"""Orchestrator — LLM-based intent router and agent pipeline."""

from __future__ import annotations

import json
from typing import Any, AsyncGenerator

from langchain_core.messages import HumanMessage, SystemMessage
from langchain_openai import ChatOpenAI

from app.config.settings import settings
from app.core.agent_registry import AgentRegistry
from app.core.agent_registry import registry as _default_registry
from app.schemas import ChatRequest, ChatResponse, ExecutionPlan, PlanStep

_FALLBACK_AGENT = "task_agent"

_CLASSIFY_SYSTEM = (
    "You are an intent classifier. Given the user message and context, decide "
    "which agent to route to.\n"
    "Available agents: {agents}\n"
    "Respond with just the agent name, nothing else."
)

_SYNTHESIZE_HUMAN = (
    "Combine the following agent results into one coherent response.\n\n"
    "Agent results:\n{results}\n\n"
    "Original message: {message}"
)


def _make_llm(model: str = "gpt-4o-mini") -> ChatOpenAI:
    return ChatOpenAI(model=model, temperature=0, api_key=settings.OPENAI_API_KEY)


async def classify_intent(
    message: str,
    context: dict[str, Any],
    reg: AgentRegistry,
) -> str:
    """Use gpt-4o-mini to classify intent and return the matching agent name.

    Falls back to ``task_agent`` when the registry is empty or the model
    returns a name that is not registered.
    """
    agents = reg.list_agents()
    if not agents:
        return _FALLBACK_AGENT

    system = _CLASSIFY_SYSTEM.format(agents=json.dumps(agents))
    # Truncate context to keep the classification prompt short
    human = f"Message: {message}\nContext summary: {json.dumps(context)[:500]}"

    llm = _make_llm()
    response = await llm.ainvoke(
        [SystemMessage(content=system), HumanMessage(content=human)]
    )

    agent_name = str(response.content).strip().lower()
    known = {a["name"] for a in agents}
    return agent_name if agent_name in known else _FALLBACK_AGENT


async def route_single(
    agent_name: str,
    message: str,
    context: dict[str, Any],
    reg: AgentRegistry,
) -> ChatResponse:
    """Route to a single agent and wrap the result in a ``ChatResponse``."""
    response_text = await reg.call_agent(agent_name, message, context)
    return ChatResponse(response=response_text)


async def route_pipeline(
    agent_names: list[str],
    message: str,
    context: dict[str, Any],
    reg: AgentRegistry,
) -> ChatResponse:
    """Execute agents sequentially; each agent receives previous results in context.

    A final LLM synthesis call merges all results into one coherent response.
    """
    previous_results: list[str] = []

    for agent_name in agent_names:
        ctx = {**context, "previous_results": list(previous_results)}
        result = await reg.call_agent(agent_name, message, ctx)
        previous_results.append(result)

    results_str = "\n\n".join(
        f"[{name}]: {res}" for name, res in zip(agent_names, previous_results)
    )
    human = _SYNTHESIZE_HUMAN.format(results=results_str, message=message)
    llm = _make_llm()
    synthesis = await llm.ainvoke([HumanMessage(content=human)])
    return ChatResponse(response=str(synthesis.content))


def _build_plan(agent_name: str, message: str) -> ExecutionPlan:
    """Build a minimal ``ExecutionPlan`` for the resolved agent.

    The full ``ExecutionPlanBuilder`` (with template registry and caching) is
    implemented in Step 5.  This function produces the single-step baseline
    plan that the orchestrator returns in ``'plan'`` mode.
    """
    return ExecutionPlan(
        agent=agent_name,
        steps=[
            PlanStep(
                action="handle",
                prompt_template=f"tpl_{agent_name}_default",
                variables={"message": message},
            )
        ],
    )


async def orchestrate(
    request: ChatRequest,
    reg: AgentRegistry | None = None,
) -> ChatResponse | ExecutionPlan:
    """Main orchestration entry point.

    * Classifies the user's intent to select an agent.
    * ``execution_mode == 'direct'``: routes to the agent and returns a
      ``ChatResponse``.
    * ``execution_mode == 'plan'``: returns an ``ExecutionPlan`` with the
      resolved agent and a template-ID-only step (prompt IP stays server-side).
    """
    if reg is None:
        reg = _default_registry

    context = request.context.model_dump()
    agent_name = await classify_intent(request.message, context, reg)

    if request.execution_mode == "direct":
        return await route_single(agent_name, request.message, context, reg)

    # plan mode — return plan, do not execute
    return _build_plan(agent_name, request.message)


async def orchestrate_stream(
    request: ChatRequest,
    reg: AgentRegistry | None = None,
) -> AsyncGenerator[str, None]:
    """Streaming orchestration — yields text chunks then a final JSON frame.

    The final frame is a JSON object:
    ``{"done": true, "response": "...", "actions": []}``.

    Agents do not yet support token-level streaming; the full response is
    fetched first, then emitted in fixed-size chunks.  Token-level streaming
    will be wired in Step 6 when agents expose ``astream()``.
    """
    if reg is None:
        reg = _default_registry

    context = request.context.model_dump()
    agent_name = await classify_intent(request.message, context, reg)
    response_text = await reg.call_agent(agent_name, request.message, context)

    chunk_size = 50
    for i in range(0, len(response_text), chunk_size):
        yield response_text[i : i + chunk_size]

    final = ChatResponse(response=response_text)
    yield json.dumps({"done": True, **final.model_dump()})