import re
import uuid
from datetime import datetime, timezone


def utc_now():
    return datetime.now(timezone.utc).isoformat()


def sanitize_channel_part(value):
    return re.sub(r"[^A-Za-z0-9_.-]+", "-", str(value)).strip("-") or "unknown"


class ResponseBuilder:
    def __init__(self, settings):
        self.settings = settings

    def reply_channel_for(self, payload):
        explicit = payload.get("reply_channel") or payload.get("reply_topic")
        if explicit:
            return explicit

        user_id = sanitize_channel_part(payload.get("user_id") or payload.get("id") or "unknown")
        session_id = sanitize_channel_part(payload.get("session_id") or "default")
        return self.settings.reply_channel_template.format(user_id=user_id, session_id=session_id)

    def build_success(self, payload):
        user_id = payload.get("user_id") or payload.get("id")
        if not user_id:
            raise ValueError("payload must include user_id")

        text = payload.get("message")
        if text is None:
            raise ValueError("payload must include message")

        display_name = payload.get("name") or payload.get("username") or user_id
        correlation_id = payload.get("correlation_id") or str(uuid.uuid4())

        return {
            "type": "space.response",
            "ok": True,
            "user_id": user_id,
            "session_id": payload.get("session_id"),
            "correlation_id": correlation_id,
            "request": {"message": text},
            "message": f"Hello {display_name}",
            "created_at": utc_now(),
        }

    def build_error(self, payload, error):
        user_id = payload.get("user_id") or payload.get("id") or "unknown"
        return {
            "type": "space.response",
            "ok": False,
            "user_id": user_id,
            "session_id": payload.get("session_id"),
            "correlation_id": payload.get("correlation_id") or str(uuid.uuid4()),
            "error": str(error),
            "created_at": utc_now(),
        }