Replanning

# Replanning when a step fails
def replan_after_failure(
    original_plan: list,
    failed_step_id: str,
    failure_reason: str,
    available_tools: set
) -> dict:
    """
    Generate a revised plan after a step failure.
    """
    failed_step = next((s for s in original_plan if s["id"] == failed_step_id), None)
    if not failed_step:
        return {"status": "error", "error": f"Step {failed_step_id} not found"}

    action = failed_step.get("action")
    remaining_steps = [s for s in original_plan
                       if s["id"] != failed_step_id
                       and failed_step_id not in s.get("depends_on", [])]

    # Strategy 1: Replace with a different tool that achieves the same result
    tool_alternatives = {
        "web_search": "document_search",  # Fallback to internal docs
        "send_email": "create_draft",     # Create a draft instead of sending
    }

    if action in tool_alternatives:
        alt_tool = tool_alternatives[action]
        if alt_tool in available_tools:
            revised_step = {**failed_step, "action": alt_tool,
                            "description": f"{failed_step['description']} (using fallback)"}
            print(f"Replanning: replacing '{action}' with '{alt_tool}'")
            return {
                "status": "replanned",
                "revised_plan": [revised_step] + remaining_steps,
                "change": f"Replaced {action} with {alt_tool}"
            }

    # Strategy 2: Skip the step if it is non-critical
    if failed_step.get("optional"):
        print(f"Replanning: skipping optional step {failed_step_id}")
        return {"status": "replanned", "revised_plan": remaining_steps,
                "change": f"Skipped optional step {failed_step_id}"}

    # Strategy 3: Escalate — cannot continue without this step
    return {"status": "escalate",
            "reason": f"Cannot complete goal: step {failed_step_id} failed — {failure_reason}"}

result = replan_after_failure(
    [{"id": "S1", "action": "web_search", "depends_on": []},
     {"id": "S2", "action": "summarise", "depends_on": ["S1"]}],
    "S1", "Network timeout",
    available_tools={"document_search", "summarise"}
)
print(result["status"], "—", result.get("change", result.get("reason")))