from __future__ import annotations

from collections.abc import Mapping
from dataclasses import dataclass
from pathlib import Path

import yaml


class AgentRegistryError(ValueError):
    pass


@dataclass(frozen=True)
class AgentDefinition:
    agent_id: str
    label: str


class AgentRegistry:
    def __init__(self, agents: list[AgentDefinition]) -> None:
        self.agents = agents
        self._by_id = {agent.agent_id: agent for agent in agents}

    def get(self, agent_id: str) -> AgentDefinition:
        try:
            return self._by_id[agent_id]
        except KeyError as exc:
            raise AgentRegistryError(f"unknown agent id: {agent_id}") from exc


def _load_registry_data(path: str | Path) -> dict[str, object]:
    try:
        raw = yaml.safe_load(Path(path).read_text(encoding="utf-8"))
    except yaml.YAMLError as exc:
        raise AgentRegistryError("invalid agent registry YAML") from exc
    if raw is None:
        return {}
    if not isinstance(raw, Mapping):
        raise AgentRegistryError("agent registry must be a mapping with an agents list")
    return dict(raw)


def load_agent_registry(path: str | Path) -> AgentRegistry:
    raw = _load_registry_data(path)
    entries = raw.get("agents")
    if not isinstance(entries, list) or not entries:
        raise AgentRegistryError("agents registry must contain a non-empty agents list")

    agents: list[AgentDefinition] = []
    seen: set[str] = set()
    for entry in entries:
        if not isinstance(entry, Mapping):
            raise AgentRegistryError("each agent entry requires id and label")
        agent_id = str(entry.get("id", "")).strip()
        label = str(entry.get("label", "")).strip()
        if not agent_id or not label:
            raise AgentRegistryError("each agent entry requires id and label")
        if agent_id in seen:
            raise AgentRegistryError(f"duplicate agent id: {agent_id}")
        seen.add(agent_id)
        agents.append(AgentDefinition(agent_id=agent_id, label=label))
    return AgentRegistry(agents)