"""Message router — routes inbound messages to the correct agent."""

from __future__ import annotations

import re

from xtrm_agent.bus import InboundMessage


class Router:
    """Routes messages to agents based on mentions, channel defaults, or delegation."""

    def __init__(
        self,
        agent_names: list[str],
        channel_defaults: dict[str, str] | None = None,
    ) -> None:
        self.agent_names = set(agent_names)
        self.channel_defaults = channel_defaults or {}

    def resolve(self, msg: InboundMessage) -> str:
        """Determine which agent should handle this message."""
        # 1. Explicit target set by delegation or system
        if msg.target_agent and msg.target_agent in self.agent_names:
            return msg.target_agent

        # 2. @agent_name mention in content
        mentioned = self._extract_mention(msg.content)
        if mentioned and mentioned in self.agent_names:
            return mentioned

        # 3. Channel default
        default = self.channel_defaults.get(msg.channel)
        if default and default in self.agent_names:
            return default

        # 4. First available agent
        return next(iter(self.agent_names)) if self.agent_names else "coder"

    def strip_mention(self, content: str) -> str:
        """Remove @agent_name from content."""
        return re.sub(r"@(\w+)\s*", "", content, count=1).strip()

    def _extract_mention(self, content: str) -> str | None:
        match = re.match(r"@(\w+)", content.strip())
        if match:
            return match.group(1).lower()
        return None