
        queryset = queryset.filter(assignee=request.user)
    if view == "created_by_me":
        queryset = queryset.filter(created_by=request.user)
    if view == "high_priority":
        queryset = queryset.filter(priority__in=["high", "urgent"])

    page = max(page, 1)
    page_size = min(max(page_size, 1), 100)
    total = queryset.count()
    total_pages = ceil(total / page_size) if total else 0
    start = (page - 1) * page_size
    end = start + page_size
    return {
        "items": [serialize_ticket(ticket) for ticket in queryset[start:end]],
        "page": page,
        "page_size": page_size,
        "total": total,
        "total_pages": total_pages,
    }


@router.get("/export")
def export_tickets(request):
    require_permission(request, "ticket.export")
    response = HttpResponse(content_type="text/csv")
    response["Content-Disposition"] = 'attachment; filename="tickets.csv"'
    writer = csv.writer(response)
    writer.writerow(["ticket_no", "title", "status", "priority", "created_at"])
    for ticket in Ticket.objects.all().order_by("ticket_no"):
        writer.writerow(
            [
                ticket.ticket_no,
                ticket.title,
                ticket.status,
                ticket.priority,
                ticket.created_at.isoformat(),
            ]
        )
    OperationAuditLog.objects.create(
        user=request.user if request.user.is_authenticated else None,
        module="tickets",
        action="export",
        target_type="ticket",
        result="success",
        request_snapshot={},
    )
    return response


@router.get("/{ticket_id}", response=TicketOut)
def get_ticket(request, ticket_id: int):
    require_permission(request, "ticket.view")
    return serialize_ticket(
        Ticket.objects.select_related("requester", "assignee").get(id=ticket_id)
    )


@router.patch("/{ticket_id}", response=TicketOut)
def update_ticket(request, ticket_id: int, payload: TicketUpdateIn):
    require_permission(request, "ticket.edit")
    ticket = Ticket.objects.get(id=ticket_id)
    before = {
        "title": ticket.title,
        "priority": ticket.priority,
        "impact_scope": ticket.impact_scope,
        "environment": ticket.environment,
        "related_system": ticket.related_system,
    }
    for field, value in payload.dict(exclude_unset=True).items():
        if field == "assignee_id":
            user = get_user_model().objects.filter(id=value).first() if value else None
            ticket.assignee = user
        else:
            setattr(ticket, field, value)
    ticket.save()
    TicketEvent.objects.create(
        ticket=ticket,
        event_type="updated",
        from_value=before,
        to_value=payload.dict(exclude_unset=True),
        operator=request.user if request.user.is_authenticated else None,
    )
    return serialize_ticket(ticket)


@router.post("/{ticket_id}/status", response=TicketOut)
def update_ticket_status(request, ticket_id: int, payload: TicketStatusIn):
    require_permission(request, "ticket.edit")
    if not payload.remark.strip():
        raise HttpError(400, "Transition remark is required")
    ticket = Ticket.objects.get(id=ticket_id)
    updated = transition_ticket(
        ticket,
        payload.status,
        payload.remark,
        request.user if request.user.is_authenticated else None,
    )
    return serialize_ticket(updated)


@router.post("/{ticket_id}/comments", response=TicketCommentOut)
def add_ticket_comment(request, ticket_id: int, payload: TicketCommentIn):
    require_permission(request, "ticket.edit")
    ticket = Ticket.objects.get(id=ticket_id)
    comment = TicketComment.objects.create(
        ticket=ticket,
        content=payload.content,
        comment_type=payload.comment_type,
        visibility=payload.visibility,
        created_by=request.user if request.user.is_authenticated else None,
    )
    TicketEvent.objects.create(
        ticket=ticket,
        event_type="commented",
        to_value={"comment_id": comment.id, "comment_type": comment.comment_type},
        operator=request.user if request.user.is_authenticated else None,
    )
    return comment


@router.post("/{ticket_id}/attachments", response=TicketAttachmentOut)
def add_ticket_attachment(request, ticket_id: int, payload: TicketAttachmentIn):
    require_permission(request, "ticket.edit")
    ticket = Ticket.objects.get(id=ticket_id)
    attachment = TicketAttachment.objects.create(ticket=ticket, **payload.dict())
    TicketEvent.objects.create(
        ticket=ticket,
        event_type="attachment_added",
        to_value={"attachment_id": attachment.id, "file_name": attachment.file_name},
    )
    return attachment