"""NodePool: shared stateless node instances across all sessions.

Stateless nodes (InputNode, PANode, ExpertNode, etc.) hold no per-session
state — only config (model, system prompt). They can safely serve multiple
concurrent sessions. Session-specific HUD routing uses contextvars.

Stateful nodes (SensorNode, MemorizerNode, UINode) hold conversational
state and must be created per-session.
"""

import logging

from .engine import load_graph, instantiate_nodes

log = logging.getLogger("runtime")

# Roles that hold per-session state — always created fresh per Runtime
STATEFUL_ROLES = frozenset({"sensor", "memorizer", "ui"})


async def _noop_hud(data: dict):
    """Placeholder HUD — shared nodes use contextvars for session routing."""
    pass


class NodePool:
    """Shared node instances for stateless LLM nodes.

    Usage:
        pool = NodePool("v4-eras")
        # Shared nodes (one instance, all sessions):
        input_node = pool.shared["input"]
        # Stateful nodes must be created per-session (not in pool)
    """

    def __init__(self, graph_name: str = "v4-eras"):
        self.graph = load_graph(graph_name)
        self.graph_name = graph_name

        # Instantiate all nodes with noop HUD (shared nodes use contextvars)
        all_nodes = instantiate_nodes(self.graph, send_hud=_noop_hud)

        # Split: shared (stateless) vs excluded (stateful)
        self.shared = {
            role: node for role, node in all_nodes.items()
            if role not in STATEFUL_ROLES
        }

        log.info(f"[pool] created for graph '{graph_name}': "
                 f"{len(self.shared)} shared, {len(STATEFUL_ROLES)} stateful")