"""LangGraph agent framework setup for HR-ATS workflows.

Pure module: no FastAPI imports and no HTTPException.
This file only owns graph construction and lifecycle:

    init_agent() -> get_graph() -> build_graph() -> graph.compile()

LLM client/config lives in llm_setup. Nodes live in agent.views.
Run entrypoint lives in agent.execute_agent.
"""

from __future__ import annotations

import logging

from langgraph.graph import END, START, StateGraph

from agent.models import AgentState
from agent.views import finalize, match_jobs, prepare_context, route_after_prepare

logger = logging.getLogger("agent")

_graph = None


def build_graph():
    """Construct and compile the HR-ATS candidate matching graph."""
    graph = StateGraph(AgentState)
    graph.add_node("prepare", prepare_context)
    graph.add_node("match_jobs", match_jobs)
    graph.add_node("finalize", finalize)
    graph.add_edge(START, "prepare")
    graph.add_conditional_edges("prepare", route_after_prepare)
    graph.add_edge("match_jobs", "finalize")
    graph.add_edge("finalize", END)
    return graph.compile()


def get_graph():
    """Return the cached compiled graph, building it on first use."""
    global _graph
    if _graph is None:
        _graph = build_graph()
        logger.info("langgraph compiled")
    return _graph


async def init_agent():
    """Warm the compiled graph. LLM init stays on llm_setup.init_llm()."""
    get_graph()


async def close_agent():
    """Drop the cached graph."""
    global _graph
    _graph = None
    logger.info("agent graph closed")