from typing import List, Set

from .graph_models import FlowGraph, Node, Edge


def _find_start_nodes(flow: FlowGraph) -> List[Node]:
    targets = {e.target for e in flow.edges}
    return [n for n in flow.nodes if n.id not in targets] or (flow.nodes[:1] if flow.nodes else [])


def simulate_flowgraph(flow: FlowGraph) -> str:
    if not flow.nodes:
        return "No nodes defined. Add some nodes first."

    start_nodes = _find_start_nodes(flow)
    visited: Set[str] = set()
    logs: List[str] = []

    def dfs(node: Node, depth: int = 0):
        if node.id in visited:
            logs.append(f"{'  '*depth}- Node `{node.id}` (already visited, skipping to avoid loops)")
            return
        visited.add(node.id)

        type_tag = f" [{node.type}]" if node.type else ""
        logs.append(f"{'  '*depth}- Node `{node.id}`{type_tag}: {node.label}")

        # Outgoing edges
        for edge in flow.edges:
            if edge.source == node.id:
                next_node = flow.find_node(edge.target)
                if next_node:
                    dfs(next_node, depth + 1)

    for start in start_nodes:
        dfs(start, 0)

    if not logs:
        return "No execution path found. Check your edges."

    return "### Simulated Flow Execution\n" + "\n".join(logs)