"""Parallel step execution: run independent plan steps concurrently.

Multi-agent acceleration: steps with satisfied dependencies and no mutual
dependencies are dispatched in parallel to maximize throughput.
"""

from __future__ import annotations

from concurrent.futures import ThreadPoolExecutor, as_completed
from dataclasses import dataclass, field
from typing import Any, Callable, Protocol

from fusionagi.schemas.plan import Plan
from fusionagi.planning import ready_steps, get_step
from fusionagi._logger import logger


@dataclass
class ParallelStepResult:
    """Result of a single step execution in parallel batch."""

    step_id: str
    success: bool
    result: Any = None
    error: str | None = None
    envelope: Any = None  # AgentMessageEnvelope from executor


@dataclass
class ExecuteStepsCallback(Protocol):
    """Protocol for executing a single step (e.g. via orchestrator)."""

    def __call__(
        self,
        task_id: str,
        step_id: str,
        plan: Plan,
        sender: str = "supervisor",
    ) -> Any:
        """Execute one step; return response envelope or result."""
        ...


def execute_steps_parallel(
    execute_fn: Callable[[str, str, Plan, str], Any],
    task_id: str,
    plan: Plan,
    completed_step_ids: set[str],
    sender: str = "supervisor",
    max_workers: int | None = None,
) -> list[ParallelStepResult]:
    """
    Execute all ready steps in parallel.

    Args:
        execute_fn: Function (task_id, step_id, plan, sender) -> response.
        task_id: Task identifier.
        plan: The plan containing steps.
        completed_step_ids: Steps already completed.
        sender: Sender identity for execute messages.
        max_workers: Max parallel workers (default: unbounded for ready steps).

    Returns:
        List of ParallelStepResult, one per step attempted.
    """
    ready = ready_steps(plan, completed_step_ids)
    if not ready:
        return []

    results: list[ParallelStepResult] = []
    workers = max_workers if max_workers and max_workers > 0 else len(ready)

    def run_one(step_id: str) -> ParallelStepResult:
        try:
            response = execute_fn(task_id, step_id, plan, sender)
            if response is None:
                return ParallelStepResult(step_id=step_id, success=False, error="No response")
            # Response may be AgentMessageEnvelope with intent step_done/step_failed
            if hasattr(response, "message"):
                msg = response.message
                if msg.intent == "step_done":
                    payload = msg.payload or {}
                    return ParallelStepResult(
                        step_id=step_id,
                        success=True,
                        result=payload.get("result"),
                        envelope=response,
                    )
                return ParallelStepResult(
                    step_id=step_id,
                    success=False,
                    error=msg.payload.get("error", "Unknown failure") if msg.payload else "Unknown",
                    envelope=response,
                )
            return ParallelStepResult(step_id=step_id, success=True, result=response)
        except Exception as e:
            logger.exception("Parallel step execution failed", extra={"step_id": step_id})
            return ParallelStepResult(step_id=step_id, success=False, error=str(e))

    with ThreadPoolExecutor(max_workers=workers) as executor:
        future_to_step = {executor.submit(run_one, sid): sid for sid in ready}
        for future in as_completed(future_to_step):
            results.append(future.result())

    logger.info(
        "Parallel step batch completed",
        extra={"task_id": task_id, "steps": ready, "results": len(results)},
    )
    return results


def execute_steps_parallel_wave(
    execute_fn: Callable[[str, str, Plan, str], Any],
    task_id: str,
    plan: Plan,
    sender: str = "supervisor",
    max_workers: int | None = None,
) -> list[ParallelStepResult]:
    """
    Execute plan in waves: each wave runs all ready steps in parallel,
    then advances to the next wave when deps are satisfied.

    Returns combined results from all waves.
    """
    completed: set[str] = set()
    all_results: list[ParallelStepResult] = []

    while True:
        batch = execute_steps_parallel(
            execute_fn, task_id, plan, completed, sender, max_workers
        )
        if not batch:
            break

        for r in batch:
            all_results.append(r)
            if r.success:
                completed.add(r.step_id)
            else:
                # On failure, stop the wave (caller can retry or handle)
                logger.warning("Step failed in wave, stopping", extra={"step_id": r.step_id})
                return all_results

    return all_results